Heavy Ion Physics at NICA Simulations G. Musulmanbekov, V Heavy Ion Physics at NICA Simulations G.Musulmanbekov, V. Toneev and the Physics Group on NICA

Search for signals of Phase Transition in Au + Au collisions at √sNN = 3 – 9 GeV Motivation The main goal of the NICA experiment is to study the behaviour of nuclear matter in vicinity of the QCD critical endpoint. To extract information on the equation-of-state of baryonic matter at high densities. Search for signals of Phase Transition in Au + Au collisions at √sNN = 3 – 9 GeV

Search for signals of Phase Transition in Au + Au collisions at √sNN = 3 – 9 GeV Signatures of Possibile Phase Transition : Strange particle enhancement Hard spectrum of strange mesons Charmonium suppression Dielectron mass spectrum enhancement at the range 0.2 – 0.6 GeV/c

Search for signals of Phase Transition in Au + Au collisions at √sNN = 3 – 9 GeV Observables : Global characteristics of identified hadrons, including strange baryons Strange to non-strange particles ratio Transverse momentum spectra Fluctuations in multiplicity and transverse momenta Directed and elliptic flows Particle correlations (femtoscopy, HBT correlations) Dilepton spectra

Search for signals of Phase Transition in Au + Au collisions at √sNN = 3 – 9 GeV Simulation Tools : UrQMD 1.3, UrQMD 2.2 104 central events at 3, 3.8, 5, 7, 9 GeV 105 min bias events at 3, 3.8, 5, 7, 9 GeV FastMC 104 central events at 3, 5, 7, 9 GeV PLUTO 106 central events at 3, 5, 7, 9 GeV

Mean multiplicities in Au-Au collisions Simulated by UrQMD min Mean multiplicities in Au-Au collisions Simulated by UrQMD min.bias events  √s GeV All Charged Protons π - π + K+ K- 3 279.6 130.5 68.62 17.76 12.63 0.5206 0.0261 5 610.8 296.8 76.20 61.31 50.81 4.548 0.9366 7 876.2 424.5 80.62 95.66 83.06 7.758 2.471 9 1067 515.6 83.27 120.7 107.1 10.03 4.006

Mean multiplicities in Au-Au collisions Simulated by UrQMD central collisions (b ≤ 3 fm)  Part. 3 GeV/n 5 GeV/n 7 GeV/n 9 GeV/n All p > 100 GeV/c p > 100 GeV/c p > 100 GeV/c |η|<1 |η|<2   Charg 305.8 196.3 281.5 993.0 406.3 635.3 1058 536.5 882.0 1332 635.7 1076 p 176.5 114.4 167.3 203.7 108.2 177.6 220.7 102.1 176.8 238.1 99.3 176.3 π+ 51.9 33.0 46.0 223.6 126.7 193.8 360.2 188.8 303.9 474.4 236.1 391.3 π- 71.7 45.0 62.7 265.6 148.4 227.6 410.8 212.1 343.5 530.2 259.6 433.9 π0 64.5 40.3 56.4 272.5 152.1 233.3 437.6 225.2 365.4 573.9 280.7 469.5 K+ 3.32 2.29 3.11 23.3 13.2 21.0 37.9 18.8 32.6 49.3 22.0 40.5 K- 0.170 0.101 0.152 4.45 2.58 3.99 11.62 6.25 10.19 18.9 9.5 16.2 K0 3.47 2.34 3.25 28.4 25.6 49.5 24.9 42.6 68.2 32.0 56.6 Λ 3.75 2.66 3.74 23.5 13.7 22.2 33.3 16.6 29.5 40.0 17.5 32.9 Σ+ 0.881 0.616 0.880 5.54 3.26 5.27 7.60 3.77 6.71 9.10 3.95 7.48 Σ- 1.231 0.873 1.230 6.26 3.58 5.90 8.28 4.08 7.36 9.85 4.19 8.00 Σ0 0.621 5.36 5.05 7.46 3.69 6.62 8.72 3.71 7.11 Ξ- 0.009 0.006 0.43 0.27 0.42 0.83 0.44 0.74 1.21 0.56 1.03 Ξ0 0.013 0.010 0.35 0.21 0.34 0.77 0.37 0.67 1.18 0.52 0.99 Ω- 0.003 0.002 0.005 0.030 0.014 0.023 K+/π+ 0.064 0.069 0.068 0.104 0.108 0.105 0.100 0.107 0.093 0.103 K-/π- .0024 .0022 0.017 0.018 0.028 0.029 0.036 0.037 ΛΣ/π0 0.072 0.081 0.082 0.106 0.111 0.117 0.090 0.099 0.085 0.077 The most topic of interest is the ratio of the yield of strange particles to non-strange ones (the last three rows). As discovered in the experiment NA49 the energetic behavior of this ratio indicates the enhanced yield of the strange hyperons and positive kaons at the energy range of √s = 6-10 GeV. This result, called the “horn” effect is not understandable up to now.

Mean multiplicities in Au-Au collisions Simulated by UrQMD central collisions (b ≤ 3 fm)  Part. 3 GeV/n 5 GeV/n 7 GeV/n 9 GeV/n All p > 100 GeV/c p > 100 GeV/c p > 100 GeV/c |η|<1 |η|<2   Charg 305.8 196.3 281.5 993.0 406.3 635.3 1058 536.5 882.0 1332 635.7 1076 p 176.5 114.4 167.3 203.7 108.2 177.6 220.7 102.1 176.8 238.1 99.3 176.3 π+ 51.9 33.0 46.0 223.6 126.7 193.8 360.2 188.8 303.9 474.4 236.1 391.3 π- 71.7 45.0 62.7 265.6 148.4 227.6 410.8 212.1 343.5 530.2 259.6 433.9 π0 64.5 40.3 56.4 272.5 152.1 233.3 437.6 225.2 365.4 573.9 280.7 469.5 K+ 3.32 2.29 3.11 23.3 13.2 21.0 37.9 18.8 32.6 49.3 22.0 40.5 K- 0.170 0.101 0.152 4.45 2.58 3.99 11.62 6.25 10.19 18.9 9.5 16.2 K0 3.47 2.34 3.25 28.4 25.6 49.5 24.9 42.6 68.2 32.0 56.6 Λ 3.75 2.66 3.74 23.5 13.7 22.2 33.3 16.6 29.5 40.0 17.5 32.9 Σ+ 0.881 0.616 0.880 5.54 3.26 5.27 7.60 3.77 6.71 9.10 3.95 7.48 Σ- 1.231 0.873 1.230 6.26 3.58 5.90 8.28 4.08 7.36 9.85 4.19 8.00 Σ0 0.621 5.36 5.05 7.46 3.69 6.62 8.72 3.71 7.11 Ξ- 0.009 0.006 0.43 0.27 0.42 0.83 0.44 0.74 1.21 0.56 1.03 Ξ0 0.013 0.010 0.35 0.21 0.34 0.77 0.37 0.67 1.18 0.52 0.99 Ω- 0.003 0.002 0.005 0.030 0.014 0.023 K+/π+ 0.064 0.069 0.068 0.104 0.108 0.105 0.100 0.107 0.093 0.103 K-/π- .0024 .0022 0.017 0.018 0.028 0.029 0.036 0.037 ΛΣ/π0 0.072 0.081 0.082 0.106 0.111 0.117 0.090 0.099 0.085 0.077 The most topic of interest is the ratio of the yield of strange particles to non-strange ones (the last three rows). As discovered in the experiment NA49 the energetic behavior of this ratio indicates the enhanced yield of the strange hyperons and positive kaons at the energy range of √s = 6-10 GeV. This result, called the “horn” effect is not understandable up to now.

Mean multiplicities in Au-Au collisions Simulated by UrQMD central collisions (b ≤ 3 fm)  Part. 3 GeV/n 5 GeV/n 7 GeV/n 9 GeV/n All p > 100 GeV/c p > 100 GeV/c p > 100 GeV/c |η|<1 |η|<2   Charg 305.8 196.3 281.5 993.0 406.3 635.3 1058 536.5 882.0 1332 635.7 1076 p 176.5 114.4 167.3 203.7 108.2 177.6 220.7 102.1 176.8 238.1 99.3 176.3 π+ 51.9 33.0 46.0 223.6 126.7 193.8 360.2 188.8 303.9 474.4 236.1 391.3 π- 71.7 45.0 62.7 265.6 148.4 227.6 410.8 212.1 343.5 530.2 259.6 433.9 π0 64.5 40.3 56.4 272.5 152.1 233.3 437.6 225.2 365.4 573.9 280.7 469.5 K+ 3.32 2.29 3.11 23.3 13.2 21.0 37.9 18.8 32.6 49.3 22.0 40.5 K- 0.170 0.101 0.152 4.45 2.58 3.99 11.62 6.25 10.19 18.9 9.5 16.2 K0 3.47 2.34 3.25 28.4 25.6 49.5 24.9 42.6 68.2 32.0 56.6 Λ 3.75 2.66 3.74 23.5 13.7 22.2 33.3 16.6 29.5 40.0 17.5 32.9 Σ+ 0.881 0.616 0.880 5.54 3.26 5.27 7.60 3.77 6.71 9.10 3.95 7.48 Σ- 1.231 0.873 1.230 6.26 3.58 5.90 8.28 4.08 7.36 9.85 4.19 8.00 Σ0 0.621 5.36 5.05 7.46 3.69 6.62 8.72 3.71 7.11 Ξ- 0.009 0.006 0.43 0.27 0.42 0.83 0.44 0.74 1.21 0.56 1.03 Ξ0 0.013 0.010 0.35 0.21 0.34 0.77 0.37 0.67 1.18 0.52 0.99 Ω- 0.003 0.002 0.005 0.030 0.014 0.023 K+/π+ 0.064 0.069 0.068 0.104 0.108 0.105 0.100 0.107 0.093 0.103 K-/π- .0024 .0022 0.017 0.018 0.028 0.029 0.036 0.037 ΛΣ/π0 0.072 0.081 0.082 0.106 0.111 0.117 0.090 0.099 0.085 0.077 The most topic of interest is the ratio of the yield of strange particles to non-strange ones (the last three rows). As discovered in the experiment NA49 the energetic behavior of this ratio indicates the enhanced yield of the strange hyperons and positive kaons at the energy range of √s = 6-10 GeV. This result, called the “horn” effect is not understandable up to now.

Simulated charged multiplicity distributions in central collisions (b < 3fm)

Simulated charged pseudorapidity distributions in central collisions (b < 3fm)

Simulated charged pseudorapidity distributions in central collisions (b < 3fm) MPD -2 < η < 2

Simulated charged pseudorapidity distributions in central collisions (b < 3fm) MPD -1 < η < 1

Strange Baryons Yield Part. 3 GeV/n 5 GeV/n 7 GeV/n 9 GeV/n All p > 100 GeV/c p > 100 GeV/c p > 100 GeV/c |η|<1 |η|<2   Λ 3.75 2.66 3.74 23.5 13.7 22.2 33.3 16.6 29.5 40.0 17.5 32.9 Σ+ 0.881 0.616 0.880 5.54 3.26 5.27 7.60 3.77 6.71 9.10 3.95 7.48 Σ- 1.231 0.873 1.230 6.26 3.58 5.90 8.28 4.08 7.36 9.85 4.19 8.00 Σ0 0.621 5.36 3.11 5.05 7.46 3.69 6.62 8.72 3.71 7.11 Ξ- 0.009 0.006 0.43 0.27 0.42 0.83 0.44 0.74 1.21 0.56 1.03 Ξ0 0.013 0.010 0.35 0.21 0.34 0.77 0.37 0.67 1.18 0.52 0.99 Ω- 0.003 0.002 0.005 0.030 0.014 0.023 Only those hyperons are measurable which have charged decay verticies. Table: Marked hyperons are accessible through their decays into charged hadrons

Registration efficiency (%) Accessible Hyperons Mass(GeV/c2) Lifetime cτ (cm) Multiplicity Decay channel BR(%) Registration efficiency (%) |p| > 0.1 GeV/c -1 < y < 1 Λ Ξ- Ω- 1.116 1.321 1.672 7.89 4.91 2.46 39.8 1.21 0.03 p + π- Λ + π- Λ + K- 63.9 99.9 67.8 16 8 5

Accessible Hyperons Λ → pπ- Ξ- → Λπ- → pπ- π- Ω- → ΛK- → pK- π- The invariant mass spectra for proton – pion pair selected in events are generated by UrQMD. To simulate the efficiency of track reconstruction we applied Gaussian dispersion for each component of particle momenta.

Strange to non-Strange ratios in central collisions “Horn” Effect <π- >/<π+> Au+Au/Pb+Pb, central <K+ >/<π+> Au+Au/Pb+Pb, central Particle ratio for central Au + Au collisions. The experimental data are from AGS and NA49 for Pb+Pb collisions. Calculations were performed with the usage of UrQMD and HSD codes. There is an effect of the maximal enhancement of K+ yield (“horn” effect) in the energy range Elab/A = 20 – 40 GeV. Transport models HSD (Hadron String Dynamics) and UrQMD contradict with the experimental data.

Strange to non-Strange ratios in central collisions “Horn” Effect Particle ratio for central Au + Au collisions. The experimental data are from AGS and NA49 for Pb+Pb collisions. Calculations were performed with the usage of UrQMD and HSD codes. There is an effect of the maximal enhancement of K+ yield (“horn” effect) in the energy range Elab/A = 20 – 40 GeV. Transport models HSD (Hadron String Dynamics) and UrQMD contradict with the experimental data.

Strange to nonStrange ratios in central collisions Particle ratio for central Au + Au collisions. The experimental data are from AGS and NA49 for Pb+Pb collisions. Calculations were performed with the usage of UrQMD and HSD codes. There is an effect of the maximal enhancement of K+ yield (“horn” effect) in the energy range Elab/A = 20 – 40 GeV. Transport models HSD (Hadron String Dynamics) and UrQMD contradict with the experimental data.

Strange to nonStrange ratios in central collisions Particle ratio for central Au + Au collisions. The experimental data are from AGS and NA49 for Pb+Pb collisions. Calculations were performed with the usage of UrQMD and HSD codes. There is an effect of the maximal enhancement of K+ yield (“horn” effect) in the energy range Elab/A = 20 – 40 GeV. Transport models HSD (Hadron String Dynamics) and UrQMD contradict with the experimental data.

Strange to nonStrange ratios in central collisions Particle ratio for central Au + Au collisions. The experimental data are from AGS and NA49 for Pb+Pb collisions. Calculations were performed with the usage of UrQMD and HSD codes. There is an effect of the maximal enhancement of K+ yield (“horn” effect) in the energy range Elab/A = 20 – 40 GeV. Transport models HSD (Hadron String Dynamics) and UrQMD contradict with the experimental data.

Transverse Mass Spectra of Mesons in central collisions T – inverse slope Left plot: Comparison of transverse mass spectra for pions and kaons from HSD and UrQMD for central Pb + Pb collisions with experimental data. Right plot: Comparison of inverse slopes for pions and kaons from HSD and UrQMD for central Pb + Pb collisions pp reactions as a function of invariant energy with experimental data. Again, the data demonstrate unusual behavior for kaons in central Pb + Pb collisions at √s = 6-10 GeV.

Transverse Mass Spectra of Mesons in central collisions

Transverse Mass Spectra of Mesons in central collisions

Scaled multiplicity variances ω (h+) ω (h-) Another topic of the study is multiplicity fluctuations. It is believed that at critical point fluctuations could drastically increase. Left column: Scaled multiplicity Middle column: Scaled multiplicity variance for Pb+Pb/Au+Au collisions compared with the UrQMD and HSD models. Right column: UrQMD predictions for NICA/MPD for 4π and geometrical MPD acceptance. ω (hch)

Scaled multiplicity variances NA49 results Measured scaled variances are close to the Poisson one – close to 1! No sign of increased fluctuations as expected for a freezeout near the critical point of strongly interacting matter was observed.

Transverse momentum fluctuations To exclude trivial fluctuations from consideration the following variable is used: When the system consist of independently emitted particles (no inter-particle correlations) ΦPT assumes a value of zero. On the other hand, if A+A collisions can be treated as an incoherent superposition, of independent N-N interactions (superposition model), then ΦPT has the constant value, the same for A+A and N+N interactions. It also eliminates geometric fluctuations due to the impact parameter variation. Thus, ΦpT is ’deaf’ to the statistical noise and ’blind’ to the collision centrality. For the system of independently emitted particles (no inter-particle correlations) Фpt goes to zero.

Directed flow v1 & elliptic flow v2 x z Non-central Au+Au collisions: Interactions between constituents leads to a pressure gradients => spartial asymmetry is converted in asymmetry in momentum space => collective flows - directed flow V2>0 indicates in-plane emission of particles V2<0 corresponds to out-of-plane emission (squeeze-out perpendicular to the reaction plane) - elliptic flow

Direct flow Au + Au collisions at √sNN = 7GeV, b = 5 – 9 fm

Direct flow slope Collision Energy Dependence Au + Au, b = 5 – 9 fm

Elliptic flow Au + Au collisions at √sNN = 7GeV, b = 5 fm

Elliptic flow Collision Energy Dependence Au+Au/Pb+Pb, b = 5 – 9 fm

HBT interferometry C (q) q (GeV/c) Two-particle interferometry: p-space separation  space-time separation Rside Rlong Rout p1 p2 x1 x2 qout qside qlong HBT: Quantum interference between identical particles q (GeV/c) C (q) 1 2 Final-state effects (Coulomb, strong) also can cause correlations, need to be accounted for Gaussian model (3-d): Sergey Panitkin

HBT interferometry

HBT interferometry

HBT interferometry

Dilepton Spectra

Dilepton Spectra

Dilepton Spectra

Dilepton Spectra

Dilepton Spectra

Conclusions New simulation codes which take into account phase transitions of deconfinement and/or chiral symmetry restoration are needed.

Thank you!