Article

# ϒ production and nuclear modification at forward rapidity in Pb–Pb collisions at s NN = 5.02 TeV

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## Abstract

The production of ϒ mesons in Pb–Pb collisions at a centre-of-mass energy per nucleon pair sNN=5.02 TeV is measured with the muon spectrometer of the ALICE detector at the LHC. The yields as well as the nuclear modification factors are determined in the forward rapidity region 2.5<y<4.0, as a function of rapidity, transverse momentum and collision centrality. The results show that the production of the ϒ(1S) meson is suppressed by a factor of about three with respect to the production in proton–proton collisions. For the first time, a significant signal for the ϒ(2S) meson is observed at forward rapidity, indicating a suppression stronger by about a factor 2–3 with respect to the ground state. The measurements are compared with transport, hydrodynamic, comover and statistical hadronisation model calculations.

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... These data suggest that thermalization is not complete, even for the bulk (low p T ) b-quark production. Data on Υ production in Pb-Pb collisions at 5.02 TeV at midrapidity by CMS [8] and at forward rapidity by ALICE [9] exhibit rich features, dominated by a suppression of production in Pb-Pb compared to pp collisions. The transport [10,11] and hydrodynamical [12] models are quite successful in describing these features. ...
... These models implement the so-called "sequential suppression" [13], in which color screening affects differently the bottomonia state, according to their respective binding energies. Also a parametrized approach called "comover model" [14] describes the data (see a comprehensive comparison in [9]). A recent theoretical advance is brought by the heavy quark quantum dynamics treatment [15] (see also reviews [16,17]). ...
... The Υ(1S), Υ(2S) data are included. In lack of published absolute yields, we calculated them employing the published R AA values [8,9] and the pp reference. The model describes the Υ(2S) data quite well, however, overestimates the Υ(1S) data significantly. ...
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Predictions are presented within the framework of the statistical hadronization model for integrated yields of bottomonia in Pb-Pb collisions at the LHC. We investigate the centrality dependence of $\Upsilon$ production and provide predictions for a large set of still-unmeasured open-beauty hadrons.
... For recent studies at LHC and RHIC experiments, see refs. [2][3][4][5][6][7][8][9][10][11]. In ref. [1], Matsui and Satz conjectured that the screening of chromoelectric fields generated by the medium at distances proportional to the inverse of the Debye mass induces quarkonium dissociation and consequently quarkonium suppression in medium. ...
... The six collapse operators in eqs. (2.31) and (2.32) (along with the Hamiltonian H) encode the full 3-dimensional evolution of Coulombic quarkonium of binding energy E propagating in a thermal medium of temperature T in the regime T E. 2 The collapse operators implement transitions between quarkonium states of different color and angular momentum. This can be made manifest in the angular momentum sector by projecting the density matrix onto the spherical harmonics Y lm ...
... -19 - In both panels, the solid line corresponds toκ =κ C (T ) and the best fit value ofγ = −2.6. The experimental measurements shown are from the ALICE [2], ATLAS [3], and CMS [4,11] collaborations. QTraj -Υ(1S) NLO predictions for R AA using H eff evolution. ...
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A bstract Using the potential non-relativistic quantum chromodynamics (pNRQCD) effective field theory, we derive a Lindblad equation for the evolution of the heavy-quarkonium reduced density matrix that is accurate to next-to-leading order (NLO) in the ratio of the binding energy of the state to the temperature of the medium. The resulting NLO Lindblad equation can be used to more reliably describe heavy-quarkonium evolution in the quark-gluon plasma at low temperatures compared to the leading-order truncation. For phenomenological application, we numerically solve the resulting NLO Lindblad equation using the quantum trajectories algorithm. To achieve this, we map the solution of the three-dimensional Lindblad equation to the solution of an ensemble of one-dimensional Schrödinger evolutions with Monte-Carlo sampled quantum jumps. Averaging over the Monte-Carlo sampled quantum jumps, we obtain the solution to the NLO Lindblad equation without truncation in the angular momentum quantum number of the states considered. We also consider the evolution of the system using only the complex effective Hamiltonian without stochastic jumps and find that this provides a reliable approximation for the ground state survival probability at LO and NLO. Finally, we make comparisons with our prior leading-order pNRQCD results and experimental data available from the ATLAS, ALICE, and CMS collaborations.
... The observation of sequential bottomonium suppression [1][2][3][4][5] in relativistic heavy-ion collisions at LHC has sparked a series of dedicated investigations, e.g. [6][7][8][9][10][11][12][13][14]. ...
... yields the input for Eqs.(4,5) for the determination of G m (φ) at T = 0 (highlighted by the subscript "0", using U 0 from Appendix B; for parameter values, see Appendix B 2), (ii) using afterwards that G m (φ) in Eqs.(2, 10) but with A(z; z H ), f (z; z H ), φ(z, z H ) determined again by V (φ) via the equations of motion(A1 -A4) following from the action (6) with boundary conditions (A5 -A10) and F(φ) from Eq. (9), see Appendix A. Some care is needed in that numerical treatment. Contour plots of the Υ spectral function L 2 ρ(ω, T, µ B ) over the temperature vs. scaled frequency L 2 ω 2 plane for µ B = 0 (left), 100 MeV (middle) and 200 MeV (right); blue, green, red and magenta contour curves correspond to L 2 ρ = 1, 3, 10 and 30. ...
... (5). (The needed holographic background quantities A 0 (z) and φ 0 (z) are determined independently by the dilaton potential V (φ) = V (φ 0 ), where the quantities at T = 0 and µ B = 0 are labeled by the subscript "0".) ...
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The shrinking of the bottomonium spectral function towards narrow quasi-particle states in a cooling strong-interaction medium at finite baryon density is followed within a holographic bottom-up model. The 5-dimensional Einstein-dilaton-Maxwell background is adjusted to lattice-QCD results of sound velocity and susceptibilities. The zero-temperature bottomonium spectral function is adjusted to experimental $\Upsilon$ ground-state mass and first radial excitations. At baryo-chemical potential $\mu_B = 0$, these two pillars let emerge the narrow quasi-particle state of the $\Upsilon$ ground state at a temperature of about 150 MeV. Excited states are consecutively formed at lower temperatures by about 10 (20) MeV for the $2S$ ($3S$) vector states. The baryon density, i.e. $\mu_B > 0$, pulls that formation pattern to lower temperatures. At $\mu_B =$ 200 MeV, we find a shift by about 15 MeV.
... For recent studies at LHC and RHIC experiments, see refs. [2][3][4][5][6][7][8][9][10][11]. In ref. [1], Matsui and Satz conjectured that the screening of chromoelectric fields generated by the medium at distances proportional to the inverse of the Debye mass induces quarkonium dissociation and consequently quarkonium suppression in medium. ...
... The six collapse operators in Eqs. (2.31) and (2.32) (along with the Hamiltonian H) encode the full 3-dimensional evolution of Coulombic quarkonium of binding energy E propagating in a thermal medium of temperature T in the regime T E. 2 The collapse operators implement transitions between quarkonium states of different color and angular momentum. This can be made manifest in the angular momentum sector by projecting the density matrix onto the spherical harmonics Y lm ...
... In the right panel of fig. 4, we show the variation ofγ in the range −3.5 ≤γ ≤ 0. As in the left panel, the solid line corresponds toγ = −2.6. In both the left and right panels, the experimental data presented are from the ALICE [2], ATLAS [3], and CMS [4,11] collaborations. ...
Preprint
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Using the potential non-relativistic quantum chromodynamics (pNRQCD) effective field theory, we derive a Lindblad equation for the evolution of the heavy-quarkonium reduced density matrix that is accurate to next-to-leading order (NLO) in the ratio of the binding energy of the state to the temperature of the medium. The resulting NLO Lindblad equation can be used to more reliably describe heavy-quarkonium evolution in the quark-gluon plasma at low temperatures compared to the leading-order truncation. For phenomenological application, we numerically solve the resulting NLO Lindblad equation using the quantum trajectories algorithm. To achieve this, we map the solution of the three-dimensional Lindblad equation to the solution of an ensemble of one-dimensional Schr\"odinger evolutions with Monte-Carlo sampled quantum jumps. Averaging over the Monte-Carlo sampled quantum jumps, we obtain the solution to the NLO Lindblad equation without truncation in the angular momentum quantum number of the states considered. We also consider the evolution of the system using only the complex effective Hamiltonian without stochastic jumps and find that this provides a reliable approximation for the ground state survival probability at LO and NLO. Finally, we make comparisons with our prior leading-order pNRQCD results and experimental data available from the ATLAS, ALICE, and CMS collaborations.
... sampling approximately 10 6 physical trajectories for each combination ofκðTÞ andγ. We compare our results with experimental data collected by the ALICE [69,70], ATLAS [71], and CMS [67,72,73] ...
... The bands, line styles, and panels represent the same variation as in Fig. 1. We observe that, within uncertainties, our The experimental data are taken from the ALICE [69], ATLAS [71], and CMS [67] collaborations. The bands represent theoretical uncertainties as in Fig. 1. results are in agreement with the experimental data. ...
... Regarding the comparison with experimental data, we see a reasonable agreement within reported uncertainties with some tension with the data seen at large p T . FIG. 3. Double ratio of the nuclear modification factor R AA ½ϒð2SÞ to R AA ½ϒð1SÞ as a function of N part compared to experimental measurements of the ALICE [69], ATLAS [71], and CMS [72] collaborations. The bands in the theoretical curves indicate variation of κðTÞ andγ as in Fig. 1. ...
Article
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We report predictions for the suppression and elliptic flow of the ϒ(1S), ϒ(2S), and ϒ(3S) as a function of centrality and transverse momentum in ultrarelativistic heavy-ion collisions. We obtain our predictions by numerically solving a Lindblad equation for the evolution of the heavy-quarkonium reduced density matrix derived using potential nonrelativistic QCD and the formalism of open quantum systems. To numerically solve the Lindblad equation, we make use of a stochastic unraveling called the quantum trajectories algorithm. This unraveling allows us to solve the Lindblad evolution equation efficiently on large lattices with no angular momentum cutoff. The resulting evolution describes the full 3D quantum and non-Abelian evolution of the reduced density matrix for bottomonium states. We expand upon our previous work by treating differential observables and elliptic flow; this is made possible by a newly implemented Monte Carlo sampling of physical trajectories. Our final results are compared to experimental data collected in sNN=5.02 TeV Pb-Pb collisions by the ALICE, ATLAS, and CMS collaborations.
... Since its typical time scale of the beaty-antibeauty pair production is small (O(1/(2mb) = 0.02 fm/c)), the pairs produced in hard initial scatterings witness the time evolution of the collision system. The production of Υ-meson states has been measured in nucleus-nucleus collisions by CMS [259][260][261][262][263][264], by ALICE [265][266][267] and ATLAS [268] at the LHC as well as STAR [269,270] and PHENIX [271] at RHIC. For the interpretation of the data, the assumptions about the feed-down contributions from excited states in absence of medium effects are taken from measurements in pp or pp collisions at collider energies. ...
... In particular, there is a need for better experimental knowledge on parton densities and potentially other physical effects not related to QGP physics that may be of relevance as cold energy loss and hadronic rescatterings. For instance, the rapidity dependence of the nuclear modification factor measured by CMS and ALICE, shown in [267], is in contrast with expectations from models [355,370], in which the rapidity dependence is driven by the rapidity dependence of the initial conditions of the medium [370] or the effect of nuclear PDFs on bottomonium production [355]. But it follows, although not at all quantitatively, the trend expected from coherent energy loss in the nucleus implementing a rapidity shift between the production in pp and nucleus-nucleus collisions [371]. ...
... The investigation of quarkonia in heavy-ion collisions at RHIC and at the LHC brings two qualitatively new insights: the sizeable regeneration of J/ψ [256,257,[278][279][280][281][282]285] and the sequential suppression of the Υ-states [259][260][261][262][263][264][265][266][267][268][269][270][271]. Both observations are interpreted as most directly possible signatures of deconfinement. ...
Preprint
The Quark-Gluon Plasma (QGP), a QCD state of matter created in ultra-relativistic heavy-ion collisions, has remarkable properties as a low shear viscosity over entropy ratio. Through the detection of multi-particle production, the bulk debris of the collision, these so-called soft probes have provided quantitative insight into the created matter. However, its fast evolution and thermalization properties remain elusive to the soft sector. Only the usage of high momentum objects as probes of the QGP can unveil its constituents at the different wavelengths. In this review, we attempt to provide a comprehensive picture of what was, so far, possible to withdraw given our current theoretical understanding of jets, heavy-flavor, and quarkonia. We will bridge the resulting qualitative picture to the experimental observations done at both the LHC and RHIC. We will focus on the phenomenological description of experimental observations, provide a brief analytical summary of the description of hard probes, and an outlook towards the main difficulties we will need to surpass in the following years. To benchmark QGP-related effects, we will also address nuclear modifications to the initial state and hadronization effects.
... This double ratio is shown in Figure 2. to J/y in Pb-Pb collisions compared to pp collisions. The preliminary ALICE data [85] seem to disfavor such an enhancement. Clearly, more precise data is needed in order to conclude. ...
... The important contribution of the Transition Radiation Detector (TRD) for the electron identification is considered based on its present performance. The measured transverse momentum spectrum [85] is also used as input. ...
Article
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ALICE (A Large Ion Collider Experiment) is studying the physics of strongly interacting matter, and in particular the properties of the Quark-Gluon Plasma (QGP), using proton-proton, proton-nucleus and nucleus-nucleus collisions at the CERN LHC (Large Hadron Collider). The ALICE Collaboration is preparing a major upgrade of the experimental apparatus, planned for installation in the second long LHC shutdown in the years 2018-2019. These plans are presented in the ALICE Upgrade Letter of Intent, submitted to the LHCC (LHC experiments Committee) in September 2012. In order to fully exploit the physics reach of the LHC in this field, high-precision measurements of the heavy-flavour production, quarkonia, direct real and virtual photons, and jets are necessary. This will be achieved by an increase of the LHC Pb-Pb instant luminosity up to 6×1027 cm-2s-1 and running the ALICE detector with the continuous readout at the 50 kHz event rate. The physics performance accessible with the upgraded detector, together with the main detector modifications, are presented.
... The bands indicate variation with respect toκ(T ) (left) andγ (right). The central curves represent the central values ofκ(T ) andγ.In both panels we show experimental measurements from the ALICE[37], ATLAS[38], and CMS[39] collaborations. ...
... p T < 15 GeV and |y| < 1.5 CMS: p T < 30 GeV and |y| < 2.4 QTraj: p T < 30 GeV and y=0 (Color online) The double ratio of the nuclear modification factor R AA [Υ(2S)] to R AA [Υ(1S)] as a function of N part compared to experimental measurements of the ALICE[37], ATLAS[38], and CMS[53] collaborations. The bands indicate variation ofκ(T ) andγ as inFig. ...
Preprint
In this proceedings contribution I review recent progress concerning the suppression of bottomonium production in the quark-gluon plasma. Making use of open quantum system methods applied to potential non-relativistic quantum chromodynamics one can show that the dynamics of heavy-quarkonium bound states satisfying the scale hierarchy 1/a_0 >> pi T ~ m_D >> E obey a Lindblad equation whose solution provides the quantum evolution of the heavy-quarkonium reduced density matrix. To solve the resulting Lindblad equation we use a quantum trajectories algorithm which allows one to include all possible angular momentum states of the quark-antiquark probe in a scalable manner. We solve the Lindblad equation using a tuned 3+1D dissipative hydrodynamics code for the background temperature evolution. We then consider a large number of Monte-Carlo sampled bottomonium trajectories embedded in this background. This allows us to extract the centrality- and p_T-dependence of the nuclear suppression factor R_AA[Upsilon] and elliptic flow v_2[Upsilon]. We find good agreement between our model predictions and available sqrt(s_NN) = 5.02 TeV Pb-Pb collision experimental data from the ALICE, ATLAS, and CMS collaborations.
... The modification of the quarkonium yields have been studied by various experiments at RHIC and LHC using the nuclear modification factor quantified as the yield ratio in nucleus-nucleus collisions (A+A) to that in p+p collisions scaled by the average number of binary N N collisions [13][14][15][16][17][18][19][20]. One of the most remarkable signatures is the ordered suppression of Υ(1S), Υ(2S), and Υ(3S) mesons by their binding energies reported in LHC [16,[18][19][20]. ...
... The modification of the quarkonium yields have been studied by various experiments at RHIC and LHC using the nuclear modification factor quantified as the yield ratio in nucleus-nucleus collisions (A+A) to that in p+p collisions scaled by the average number of binary N N collisions [13][14][15][16][17][18][19][20]. One of the most remarkable signatures is the ordered suppression of Υ(1S), Υ(2S), and Υ(3S) mesons by their binding energies reported in LHC [16,[18][19][20]. ...
Preprint
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Quarkonium production has been studied extensively in relativistic heavy-ion collision experiments to understand the properties of the quark gluon plasma. The experimental results on the yield modification in heavy-ion collisions relative to that in $p$+$p$ collisions can be described by several models considering dissociation and regeneration effects. A yield modification beyond initial-state effects has also been observed in small collision systems such as $p$+Au and $p$+Pb collisions, but it is still premature to claim any hot medium effect. A model study in various small collision systems such as $p$+$p$, $p$+Pb, $p$+O, and O+O collisions will help quantitatively understanding nuclear effects on the $\Upsilon(nS)$ production. A theoretical calculation considering the gluo-dissociation and inelastic parton scattering and their inverse reaction reasonably describes the suppression of $\Upsilon(1S)$ in Pb+Pb collisions. Based on this calculation, a Monte-Carlo simulation is developed to more realistically incorporate the medium produced in heavy-ion collisions with event-by-event initial collision geometry and hydrodynamic evolution. We extend this framework to small systems to study the medium effects. In this work, we quantify the nuclear modification factor of $\Upsilon(nS)$ as a function of charged particle multiplicity ($dN_{ch}/d\eta$) and transverse momentum. We also calculate the elliptic flow of $\Upsilon(nS)$ in small collision systems.
... The central curves represent the central values ofκ(T ) andγ. In both panels we show experimental measurements from the ALICE[37], ATLAS[38], and CMS[39] collaborations. ...
... (Color online) The double ratio of the nuclear modification factor RAA[Υ(2S)] to RAA[Υ(1S)] as a function of Npart compared to experimental measurements of the ALICE[37], ATLAS[38], and CMS[39] collaborations. The bands indicate variation ofκ(T ) andγ as inFig. ...
Article
Full-text available
In this proceedings contribution I review recent progress concerning the suppression of bottomonium production in the quark-gluon plasma. Making use of open quantum system methods applied to potential non-relativistic quantum chromodynamics one can show that the dynamics of heavy-quarkonium bound states satisfying the scale hierarchy 1/a0 » πT ∼ mD » E obey a Lindblad equation whose solution provides the quantum evolution of the heavy-quarkonium reduced density matrix. To solve the resulting Lindblad equation we use a quantum trajectories algorithm which allows one to include all possible angular momentum states of the quark-antiquark probe in a scalable manner. We solve the Lindblad equation using a tuned 3+1D dissipative hydrodynamics code for the background temperature evolution. We then consider a large number of Monte-Carlo sampled bottomonium trajectories embedded in this background. This allows us to extract the centrality- and pT-dependence of the nuclear suppression factor RAA[Υ] and elliptic flow v2[Υ]. We find good agreement between our model predictions and available √ sNN = 5.02 TeV = 5.02 TeV Pb-Pb collision experimental data from the ALICE, ATLAS, and CMS collaborations.
... The observation of sequential bottomonium suppression [1][2][3][4][5] in relativistic heavy-ion collisions at LHC has sparked a series of dedicated investigations, e.g., [6][7][8][9][10][11][12][13][14]. Such heavy-quark flavor degrees of freedom receive currently some interest as valuable probes of hot and dense strong-interaction matter produced in heavy-ion collisions at LHC energies. ...
Article
Full-text available
The shrinking of the bottomonium spectral function towards narrow quasiparticle states in a cooling strong-interaction medium at finite baryon density is followed within a holographic bottom-up model. The five-dimensional Einstein-dilaton-Maxwell background is adjusted to the lattice-QCD results of sound velocity and susceptibilities. The zero-temperature bottomonium spectral function is adjusted to the experimental ϒ ground state mass and the first radial excitations. At baryo-chemical potential μB=0, these two pillars let emerge the narrow quasiparticle state of the ϒ ground state at a temperature of about 150 MeV. Excited states are consecutively formed at lower temperatures by about 10 (20) MeV for the 2S (3S) vector states. The baryon density, i.e., μB>0, pulls that formation pattern to lower temperatures. At μB=200 MeV, we find a shift by about 15 MeV.
... The strong suppression of bottomonium production in heavy-ion collisions relative to their production in proton-proton collisions is a smoking gun for the creation of a hot quark-gluon plasma (QGP) in relativistic heavyion collisions [1][2][3][4][5][6][7][8][9][10]. In the seminal work of Matsui and Satz [11], suppression of heavy quarkonium was proposed as a signal of the formation of a color-ionized QGP. ...
Preprint
We compute bottomonium suppression and elliptic flow within the pNRQCD effective field theory using an open quantum systems approach. For the hydrodynamical background, we use 2+1D MUSIC second-order viscous hydrodynamics with IP-Glasma initial conditions and evolve bottom/antibottom quantum wave packets in real time in these backgrounds. We find that the impact of fluctuating initial conditions is small when compared to results obtained using smooth initial conditions. Including the effect of fluctuating initial conditions, we find that the Upsilon(1S) integrated elliptic flow is v_2[1S] = 0.005 +/- 0.002 +/- 0.001, with the first and second variations corresponding to statistical and systematic theoretical uncertainties, respectively.
... These developments highlight the close connection between the transport of open-and hidden-charm particles that become empirically accessible through precision data. [210], ATLAS [211] and ALICE [212], compared to model calculations of the semiclassical TAMU transport approach [15] (upper panels) and the quantum transport approach of TU Munich/Kent State [213]; figures taken from Refs. [15] and [185]. ...
Preprint
The diffusion of heavy quarks through the quark-gluon plasma (QGP) as produced in high-energy heavy-ion collisions has long been recognized as an excellent probe of its transport properties. In addition, the experimentally observed heavy-flavor hadrons carry valuable information about the hadronization process of the transported quarks. Here we review recent progress in the theoretical developments of heavy-quark interactions in the QGP and how they relate to the nonperturbative hadronization process, and discuss the recent status of the pertinent phenomenology in heavy-ion collisions at the RHIC and the LHC. The interactions of heavy quarks in the QGP also constitute a central building block in the description of the heavy quarkonia which controls their transport parameters as well. We will thus focus on theoretical approaches that aim for a unified description of open and hidden heavy-flavor particles in medium, and discuss how they can be constrained by lattice QCD "data" and utilized to deduce fundamental properties of the microscopic interactions and emerging spectral properties of the strongly coupled QGP.
... At the LHC, the suppression of J/ψ production is significantly smaller than the one observed at the SPS and RHIC and shows a characteristic p T -dependence, which represents a significant piece of evidence for the importance of regeneration for J/ψ production at low p T [50,51]. In the bottomonium sector, studies of the ϒ(1S) and the 2S, and 3S radial excitations at the LHC have shown a clear hierarchy in the suppression, that becomes stronger for the less bound states, a behaviour expected in presence of a high-temperature deconfined medium [68,69]. ...
Preprint
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This document describes the plans of the ALICE Collaboration for a major upgrade of its detector, referred to as ALICE 3, which is proposed for physics data-taking in the LHC Run 5 and beyond. ALICE 3 will enable an extensive programme to fully exploit the LHC for the study of the properties of strongly interacting matter with high-energy nuclear collisions. The proposed detector layout, based on advanced silicon sensors, features superb pointing resolution, excellent tracking and particle identification over a large acceptance and high readout-rate capabilities. This document discusses the proposed physics programme, the detector concept, and its physics performance for a suite of benchmark measurements.
... The sequential suppression of the three Υ states have been observed at the LHC [30][31][32]. In Pb+Pb collisions at √ s NN = 5.02 TeV [31], Υ(2S) is further suppressed by about a factor of 3.2 than Υ(1S), while an additional suppression factor of approximately 5.3 is found for Υ(3S) compared to Υ(2S). ...
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We report on measurements of sequential $\Upsilon$ suppression in Au+Au collisions at $\sqrt{s_{_\mathrm{NN}}}$ = 200 GeV with the STAR detector at the Relativistic Heavy Ion Collider (RHIC) through both the di-electron and di-muon channels. In the 0-60% centrality class, the nuclear modification factors ($R_{\mathrm{AA}}$), which quantify the level of yield suppression in heavy-ion collisions compared to $p$+$p$ collisions, for $\Upsilon$(1S) and $\Upsilon$(2S) are $0.40 \pm 0.03~\textrm{(stat.)} \pm 0.03~\textrm{(sys.)} \pm 0.07~\textrm{(norm.)}$ and $0.26 \pm 0.07~\textrm{(stat.)} \pm 0.02~\textrm{(sys.)} \pm 0.04~\textrm{(norm.)}$, respectively, while the upper limit of the $\Upsilon$(3S) $R_{\mathrm{AA}}$ is 0.20 at a 95% confidence level. This observation provides experimental evidence that the $\Upsilon$(3S) is significantly more suppressed than the $\Upsilon$(1S) at RHIC. The level of suppression for $\Upsilon$(1S) is comparable to that observed at the much higher collision energy at the Large Hadron Collider. These results point to the creation of a deconfined medium at RHIC whose temperature is sufficiently high to strongly suppress excited $\Upsilon$ states.
... . QTraj - Fig. 13 The nuclear modification factor R AA of the ϒ (1S), ϒ (2S), and ϒ (3S) as a function of N part compared to experimental measurements from the ALICE [174], ATLAS [176], and CMS [175] collaborations. The bands in the theoretical curves indicate variation with respect toκ(T ) (left) andγ (right). ...
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Heavy quarks have been instrumental for progress in our exploration of strong interactions. Quarkonium in particular, a heavy quark-antiquark nonrelativistic bound state, has been at the root of several revolutions. Quarkonium is endowed with a pattern of separated energy scales qualifying it as special probe of complex environments. Its multiscale nature has made a description in Quantum Field Theory particularly difficult up to the advent of Nonrelativistic Effective Field Theories. We will focus on systems made by two or more heavy quarks. After considering some historical approaches based on the potential models and the Wilson loop approach, we will introduce the contemporary nonrelativistic effective field theory descriptions, in particular potential Nonrelativistic QCD which entails the Schoedinger equation as zero order problem, define the potentials as matching coefficients and allows systematic calculations of the physical properties. The effective field theory allows us to explore quarkonium properties in the realm of QCD. In particular it allows us to make calculations with unprecedented precision when high order perturbative calculations are possible and to systematically factorize short from long range contributions where observables are sensitive to the nonperturbative dynamics of QCD. Such effective field theory treatment can be extended at finite temperature and in presence of gluonic and light quark excitations. We will show that in this novel theoretical framework, quarkonium can play a crucial role for a number of problems at the frontier of our research, from the investigation of the confinement dynamics in strong interactions to the study of deconfinement and the phase diagram of nuclear matter, to the precise determination of Standard Model parameters up to the emergence of exotics X Y Z states of an unprecedented nature.
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The study of heavy quarkonium suppression in heavy-ion collisions represents an important source of information about the properties of the quark-gluon plasma produced in such collisions. In a previous paper, we have considered how to model the evolution of a quarkonium in such a way that the solution of the resulting equations evolves toward the correct thermal equilibrium distribution for a homogeneous and static medium. We found that it is crucial to take into account the energy gap between singlet and octet configurations when the temperature is not much greater than this energy gap. In this paper, we explore in more detail the phenomenological consequences of this observation in the more realistic situation of an expanding system. We consider two different scenarios, based on the same approximation scheme, but on different choices of parameters. In the first case, we rely on a Hard Thermal Loop approximation, while the second case is based on a recent determination of the static potential in lattice QCD. In both cases, we compute the decay width and the nuclear modification factor, both taking the energy gap into account and ignoring it. We find that the impact on the predictions is as large in the expanding medium as it is in the static case. Our conclusion is that this energy gap should be taken into account in phenomenological studies.
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A bstract We develop a framework of coupled transport equations for open heavy flavor and quarkonium states, in order to describe their transport inside the quark-gluon plasma. Our framework is capable of studying simultaneously both open and hidden heavy flavor observables in heavy-ion collision experiments and can account for both, uncorrelated and correlated recombination. Our recombination implementation depends on real-time open heavy quark and antiquark distributions. We carry out consistency tests to show how the interplay among open heavy flavor transport, quarkonium dissociation and recombination drives the system to equilibrium. We then apply our framework to study bottomonium production in heavy-ion collisions. We include ϒ(1 S ), ϒ(2 S ), ϒ(3 S ), χ b (1 P ) and χ b (2 P ) in the framework and take feed-down contributions during the hadronic gas stage into account. Cold nuclear matter effects are included by using nuclear parton distribution functions for the initial primordial heavy flavor production. A calibrated 2 + 1 dimensional viscous hydrodynamics is used to describe the bulk QCD medium. We calculate both the nuclear modification factor R AA of all bottomonia states and the azimuthal angular anisotropy coefficient v 2 of the ϒ(1 S ) state and find that our results agree reasonably with experimental measurements. Our calculations indicate that correlated cross-talk recombination is an important production mechanism of bottomonium in current heavy-ion experiments. The importance of correlated recombination can be tested experimentally by measuring the ratio of R AA ( χ b (1 P )) and R AA (ϒ(2 S )).
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We compute the suppression and elliptic flow of bottomonium using real-time solutions to the Schrödinger equation with a realistic in-medium complex-valued potential. To model the initial production, we assume that, in the limit of heavy quark masses, the wave-function can be described by a lattice-smeared (Gaussian) Dirac delta wave-function. The resulting final-state quantum-mechanical overlaps provide the survival probability of all bottomonium eigenstates. Our results are in good agreement with available data for RAA as a function of Npart and pT collected at sNN=5.02 TeV. In the case of v2 for the various states, we find that the path-length dependence of ϒ(1s) suppression results in quite small v2 for ϒ(1s). Our prediction for the integrated elliptic flow for ϒ(1s) in the 10−90% centrality class is v2[ϒ(1s)]=0.0026±0.0007. We additionally find that, due to their increased suppression, excited bottomonium states have a larger elliptic flow and we make predictions for v2[ϒ(2s)] and v2[ϒ(3s)] as a function of centrality and transverse momentum. Similar to prior studies, we find that it is possible for bottomonium states to have negative v2 at low transverse momentum.
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The relative yields of ϒ mesons produced in pp and Pb-Pb collisions at sNN=5.02 TeV and reconstructed via the dimuon decay channel are measured using data collected by the CMS experiment. Double ratios are formed by comparing the yields of the excited states, ϒ(2S) and ϒ(3S), to the ground state, ϒ(1S), in both Pb-Pb and pp collisions at the same center-of-mass energy. The double ratios, [ϒ(nS)/ϒ(1S)]Pb−Pb/[ϒ(nS)/ϒ(1S)]pp, are measured to be 0.308±0.055(stat)±0.019(syst) for the ϒ(2S) and less than 0.26 at 95% confidence level for the ϒ(3S). No significant ϒ(3S) signal is found in the Pb-Pb data. The double ratios are studied as a function of collision centrality, as well as ϒ transverse momentum and rapidity. No significant dependencies are observed.
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The inclusive J/ψ production has been studied in Pb–Pb and pp collisions at the centre-of-mass energy per nucleon pair , using the ALICE detector at the CERN LHC. The J/ψ meson is reconstructed, in the centre-of-mass rapidity interval and in the transverse-momentum range , via its decay to a muon pair. In this Letter, we present results on the inclusive J/ψ cross section in pp collisions at and on the nuclear modification factor . The latter is presented as a function of the centrality of the collision and, for central collisions, as a function of the transverse momentum of the J/ψ. The measured values indicate a suppression of the J/ψ in nuclear collisions and are then compared to our previous results obtained in Pb–Pb collisions at . The ratio of the values at the two energies is also computed and compared to calculations of statistical and dynamical models. The numerical value of the ratio for central events (0–10% centrality) is . In central events, as a function of , a slight increase of with collision energy is visible in the region . Theoretical calculations qualitatively describe the measurements, within uncertainties.
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We introduce a global analysis of collinearly factorized nuclear parton distribution functions (PDFs) including, for the first time, direct data constraints from the LHC proton-lead collisions. In comparison to our previous analysis, EPS09, where data only from charged-lepton-nucleus deep inelastic scattering (DIS), Drell-Yan (DY) dilepton production in proton-nucleus collisions and inclusive pion production in deuteron-nucleus collisions were used as input, we now increase the variety of data constraints to cover also neutrino-nucleus DIS as well as low-mass DY production in pion-nucleus collisions. The new LHC data significantly extend the kinematic reach of the available data constraints. The larger number of data points allows, in particular, to let much more freedom for the flavour dependence of nuclear effects than in other currently available analyses. As a result, especially the uncertainty estimates are now less biased and more objectively reflect the uncertainties flavour by flavour. From the new data, the neutrino DIS plays a pivotal role in obtaining a mutually consistent behaviour for both up and down valence quarks, and the LHC dijet data place clear constraints for the gluons at large momentum fraction. Mainly for insufficient statistics, the data for pion-nucleus DY and heavy gauge boson production in proton-lead collisions impose less visible constraints. The outcome of the analysis - a new set of next-to-leading order nuclear PDFs we call EPPS16 - is made available for applications in high-energy nuclear collisions.
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The production of J/psi and psi (2S) was studied with the ALICE detector in Pb-Pb collisions at the LHC. The measurement was performed at forward rapidity (2.5 < y < 4) down to zero transverse momentum (p(T)) in the dimuon decay channel. Inclusive J/psi yields were extracted in different centrality classes and the centrality dependence of the average p(T) is presented. The J/psi suppression, quantified with the nuclear modification factor (R-AA), was measured as a function of centrality, transverse momentum and rapidity. Comparisons with similar measurements at lower collision energy and theoretical models indicate that the J/psi production is the result of an interplay between color screening and recombination mechanisms in a deconfined partonic medium, or at its hadronization. Results on the psi(2S) suppression are provided via the ratio of psi(2S) over J/psi measured in pp and Pb-Pb collisions.
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Two-particle angular correlations are studied in proton-lead collisions at a nucleon-nucleon centre-of-mass energy of $\sqrt{s_{\text{NN}}}=5$TeV, collected with the LHCb detector at the LHC. The analysis is based on data recorded in two beam configurations, in which either the direction of the proton or that of the lead ion is analysed. The correlations are measured as a function of relative pseudorapidity, $\Delta\eta$, and relative azimuthal angle, $\Delta\phi$, for events in different classes of event activity and for different bins of particle transverse momentum. In high-activity events a long-range correlation on the near side, $\Delta\phi \approx 0$, is observed in the pseudorapidity range $2.0<\eta<4.9$. This measurement of long-range correlations on the near side in proton-lead collisions extends previous observations into the forward region up to $\eta=4.9$. The correlation increases with growing event activity and is found to be more pronounced in the direction of the lead beam. However, the correlation strengths in the direction of the lead and proton beams are found to be compatible when comparing events with similar absolute activity in the direction analysed.
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The production of Upsilon mesons in pp collisions at root s = 7 and 8 TeV is studied with the LHCb detector using data samples corresponding to an integrated luminosity of 1 fb(-1) and 2 fb(-1) respectively. The production cross-sections and ratios of cross-sections are measured as functions of the meson transverse momentum p and rapidity y, for p < 30 GeV/c and 2.0 < y < 4.5.
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The inclusive production cross sections at forward rapidity of , , (1S) and (2S) are measured in collisions at with the ALICE detector at the LHC. The analysis is based on a data sample corresponding to an integrated luminosity of 1.35 pb. Quarkonia are reconstructed in the dimuon-decay channel and the signal yields are evaluated by fitting the invariant mass distributions. The differential production cross sections are measured as a function of the transverse momentum and rapidity , over the ranges GeV/c for , GeV/c for all other resonances and for . The measured cross sections integrated over and , and assuming unpolarized quarkonia, are: b, b, nb and nb, where the first uncertainty is statistical and the second one is systematic. The results are compared to measurements performed by other LHC experiments and to theoretical models.
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The polarizations of the Υ(1S), Υ(2S), and Υ(3S) mesons are measured in proton-proton collisions at s=7 TeV, using a data sample of Υ(nS)→μ+μ− decays collected by the CMS experiment, corresponding to an integrated luminosity of 4.9 fb−1. The dimuon decay angular distributions are analyzed in three different polarization frames. The polarization parameters λϑ, λφ, and λϑφ, as well as the frame-invariant quantity λ˜, are presented as a function of the Υ(nS) transverse momentum between 10 and 50 GeV, in the rapidity ranges |y|<0.6 and 0.6<|y|<1.2. No evidence of large transverse or longitudinal polarizations is seen in the explored kinematic region.
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We present the new nCTEQ15 set of nuclear parton distribution functions with uncertainties. This fit extends the CTEQ proton PDFs to include the nuclear dependence using data on nuclei all the way up to 208^Pb. The uncertainties are determined using the Hessian method with an optimal rescaling of the eigenvectors to accurately represent the uncertainties for the chosen tolerance criteria. In addition to the Deep Inelastic Scattering (DIS) and Drell-Yan (DY) processes, we also include inclusive pion production data from RHIC to help constrain the nuclear gluon PDF. Furthermore, we investigate the correlation of the data sets with specific nPDF flavor components, and asses the impact of individual experiments. We also provide comparisons of the nCTEQ15 set with recent fits from other groups.
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We report on the production of inclusive ϒ (1S) and ϒ (2S) in p–Pb collisions at View the MathML sourcesNN=5.02 TeV at the LHC. The measurement is performed with the ALICE detector at backward (−4.46<ycms<−2.96−4.46<ycms<−2.96) and forward (2.03<ycms<3.532.03<ycms<3.53) rapidity down to zero transverse momentum. The production cross sections of the ϒ(1S) and ϒ(2S) are presented, as well as the nuclear modification factor and the ratio of the forward to backward yields of ϒ(1S). A suppression of the inclusive ϒ(1S) yield in p–Pb collisions with respect to the yield from pp collisions scaled by the number of binary nucleon–nucleon collisions is observed at forward rapidity but not at backward rapidity. The results are compared to theoretical model calculations including nuclear shadowing or partonic energy loss effects.
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ALICE is the heavy-ion experiment at the CERN Large Hadron Collider. The experiment continuously took data during the first physics campaign of the machine from fall 2009 until early 2013, using proton and lead-ion beams. In this paper we describe the running environment and the data handling procedures, and discuss the performance of the ALICE detectors and analysis methods for various physics observables.
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The suppression of the individual Upsilon(nS) states in PbPb collisions with respect to their yields in pp data has been measured. The PbPb and pp datasets used in the analysis correspond to integrated luminosities of 150 inverse microbarns and 230 inverse nanobarns, respectively, collected in 2011 by the CMS experiment at the LHC, at a center-of-mass energy per nucleon pair of 2.76 TeV. The Upsilon(nS) yields are measured from the dimuon invariant mass spectra. The suppression of the Upsilon(nS) yields in PbPb relative to the yields in pp scaled by the number of nucleon-nucleon collisions, R[AA], is measured as a function of the collision centrality. Integrated over centrality, the R[AA] values are 0.56 +/- 0.08 (stat.) +/- 0.07 (syst.), 0.12 +/- 0.04 (stat.) +/- 0.02 (syst.), and lower than 0.10 (at 95% confidence level), for the Upsilon(1S), Upsilon(2S), and Upsilon(3S) states, respectively. The results demonstrate the sequential suppression of the Upsilon(nS) states in PbPb collisions at LHC energies.
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The production of ground-state and excited bottomonia in ultrarelativistic heavy-ion collisions is investigated within a kinetic-rate equation approach including regeneration. We augment our previous calculations by an improved treatment of medium effects, with temperature-dependent binding energies and pertinent reaction rates, B-meson resonance states in the equilibrium limit near the hadronization temperature, and a lattice-QCD based equation of state for the bulk medium. In addition to the centrality dependence of the bottomonium yields, we compute their transverse-momentum (pT) spectra and elliptic flow with momentum-dependent reaction rates and a regeneration component based on b-quark spectra from a nonperturbative transport model of heavy-quark diffusion. The latter has noticeable consequences for the shape of the bottomonium pT spectra. We quantify how uncertainties in the various modeling components affect the predictions for observables. Based on this we argue that the Υ(1S) suppression is a promising observable for mapping out the in-medium properties of the QCD force, while Υ(2S) production can help to quantify the role of regeneration from partially thermalized b quarks.
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Quantum Chromodynamics (QCD), the fundamental theory of strong interactions in the Standard Model of particle physics predicts that deconfinement of color and chiral symmetry restoration are two essential properties to be expected in high density matter. Indeed, a non perturbative solution of QCD at finite temperature and density, based on Lattice Gauge Theory (LQCD), confirmed, that there is a phase change from hadronic matter, where the chiral symmetry is spontaneously broken and color is confined, to a deconfined quark-gluon plasma with partially restored chiral symmetry, where quarks and gluons can travel distances largely exceeding typical size of hadrons. We demonstrate that the phase structure of strongly interacting matter described by LQCD can be decoded via analysis of particle production in high energy nuclear collisions. This is achieved by making use of the observed thermalization pattern of particle abundances within the framework of the statistical hadronization approach at various collision energies. We show that thermalization holds not only for hadronic constituents composed of light quarks but also applies to hadrons containing charm quarks. The observed energy dependence of the production yields of different particle species contains characteristic features which are used to determine the temperature and baryo-chemical potential of the matter produced. The above observations imply quark-hadron duality at the QCD phase boundary and establish the first experimental delineation of the location of the phase change in strongly interacting matter.
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We review the progress achieved in extracting the properties of hot and dense matter from relativistic heavy ion collisions at the relativistic heavy ion collider (RHIC) at Brookhaven National Laboratory and the large hadron collider (LHC) at CERN. We focus on bulk properties of the medium, in particular the evidence for thermalization, aspects of the equation of state, transport properties, as well as fluctuations and correlations. We also discuss the in-medium properties of hadrons with light and heavy quarks, and measurements of dileptons and quarkonia. This review is dedicated to the memory of Gerald E. Brown.
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107 pages, 88 captioned figures, 12 tables, authors from page 102 to page 104 ; see paper for full list of authors
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See paper for full list of authors - 5 pages plus author list (18 pages total), 4 figures, submitted to Physical Review Letter. Addtional auxiliary plots can be found at http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HION-2012-13/
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Submitted to the Journal of High Energy Physics - see paper for full list of authors
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37 pages, 16 figures, authors from page 31 ; see paper for full list of authors
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The production of mesons in proton–proton collisions at is studied with the LHCb detector at the LHC. The differential cross-section for prompt production is measured as a function of the transverse momentum pT and rapidity y in the fiducial region and y∈[2.0;4.5]. The differential cross-section and fraction of from b-hadron decays are also measured in the same pT and y ranges. The analysis is based on a data sample corresponding to an integrated luminosity of 5.2 pb−1. The measured cross-sections integrated over the fiducial region are production and from b-hadron decays, where the first uncertainty is statistical and the second systematic. The prompt production cross-section is obtained assuming no polarisation and the third error indicates the acceptance uncertainty due to this assumption.
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The effect of parton energy loss in cold nuclear matter on the suppression of quarkonia (J/psi, Upsilon) in heavy-ion collisions is investigated, by extrapolating a model based on coherent radiative energy loss recently shown to describe successfully J/psi and Upsilon suppression in proton-nucleus collisions. Model predictions in heavy-ion collisions at RHIC (Au-Au, Cu-Cu, and Cu-Au) and LHC (Pb-Pb) show a sizable suppression arising from the sole effect of energy loss in cold matter. This effect should thus be considered in order to get a reliable baseline for cold nuclear matter effects in quarkonium suppression in heavy-ion collisions, in view of disentangling hot from cold nuclear effects.
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ALICE (A Large Ion Collider Experiment) is the LHC (Large Hadron Collider) experiment devoted to investigating the strongly interacting matter created in nucleus-nucleus collisions at the LHC energies. The ALICE ITS, Inner Tracking System, consists of six cylindrical layers of silicon detectors with three different technologies; in the outward direction: two layers of pixel detectors, two layers each of drift, and strip detectors. The number of parameters to be determined in the spatial alignment of the 2198 sensor modules of the ITS is about 13,000. The target alignment precision is well below 10 mu m in some cases (pixels). The sources of alignment information include survey measurements, and the reconstructed tracks from cosmic rays and from proton-proton collisions. The main track-based alignment method uses the Millepede global approach. An iterative local method was developed and used as well. We present the results obtained for the ITS alignment using about 10(5) charged tracks from cosmic rays that have been collected during summer 2008, with the ALICE solenoidal magnet switched off.
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ALICE is an LHC experiment devoted to the study of strongly interacting matter in proton-proton, proton-nucleus and nucleus-nucleus collisions at ultra-relativistic energies. The ALICE VZERO system, made of two scintillator arrays at asymmetric positions, one on each side of the interaction point, plays a central role in ALICE. In addition to its core function as a trigger source, the VZERO system is used to monitor LHC beam conditions, to reject beam-induced backgrounds and to measure basic physics quantities such as luminosity, particle multiplicity, centrality and event plane direction in nucleus-nucleus collisions. After describing the VZERO system, this publication presents its performance over more than four years of operation at the LHC.