BB Hadronic matter Quark-Gluon Plasma Chiral symmetry broken x Exploring QCD Phase Diagram in Heavy Ion Collisions Krzysztof Redlich University of Wroclaw QCD phase boundary and freezeout in HIC Cumulants and probability distributions of conserved charges as Probe for the Chiral phase transition: theoretical expectations and recent STAR data at RHIC -CEP ? ? AA collisions

2 – probing the response of a thermal medium to an external fields, i.e. variation of one of its external control parameters: (generalized) response functions == (generalized) susceptibilities pressure: thermal fluctuations density fluctuations condensate fluctuations generalized susceptibilities: energy density order parameter Bulk thermodynamics and critical behaviour Mean particle yields

3 Susceptibilities of net charge number – The generalized susceptibilities probing fluctuations of net -charge number in a system and its critical properties pressure: particle number density quark number susceptibility 4 th order cumulant net-charge q susceptibilities expressed by and central moment

4 Only 3-parameters needed to fix all particle yields Tests of equlibration of 1 st “moments”: particle yields resonance dominance: Rolf Hagedorn partition funct ion Breit-Wigner res. particle yield thermal density BR thermal density of resonances

Chemical freezeout and the QCD chiral crossover A. Andronic et al., Nucl.Phys.A837:65-86,2010. O(4) universality HRG model Chiral crossover Thermal origin of particle production: with respect to HRG partition function A. Andronic et al., Nucl.Phys.A837:65-86,2010. P. Braun-Munzinger et al. QM (2012)

Chemical freezeout and the QCD chiral crossover A. Andronic et al., Nucl.Phys.A837:65-86,2010. O(4) universality HRG model Chiral crossover Is there a memory that the system has passed through a region of QCD chiral transition ? What is the nature of this transition? Chiral crosover Temperature from LGT HotQCD Coll. (QM’12) Chemical Freezeout LHC (ALICE) P. Braun-Munzinger (QM’12)

QCD phase diagram and the O(4) criticality In QCD the quark masses are finite: the diagram has to be modified Expected phase diagram in the chiral limit, for massless u and d quarks: Pisarki & Wilczek conjecture TCP: Rajagopal, Shuryak, Stephanov Y. Hatta & Y. Ikeda TCP

The phase diagram at finite quark masses The u,d quark masses are small There is a remnant of the O(4) criticality at the QCD crossover line: CP Asakawa-Yazaki Stephanov et al., Hatta & Ikeda At the CP: Divergence of Fluctuations, Correlation Length and Specific Heat Critical region Phys. Rev. D83, (2011 ) Phys. Rev. D80, (2009) LQCD results: BNL-Bielefeld group

9 singular critical behavior controlled by two relevant fields: t, h Close to the chiral limit, thermodynamics in the vicinity of the QCD transition(s) is controlled by a universal scaling function K. G. Wilson, Nobel prize, 1982 Bulk Thermodynamics and Critical Behavior non-universal scales control parameter for amount of chiral symmetry breaking regular

O(4) scaling and magnetic equation of state Phase transition encoded in the magnetic equation of state pseudo-critical line F. Karsch et al universal scaling function common for all models belonging to the O(4) universality class: known from spin models J. Engels & F. Karsch (2012) QCD chiral crossover transition in the critical region of the O(4) 2 nd order O(4)

11 Find a HIC observable which is sensitive to the O(4) criticality Consider generalized susceptibilities of net-quark number Search for deviations from the HRG results, which for quantifies the regular part Quark fluctuations and O(4) universality class To probe O(4) crossover consider fluctuations of net- baryon and electric charge: particularly their higher order cumulants with F. Karsch & K. R. Phys.Lett. B695 (2011) 136 B. Friman, V. Skokov et al, P. Braun- Munzinger et al. Phys.Lett. B708 (2012) 179 Nucl.Phys. A880 (2012) 48 or compare HIC data directly to the LGT results, S. Mukheriee QM^12 for BNL lattice group

Effective chiral models Renormalisation Group Approach coupling with meson fileds PQM chiral model FRG thermodynamics of PQM model: Nambu-Jona-Lasinio model PNJL chiral model the SU(2)xSU(2) invariant quark interactions described through: K. Fukushima ; C. Ratti & W. Weise; B. Friman, C. Sasaki., …. B.-J. Schaefer, J.M. Pawlowski & J. Wambach; B. Friman, V. Skokov,... the invariant Polyakov loop potential (Get potential from YM theory, C. Sasaki &K.R. Phys.Rev. D86, (2012); Parametrized LGT data: Pok Man Lo, B. Friman, O. Kaczmarek &K.R. ) B. Friman, V. Skokov, B. Stokic & K.R. fields

Deviations from low T HRG value: are increasing with and the cumulant order Ratios of cumulants at finite density: LGT and PQM with FRG HRG B. Friman, F. Karsch, V. Skokov &K.R. Eur.Phys.J. C71 (2011) 1694 HRG value HRG Ch. Schmidt et al. S. Ejiri et al.

STAR data on the first four moments of net baryon number Deviations from the HRG Data qualitatively consistent with the change of these ratios due to the contribution of the O(4) singular part to the free energy HRG

Kurtosis saturates near the O(4) phase boundary The energy dependence of measured kurtosis consistent with expectations due to contribution of the O(4) criticality. Can that be also seen in the higher moments? B. Friman, et al. EPJC 71, (2011)

STAR DATA Presented at QM’12 Lizhu Chen for STAR Coll. V. Skokov, B. Friman & K.R., F. Karsch et al. The HRG reference predicts: HRG O(4) singular part contribution: strong deviations from HRG: negative structure already at vanishing baryon density

Moments obtained from probability distributions Moments obtained from probability distribution Probability quantified by all cumulants In statistical physics Cumulants generating function:

Probability distribution of the net baryon number For the net baryon number P(N) is described as Skellam distribution P(N) for net baryon number N entirely given by measured mean number of baryons and antibaryons In Skellam distribution all cummulants expressed by the net mean and variance P. Braun-Munzinger, B. Friman, F. Karsch, V Skokov &K.R. Phys.Rev. C84 (2011) Nucl. Phys. A880 (2012) 48)

Take the ratio of which contains O(4) dynamics to Skellam distribution with the same Mean and Variance at different Ratios less than unity near the chiral critical point, indicating the contribution of the O(4) singular part to the thermodynamic pressure K. Morita, B. Friman et al. The influence of O(4) criticality on P(N) for

Take the ratio of which contains O(4) dynamics to Skellam distribution with the same Mean and Variance near Asymmetric P(N) Near the ratios less than unity for For sufficiently large the for K. Morita, B. Friman et al.

The influence of O(4) criticality on P(N) for K. Morita, B. Friman & K.R. In central collisions the probability behaves as being influenced by the chiral transition For preliminary STAR data QM 2012

Centrality dependence of probability ratio O(4) critical Non- critical behavior For less central collisions, the freezeout appears away the pseudocritical line, resulting in an absence of the O(4) critical structure in the probability ratio. STAR analysis of freezeoutK. Morita et al. Cleymans & Redlich Andronic, Braun- Munzinger & Stachel

Conclusions: Hadron resonance gas provides reference for O(4) critical behavior in HIC and LGT results Probability distributions and higher order cumulants are excellent probes of O(4) criticality in HIC Observed deviations of the and by STAR from the HRG qualitatively expected due to the O(4) criticality (check for the influence of : efficiency, volume fluctuations and baryon number conservation!!!) Deviations of the P(N) from the HRG Skellam distribution follows expectations of the O(4) criticality Present STAR data are consistent with expectations, that in central collisions the chemical freezeout appears near the O(4) pseudocritical line on QCD phase diagram