QGP Brookhaven National Laboratory 8102016 JPARC HI collaboration

重イオンによるQGP物理 坂口貴男 Brookhaven National Laboratory 8/10/2016 J-PARC HI collaboration meeting 1

Heavy Ion collisions at J-PARC Low energy （Landau picture） FAIR@GSI, NICA@Dubna, JPARC, RHIC@BNL JAM model, Y. Nara, Phys. Rev. C 61, 024901(1999) r/r 0 Au+Au U+U (reaches 8. 6 r 0) 5/26/2016 8/10/2016 J-PARC 2 HI collaboration meeting Stopping High T, High m. B

Strange matter production at J-PARC • Production rate of hypernuclei is highest at J-PARC energy J-PARC A. Andronic, PLB 697 (2011) 203 – Produced through coalescence • Strange-rich matter may be produced – Strangelets is one object to look at. – Historical and on-going research • AGS: e. g. PRC 54, R 15 (1996) • RHIC: PRC 76, 011901(R), (2007) • Study strangeness-rich system RHIC, LHC J-PARC N(u)=N(ubar), N(d)=N(dbar) N(u, d)>N(ubar, dbar) s u d s d u u u d d u s s d s s u u s d d u d 8/10/2016 d Neutron star N(ubar, dbar, sbar)=0 J-PARC HI collaboration meeting u d d d u u s s s 3

イベント選定ー衝突中心度 • Centrality: Event class variable proportional to impact parameters – 0%: b=0, Central collisions – 100%: b=bmax, Peripheral collisions 0% centrality 100% centrality • Number of participant nucleons (Npart) – Calculable from impact parameters – A measure of energy density • Number of nucleon collisions (Ncoll) – Number of nucleon collisions in an event – Nucleons are considered to collide individually in high energy collisions 8/10/2016 Participant nucleons Spectator nucleons J-PARC HI collaboration meeting 4

新しいイベント選定 • We could approach high dense matter by exploring new event selection methods TS, H. Sako and M. Kitazawa, in prep. • Select events by strangeness or anti-protons – Classify events by the fraction of strange particles to all the particles, “Strangity”, “Baryonity” • In addition to “centrality” • Statistics-starved measurement realized only by using J-PARC Heavy Ion machine 8/10/2016 J-PARC HI collaboration meeting 5

Nagamiya plots at J-PARC • At the beginning of RHIC, a set of fancy plots for advertising the QGP study feasibility at RHIC was produced • We should make similar plots for J-PARC HI 8/10/2016 J-PARC HI collaboration meeting 6

RHIC実験開始前の測定量候補 8/10/2016 J-PARC HI collaboration meeting 7

J-PARC HI case (Preview) • Measurements as a function of strangity or baryonity 8/10/2016 J-PARC HI collaboration meeting 8

0. Know your position • Temperature and Baryo-chemical potential ( baryon density) at freezeout is estimated from particle ratios and by using Grand Canonical Stat Model Spin DOF Chemical potential mi mb: Baryon, m. I 3: Isospin m. S: Strangeness, m. C: Charm Number of particles: ni See, e. g. , A. Andonic, et al. , NPA 772(2006)167 8/10/2016 J-PARC HI collaboration meeting 9

1. Thermal photons • Emitted from all the stages after collisions • Penetrate the system unscathed after emission Small Rate: Yield aas e+ e- g* – Carry out thermodynamical information such as temperature • Photons will be produced by Compton scattering or qqbar annihilation at LO em: photon self energy g • Product of Bose distribution and transition probability • Slope at E>>T tells temperature (T~200 Me. V) 8/10/2016 J-PARC HI collaboration meeting 10

Temperature via dileptons Dimuon landscape at the J-PARC energy dileptons Axel Drees Kinematically, not available f. B: Bose dist. em: photon self energy • Instead of real photons, we look for virtual photons (dileptons) – g->l+l– PHENIX succeeded measuring virtual photons via e+e- channel g->m+m- • PRL 104, 132301(2010) • g-> m+m- • Measurement of dileptons at this beam energy has never been performed – p 0 and h don’t contribute – Better S/B expected 8/10/2016 J-PARC HI collaboration meeting 11

Temperature via dileptons Dimuon landscape at the J-PARC energy dileptons Axel Drees Kinematically, not available f. B: Bose dist. em: photon self energy • Instead of real photons, we look for virtual photons (dileptons) – g->l+l– PHENIX succeeded measuring virtual photons via e+e- channel g->m+m- • PRL 104, 132301(2010) • g-> m+m- • Measurement of dileptons at this beam energy has never been performed – p 0 and h don’t contribute – Better S/B expected 8/10/2016 J-PARC HI collaboration meeting 12

2. Particle flow • In non-central collisions, the collision area is not isotropic – Different pressure gradient produces momentum anisotropy of emitted particles F 3 F 2 8/10/2016 J-PARC HI collaboration meeting Fluctuation of nucleon position yields higher order anisotropy (v 3, v 4, … vn) Sensitive to EOS, shear viscosity (h) to Entropy density (s) ratio (h/s)13

v 1, v 2, v 3, v 4…. • v 1: Slope of directed flow (dv 1/dy) for protons will change its sign from positive to negative around mid-rapidity, if a phase transition occurs • v 2: Flow of protons and anti-protons merges at higher energies. – Low p. T, the pressure from the partonic phase is not well developed • v 3, v 4: mainly from fluctuations. Will be increased in partonic phase 8/10/2016 J-PARC HI collaboration meeting 14

v 1, v 2, v 3, v 4…. • v 1: Slope of directed flow (dv 1/dy) for protons will change its sign from positive to negative around mid-rapidity, if a phase transition occurs • v 2: Flow of protons and anti-protons merges at higher energies. – Low p. T, the pressure from the partonic phase is not well developed • v 3, v 4: mainly from fluctuations. Will be increased in partonic phase 8/10/2016 J-PARC HI collaboration meeting 15

3. Fluctuation of Net-X ~Moments of distributions The correlation length ( ) is related to various moments of conserved quantities: Variance : 2 = <( N)2> ~ 2 [c(2)/c(1)] Skewness: S = <( N)3>/ 2 ~ 5. 5 [c(3)/c(2)] Kurtosis: K 2 = <( N)4>/ 2 -3 2~ 9 [c(4)/c(2)] Since the correlation length is expected to diverge at the critical point, it is expected that the quantities S and k 2 will be large there. Skewness 8/10/2016 Kurtosis “bulging” Black: k=0 Red: k=∞ J-PARC HI collaboration meeting 16

Net-protons • Net-Protons – Variance follows Poisson – Skewness doesn’t – Kurtosis does follow Poisson, except for 0 -10% centrality – Need confirmation at JPARC/FAIR – Also, a strong tool to point the critical point • Ur. QMD describes peripheral, but not central – no Critical Point 8/10/2016 J-PARC HI collaboration meeting 17

Net-protons • Net-Protons – Variance follows Poisson – Skewness doesn’t – Kurtosis does follow Poisson, except for 0 -10% centrality – Need confirmation at JPARC/FAIR – Also, a strong tool to point the critical point • Ur. QMD describes peripheral, but not central – no Critical Point 8/10/2016 J-PARC HI collaboration meeting 18

4. Chiral symmetry restoration • q-qbar condensate changes more rapidly in baryon density axis. • Studying chiral symmetry restoration is essential in understanding the property of the QCD vacuum. 8/10/2016 J-PARC HI collaboration meeting 19

Charmonium at D+D- threshold • At the threshold energy of D+D- production, the yield of D mesons affects on that of J/y – D+: c-dbar, D-: cbar-d (both are 1. 87 Ge. V/c 2), J/y: c-cbar (3. 10 Ge. V/c 2) • Yield ratio of (D+D) to J/y will change if the mass of d-quark changes due to chiral symmetry restoration Following is the case that D mesons become lighter At high energy, r=0 d D+ d d c c D- d d c d D+ 2×(D++D-), 1× J/y 8/10/2016 c D- J/y c D+D- threshold energy d c c d J/y d c d Chiral symmetry restored J/y c 0×(D++D-), 3× J/y J-PARC HI collaboration meeting d c c c DJ/y c d d c c d d D+ 1×(D++D-), 2× J/y 20

Possible observables • J/y/(all m) – D->m+X, J/y -> mm • Energy upgrade of J-PARC MR is necessary for A+A – �s. NN=5 Ge. V in A+A, not enough for c-cbar production – Nevertheless, it is important to observe this • Kaon mass is also said to shift – Recent PHSD calculation with c-sym. restoration reproduces K/p “horn” – Cassing, Palmese, Moreau, Bratkovskaya, PRC 93, 014902 (2016) 8/10/2016 J-PARC HI collaboration meeting 21

Summary • New event selection (trigger) is a key for QGP physics at J-PARC • Key observables may be shown in a set of plots for advertisement – Some can be removed, and/or more can be added 8/10/2016 J-PARC HI collaboration meeting 22

Backup 8/10/2016 J-PARC HI collaboration meeting 23

4. Charge Asymmetry (local CP violation) • Quark degree of freedom would manifest when Chiral symmetry is restored – Charged quarks are affected by the strong magnetic field created in non-central collisions – Yields QCD local CP violation (Chiral magnetic effect) • Idea to extract the emission angle anisotropy due to the effect – From two-particle angular distribution with respect to the event plane. – Sin term in the Fourier series 8/10/2016 J-PARC HI collaboration meeting Cartoon taken from S. Esumi’s talk 24

Charge Asymmetry (local CP violation) • • • H: chiral magnetic field effect signal F: background v 2: elliptic flow, k: free parameter 8/10/2016 PRL 113, 052302 (2014) J-PARCSTAR, HI collaboration meeting 25

Charge Asymmetry (local CP violation) • HSS: Chiral magnetic effect signal from same sign particles • HOS: Chiral magnetic effect signal from opposite sign particles • Three k cases are shown (k=1, 1. 5, 2) • Big change in (HSS-HOS) is expected where CP violation starts to manifest – No such sign is seen at this moment 8/10/2016 J-PARC HI collaboration meeting 26

Charge Asymmetry (local CP violation) • HSS: Chiral magnetic effect signal from same sign particles • HOS: Chiral magnetic effect signal from opposite sign particles • Three k cases are shown (k=1, 1. 5, 2) • Big change in (HSS-HOS) is expected where CP violation starts to manifest – No such sign is seen at this moment 8/10/2016 J-PARC HI collaboration meeting 27

Analogy to cosmology • Fluctuation of temperature in cosmic microwave background – A trace of phase transition. • An input to cosmological model From NASA and Rev. of Part. Phys. 8/10/2016 J-PARC HI collaboration meeting 28

Charm is still charming, hard to pursue • D-meson mass will be reduced if the chiral symmetry is restored – Charm quark mass will not be reduced, but light quark masses (u, d) will be reduced. – J/y mass will not be reduced. • Therefore… • D-meson yield will not be reduced even at the threshold energy – J/y yield will be reduced We can readily do this physics in p+A at J-PARC. CBM Physics Jan 2011 For A+A, we need upgrade of MR energy from 30 to. Book, 50 Ge. V 8/10/2016 J-PARC HI collaboration meeting 29

Shooting thermal photons • Hadron contamination to the photon samples has been a big issue • Smallest hadron contamination when using photons converted to electron pairs Internal conversions (virtual photon) 8/10/2016 External conversions (real photon) J-PARC HI collaboration meeting 30

Frithjof’s conclusion at x. QCD conference 8/10/2016 J-PARC HI collaboration meeting 31

v 32/v 22 and v 32/nch, PP • Dips in v 32/v 22 and v 32/nch, PP sit around the same energy – ~20 Ge. V? – nch, PP =(2/Npart)d. Nch/dh (multiplicity per participant pair) ≈ density of the system • Change of the sign in dv 1/dy is found around the same energy – Signature of Hadron-Quark phase change? – Needs more statistics for low energy region J-PARC/FAIR 8/10/2016 L. Song, QM 2015 J-PARC HI collaboration meeting 32

• • New: v 3 or v 4 Using two-particle correlation method, STAR obtained v 32 for √s. NN=7. 7 -200 Ge. V v 3 vanishes for the lowest energy peripheral data v 32 = v 3(p 1) × v 3(p 2) – Consistent with the hybrid Ur. QMD model’s expectation with QGP formation turned off • Dips in v 32/v 22 around 20 Ge. V 8/10/2016 L. Song, QM 2015 J-PARC HI collaboration meeting 33

• New: v 3 Using two-particle correlation method (combine two particles with a large rapidity gap), STAR obtained v 32 for √s. NN=7. 7 -200 Ge. V v 32 = v 3(p 1) × v 3(p 2) • v 3 vanishes for the lowest energy peripheral data – Consistent with the hybrid Ur. QMD model’s expectation with QGP formation turned off 8/10/2016 L. Song, QM 2015 J-PARC HI collaboration meeting 34

Your position 8/10/2016 J-PARC HI collaboration meeting 35

Directed flow (v 1) • Slope of directed flow (dv 1/dy) for baryons will change its sign from positive to negative around mid-rapidity, if a phase transition occurs • Sign change in proton dv 1/dy unexpected from Ur. QMD is seen below s<40 Ge. V 8/10/2016 J-PARC HI collaboration meeting 36

Directed flow (v 1) • Slope of directed flow (dv 1/dy) for baryons will change its sign from positive to negative around midrapidity, if a phase transition occurs • Protons deviate for √s. NN<40 Ge. V, Kaons for √s. NN<20 Ge. V, compared to Ur. QMD expectation (protons are not shown) – Cross-over transition preferable (arxiv: 1601. 03902) STAR preliminary P. Shanmuganathan, 8/10/2016 QM 2015 J-PARC HI collaboration meeting HSD: W. Cassing et al. , ar. Xiv: 1408. 4313 37

Temperature of the collision system • Consistent results between virtual and real photons • Tave = 239 25(stat) 7(syst) Me. V (0 -20%)*Phase transition would occur at T~180 Me. V – c. f. LHC, Pb+Pb 2. 76 Te. V: Tave = 304 51(stat+syst) Me. V (0 -40% centrality) Thermal photon spectra Direct photon spectra Virtual photon 8/10/2016 J-PARC HI collaboration meeting PRC 91, 064904 (2015) p. T[Ge. V/c] 38

Dynamics after collisions • Gold ions pass through each other – High momentum (high-x) partons fly away – Low momentum (low-x) gluons remain in the mid-rapidity (y=0), and create “gluon matter” Rapidity: • Transition temperature (quark to hadron)： T=~180 Me. V Gluon Plasma 8/10/2016 QGP phase Mixed phase J-PARC HI collaboration meeting Hadronization + Expansion 39

vn results with hydrodynamics model • PHENIX (RHIC) and ATLAS (LHC) vn are compared with a hydrodynamics model – QGP as fluid consisting of partons • The model reproduces the higher order flow at RHIC, LHC very well – Almost perfect fluid is realized at RHIC（h/s from quantum limit: ~1/4 p） LHC RHIC B. Schenke, S. Jeon and C. Gale, PRC 85, 024901 (2012) 8/10/2016 J-PARC HI collaboration meeting C. Gale et al. , PRL 110, 012302(2013) 40

8/10/2016 J-PARC HI collaboration meeting 41

Discussion with Mike Tannenbaum at BNL • Individual production of protons? k 2 seems to be going down as going to lower √s. NN – Is it a sign of phase transition? What makes k 2<1? • At lower √s. NN, anti-protons are barely produced – Not a combined distribution? • Single binomial distribution can explain the observed k 2 and is consistent with baryon stopping happening at the √s. NN STAR, PRC 81, 024911(2010) 8/10/2016 BRAHMS, PRL 93, 102301(2004) J-PARC HI collaboration meeting Ss=k 3/k 2 Ks 2=k 4/k 2 Pois. 1 1 Bino. 1 -2 p 1 -6 p+6 p 2 Neg. Bino. 1+2 m/k 1+6 m/k+6 m 2/k 2 42

Reality of collisions Low energy （Landau picture） High energy （Bjorken picture） Stopping High T, High m. B 8/10/2016 Passing through High T, Low m. B Expansion in beam and transverse direction J-PARC HI collaboration meeting 43

Net-charge (with new PHENIX results) Variance : 2 = <( N)2> ~ 2 [c(2)/c(1)] 3 2 5. 5 Skewness: S = <( N) >/ ~ [c(3)/c(2)] Kurtosis: K 2 = <( N)4>/ 2 -3 2~ 9 [c(4)/c(2)] • PHENIX and STAR results are consistent for Skewness • Monotonic increase/decrease is seen down to 7. 7 Ge. V 8/10/2016 J-PARC HI collaboration meeting STAR, PRL 113, 092301 (2014) 44

Elliptic flow result (v 2) • Large flow is observed as a function p. T – As particles become heavier, the flows become smaller in low p. T • Plotting the per-quark v 2 (v 2/n) vs kinetic energy (KET/n) – All the particles follow a universal line, suggesting the flow is built at quark level PHENIX, PRL 99, 052301(2007) Au+Au √s. NN=200 Ge. V 20 -60% centrality 8/10/2016 J-PARC HI collaboration meeting 45