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![Extrapolation of midrapidity particle density per participant pair, for central PbPb collisions at √ s NN = 5.5TeV. The data are from a PHOBOS compilation [4, 45]. The predicted value for dN c h dη /(N part /2) = 6.2 ± 0.4, which for N part = 386 (top 3 %) corresponds to dN ch /dη = 1200 ± 100.](profile/J-Barrette/publication/41786702/figure/fig5/AS:650806751670280@1532175829424/Extrapolation-of-midrapidity-particle-density-per-participant-pair-for-central-PbPb.png)
Extrapolation of midrapidity particle density per participant pair, for central PbPb collisions at √ s NN = 5.5TeV. The data are from a PHOBOS compilation [4, 45]. The predicted value for dN c h dη /(N part /2) = 6.2 ± 0.4, which for N part = 386 (top 3 %) corresponds to dN ch /dη = 1200 ± 100.
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This writeup is a compilation of the predictions for the forthcoming Heavy Ion Program at the Large Hadron Collider, as presented at the CERN Theory Institute 'Heavy Ion Collisions at the LHC - Last Call for Predictions', held from May 14th to June 10th 2007.
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... present rapidity distributions as well as scaled multiplicities at mid-rapidity as function of the collision energy and the number of participants. Pb-Pb 5500 GeV % Pb-Pb 5500 GeV |etacm| < 2.5 % Pb-Pb 5500 GeV 0-10 % Pb-Pb 5500 GeV 0-10 % |etacm| < 2.5 % Pb-Pb 2000 GeV % Pb-Pb 2000 GeV |etacm| < 2.5 % Pb-Pb 700 GeV % Pb-Pb 700 GeV |etacm| < 2.5 % Figure 12: Multiplicity distributions in minimum bias and 0-10% central collisions in Pb-Pb collisions in the full η cm range and for |η cm | ≤ 2.5 (from DPMJET-III). ...
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... pairs to be softer, since it is less likely for high-p T c and ¯ c quarks from independent scatterings to be close enough in phase-space to coalesce into a J/ψ. Results for RHIC were presented in Ref. [327], where the primary signal was found to be a narrowing of the non-diagonal y and p T spectra, relative to the diagonal ones. We show in Fig. 120 ...
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... this most binding potential some of the quarkonium states survive above deconfinement, but their strongly temperature-dependent binding energy is significantly reduced. This is shown in figure 121. Due to the reduced binding energy thermal activation can lead to the dissociation of quarkonia, even when the corresponding peak is present in the spectral function. ...
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... the above formulas we estimate the thermal width of charmonium and bottomonium states. Since in the deconfined phase E bin < T the 1S charmonium and 2S and 1P bottomonium states are in the regime of weak binding, and their width is large, as shown in figure 121. The 1S bottomonium is strongly bound for T < 1.6T c and its thermal width is smaller than 40 MeV. ...
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... 1S bottomonium is strongly bound for T < 1.6T c and its thermal width is smaller than 40 MeV. For T > 1.6T c , however, even the 1S bottomonium states is in the weak binding regime resulting in the large increase of the width, see figure 121. When the thermal width is significantly larger than the binding energy no peak structure will be present in the spectral functions, even though the simple potential model calculation predicts a peak. ...
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... for the baseline D 0 , D+, B 0 , B+ cross sections in p+p collisions at the LHC at s 1/2 = 5.5 TeV are given in the left panel of Fig. 122 [332]. At lowest order we also include Q + g → Q + g, Q + q( ¯ q) → Q + q( ¯ q) and processes that give a dominant contribution to the single inclusive D-and B-mesons [332]. The right panel of Fig. 122 illustrates a method to determine the underlying heavy flavor production mechanism through the away-side hadron composition of D− and B−meson triggered jets ...
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... for y > −2.5. Thus relying on ratios of pA to pp collisions at different energies to study shadowing (or other small x effects) may be difficult because the shadowing function is hard to unfold when accounting for the pA ∆y as well as the difference in x. If d+Pb collisions were used, ∆y would be significantly reduced [341]. The lower part of Fig. 124 shows R PbPb (y) for the J/ψ and Υ at 5.5 TeV for both systems. No additional dense matter effects such as QQ coalescence or plasma screening are included. The EKS98 (dashed) and nDSg [15] (dot-dashed) shadowing parameterizations are compared. The results are very similar over the entire rapidity range. (Other shadowing ...
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... is calculated as first discussed in Ref. [347]. Since it may be unlikely for feed down contributions to be separated from the inclusive ψ and Υ yields in AA collisions, we present the indirect ψ ′ /ψ and Υ ′ /Υ ratios, with feed down included, in Fig. 125. While the individual suppression factors are smooth as a function of p T , as shown in Fig. 126 for all four sets of initial conditions and dissociation temperatures, due to their different predicted dissociation temperatures and formation times, they contribute differently to the ratios in Fig. ...
Citations
... In such heavy ion collisions, it becomes possible to study the properties of the Quark Gluon Plasma (QGP), the hot and dense medium created first in the early Universe and that now we can replicate in the laboratory. Nuclear PDFs enter the initial state of heavy ion collisions whenever hard probes such as jets, weak bosons, or heavy quarks are produced [Abreu et al., 2008]. Therefore, improving our understanding of the nPDFs is important in order tell apart the cold from the hot nuclear matter effects in those complex events, involving hundreds or even thousands of produced particles. ...
Deepening our knowledge of the partonic content of nucleons and nuclei represents a central endeavour of modern high-energy and nuclear physics, with ramifications in related disciplines such as astroparticle physics. There are two main scientific drivers motivating these investigations of the partonic structure of hadrons. On the one hand, addressing fundamental open issues in our understanding in the strong interactions such as the origin of the nucleon mass, spin, and transverse structure; the presence of heavy quarks in the nucleon wave function; and the possible onset of novel gluon-dominated dynamical regimes. On the other hand, pinning down with the highest possible precision the substructure of nucleons and nuclei is a central component for theoretical predictions in a wide range of experiments, from proton and heavy ion collisions at the Large Hadron Collider to ultra-high energy neutrino interactions at neutrino telescopes. In this Article, I present a succinct non-technical overview of our modern understanding of the quark, gluon, and photon substructure of nucleons and nuclei, focusing on recent trends and results and discussing future perspectives for the field
... As they are rarely discussed it will not be easy to convince you. A quantum statistical effect in high energy heavy ion scattering called Bose Einstein enhancement might be the best hope as it is closest to our background [1]. ...
The interrelation of macroscopic classical and usually microscopic quantum physics is considered. Arguments for fixed two state vector quantum mechanics are outlined in a somewhat pedagogic way. An heuristic concept is developed how something like classical physics could emerge in an early epoch of a finite universe with a compact initial state and an extremely extended final one. The concept contains no intrinsic paradoxes. However it can not incorporate free agents which are considered essential. To allow for something like free agents the fixed final state is replaced by a matching state of maximum extend between an expanding and a contracting universe. How a bidirectional macroscopic world with possible free agents could emerge in such a big bang / big crunch universe is the central point of the paper
... Also a clear centrality dependence is observed. Two unexpected features [21] also emerge from those studies: R AA increases only very slowly with increasing jet p T , and no dependence of R AA on jet rapidity is observed. Measurements by the ATLAS and CMS Collaborations can be complemented by the measurement by the ALICE Collaboration which reports R AA for jets measured in p T interval of 30-120 GeV in central Pb+Pb collisions [22]. ...
Measurements of the yield and nuclear modification factor, RAA, for inclusive jet production are performed using 0.49 nb⁻¹ of Pb+Pb data at sNN=5.02TeV and 25 pb⁻¹ of Pb+Pb data at s=5.02TeV with the ATLAS detector at the LHC. Jets are reconstructed with the anti-kt algorithm with radius parameter R=0.4 and are measured over the transverse momentum range of 40–1000 GeV in six rapidity intervals covering |y|<2.8. The magnitude of RAA increases with increasing jet transverse momentum, reaching a value of approximately 0.6 at 1 TeV in the most central collisions. The magnitude of RAA also increases towards peripheral collisions. The value of RAA is independent of rapidity at low jet transverse momenta, but it is observed to decrease with increasing rapidity at high transverse momenta.
... Also a clear centrality dependence is observed. Two unexpected features [21] also emerge from those studies: R AA increases only very slowly with increasing jet p T , and no dependence of R AA on jet rapidity is observed. ...
Measurements of the yield and nuclear modification factor, , for inclusive jet production are performed using 0.49 nb of Pb+Pb data at TeV and 25 pb of pp data at TeV with the ATLAS detector at the LHC. Jets are reconstructed with the anti- algorithm with radius parameter R=0.4 and are measured over the transverse momentum range of 40-1000 GeV in six rapidity intervals covering . The magnitude of increases with increasing jet transverse momentum, reaching a value of approximately 0.6 at 1 TeV in the most central collisions. The magnitude of also increases towards peripheral collisions. The value of is independent of rapidity at low jet transverse momenta, but it is observed to decrease with increasing rapidity at high transverse momenta.
... The difference between flow harmonics measured at RHIC and LHC run 1 have been studied in [87] while in [88][89][90] the corresponding differences between LHC run [8], the 2+1 WB EoS from [3], and the 2+1+1 WB EoS from 2016 [5]. 1 and LHC run 2 were investigated. However, the largest difference between collision energies where the assumption that µ B ∼ 0 holds is between AuAu collisions at √ s N N = 200 GeV and PbPb collisions at √ s N N = 5.02 ...
The QCD equation of state at zero baryon chemical potential is the only element of the standard dynamical framework to describe heavy ion collisions that can be directly determined from first principles. Continuum extrapolated lattice QCD equations of state have been computed using 2+1 quark flavors (up/down and strange) as well as 2+1+1 flavors to investigate the effect of thermalized charm quarks on QCD thermodynamics. Lattice results have also indicated the presence of new strange resonances that not only contribute to the equation of state of QCD matter but also affect hadronic afterburners used to model the later stages of heavy ion collisions. We investigate how these new developments obtained from first principles calculations affect multiparticle correlations in heavy ion collisions. We compare the commonly used equation of state S95n-v1, which was constructed using what are now considered outdated lattice results and hadron states, to the current state-of-the-art lattice QCD equations of state with 2+1 and 2+1+1 flavors coupled to the most up-to-date hadronic resonances and their decays. New hadronic resonances lead to an enhancement in the hadronic spectra at intermediate . Using an outdated equation of state can directly affect the extraction of the shear viscosity to entropy density ratio, , of the quark-gluon plasma and results for different flow observables. The effects of the QCD equation of state on multiparticle correlations of identified particles are determined for both AuAu GeV and PbPb TeV collisions. New insights into the to puzzle in ultracentral collisions are found. Flow observables of heavier particles exhibit more non-linear behavior regardless of the assumptions about the equation of state, which may provide a new way to constrain the temperature dependence of .
... In ultra-peripheral nucleus-nucleus collisions, vector mesons can be produced in γ + A interactions off one of the nuclei [12][13][14][15][16][17][18][19][20]. Such interactions are characterized by very low multiplicity, and indeed the majority of such events are exclusive, i.e. γ + A → J/ψ + A. ...
... This procedure enables the identification of single muons with very low transverse momenta. To reduce additional muons or charged particle tracks that can be misidentified as muons and to ensure good-quality reconstructed tracks, the single muons are required to pass the following criteria: more than 4 hits in the tracker, at least one of which is required to be in a pixel layer, a track fit with a χ 2 per degree of freedom less than three, and a transverse (longitudinal) impact parameter of less than 0.3 (20) cm from the measured vertex. For this analysis, only events with dimuons having p T < 1.0 GeV, in the rapidity interval 1.8 < |y| < 2.3, are considered. ...
The cross section for coherent photoproduction accompanied by at least one neutron on one side of the interaction point and no neutron activity on the other side, , is measured with the CMS experiment in ultra-peripheral PbPb collisions at . The analysis is based on a data sample corresponding to an integrated luminosity of 159 , collected during the 2011 PbPb run. The mesons are reconstructed in the dimuon decay channel, while neutrons are detected using zero degree calorimeters. The measured cross section is in the rapidity interval . Using a model for the relative rate of coherent photoproduction processes, this measurement gives a total coherent photoproduction cross section of . The data strongly disfavour the impulse approximation model prediction, indicating that nuclear effects are needed to describe coherent photoproduction in Image 1 interactions. The data are found to be consistent with the leading twist approximation, which includes nuclear gluon shadowing.
... The relevant values of x that can be explored in this analysis are in the 10 −2 to 10 −4 range. In ultra-peripheral nucleus-nucleus collisions, vector mesons can be produced in γ +A interactions off one of the nuclei [12][13][14][15][16][17][18][19][20]. ...
The cross section for coherent J/psi photoproduction accompanied by at least one neutron on one side of the interaction point and no neutron activity on the other side, , is measured with the CMS experiment in ultra-peripheral PbPb collisions at . The analysis is based on a data sample corresponding to an integrated luminosity of 159 inverse microbarns, collected during the 2011 PbPb run. The mesons are reconstructed in the dimuon decay channel, while neutrons are detected using zero degree calorimeters. The measured cross section is in the rapidity interval . Using a model for the relative rate of coherent photoproduction processes, this X[z,n,z] measurement gives a total coherent photoproduction cross section of . The data strongly disfavour the impulse approximation model prediction, indicating that nuclear effects are needed to describe coherent photoproduction in interactions. The data are found to be consistent with the leading twist approximation, which includes nuclear gluon shadowing.
... In QCD the situation is different. The appearance of the finite region of space filled by the given state of quark matter is typical, for example, for the heavy ion collisions [55], or inside the stars [56]. However, out of such regions of space instead of Nothing there is the same quark matter, which is typically in the state with different symmetry. ...
We discuss the possibility to consider quark matter as the topological material. In our consideration we concentrate on the hadronic phase (HP), on the quark - gluon plasma phase (QGP), and on the color - flavor locking (CFL) phase. In those phases we identify the relevant topological invariants in momentum space. The formalism is developed, which relates those invariants and massless fermions that reside on vortices and at the interphases. This formalism is illustrated by the example of vortices in the CFL phase.
... However, in a more realistic scenario, the plasma might have some angular momentum, such as the QGP produced by heavy ion collisions at the RHIC and the LHC. It is natural to think that the peripheral collisions of two nuclei would produce angular momentum to the plasma [10,11]. Although the amount of angular momentum left to the resulting plasma is small compared to the initial angular momentum of the two nuclei, it is expected that the angular momentum fraction increases when the collision energy is increased; as such, the effect of the angular momentum would be significant. ...
We study the screening length Lmax of a moving quark–antiquark pair in a hot plasma, which lives in a two sphere, S2, using the AdS/CFT correspondence in which the corresponding background metric is the four-dimensional Schwarzschild–AdS black hole. The geodesic of both ends of the string at the boundary, interpreted as the quark–antiquark pair, is given by a stationary motion in the equatorial plane by which the separation length L of both ends of the string is parallel to the angular velocity ω. The screening length and total energy H of the quark–antiquark pair are computed numerically and show that the plots are bounded from below by some functions related to the momentum transfer Pc of the drag force configuration. We compare the result by computing the screening length in the reference frame of the moving quark–antiquark pair, in which the background metrics are “Boost-AdS” and Kerr–AdS black holes. Comparing both black holes, we argue that the mass parameters MSch of the Schwarzschild–AdS black hole and MKerr of the Kerr–AdS black hole are related at high temperature by MKerr=MSch(1-a2l2)3/2, where a is the angular momentum parameter and l is the AdS curvature.
... Measuring identified particles at LHC was considered a somewhat boring but necessary exercise, as finding thermal particle ratios essentially identical to the ones measured at SPS and RHIC (save expected differences related to the ratios of particles and antiparticles) was thought to be one of the safest predictions [36]. It therefore came as a surprise when some particle fractions, in particular for the mundane proton, one of the most frequently produced hadrons, were found to differ considerably from expectations (and, to a lesser extent, from the ones measured at RHIC), while others, including those for multi-strange hyperons, were well in line with thermal predictions. ...
Strongly interacting matter as described by the thermodynamics of QCD
undergoes a phase transition, from a low temperature hadronic medium to a high
temperature quark-gluon plasma state. In the early universe this transition
occurred during the early microsecond era. It can be investigated in the
laboratory, in collisions of nuclei at relativistic energy, which create
"fireballs" of sufficient energy density to cross the QCD Phase boundary. We
describe 3 decades of work at CERN, devoted to the study of the QCD plasma and
the phase transition. From modest beginnings at the SPS, ultra-relativistic
heavy ion physics has evolved today into a central pillar of contemporary
nuclear physics and forms a significant part of the LHC program.
