Questions for the LHC resulting from RHIC Strangeness

Transcription

1 Questions for the LHC resulting from RHIC Strangeness Outline Intermediate p T strangeness production not jets! (Credit for work goes to Betty Abelev & Jana Bielcikova) Helen Caines Yale University ALICE Physics Week - Muenster - Feb. 7

2 Excitation function of central mid-rapidity yields dn/dy extrapolations at the LHC Baryon yields ~flat Λ : ~ Anti-baryon rise sharply Ξ : ~6 Ω :.4~.7 Helen Caines ALICE Physics Week - Muenster Feb 7

3 Reconstruction rates Total Efficiency (%) STAR Au-Au s NN = GeV Total Efficiency (%) ALICE ALICE Pb-Pb s NN = 5 TeV p T (Gev/c) LHC final yield ~ RHIC final yield ALICE effic ~ STAR effic Events from LHC year ~ Events from RHIC year Approx same statistics to play with at ALICE Helen Caines ALICE Physics Week - Muenster Feb 7

4 Ideal hydrodynamics π -, K -, p Best agreement for : T dec = MeV α =. fm α : importance of initial conditions τ =.6 fm/c Central Data T dec = 65 MeV T dec = MeV α : initial (at τ ) transverse velocity : v T (r)=tanh(αr) P.F. Kolb, J. Sollfrank and U.Heinz, Phys. Rev. C 6 () 5499 P.F. Kolb and R. Rapp, Phys. Rev. C 67 () 449 P.F. Kolb and U.Heinz, nucl-th/584 Fails at higher p T as energy increases Helen Caines ALICE Physics Week - Muenster Feb 7 4

5 Intermediate p T baryon/meson anomaly Enhancement of baryon/meson ratio in central Au-Au relative to p-p at intermediate p T All ratios equivalent p T <.5GeV/c and p T >5 GeV/c Only at p T >5 GeV/c do all particles have similar R cp suppression Jet fragmentation not a dominant source of particle production until p T > 5 GeV/c Helen Caines ALICE Physics Week - Muenster Feb 7 5

6 Coalescence and Recombination of partons dn/p T dp T dy ReCo cartoon GeV/c hadron from:. Fragmentation. Meson: coalescence of.5 GeV/c partons. Baryon: coalescence of GeV/c partons More baryons than meson at intermediate p T 4 5 [GeV/c] Exponential (thermal) parton spectrum qualitatively explains baryon excess at mid p T Recombination: Shower (S) Thermal (T) S & T can mix Particle spectra are a sum of various components R.Hwa et al, Phys.Rev.C7 (494) 4. mesons baryons TT SS TS TTT SSS TSS STT Helen Caines ALICE Physics Week - Muenster Feb 7 6

7 Ω triggered correlations Shower s-quarks suppressed w.r.t u & d quarks -- Ω(sss) at intermediate p T (<8 GeV/c) come mostly from TTT! Differs significantly from Λ, which includes non-strange quarks Λ(STAR) Azimuthal correlations! Measure fragmentation (shower quark contribution). If Ω comes from TTT at intermediate p T no Ω correlations will be seen Ω(STAR) Statistically challenging but doable with large event samples! R.C Hwa & C.B. Yang nucl-th/64 Helen Caines ALICE Physics Week - Muenster Feb 7 7

8 Statistical jet measurements Particles from same jet closely aligned in φ Use characteristic jet cone shape for a statistical jet study y x q. Find a trigger particle (p T > GeV/c). Find an associated particle (.5 GeV/c < p as T < q p trg T ) in the same event. Compute φ at primary vertex for each 4. Compute Δφ at primary vertex Helen Caines ALICE Physics Week - Muenster Feb 7 8

9 Components of azimuthal correlation functions A double-peaked correlation function Normalized by N triggers B same-side away-side + Flat uncorrelated background - p-p and d-au + Elliptic flow - Au-Au If no SSS contribution to Ω spectrum Ω-h correlation will be flat after v subtraction Helen Caines ALICE Physics Week - Muenster Feb 7 9

10 Subtracting the v Ξ and Ω v not well measured v Appeal to Number of. Constituent Quark.5 scaling Use more precise light hadron v to estimate that for multi-strange Fit to K S and Λ K S Ω Ξ Ξ Λ+ Λ Transverse momentum p [GeV/c] T Ω + + Helen Caines ALICE Physics Week - Muenster Feb 7

11 Au-Au azimuthal correlations Multi-strange correlations observable above v +background Helen Caines ALICE Physics Week - Muenster Feb 7

12 After background subtraction Uncertainty due to v determination methods Correlation similar for all strange baryons Helen Caines ALICE Physics Week - Muenster Feb 7

13 p T trigger dependence on near-side yields No dependence on strangeness content Meson and baryon yields same within errors Possible yield saturation for p T trig >.5 End of RECO? Helen Caines ALICE Physics Week - Muenster Feb 7

14 -dimensional correlations: Δφ-Δη Extend analysis in dimensions Same procedure as for φ, only use η coordinates of trigger and associated Elongation in Δη under the jet peak: the ridge p trigger T =-6 GeV/c,.5 GeV/c <p associated T < pt trigger Near-side yield : Δη Δɸ(J+R) = Δɸ(J) + Δɸ(R) beam direction Jet yield : Δɸ(J) = Δɸ(Δη<.7) - Δɸ(Δη>.7) Ridge yield: Δɸ(R) = Δɸ(J+R) - Δɸ(J) jet+ridge Δφ Δη Δφ Helen Caines ALICE Physics Week - Muenster Feb 7 4 Δη ridge ridge jet D. Magestro, Hard Probes 4; STAR, PRC7, 6497 (6)

15 Δφ-Δη for strange particles correlations Λ-h correlations Ξ-h correlations.5<p trig T <4.5 GeV/c.5<p as T <p trig T (c) STAR Preliminary STAR Preliminary "# "! Insufficient statistics for the Ω studies Ξ jet signal is indistinguishable from the ridge Need more data to go further with multi-strange Helen Caines ALICE Physics Week - Muenster Feb 7 5

16 V correlations Selection criteria:. GeV/c < p T trigger <.5 GeV/c GeV/c < p T associated < GeV/c η < Corrections applied: reconstruction efficiency of charged particles TPC sector boundaries v subtraction syst. error due to v uncertainty ~ 5% Helen Caines ALICE Physics Week - Muenster Feb 7 6

17 Centrality dependence of correlations Jet + Ridge Ridge Jet (sys. errors correlated) Steep increase of near-side yield with centrality in Au-Au Ratio of yields in central Au-Au/d-Au ~ 4-5 -> ridge yield increases with centrality Yield K S < yield of Λ (effects of merged tracks under study) -> jet yield same in Au-Au and d-au independent of centrality Helen Caines ALICE Physics Week - Muenster Feb 7 7

18 Exploring the ridge in central data J. Putschke (STAR) QM jet slope ridge slope inclusive slope STAR preliminary h-h correlations p T associated >GeV/c Trigger particle T(Ridge) MeV T (Jet) MeV h +/- 48 ± 4 (stat.) 478 ± 8 K S 46 ± (stat.) 5 ± 6 Λ 46 ± (stat.) 445 ± 49 Ridge spectra similar to particles from the bulk Jet spectra are slightly harder ~ 5 MeV Helen Caines ALICE Physics Week - Muenster Feb 7 8

19 Correlation dependence on p T trigger Jet + Ridge Ridge Jet Near-side associated yield is ridge dominated at intermediate p T Ridge yield plateaus at high p trigger T Jet yield rises steeply with increasing p trigger T Jet/Ridge ratio rises from ~5-5% with increasing p trigger T Helen Caines ALICE Physics Week - Muenster Feb 7 9

20 Back to multi-strange correlations in d-au Is the ridge the cause of the multi-strange correlations? What s expected from pure jet signal? η <.75 STAR Preliminary p T trig >. GeV/c.5 GeV/c <p T as <p T trig Same-side yield:.5 ±.6 Away-side yield:.4 ±.6 (work still in progress on improving data) Larger away side peak due to trigger bias? Helen Caines ALICE Physics Week - Muenster Feb 7

21 Compare yields at same p T trigger Ridge Jet Near side yield fits in systematics Assume Jet yield is as in d-au (.5±.6) Again fits into systematics All multi-strange yield from the ridge - ~factor increase Helen Caines ALICE Physics Week - Muenster Feb 7

22 Conclusions/Questions for LHC Ω and Ξ azimuthal correlations have been measured in Au-Au Ξ baryon same-side yield in central Au-Au x that in d-au data Ξ Ω baryon same-side yield peak in in central most central Au-Au x Au-Au, that contrary in d-au to data predictions Appearance of the ridge in Au-Au correlations - cause of multi-strange correlations? Ω baryon same-side peak in most central Au-Au, contrary to predictions ridge concentrated at intermediate p T p T distribution like the bulk Appearance of the ridge in Au-Au correlations - cause of multi-strange correlations? LHC: Only ALICE able to make these measurements acceptance Does this effect exist at LHC? at what p T? Is there really no dependence on quark content? - High stats. measurement to high p T What is the ridge? - PID to look into its composition What about the away-side? ridge concentrated at intermediate p T p T distribution like the bulk Helen Caines ALICE Physics Week - Muenster Feb 7

23 Particle composition of ridge and jet STAR preliminary STAR preliminary Correlations with identified associated particles should help to constrain the ridge origin: parton energy loss and coupling to longitudinal flow? radial flow+jet quenching? parton recombination? Armesto, Salgado,Wiedemann Phys.Rev.Lett.9, 4 Voloshin, Nucl.Phys.A749, 5 Chiu, Hwa, Phys. Rev. C7, 5 D-analysis + systematic error estimates (v, merged tracks) missing I will probably drop this one, to premature See also talk by J. Putschke (STAR) Helen Caines ALICE Physics Week - Muenster Feb 7

24 System size dependence: Cu+Cu vs Au+Au central Cu+Cu: yield increases with p T trigger no significant particle type dependence observed Central Cu+Cu is qualitatively similar to central Au+Au Let s compare the yields corresponding to the same N part Near-side yield in Cu+Cu consistent with Au+Au at similar N part High statistics of Cu+Cu data will allow to study jet/ridge yields at low N part Helen Caines ALICE Physics Week - Muenster Feb 7 4

25 Correcting for detector acceptance in D (a) (b) "# "! "# "! (c) "#.5 (d) "# "! "! ! (e) 45 4 (f) $ / ndf.674e+4 / 77 p.5 ". p 4. " "! "# Helen Caines ALICE Physics Week - Muenster Feb 7 5

26 Ξ-h same side yields p T trig dn pairs /N trig dδφ η <.75 5 p T -trigger bins 4 ZeroYieldAtMin calculations (different number of points to find minimum) + fit determines the systematic error on the yield assumes Helen Caines only background at C(Δφ) ALICE minimum Physics Week - Muenster Feb 7 6

27 Δφ correlations is Au+Au: ZYAM Alternative to fitting in Au+Au data: Assumes that the same-side and away-side are independent (Zero Yield At Minimum): the height of the trough is due to background (flow+uncorrelated BG) only! N. Ajitanand et al, Phys. Rev. C 7 (9) 5 Can calculate the uncorrelated BG height B: = B Minimum of C(Δφ) Calculated Δφ at minimum C(Δφ) Helen Caines ALICE Physics Week - Muenster Feb 7 7

28 4 4 "#.5 Δφ-Δη for strange particles correlations # trig<4.5.5<p GeV/c Λ-h Tcorrelations - - "! "# "# # "! "! "! (e) Insufficient statistics for the Ω studies (e) (f) Jet signal is indistinguishable from the ridge There is evidence of a dip in the signal in the Δη=Δφ= region Dip is still under investigation think it is track merging!! " 6.8 $ / ndf p p e+4 / 77.5 ". 4. " Need more data to go further Helen Caines "! Week - Muenster Feb 7 ALICE Physics "! "# (f (d (c) (d).5.5 "! Ξ-h correlations as<p trig.5<p T (c) T "! "# " "#.5.5 "#