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![Multiplicity densities for Au-Au central collisions at RHIC (experimental data taken from [4]), and prediction for Pb-Pb central collisions at √ s NN = 5.5 TeV. The best fits to data (solid lines) are obtained with Q 0 = 1 GeV, ∆Y ev = 1 and m e f f = 0.25 GeV. The upper limit of the error bands correspond to ∆Y ev = 3 and Q 0 = 0.75 GeV, and the lower limit to ∆Y ev = 0.5 and Q 0 = 1.25 GeV, with m e f f = 0.25 GeV in both cases.](profile/J-Barrette/publication/41786702/figure/fig1/AS:650806751686657@1532175829329/Multiplicity-densities-for-Au-Au-central-collisions-at-RHIC-experimental-data-taken-from.png)
Multiplicity densities for Au-Au central collisions at RHIC (experimental data taken from [4]), and prediction for Pb-Pb central collisions at √ s NN = 5.5 TeV. The best fits to data (solid lines) are obtained with Q 0 = 1 GeV, ∆Y ev = 1 and m e f f = 0.25 GeV. The upper limit of the error bands correspond to ∆Y ev = 3 and Q 0 = 0.75 GeV, and the lower limit to ∆Y ev = 0.5 and Q 0 = 1.25 GeV, with m e f f = 0.25 GeV in both cases.
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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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... results for the pseudorapidity density of charged particles in central Au-Au collisions at √ s NN = 130, 200 and 5500 GeV are shown in Fig. 3 The single inclusive charged hadron p T spectra in Pb-Pb collisions at the LHC, predicted by a combined hydrodynamics+perturbative QCD (pQCD) approach are presented. We present predictions for the inclusive transverse momentum distributions of pions, kaons and (anti)protons produced at mid-rapidity in Pb-Pb collisions at √ s NN = 5.5 ...
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... From the positions and momenta of pions or kaons at freeze out, their correlation functions in the longitudinally comoving frame can be calculated using the program Correlation After Burner [63] to take into account their final-state strong and Coulomb interactions. Shown in the left and right windows of Fig. 23 are, respectively, one-dimensional projections of the correlation functions of midrapidity (−0.5 < y < 0.5) charged pions and kaons with transverse momentum 300 < p T < 1500 MeV/c and their comparison with corresponding ones for central Au+Au collisions at √ s NN = 200 GeV at RHIC, which have been shown to reproduce reasonably measured ...
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... functional form of this expression is motivated by the solution to the nonlinear QCD evolution equations with running coupling [86,87], while the actual values of the numbers B and Y 0 have been chosen in such a way to agree with the HERA/RHIC phenomenology. As shown in Fig. 30, with increasing Y the two saturation momenta approach to each other and clearly for sufficiently large Y, a nucleus will not be more dense than a proton [87]. For momenta p ⊥ larger than Q s , the gluon distribution satisfies geometrical scaling [86,88], i.e. it is a function of only the combined variable p ⊥ /Q s ...
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... for large Y this is proportional to Y 1/6 . The geometrical scaling lines for a proton and a nucleus are shown in Fig. 30. Note that, since Q g is increasing much faster than Q s , a common scaling window exists, at Q s (A, Y) p ⊥ Q g (p, Y) (and for sufficiently large Y), where the gluon distributions for both the nucleus and the proton are described by Eq. ...
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... this window, it is straightforward to calculate the R pA ratio. This is shown in Fig. 31 for two values of pseudorapidity. The upper, dotted, line is the asymptotic prediction of a fixed-coupling scenario, in which the ratio Q 2 s (A, Y)/Q 2 s (p, Y) = const. = A 1/3 , while the lowest, straight, curve is the line of total shadowing R pA = 1/A 1/3 . Our prediction with running coupling is the line in between and it is very ...
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... the d 2 N/dη 2 with simple functions in two slightly different ways (for details see reference [91], we can easily extrapolate to the LHC energy as shown in figure 33. Our prediction is slightly higher than purely linear extrapolation carried out by W. Busza in reference [44]. ...
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... hadronization is implemented through the local parton-hadron duality -namely, we assume that the transformation of partons to hadrons is a soft process which does not change significantly the angular (and thus pseudo-rapidity) distribution of the produced particles. Because of these assumptions, we do not expect our results be accurate for the transverse momentum distributions in AA collisions, but hope that our calculations (see figure 34a) will apply to the total multiplicities. While our approach has been extensively tested at RHIC, an extrapolation of our calculations to the LHC energies requires a good theoretical control over the rapidity dependence of the saturation momentum Q s (y). ...
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... B = 1/(32 π 2 ) (π R 2 A /α S ); R A is the area of the nucleus, and α S is the strong coupling constant. At moderate energies, equation (17) describes an exponential growth of the saturation momentum with rapidity; when extrapolated to the LHC energy this results in the corresponding growth of hadron multiplicity, see curve "1" in figure 34b. At high energies, equation (17) predicts substantial slowing down of the evolution, which results in the decrease of hadron multiplicity as shown in figure 34b by the curve "2". ...
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... moderate energies, equation (17) describes an exponential growth of the saturation momentum with rapidity; when extrapolated to the LHC energy this results in the corresponding growth of hadron multiplicity, see curve "1" in figure 34b. At high energies, equation (17) predicts substantial slowing down of the evolution, which results in the decrease of hadron multiplicity as shown in figure 34b by the curve "2". In both cases, the growth of multiplicity is much slower than predicted in the conventional "soft plus hard" models, see figure 34. ...
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... high energies, equation (17) predicts substantial slowing down of the evolution, which results in the decrease of hadron multiplicity as shown in figure 34b by the curve "2". In both cases, the growth of multiplicity is much slower than predicted in the conventional "soft plus hard" models, see figure 34. We thus expect that the LHC data on hadron multiplicities will greatly advance the understanding of QCD in the strong color field regime. ...
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... can access the gluons only at sufficiently high energies. Relying on the above consideration, a very weak Cronin enhancement was predicted in [98] at √ s NN = 200 GeV, as is depicted in figure 35. A several times stronger effect was predicted in [99] * , and a suppression, rather than enhancement, was the expectation of the color glass condensate (CGC) model [100]. ...
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... we expect that the effects of CGC, both the Cronin enhancement and shadowing * The extremely strong gluon shadowing implemented into the HIJING model is ruled out by the recent NLO analysis [15] of DIS data. Figure 35: Nucleus-to-proton ratio for pion production versus p T . Dashed and solid curves correspond to calculations without or with gluon shadowing [98]. ...
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... ratio is a measure of the number of particles produced in a proton-nucleus collision versus the number of particles in proton-proton collisions times the number of collisions. The transverse momentum of gluons is denoted by k ⊥ and the rapidity variable by Y. In the geometric scaling region shown in Fig. 36a the small-x physics is reasonably described by the BK-equation which emerges in the mean field approximation. Using the BK- equation one finds in the geometric scaling regime in the fixed coupling case that the shape of the unintegrated gluon distribution of the nucleus and proton as a function of k ⊥ is preserved with increasing Y, ...
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... The diffusive scaling, see Fig. 36a, sets in when the dispersion of the different events is ...
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... total gluon shadowing, R pA = 1/A 1/3 , at asymptotic rapidity Y (at fixed A). This result is universal since it does not depend on the initial conditions. Moreover the slope of R pA as a function of k ⊥ descreases with increasing Y. The qualitative behaviour of R pA at fixed α s due to fluctuation effects is shown in Fig. 36b. The above effects of fluctuations on R pA are valid in the fixed coupling case and at very large energy. It isn't clear yet whether the energy at LHC is high enough for them to become important. Moreover, in the case where fluctuation effects are neglected but the coupling is allowed to run, a similar behaviour for R pA is obtained ...
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... first show in fig. 37 pseudorapidity and transverse momentum spectra of charged particles and of different identified hadrons, as well as some particle ratios, in proton-proton scattering at 14 TeV. As for heavy ions, the default version of EPOS considers also in proton- proton scattering the formation of a core (dense area), with a hydrodynamical ...
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... in proton-proton scattering at RHIC, they play an important role at the LHC, which can be seen from the difference between the full curves (full EPOS, including "mini-plasma") and the dotted curves ("mini-plasma option turned off"). The effect is even more drastic when we investigate the multiplicity dependence of particle production, see fig. ...
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... the following, we investigate lead-lead collisions at 5.5 TeV. In fig. 38, we plot the centrality dependence of particle yields for charged particles and different identified hadrons. We observe an increase by roughly 2.5 for pions, and a bigger factor for the heavier ...
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... fig. 39, we show pseudorapidity spectra, for different particles, at different centralities. The pseudorapidity density of charged particles at η = 0 is around 2500, for central ...
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... the total (p T -integrated) pion elliptic flow increases from RHIC to LHC by about 25% [133], very little of this increase (∼ 5%) is of ideal fluid dynamical origin, most of it stemming from the disappearance of late hadronic viscous effects between RHIC and LHC. At fixed p T , Figure 52 shows a decrease of v 2 , reflecting a shift of the momentum anisotropy to larger p T by increased radial flow, which flattens the LHC p T -spectra, affecting the heavier protons more than the lighter pions ( Figure 53, right column). These radial flow effects on v 2 (p T ) are very small for pions but clearly visible for protons. ...
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... p T -dependence of hadron ratios: Hydrodynamic flow, which leads to flatter p T -spectra for heavy than light particles, is a key contributor to the observed strong rise of the ¯ p/π and Λ/K ratios at low p T at RHIC [134]. Figure 53 shows that this rise is slower at LHC than at RHIC (left column) since all spectra are flatter at LHC due to increased radial flow (right column) while their asymptotic ratios at p T → ∞ (given by their fugacity and spin degeneracy ratios [134]) remain similar. ...
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... hydrodynamic evolution is stopped after a time of 7.2 fm/c. Using a Monte Carlo simulation based on the SHARE program [171] Figure 63 shows the angular distribution of particles for the first (left panel) and second (right panel) scenario, without any background subtraction. The omitted near-side jet would appear at φ = 0. ...
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... contour of the loop at zero temperature is depicted in Fig. 73. We have calculated the jet quenching parameterˆqparameterˆ parameterˆq in the SU(3) quenched theory through the evaluation of the Wilson loop (39). To this end, we have used the stochastic vacuum model [217] at T > T c , where T c = 270 MeV is the deconfinement temperature. This model incorporates the gluon condensate which, together ...
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... from the results obtained within perturbative QCD [218] and conformal field theories [216], wherê q ∝ T 3 . The hierarchy of scales in our problem is µ −1 ≪ L ⊥ ≪ β ≪ L , where β is the inverse temperature, and µ = 894 MeV is the inverse vacuum correlation length. Due to the x 4 - periodicity at finite temperature, the contour depicted in Fig. 73 effectively splits into segments whose extensions along the 3rd and the 4th axes are β. Furthermore, due to the short-rangeness of gluonic correlations, which fall off at the vacuum correlation length, the dominant contribution tô q stems from self-interactions of individual segments. We have also calculated the contribution stemming ...
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... with the most simple observables, single particle inclusives in central collisions, we have three dependences to test: the dependence on medium density, jet energy and jet mass. The first is tested by the predicted increased density of the medium to be produced at the LHC (consistency between the left plot and either the central or right plot in Fig. 83). The very high momentum reach available for measurements involving gluon and light quark jets is valuable for the second (radiative versus radiative plus collisional in the central and right hand plots of Fig. 83), and the separate detection of D and B mesons gives us the third (as in Fig. 84). All these together will provide very ...
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... increased density of the medium to be produced at the LHC (consistency between the left plot and either the central or right plot in Fig. 83). The very high momentum reach available for measurements involving gluon and light quark jets is valuable for the second (radiative versus radiative plus collisional in the central and right hand plots of Fig. 83), and the separate detection of D and B mesons gives us the third (as in Fig. 84). All these together will provide very strong constraints on the energy loss models, even before considering observables beyond the single-particle ...
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... "jet fragmentation function" (JFF), D(z), is defined as the probability for a given product of the jet fragmentation to carry a fraction z of the jet transverse energy. Figure 93 shows JFF's in central PbPb collisions with and without partonic energy loss. The number of entries and the statistical errors correspond again to the estimated event rate for one month of LHC run. ...
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... approach show that, in contract to final-state energy loss, the cancellation of the bremsstrahlung in the initial-state is finite [285]. With ∆E/E ∼few %, the observable effect of the bremsstrahlung associated with the multiple soft scattering in nuclei is non-negligible even for very energetic partons in the nuclear rest frame. See left panel of Fig. 103. At the LHC, in central Pb+Pb collisions, the effect of cold nuclear matter energy loss can be as large as doubling the parton rapidity density dN g /dy mainly due to reduced sensitivity in the final state. See right panel of Fig. ...
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... in nuclei is non-negligible even for very energetic partons in the nuclear rest frame. See left panel of Fig. 103. At the LHC, in central Pb+Pb collisions, the effect of cold nuclear matter energy loss can be as large as doubling the parton rapidity density dN g /dy mainly due to reduced sensitivity in the final state. See right panel of Fig. ...
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... predictions for the rapidity distributions are presented in figure 113 and for the total cross section in table 6. The main uncertainties are the photon flux, the quark mass and the size of nuclear effects for the photonuclear case. ...
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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 ...
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... GLV approach is to multiple parton scattering [333] can be easily generalized to various compelling high energy nuclear physics problems, such as meson dissociation in dense nuclear matter [334]. R AA (p T ) results for charm and beauty from this novel suppression mechanism at RHIC and LHC are shown in the left panel of Fig. 123. Attenuation rate similar to the light hadron quenching from radiative energy loss [333] is achieved. The right panel of Fig. 123 shows the suppression of the single non-photonic 0.5(e + + e − ) in central Au+Au and Pb+Pb collisions at RHIC and LHC respectively [334]. The separate measurement of intermediate p T D− and B−meson ...
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... energy nuclear physics problems, such as meson dissociation in dense nuclear matter [334]. R AA (p T ) results for charm and beauty from this novel suppression mechanism at RHIC and LHC are shown in the left panel of Fig. 123. Attenuation rate similar to the light hadron quenching from radiative energy loss [333] is achieved. The right panel of Fig. 123 shows the suppression of the single non-photonic 0.5(e + + e − ) in central Au+Au and Pb+Pb collisions at RHIC and LHC respectively [334]. The separate measurement of intermediate p T D− and B−meson quenching will allow to experimentally determine the correct physics mechanism of heavy flavor suppression ...
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... predictions for the direct photon spectra at y=0 in Pb-Pb at 5.5 TeV are shown in Fig. 130. The thermal contribution dominates over the (quenched) pQCD one up to p T ≈ 4 (1.5) GeV/c in central (peripheral) Pb-Pb. Two differences are worth noting compared to RHIC results [10]: (i) the thermal-prompt crossing point moves up from p T ≈ 2.5 GeV/c to p T ≈ 4.5 GeV/c, and (ii) most of the thermal production in this transition ...
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... hydrodynamic initial conditions for RHIC collisions are described in [360]. For the Figure 131 shows the thermal photon p T -spectra (angle- integrated) for RHIC and LHC. At both collision energies the total spectrum is dominated by quark matter once p T exceeds a few hundred MeV. ...
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... both collision energies the total spectrum is dominated by quark matter once p T exceeds a few hundred MeV. Its inverse slope ("effective tempera- ture") in the range 1.5 < p T < 3 GeV/c increases by almost 50%, from 303 MeV at RHIC to 442 MeV at LHC, reflecting the higher initial temperature and significantly increased radial flow (visible in the HM contribution) at LHC. Figure 132 shows the differential elliptic flow of thermal photons at RHIC and LHC, with quark matter (QM) and hadronic matter (HM) radiation shown separately for comparison. The decrease at high p T of the QM and total photon v 2 reflects the dominance of QM radiation at high p T (emission from the early, hot stage when radial and elliptic flow are still small). ...
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... even lower p T and M thermal radiation from the quark gluon plasma (and also the hadronic phase not considered here) has to be taken into account. Figure 133 shows numerical evaluations of the different contributions discussed above to the e + e − transverse momentum and mass spectrum for central Pb+Pb collisions at LHC. We use next-to-leading order pQCD calculations for Drell Yan and a leading order calculation for jet production. ...
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... cross section σ q ¯ q of interaction of a ¯ qq dipole. For the dipole cross section, we employ the saturation model of Golec-Biernat and Wüsthoff coupled to DGLAP evolution (GBW-DGLAP) [371] which is better suited at large transverse momenta. Without inclusion of DGLAP evolution, the direct photon cross section is overestimated [370]. In Fig. 134, we show the GBW-DGLAP dipole model predictions for inclusive direct photon production at midrapidities for RHIC, CDF and LHC energies. We stress that the theoretical curves in Fig. 134, are the results of a parameter free calculation. Notice also that in contrast to the parton model, neither K-factor (NLO corrections), nor higher ...
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... [371] which is better suited at large transverse momenta. Without inclusion of DGLAP evolution, the direct photon cross section is overestimated [370]. In Fig. 134, we show the GBW-DGLAP dipole model predictions for inclusive direct photon production at midrapidities for RHIC, CDF and LHC energies. We stress that the theoretical curves in Fig. 134, are the results of a parameter free calculation. Notice also that in contrast to the parton model, neither K-factor (NLO corrections), nor higher twist corrections are to be added. No quark-to-photon fragmentation function is needed either. Indeed, the phenomenological dipole cross section is fitted to DIS data and incorporates all ...
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... non-perturbative radiation contributions. For the same reason, in contrast to the parton model, in the dipole approach there is no ambiguity in defining the primordial transverse momentum of partons. Such a small purely non-perturbative primordial momentum does not play a significant role for direct photon production at the given range of p T in Fig. 134. Notice that the color dipole picture accounts only for Pomeron exchange from the target, while ignoring its valence content. Therefore, Reggeons are not taken into account, and as a consequence, the dipole is well suited mainly for high-energy processes. As our result for RHIC and CDF energies indicate, we expect that dipole ...
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... predictions are summarized in Fig. 135. At low mass thermal dileptons are dominated by hadronic radiation, with large modifications due to in-medium vector-meson spectral functions. The QGP contribution takes over at around M1.1 GeV. The yield from correlated open-charm decays is comparable to hadronic emission already at low mass, and dominant at intermediate mass. ...
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... has been argued that direct photon production and direct photon tagged jets provide error-free gauge for the quenching of quarks and gluons and for fixing their initial energy. We show that quantitatively large nuclear corrections must be taken into account for direct γ to become precision probes of the QGP. The left panel of Fig. 136 shows the direct photon production cross section in p+p collisions at √ s = 5.5 TeV the LHC compared to the corresponding cross section at RHIC √ s = 200 GeV to LO in perturbative QCD [376]. Insert shows the fraction of fragmentation to prompt photons versus p T . The right panel of Fig. 136 shows cold nuclear effects, the Cronin ...
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... become precision probes of the QGP. The left panel of Fig. 136 shows the direct photon production cross section in p+p collisions at √ s = 5.5 TeV the LHC compared to the corresponding cross section at RHIC √ s = 200 GeV to LO in perturbative QCD [376]. Insert shows the fraction of fragmentation to prompt photons versus p T . The right panel of Fig. 136 shows cold nuclear effects, the Cronin [283], dynamical shadowing [377] and cold nuclear matter energy loss [285], in d+A reactions at LHC energies. Comparison to data in 0-20% central d+Au collisions at RHIC is also ...
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... left panel of Fig. 137 shows the QGP effect (final-state interactions) in central Pb+Pb collisions at √ s = 5.5 TeV. Parton rapidity densities dN g /dy ∼ 2000 − 4000 [283], as for π 0 quenching and heavy meson dissociation, are used. Direct photon quenching closely follows the ratio γ prompt /γ fragmentation [376]. At low p T attenuation is QGP-dominated ...
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... quenching closely follows the ratio γ prompt /γ fragmentation [376]. At low p T attenuation is QGP-dominated with significant and measurable suppression R AA (p T ) ∼ 0.5. Nevertheless, such quenching is smaller than the one for π 0 's and reflects the C F /C A average squared color charge difference for quark and gluon jets. The right panel of Fig. 137 includes the effect of initial-state cold nuclear matter energy loss. At high p T these can be comparable to the final-state quenching in the QGP ...
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... reasonable assumptions, the main observables which signal the presence of an equilibrated spinning system are (see figure 138): a decrease of chemical freeze-out temperature and an increase of transverse momentum spectra broadening (enhanced radial flow) as a function of centrality; a large enhancement of elliptic flow and a polarization of emitted particles along the direction of angular momentum. The latter is the cleanest signature of a spinning system. ...
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... the Frankfurt Institute for Theoretical Physics and FIAS for continued support, and CERN theory division for providing local support necessary for attending the workshop where this work is presented. He would also like to thank Sangyong Jeon, Marek Gazdzicki, Mike Hauer, Johann Rafelski and Mark Gorenstein for useful and productive discussions. Fig. 43 and Fig. 44. He would like to thank RIKEN, BNL and the U.S. Department of Energy (Contract No. DE-AC02-98CH10886) for providing the facilities essential for the completion of this ...
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.
