HBT two-pion correlations at LHC Qingfeng Li ( 李庆峰 ) (Huzhou Teachers College)

Q.Li for 14th NCNS in Huzhou2 Outline LHC physics and QGP phase UrQMD updates (cascade & dynamic modes) HBT Correlations and EoS status Calculation Results at LHC Some words of onset of QGP at SPS Summary and Outlook Q.Li, G. Graef, M. Bleicher, PRC 85, (2012); G. Graef, M. Bleicher, Q.Li, PRC, 85, (2012); G. Graef, Q.Li, M. Bleicher, JPG 39, ?(2012); arXiv:

Q.Li for 14th NCNS in Huzhou3 LHC physics TeV physics To find: Higgs;micro black holes; extra dimensions (Kaluza – Klein Theory); dark matters …a large number of unsolved questions in fundamental physics CERN

Q.Li for 14th NCNS in Huzhou4 QGP phase Onset/order of the QGP phase/QCD phase transition Properties of the QGP phase Problems, problems…

Q.Li for 14th NCNS in Huzhou5 What to do now… The extracted bulk properties of the high temperature fireball created in such ultrarelativistic collisions have provided unprecedented information for fundamental investigations of the phase diagram of quantum chromodynamics. 1.to explore collective features of the strong interaction in high multiplicity pp events; 2.to explore expansion properties of the created matter by investigating the spatial shape of the fireball from AA collisions; 3.to explore the spatial structure of the source created in collisions of various heavy ions at different energies and centralities to shed light on the observed scaling violation when going from pp to AA collisions at the LHC.

Q.Li for 14th NCNS in Huzhou6 UrQMD a microscopic many-body approach to p-p, p-A, and A-A interactions at energies ranging from SIS up to LHC. It is based on the covariant propagation of mesons and baryons. Furthermore it includes rescattering of particles, the excitation and fragmentation of color strings, and the formation and decay of hadronic resonances. At LHC, the inclusion of hard partonic interactions in the initial stage is important and is treated via the PYTHIA model. The model can be downloaded from ……

Q.Li for 14th NCNS in Huzhou7 Main updates in recent years 1.In cascade mode: the newest version is 3.3 (to include LHC physics); Phys. Rev. C 84, (2011); 2.In the Boltzmann+hydrodynamics hybrid mode: the newest version is 2.3p1 (can be downloaded from the website); Phys. Rev. C 78, (2008); 3.In the “ mean-field potential ” version: based on v2.1, adding mean field potentials for hadrons. V1.3+PYTHIA  V2.1+hydrodynamics  V2.3+LHC collisions  V3.3 Q.Li version  SPS  RHIC  LHC

Q.Li for 14th NCNS in Huzhou8 Explorations of EoS stiffness At INDRA/SIS/CSR energies: soft!?... At AGS/SPS/FAIR energies: ?... At RHIC/LHC energies: …

Q.Li for 14th NCNS in Huzhou9 The “ pre-formed ” hadronic potential To modify the interactions at early stage, more collisions (by considering a shorter formation time or larger cross sections for “ pre-formed ” particles) or a mean-field potential for “ pre-formed ” hadrons might be taken into account. The former idea has been checked in the AMPT and the HRM models. Here we would like to consider the latter idea. As the first step, ① the density dependent term used for formed baryons is used for “ pre-formed ” particles. ② The “ pre-formed ” mesons act like “ pre-formed ” baryons but with a reduction factor (2/3) due to the quark-number difference. ③ The potential interaction between formed and “ pre-formed ” particles is neglected. ④ The “ pre-formed ” particles also contribute to the hadronic density (for “ pre-formed ” mesons, the 2/3 factor is considered). See: PLB659, 525(2008) PLB663, 395(2008) For more details

Q.Li for 14th NCNS in Huzhou10 HBT, half century in NP HBT=Robert Hanbury-Brown and Richard Q. Twiss  In 1950 ’ s, in order to measure stellar radii through the angle subtended by nearby stars, Robert invited Richard to develop the mathematical theory of intensity interference. They found by astro-observation that two-photons arriving to the correlators behaved as a consequence of B-E statistics. In 1959, during the measurements of the ρ 0 resonance (by means of ρ 0   -  +), Goldhaber etc (Berkeley) found an angular correlation among identical pions, which were also explained by the B-E. What ’ s more, they parameterized the observed correlation as: C(Q 2 )=1+exp(-Q 2 r 2 ) The subsequential HBT researches in nuclear physics are based on this Gaussian form. *R. Hanbury Brown and R.Q. Twiss, Philos. Mag. 45, 663 (1954). *G. Goldhaber, S. Goldhaber, W. Lee, and A. Pais, Phys. Rev. 120, 300 (1960)

Q.Li for 14th NCNS in Huzhou11 The HBT correlation and paramerization The quotient of two-particle and one-particle spectra The two-particle correlator C(q,K) is related to the emission function s(x,K), which is the Wigner phase-space density of the particle emitting system and can be viewed as the probability that a particle with average momentum K is emitted from the space-time point x in the collision region.  the two-particle relative wave function. Experimentally: Theoretically: The correlator is constructed with the help of the CRAB program

Q.Li for 14th NCNS in Huzhou12 Cont ’ d CRAB analyzing program: me.html Three-dimensional Gaussian parameterization LCMS is employed in usual calculations Coulomb effect in FSI is considered for charged two-kaon correlation with a Bowler-Sinyukov method non-Gaussian effect can be discussed under the Edgeworth expansion The fitting work can be done by the ROOT or the ORIGIN software (using  -squared method)

Q.Li for 14th NCNS in Huzhou13 One task of HBT: to probe the QGP fireball A non-trivial structure in the excitation function of HBT probes might be seen IF there is a (phase) transition. Energy density Predictions by Rischke, Gyulassy, in Nucl.Phys.A608: ,1996  long life times in the mixed phase?

Q.Li for 14th NCNS in Huzhou14 Effects of EOS and freeze-out criteria on the R O /R S ratio Note: Different hydro freeze-out criteria affects slightly the ratio, if one considers HR. The BG-EoS is too soft to explain the ratio. From PLB674,111(2009)

Q.Li for 14th NCNS in Huzhou15 Calculation Results at LHC 1.Q1: p+p collisions at √s NN =7 TeV 2.Q2: : Pb+Pb collisions at √s NN =2.76 TeV 3.Q3: Examination of scaling of HBT radii with charged particle multiplicity

Q.Li for 14th NCNS in Huzhou16 Q1: p+p collisions at √s NN =7 TeV It seems like in massive nucleus-nucleus collisions, a strongly interacting medium is created even in pp collisions, that exhibits similar bulk properties such as space momentum correlations and collective behaviour; While it is often argued, that the particle emitting system in p+p collisions is too small to create a medium that exhibits bulk properties, this should be different at a center of mass energy of √s= 7 TeV. an essential quantity that influences the particle freezeout radii is the formation time in flux tube fragmentation  the recent LHC data on pp collisions allows to determine the formation time in the flux tube break-up From JPG; arXiv:

Q.Li for 14th NCNS in Huzhou17 Formation time in UrQMD For the Lund model the formation times are proportional to the transverse mass of the created hadron and inversely proportional to the string tension. For simplicity UrQMD uses a constant formation time of t f = 0.8 fm/c for hard collisions. The average dN ch/d  from UrQMD is 15% smaller than ALICE data

Q.Li for 14th NCNS in Huzhou18 Projections of Correlation function Non-Gaussian effect is visible in out and long directions and at large q

Q.Li for 14th NCNS in Huzhou19 K T dependence of HBT radii for diff. dN classess and diff. formation times the present ALICE data allows to constrain the formation time to values of t f ≈ fm/c. An additional momentum dependence in t f is needed.

Q.Li for 14th NCNS in Huzhou20 Q2: : Pb+Pb collisions at √s NN =2.76 TeV Non-Gaussian effect is stronger at LHC than at lower energies Calculated non-Gaussian effect is more obvious than data From PRC 85, (2012)

Q.Li for 14th NCNS in Huzhou21 K T dependence of HBT radii 1,Strong kT dependence  substantial expansion of the source 2,As RHIC  LHC, HBT radii (esp. R L ) rise. 3,At LHC, R L and R O are larger than data, separately & R O /R S ratio is larger than data.

Q.Li for 14th NCNS in Huzhou22 x-t correlation even in the cascade calculation, there exists a visibly positive correlation between the emission time and position. The most important contribution to R O comes from the emission duration term

Q.Li for 14th NCNS in Huzhou23 Contribution of emission duration to the HBT radii To lead to smaller R O values in all k T bins but leaves R S unchanged; Overall it results in an improved agreement with the data of the ratio.

Q.Li for 14th NCNS in Huzhou24 Some hints 1.The overestimation of both R O and R L can be attributed to the known fact that the pressure in the early stage is not strong enough in the cascade model calculations. 2.A higher pressure would lead to a more explosive expansion, a stronger phase-space correlation, and a faster decoupling of the system, thus leading to smaller regions of homogeneity. 3.A more satisfactory solution is possible in the near future by improving the dynamic processes for both QGP and HG phases.

Q.Li for 14th NCNS in Huzhou25 Q3: Examination of scaling of HBT radii with charged particle multiplicity Same: 1) charged particle multiplicity at midrapidity: |  |<1.2 for pp; |  |<0.8 for other classes. 2) K T bin: MeV/c. Different solutions: To change: a) beam energy: Pb+Pb at √s=2760, 200, 130, 62.4 GeV and E lab = 158 GeV; b) centrality: Pb+Pb within 0-5%, 5-20%, 20-50% and 50-80% centralities; c) colliding system: Pb+Pb, Cu+Cu, C+C, p+p. From PRC, 85, (2012)

Q.Li for 14th NCNS in Huzhou26 Scaling of the HBT radii 1,The scaling is good if the change in N ch is caused by a change of centrality at a fixed energy. 2,A small offset on the order of 2-3 fm is visible for different system sizes, due to the finite size of the nuclei. 3,Increasing the center-of-mass energy leads to a reduction of the radii at a given fixed N ch -bin.

Q.Li for 14th NCNS in Huzhou27 Some hints 1.The scaling of the source size with (dN ch /d  ) 1/3 for different centralities is a hint that the underlying physics, e.g. pion production via resonance decay versus production via string fragmentation, is nearly unchanged by changes in the collision geometry. 2.A change in √s on the other hand results not only in different weights of the production mechanisms, but also in changed expansion dynamics towards a more violent expansion with increased energy. Different pp and AA result is attributed to the strongly different particle production mechanisms in AA and pp. I.e., bulk emission vs. string/jet dominated emission.

Q.Li for 14th NCNS in Huzhou28 Volume of the homogeneity region 1.A good agreement between experiment and theory is observed for the quantity R 2 S R L while the experimental results for R O R S R L are slightly overestimated. 2.A steeper slope with decreasing energy.

Q.Li for 14th NCNS in Huzhou29 Freeze-out time By fitting the hydrodynamic expression: 1, a shorter decoupling time with increased energy 2, UrQMD overestimates the source lifetime by a factor of ∼ 2–3 when compared to LHC data  back to the duration time

Q.Li for 14th NCNS in Huzhou30 Some words of onset of QGP at SPS Currently a more detailed study on the onset of QGP at SPS is more urgent. –Extracting EoS of QGP based on lQCD calculations (potentials of preformed hadrons, like PHSD). –Extracting potentials of different formed hadrons in HG via RMF, Chiral, etal., (like AMPT) Comparison with cascade and hybrid mode calculations and with RHIC-BES/ SPS-SHINE/ FAIR data in the near future.

Q.Li for 14th NCNS in Huzhou31 Summary and Outlook Two-pion HBT correlations at LHC are calculated by using the UrQMD v the present ALICE pp data allows to constrain the formation time to values of t f ≈ fm/c. 2.The overestimation of both R O and R L from Pb+Pb central collisions can be attributed to the known fact that the pressure in the early stage is not strong enough in the cascade model calculations. 3.The scaling of the source size with (dN ch /d  ) 1/3 for different centralities is a hint that the underlying physics, e.g. pion production via resonance decay versus production via string fragmentation, is nearly unchanged by changes in the collision geometry, while change in √s on the other hand results not only in different weights of the production mechanisms, but also in changed expansion dynamics towards a more violent expansion with increased energy. 4.Different pp and AA result is attributed to the strongly different particle production mechanisms in AA and pp. I.e., bulk emission vs. string/jet dominated emission. Call for a better dynamics for both phases, which, currently, might be concentrated in the SPS energy region, as the RHIC-BES/ SPS- SHINE/ FAIR data come forth.

Q.Li for 14th NCNS in Huzhou32 Thank you for your concern! Using the for more Thank you for your concern! Using the for more 你念 或者不念我 情就在那里 不来不去 你爱 或者不爱我 爱就在那里 不增不减 --- 《班扎古鲁白玛的沉默》