Suppression of neutral pion production at large transverse momentum measured with the ALICE experiment in Pb-Pb collisions at s NN =2.

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1 Suppression of neutral pion production at large transverse momentum measured with the ALICE experiment in Pb-Pb collisions at s NN =.76 ev Gustavo Conesa Balbastre for the ALICE collaboration 6/5/11 G. Conesa QM11 1/6

2 Outline and motivation π measurement, performance in ALICE π R AA Study of parton energy loss π v Particles collective movement reflected in momentum space 6/5/11 G. Conesa QM11 /6

3 EMCal Sandwich scintillator-pb pp - E π = 5 GeV σ π MeV/c Δφ =4º (º in 11) η <.7 Poster: E. Braidot and F. Zhou on π performance in Pb-Pb PC+IS s converted into e ± pairs between beam pipe and middle of PC can be detected Conversion probability 8.5% pp - E π = 5 GeV σ π 4 MeV/c Δφ =36º η <.9 alk: K. Reygers on π in pp PHOS PbWO 4 crystals pp - E π = 5 GeV σ π 7 MeV/c Δφ = 6º η <.1 Posters: - H. orii on π performance in Pb-Pb - D. Blau on π v 3/6

4 Subsystems Performance: EMCAL EMCAL can measure π s via invariant mass in 1 < p < GeV/c 6/5/11 G. Conesa QM11 4/6

5 Subsystems Performance: PHOS N events per 8 MeV/c Real pairs Mixed pairs N events per 8 MeV/c 3.6<p <1. GeV/c t PHOS performance Pb-Pb s =.76 ev NN Centrality 4-6% <p <5. GeV/c t M M N events per 8 MeV/c N events per 8 MeV/c <p <3. GeV/c t Data Background estimation <p <15. GeV/c t M 4-6% M PHOS can measure π s via invariant mass method in.6 < p < GeV/c 6/5/11 G. Conesa QM11 5/6

6 Subsystems Performance: PHOS Combinatorial background subtracted N events per 8 MeV/c N events per 8 MeV/c <p <1. GeV/c t m = ±.4 MeV/c = 7.5 ±.4 MeV/c <p <5. GeV/c t m M = ±. MeV/c = 6.9 ±. MeV/c M N events per 8 MeV/c N events per 8 MeV/c <p <3. GeV/c t m = 134. ±.1 MeV/c = 7.1 ±.1 MeV/c <p <15. GeV/c t PHOS performance Pb-Pb s =.76 ev NN Centrality 4-6% m = ±.3 MeV/c 35 = 6.9 ±.4 MeV/c M 4-6% M PHOS can measure π s via invariant mass method :.6 < p < GeV/c Width similar to the one measured in pp collisions 6/5/11 G. Conesa QM11 6/6

7 Subsystems Performance: PHOS N events per 8 MeV/c Real pairs Mixed pairs N events per 8 MeV/c 3.6<p <1. GeV/c t PHOS performance Pb-Pb s NN =.76 ev Centrality -% <p <5. GeV/c t M -% N events per 8 MeV/c N events per 8 MeV/c 3 1.<p <3. GeV/c t Data Background estimation <p <15. GeV/c t M M PHOS can measure π s via invariant mass method in.6 < p < GeV/c M 6/5/11 G. Conesa QM11 7/6

8 Subsystems Performance: PHOS Combinatorial background subtracted N events per 8 MeV/c N events per 8 MeV/c 8 m = ± 1.1 MeV/c = 9. ± 1.3 MeV/c 6 4.6<p <1. GeV/c t <p <5. GeV/c t 16 m = ±.4 MeV/c 14 = 7.8 ±.4 MeV/c M -% N events per 8 MeV/c N events per 8 MeV/c <p <3. GeV/c t m = ±.3 MeV/c = 8. ±.3 MeV/c PHOS performance Pb-Pb s NN =.76 ev Centrality -% <p <15. GeV/c t M m = ±.6 MeV/c = 7. ±.6 MeV/c /5/11 G. Conesa QM11 M PHOS can measure π s via invariant mass method in.6 < p < GeV/c Width increases to a few MeV at very central events and low momenta, at high momenta same as in pp collisions M 8/6

9 Subsystems Performance: Conversions e - e + e - e + 9/6

10 ALICE tomography with conversions Layer nd PC Inner Field Cage Vessel ALICE Performance s = 7 ev th May 11 Phojet LHCd.15 PC drift gas SPD PC inner field cage vessel -15 PC Rods PC inner containment vessel 15. PC Gas - st PC Inner Containment Vessel.5 SSD 5 SDD 1 Layer.3 st SSD 1 Layer 3 Layer + Support Structures.35 SDD Data MC converison candidates MC true converison MC true π Dalitz MC true η Dalitz MC true Combinatorics nd SSD SDD 15-3 Beam Pipe SPD ALICE Performance s = 7 ev th May 11 η <.9 Nγ Nch Y (cm) Measurement of conversions vertex is a powerful technique to x-ray ALICE, from beam pipe to half PC X (cm) 18 R (cm) ALICE material budget, 11.4% X up to middle of PC, agrees within +3.4%/-6% with its implementation in GEAN 6/5/11 G. Conesa QM11 /6

11 Counts/ 4.e+ MeV/c π π γ γ e + e e + e p >.5 GeV/c γ γ M γ γ - ALICE Performance s NN =.76 ev Data:.7e+6, 6-8% Centrality 18th May 11 η Subsystems Performance: Conversions Precise π measurement via invariant mass method,.5 < p < GeV/c Peak has a narrow width, like in pp collisions even in very central Pb-Pb collisions 11/6 Counts GeV/c < p <. GeV/c ALICE Performance s NN =.76 ev Data:.7e+6, 6-8% Centrality 18th May 11 π γ γ e + e - e + e - Counts GeV/c < p <. GeV/c ALICE Performance s NN =.76 ev Data:.7e+6, -% Centrality 18th May π γ γ e e e e % Data (BG substracted) Fit 6 4 -% Data (BG substracted) Fit M γ γ M

12 π uncorrected yield with calorimeters Poster: E. Braidot and F. Zhou on π performance in Pb-Pb EMCAL PHOS Poster: H. orii on π performance in Pb-Pb pp Pb-Pb pp Min Bias pp rigger pp Pb-Pb Pb-Pb pp (uncorrected, A.U.) dp 1/N ev dn/p % -4% 4-6%.1 6-9%.1 PHOS performance, May, 11 Pb-Pb s NN =.76 ev (GeV/c) π measured in Pb-Pb and pp collisions at s NN =.76 ev up to p GeV/c with invariant mass method EMCAL trigger enhances p reach in pp collisions p 6/5/11 G. Conesa QM11 1/6

13 π yield with conversions (c/gev) N dy d dp 1 p N ev π ALICE Preliminary s NN =.76 ev + - π γ γ e e + - e e π π π π π Pb-Pb -% (x5) Pb-Pb -4% (x5) Pb-Pb 4-6% (x4) Pb-Pb 6-8% (x1) pp (x1) p (GeV/c) π spectra from p =.5 to GeV/c for different centralities 6/5/11 G. Conesa QM11 13/6

14 Outline and motivation π measurement, performance in ALICE π R AA Study of parton energy loss π v Particles collective movement reflected in momentum space 6/5/11 G. Conesa QM11 14/6

15 R AA : Motivation Partons traversing the QGP lose energy Suppression of high energy particles compared to pp collisions he measurement: he nuclear modification factor, g g g g QGP π alks: - A. oia on Centrality - H. Appelshaeuser on R AA - J. Otwinowski on h ± R AA Why π? R AA dependence on baryon/meson R AA for charged hadrons with p >7 GeV/c increases, is this the same for baryons and mesons? Possibility to identify up to rather large momentum 6/5/11 G. Conesa QM11 Phys. Lett. B 696 (11) /6

16 π R AA with conversions R AA 1. π π 6-8% -% ALICE Preliminary s NN =.76 ev + - π γ γ e e + - e e p (GeV/c) Strong suppression at -%, for 4<p < GeV/c R AA.15 6/5/11 G. Conesa QM11 16/6

17 π and π ± R AA R AA 1. π 6-8% - (π + +π ) 6-8% ALICE Preliminary s NN =.76 ev 6-8% Centrality π γ γ e e e e p (GeV/c) Agreement within uncertainty with charged pions 6/5/11 G. Conesa QM11 17/6

18 π and π ± R AA R AA 1. π 4-6% - (π + +π ) 4-6% ALICE Preliminary s NN =.76 ev 4-6% Centrality π γ γ e e e e p (GeV/c) Agreement within uncertainty with charged pions 6/5/11 G. Conesa QM11 18/6

19 π and π ± R AA R AA 1. π -4% - (π + +π ) -4% ALICE Preliminary s NN =.76 ev -4% Centrality π γ γ e e e e p (GeV/c) Agreement within uncertainty with charged pions 6/5/11 G. Conesa QM11 19/6

20 π and π ± R AA R AA 1. π -% - (π + +π ) -%, ALICE ALICE Preliminary s NN =.76 ev -% Centrality π γ γ e e e e p (GeV/c) Agreement within uncertainty with charged pions 6/5/11 G. Conesa QM11 /6

21 π and h ± R AA R AA 1. π 6-8% π -% + - (h +h ) 6-8% + - (h +h ) -% ALICE Preliminary s NN =.76 ev + - π γ γ e e + - e e p (GeV/c) Different shape in -% compared to h ±, due to baryon/meson difference 6/5/11 G. Conesa QM11 1/6

22 Outline and motivation π measurement, performance in ALICE π R AA Study of parton energy loss π v Particles collective movement reflected in momentum space 6/5/11 G. Conesa QM11 /6

23 v : Motivation If the created system has interactions the original anisotropies in coordinate space will transfer into the anisotropies in momentum space, which are quantified via anisotropic flow harmonics v n Second harmonic, elliptic flow (v ) is dominant Why π? Does flow depend on particle ID? v /n q At RHIC, v scales with number of constituent quarks for p -6 GeV/c It does not seem to work at LHC alks: - R. Snellings on flow - A. Dobrin on flow at high p - A. Bilandzic on h ± flow - M. Krzewicki on identified particles flow ALICE preliminary, Pb-Pb events at centrality 4%-5% π ±, v {SP, Δη >1} ± K, v {SP, Δη >1} p, v {SP, Δη >1} (m -m )/n (GeV/c) q t =.76 ev s NN 6/5/11 G. Conesa QM11 3/6

24 π flow compared to π ± v {EP} ALICE subsystems, centrality -4% PHOS, PC, ± OF, ± conversions, Poster: D. Blau on π v ALICE performance 18/5/11 Pb-Pb-> s NN =.76 ev Non flow effects (quenching) taken into account in PC π ± points. alk: A. Dobrin for details Pink line represents approximately PC π ± without non flow correction p (GeV/c) v of π measured with PHOS and conversions up to GeV/c, compatible with π ± within uncertainty 6/5/11 G. Conesa QM11 4/6

25 π flow compared to π ± v {EP} ALICE subsystems, centrality 5-% PHOS, π PC, π ± OF, π ± conversions, π Poster: D. Blau on π v ALICE performance 18/5/11 Pb-Pb->π s NN =.76 ev Non flow effects (quenching) taken into account in PC π ± points. alk: A. Dobrin for details Pink line represents approximately PC π ± without non flow correction p (GeV/c) v of π measured with PHOS and conversions up to GeV/c, compatible with π ± within uncertainty 6/5/11 G. Conesa QM11 5/6

26 Summary First π results in ALICE with Pb-Pb collisions with the calorimeters and with the conversion photons method R AA with π has been measured up to p = GeV/c with the conversions method Observed strong suppression consistent with π ± R AA Calorimeters will extend the p reach up to p GeV/c with data with the invariant mass method Elliptic flow with π has been measured up to p = GeV/c with PHOS and conversions method Result consistent with v of π ± 6/5/11 G. Conesa QM11 6/6

27 Back-up 6/5/11 G. Conesa QM11 7/6

28 π R AA with conversions R AA 1. π π π π 6-8% 4-6% -4% -% ALICE Preliminary s NN =.76 ev + - π γ γ e e + - e e p (GeV/c) π suppression observed for the different centralities Strong suppression at -%, for 4<p < GeV/c R AA.15 6/5/11 G. Conesa QM11 8/6

29 R AA with identified particles R AA 1 ALICE, Pb-Pb, s =.76 ev unidentified charged particles, - 5% π, - % + - π + π, - % K, - 5% Λ, - 5% -1 ALICE Preliminary 1 p (GeV/c) 6/5/11 G. Conesa QM11 9/6

30 Performance in pp ) 5 (MeV/c 15 ALICE Performance s = 7 ev CS: PHOS/EMCAL: - e + e - e + e Width m-m PDG -m CS PHOS EMCAL Mass: m- m PDG - m o Data MC m (MeV/c ) 5 15 Width Data MC FWHM/.36 1 p (GeV/c) 6/5/11 G. Conesa QM11 3/6

31 v with Event plane Method 6/5/11 G. Conesa QM11 31/6

32 Centrality selection Events 3 Pb-Pb at s NN =.76 ev Data Glauber fit NBD x f N coll + (1-f)N f=.194, µ=9.3, κ=1. part ALICE Performance 7/5/11 8-9% 7-8% 6-7% % 4-5% 3-4% -3% -% 5-% -5% VZERO Amplitude (a.u.) See plenary talk by A. oia 6/5/11 G. Conesa QM11 3/6