Abstract: Nonmonotonic variation with collision energy (sqrt[s_{NN}]) of the moments of the net-baryon number distribution in heavy-ion collisions, related to the correlation length and the susceptibilities of the system, is suggested as a signature for the quantum chromodynamics critical point. We report the first evidence of a nonmonotonic variation in the kurtosis times variance of the net-proton number (proxy for net-baryon number) distribution as a function of sqrt[s_{NN}] with 3.1 σ significance for head-on (central) gold-on-gold (Au+Au) collisions measured solenoidal tracker at Relativistic Heavy Ion Collider. Data in noncentral Au+Au collisions and models of heavy-ion collisions without a critical point show a monotonic variation as a function of sqrt[s_{NN}].

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Topics: Critical point (thermodynamics) (51%)

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33 results found

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Abstract: The beam energy scan (BES) program at the BNL Relativistic Heavy Ion Collider (RHIC) was extended to energies below sNN=7.7 GeV in 2015 by successful implementation of the fixed-target mode of operation in the STAR (Solenoidal Tracker At RHIC) experiment. In this mode, ions circulate in one ring of the collider and interact with a stationary target at the entrance of the STAR time projection chamber. The first results for Au+Au collisions at sNN=4.5 GeV are presented, demonstrating good performance of all the relevant detector subsystems in fixed-target mode. Results presented here include directed and elliptic flow of identified hadrons, and radii from pion femtoscopy. The latter, together with recent HADES results, reveal a long-sought peak structure that may be caused by the system evolving through a first-order phase transition from quark-gluon plasma to the hadronic phase. Directed and elliptic flow for pions are presented for the first time at this beam energy. Pion and proton elliptic flow show behavior which hints at constituent quark scaling, and demonstrate that a definitive conclusion will be achievable using the full statistics of the ongoing second phase of BES (BES-II). In particular, BES-II to date has recorded fixed-target data sets with two orders of magnitude more events at each of nine energies between sNN=3.0 and 7.7 GeV.

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Topics: Elliptic flow (60%), Relativistic Heavy Ion Collider (57%), Collider (53%) ... show more

11 Citations

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Abstract: We studied the effects of centrality fluctuation and deuteron formation on the cumulant ( \begin{document}$C_n$\end{document} ) and correlation functions ( \begin{document}$\kappa_n$\end{document} ) of protons up to the sixth order in the most central ( \begin{document}$b$\end{document} \begin{document}$ \sqrt {{s_{{{NN}}}}}\; $\end{document} = 3 GeV in a microscopic transport model (JAM). The results are presented as a function of rapidity acceptance within the transverse momentum 0.4 < pT < 2 GeV/c. We compared the results obtained by the centrality bin width correction (CBWC) using charged reference particle multiplicities with the CBWC using impact parameter bins. It was found that, at low energies, the centrality resolution for determining the collision centrality using charged particle multiplicities is not sufficient to reduce the initial volume fluctuation effect for higher-order cumulant analysis. New methods need to be developed to classify events with high centrality resolution for heavy-ion collisions at low energies. Finally, we observed that the formation of deuterons suppresses the higher-order cumulants and correlation functions of protons and found it to be similar to the efficiency effect. This work can serve as a noncritical baseline for the QCD critical point search in the high baryon density region.

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Topics: Impact parameter (59%), Centrality (53%)

10 Citations

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Abstract: Author(s): Abdallah, MS; Adam, J; Adamczyk, L; Adams, JR; Adkins, JK; Agakishiev, G; Aggarwal, I; Aggarwal, MM; Ahammed, Z; Alekseev, I; Anderson, DM; Aparin, A; Aschenauer, EC; Ashraf, MU; Atetalla, FG; Attri, A; Averichev, GS; Bairathi, V; Baker, W; Ball Cap, JG; Barish, K; Behera, A; Bellwied, R; Bhagat, P; Bhasin, A; Bielcik, J; Bielcikova, J; Bordyuzhin, IG; Brandenburg, JD; Brandin, AV; Bunzarov, I; Butterworth, J; Cai, XZ; Caines, H; Calderon De La Barca Sanchez, M; Cebra, D; Chakaberia, I; Chaloupka, P; Chan, BK; Chang, FH; Chang, Z; Chankova-Bunzarova, N; Chatterjee, A; Chattopadhyay, S; Chen, D; Chen, J; Chen, JH; Chen, X; Chen, Z; Cheng, J; Chevalier, M; Choudhury, S; Christie, W; Chu, X; Crawford, HJ; Csanad, M; Daugherity, M; Dedovich, TG; Deppner, IM; Derevschikov, AA; Dhamija, A; Di Carlo, L; Didenko, L; Dong, X; Drachenberg, JL; Dunlop, JC; Elsey, N; Engelage, J; Eppley, G; Esumi, S; Evdokimov, O; Ewigleben, A; Eyser, O; Fatemi, R; Fawzi, FM; Fazio, S; Federic, P; Fedorisin, J; Feng, CJ; Feng, Y; Filip, P; Finch, E; Fisyak, Y; Francisco, A; Fu, C | Abstract: We report a systematic measurement of cumulants, Cn, for net-proton, proton, and antiproton multiplicity distributions, and correlation functions, κn, for proton and antiproton multiplicity distributions up to the fourth order in Au+Au collisions at sNN=7.7, 11.5, 14.5, 19.6, 27, 39, 54.4, 62.4, and 200 GeV. The Cn and κn are presented as a function of collision energy, centrality and kinematic acceptance in rapidity, y, and transverse momentum, pT. The data were taken during the first phase of the Beam Energy Scan (BES) program (2010-2017) at the BNL Relativistic Heavy Ion Collider (RHIC) facility. The measurements are carried out at midrapidity (|y|l 0.5) and transverse momentum 0.4

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9 Citations

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Abstract: We studied the effects of centrality fluctuation and deuteron formation on the cumulants ($C_n$) and correlation functions ($\kappa_n$) of protons up to sixth order in most central ($b<3$ fm) Au+Au collisions at $\sqrt{s_\mathrm{NN}}$ = 3 GeV from a microscopic transport model (JAM). The results are presented as a function of rapidity acceptance within transverse momentum $0.4

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Topics: Impact parameter (53%)

5 Citations

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Abstract: We develop a flexible, relativistically covariant parameterization of dense nuclear matter equation of state suited for inclusion in computationally demanding hadronic transport simulations. Within an implementation in the hadronic transport code SMASH, we show that effects due to bulk thermodynamic behavior are reproduced in dynamic hadronic systems, demonstrating that hadronic transport can be used to study critical behavior in dense nuclear matter, both at and away from equilibrium. We also show that two-particle correlations calculated from hadronic transport simulation data follow theoretical expectations based on the second order cumulant ratio, and constitute a clear signature of crossing the phase diagram above the critical point.

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Topics: Nuclear matter (53%), Critical point (thermodynamics) (52%)

3 Citations

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53 results found

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Abstract: The standard model of particle physics predicts two phase transitions that are relevant for the evolution of the early Universe. One, the quantum chromodynamics transition, involves the strong force that binds quarks into protons and neutrons. Despite much theoretical effort, the nature of this transition remains ambiguous. Now Aoki et al. report computationally demanding calculations that suggest that there was no true phase transition. Instead, an analytic crossover took place, involving a rapid, continuous change with temperature as opposed to a jump. This means that it will be difficult to find experimental evidence of a transition from astronomical observations. The standard model of particle physics predicts two transitions that are relevant for the evolution of the early Universe. Computationally demanding calculations now reveal that a real phase transition did not occur, but rather an analytic crossover, involving a rapid change (as opposed to a jump) as the temperature varies. Quantum chromodynamics (QCD) is the theory of the strong interaction, explaining (for example) the binding of three almost massless quarks into a much heavier proton or neutron—and thus most of the mass of the visible Universe. The standard model of particle physics predicts a QCD-related transition that is relevant for the evolution of the early Universe. At low temperatures, the dominant degrees of freedom are colourless bound states of hadrons (such as protons and pions). However, QCD is asymptotically free, meaning that at high energies or temperatures the interaction gets weaker and weaker1,2, causing hadrons to break up. This behaviour underlies the predicted cosmological transition between the low-temperature hadronic phase and a high-temperature quark–gluon plasma phase (for simplicity, we use the word ‘phase’ to characterize regions with different dominant degrees of freedom). Despite enormous theoretical effort, the nature of this finite-temperature QCD transition (that is, first-order, second-order or analytic crossover) remains ambiguous. Here we determine the nature of the QCD transition using computationally demanding lattice calculations for physical quark masses. Susceptibilities are extrapolated to vanishing lattice spacing for three physical volumes, the smallest and largest of which differ by a factor of five. This ensures that a true transition should result in a dramatic increase of the susceptibilities. No such behaviour is observed: our finite-size scaling analysis shows that the finite-temperature QCD transition in the hot early Universe was not a real phase transition, but an analytic crossover (involving a rapid change, as opposed to a jump, as the temperature varied). As such, it will be difficult to find experimental evidence of this transition from astronomical observations.

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Topics: Quantum chromodynamics (58%), Phase transition (58%), Strong interaction (57%) ... show more

1,390 Citations

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Abstract: Hadron-hadron collisions at high energies are investigated in the Ultra-relativistic-Quantum-Molecular-Dynamics approach (UrQMD). This microscopic transport model is designed to study pp, pA and A+A collisions. It describes the phenomenology of hadronic interactions at low and intermediate energies ($\sqrt s 5$ GeV, the excitation of color strings and their subsequent fragmentation into hadrons dominates the multiple production of particles in the UrQMD model. The model shows a fair overall agreement with a large body of experimental h-h data over a wide range of h-h center-of-mass energies. Hadronic reaction data with higher precision would be useful to support the use of the UrQMD model for relativistic heavy ion collisions.

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1,085 Citations

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Abstract: Combining perturbative-QCD inspired models for multiple jet production with low ${p}_{T}$ multistring phenomenology, we develop a Monte Carlo event generator hijing to study jet and multiparticle production in high energy $\mathrm{pp}$, $\mathrm{pA}$, and $\mathrm{AA}$ collisions. The model includes multiple minijet production, nuclear shadowing of parton distribution functions, and a schematic mechanism of jet interactions in dense matter. Glauber geometry for multiple collisions is used to calculate $\mathrm{pA}$ and $\mathrm{AA}$ collisions. The phenomenological parameters are adjusted to reproduce essential features of $\mathrm{pp}$ multiparticle production data for a wide energy range ($\sqrt{s}=5\ensuremath{-}2000$ GeV). Illustrative tests of the model on $p+A$ and light-ion $B+A$ data at $\sqrt{s}=20$ GeV/nucleon and predictions for Au+Au at energies of the BNL Relativistic Heavy Ion Collider ($\sqrt{s}=200$ GeV/nucleon) are given.

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Topics: Distribution function (60%)

1,066 Citations

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Marcus Bleicher^{1}, E. E. Zabrodin^{1}, E. E. Zabrodin^{2}, E. E. Zabrodin^{3} +11 more•Institutions (5)

Abstract: Hadron-hadron (h-h) collisions at high energies are investigated in the ultra-relativistic quantum molecular dynamics (UrQMD) approach. This microscopic transport model describes the phenomenology of hadronic interactions at low and intermediate energies ( 5 GeV, the excitation of colour strings and their subsequent fragmentation into hadrons dominates the multiple production of particles in the UrQMD model. The model shows a fair overall agreement with a large body of experimental h-h data over a wide range of h-h centre-of-mass energies. Hadronic reaction data with higher precision would be useful to support the use of the UrQMD model for relativistic heavy-ion collisions.

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Topics: Quark (51%)

991 Citations

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Alexei Bazavov^{1}, Tanmoy Bhattacharya^{2}, M. Cheng^{3}, Carleton DeTar^{4} +19 more•Institutions (12)

Abstract: We present results on the chiral and deconfinement properties of the QCD transition at finite temperature. Calculations are performed with $2+1$ flavors of quarks using the p4, asqtad, and HISQ/tree actions. Lattices with temporal extent ${N}_{\ensuremath{\tau}}=6$, 8, and 12 are used to understand and control discretization errors and to reliably extrapolate estimates obtained at finite lattice spacings to the continuum limit. The chiral transition temperature is defined in terms of the phase transition in a theory with two massless flavors and analyzed using $O(N)$ scaling fits to the chiral condensate and susceptibility. We find consistent estimates from the HISQ/tree and asqtad actions and our main result is ${T}_{c}=154\ifmmode\pm\else\textpm\fi{}9\text{ }\text{ }\mathrm{MeV}$.

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Topics: Quantum chromodynamics (52%), Deconfinement (51%)

884 Citations