Probing the Quark Gluon Plasma with hard probes at the LHC

Transcription

1 Probing the Quark Gluon Plasma with hard probes at the LHC J. Stachel Physikalisches Institut der Universität Heidelberg ESQGP 'Edward Shuryak Quark Gluon Plasma' Workshop Stony Brook October2, 2008

2 expected initial conditions in central nuclear collisions at LHC initial conditions from pqcd+saturation of produced gluons K. Eskola et al., hep ph/ LHC using pqcd cross sections find for central PbPb at LHC p0 = psat = 2 GeV and a formation time of 0=1/psat=0.1 fm/c and with Bjorken formula: ² 0 = det =d =( 0 ¼R2 ) w. Jacobian d dz=1/ hep ph/ as compared to RHIC: more than order of magnitude increase in intial energy density initial temperature T0 1 TeV (factor 2 3 above RHIC) depending on evolution of saturation scale get dnch/d = RHIC

3 the challenge: identification and reconstruction of 5000 (up to 15000) tracks of charged particles cut through the central barrel of ALICE: tracks of charged particles in a 1 degree segment (1% of tracks) ALICE is dedicated experiment to study all aspects of heavy ion collisions at LHC detector is starting operation after more than 10 years of hard work and many novel developments

4 1. high pt partons as probe of the medium, i.e. the QGP prediction: in dense partonic matter a jet is losing energy rapidly order several GeV/fm

5 RHIC result: jet quenching RAA=yield(AuAu)/Ncoll yield(pp) new run 4 data high gluon density of the plasma induces energy loss of partons most calculations based on radiation

6 jet quenching indicative of high gluon rapidity density I. Vitev, JPG 30 (2004) S791 SPS RHIC LHC τ 0 [ fm] T [ MeV ] ε [GeV / fm3 ] τ tot [ fm] dn g / dy Consistent estimate with hydrodynamic analysis several mechanisms describe jet quenching at RHIC > predictions for LHC span very wide range RAA stays at 0.2 out to 100 GeV or so RAA rises slowly toward high pt RAA much smaller than at RHIC need to cover large pt range go beyond leading particle analysis identified jets, frag. function,...

7 LHC: increase in gluon density and very high jet energy reach to pin down energy loss mechanism Renk and Eskola, expanding QGP BDMPS energy loss; midrapidity at LHC Wicks and Gyulassy, sensitivity to gluon dens. and E loss mechanism

8 jet measurements in ALICE 2 GeV 20 GeV Mini Jets 100/event 1/event 100 GeV 1 Hz at p > 2 GeV/c : leading particle analysis correlation studies (similar to RHIC) Example : 100 GeV jet + underlying event for jet physics recently added EmCal will play important role in conjunction with existing charged particle tracking 200 GeV 100k/month at high p: reconstructed jets event by event well distinguishable objects

9 reconstructed jet energy spectrum pp events, unfolded for detectors response and cuts Ch. Klein Boesing

10 reconstruction of jets in PbPb collisions statistics corresponding to 1 month of PbPb running charged jets: reconstruct 33% of energy charged + EMCal: 68% Ch. Klein Boesing

11 measurement of jet fragmentation function z: energy fraction carried by leading hadron sensitive to energy loss mechanism N. Borghini, U. Wiedemann Increase on # of particles with low z 1% 13 % Decrease on # of particles with high z = ln(1/z) good reconstruction in ALICE = ln(1/z)

12 even more sensitivity with identified hadrons from jet

13 2. Charmonia as signature for deconfinement T. Matsui and H. Satz (PLB178 (1986) 416) predict J/ suppression in QGP due to Debye screening significant suppression seen in central PbPb at top SPS energy (NA50) in line with QGP expectations

14 J/ production in AuAu collisions at RHIC PRL 98 (2007) at mid rapidity suppression at RHIC very similar to SPS suppression at forward/backward rapidity stronger! but prediction: at hadronization of QGP J/ can form again from deconfined quarks, in particular if number of ccbar pairs is large NJ/ Ncc2 RAA: J/ yield in AuAu / J/ yield in pp times Ncoll (P. Braun Munzinger and J.Stachel, PLB490 (2000) 196)

15 what happens at higher beam energy when more and more charm anticharm quark pairs are produced? low energy: few c quarks per collision suppression of J/ high energy: many enhancement unambiguous signature for QGP!

16 but there is a more revealing normalization: RAA: J/ yield in AuAu / J/ yield in pp times Ncoll quantitative agreement! data: PHENIX nucl ex/ additional 14% syst error beyond shown model: A. Andronic, P. Braun Munzinger, K. Redlich, J. Stachel Phys. Lett. B652 (2007) 259 remark: y dep opposite in 'normal Debye screening' picture; suppression strongest at midrapidity (largest density of color charges)

17 energy dependence of quarkonium production in statistical hadronization model A. Andronic, P. Braun Munzinger, K. Redlich, J. Stachel Phys. Lett. B652 (2007) 259 centrality dependence and enhancement beyond pp value will be fingerprint of statistical hadronization at LHC > direct signal for deconfinement

18 predictions for charmonium rapidity and centrality distributions at LHC yellow band: uncertainty of pqcd prediction for ccbar prod. ALICE central barrel muon arm line: central value

19 measurement of charmonia in ALICE at mid rapidity electron identification with TPC and TRD J/ ee Good mass resolution and signal to background expect w full TRD and trigger 2500 Upsilon per PbPb Johannayear Stachel Simulation: W. Sommer (Frankfurt) central PbPb coll.

20 full simulation of central barrel performance D. Krumbhorn, Heidelberg

21 Charmonia in the di muon channel at y= J/psi and 6800 Upsilon for PbPb collisions (1 month) resolution 74 MeV resolution 109 MeV

22 flow of quarkonia at LHC? there is evidence from RHIC that fireball is expanding hydrodynamically do heavy quarks follow? pt spectra with flow are very different for charmonia from those measured in pp_bar e.g. at Fermilab or expected for pp at LHC should be easy to discriminate at LHC

23 charm quarks at RHIC: spectra don't show initial state scattering effects follow elliptic flow PRELIM. minimum-bias Run-4 Run-7 Rapp & van Hees, PRC 71, (2005)

24 bottomonium at LHC predictions with statistical hadronization model in terms of number of produced quarks, beauty at LHC like charm at RHIC do they thermalize and hadronize statistically?? if yes, population of 2s and 3s states completely negligible (exp m/t) hydrodynamic flow? need to measure spectrum to 15 GeV

25 3. Open charm and beauty normalization for quarkonia jet quenching for heavy flavors thermalization and hydrodynamic expansion in QGP

26 heavy quark distributions from inclusive electron spectra STAR preliminary surprize: suppression very similar to pions prediction (Dokshitzer, Kharzeev) less energy loss for heavy quarks (radiation suppr.)

27 open/hidden heavy flavor measurements in ALICE Hadronic decays: D0 Kπ, D+ Kππ, Ds K K*, Ds φπ, Leptonic decays: B l (e or µ) + anything Invariant mass analysis of lepton pairs: BB, DD, BDsame, J/Ψ, Ψ, ϒ family, B J/Ψ + anything BB µ µ µ (J/Ψ µ) e µ correlations id. hadrons, electrons: 0.9 < y < 0.9 muons: y= in central barrel: vertex cut effective for heavy quark identification expected ITS resolution

28 D0 Kπ channel ALICE PPR vol2 JPG 32 (2006) 1295 high precision vertexing, better than 100 µm (ITS) high precision tracking (ITS+TPC) K and/or π identification (TOF) 1<pT<2 GeV/c 107 central PbPb S/B = 10% S/ (S+B) = pp 108 ppb 107 PbPb

29 open beauty from single electrons 107 central PbPb B fie in ALICE ITS/TPC/TRD pt > 2 GeV/c & d0 = x m: electrons with S/(S+B) = 80% ALICE PPR vol2 JPG 32 (2006) 1295

30 J/ from B decay N(B J/ψ) / N(direct J/ψ) ~ 20% in LHC " (d0) < 50 µm for pt > 1.5 GeV/c in ALICE " disentangle primary & secondary J//y " measure inclusive b cross section " probe b quark in medium energy loss

31 high precision charm measurement pp at 14 TeV sensitivity to PDF s Central PbPb shadowing + kt + energy loss shadowing region ALICE PPR vol2 JPG 32 (2006) 1295

32 jet quenching for b quarks relative to c quarks data of one full luminosity PbPb run (106 s) should clarify heavy flavor quenching story

33 ALICE HMPID TOF TRD PMD ITS Muon Arm PHOS 33 Size: 16 x 26 meters Weight: 10,000 tons TPC 1000 scientists from 90 institutes in 27 countries 11/2006 PSI J. Schukraft

34 the TPC (Time Projection Chamber) 3D reconstruction of up to tracks of charged particles per event with 95 m3 the largest TPC ever 560 million read out pixels! precision better than 500 m in all 3 dim. 180 space and charge points per track

35 TPC calibration and alignment laser system Krypton gain calibration Laser cosmic radiation

36 tracking cosmic rays in magnetic field M. Ivanov, A. Kalweit particle identif cosmics & Kr calibration momentum resolution J.P. Wessels Prospects for First Physics with ALICE

37 the TRD (Transition Radiation Detector) identifies electrons at the trigger level read out electronics: 2 custom ASICS on multichip modules developed at PI and KIP in Heidelberg chamber: deflect ion time bins 540 chambers (radiator + drift+ multiwire proportional chamber + read out with segmented cathode pad plane, operated with Xenon) typical chamber size 1.7 m2 over all detector area 750 m2 in 18 supermodules (8m long) 1.16 million read out channels 30 million pixels from charge-clustern zu track segments 500 cpu Local Tracking Unit on each orig in CPU's process raw data of 65 Mbyte to reconstruct tracks (of 6 seg ments) in 6.5 s for trigger decision: high momentum electron pair

38 Trigger on cosmics with TRD at Level 1 TRD Global Tracking Unit GTU Level 1 trigger (7 s) for cosmics first L1 contribution to CTP in ALICE (planned for high energy electrons or jets)

39 cosmic ray induced shower, coincidene TRD and TPC

40 Cosmic ray event with magnetic field on

41 ITS Russian Dolls Sliding the SSD/SDD over the SPD TPC SPD SSD/SDD

42 ALICE Inner Tracking System alignment with cosmics Silicon Pixel Detector (SPD): ~10M channels 240 sensitive vol. (60 ladders) Silicon Drift Detector (SDD): ~133k channels 260 sensitive vol. (36 ladders) Silicon Strip Detector (SSD): ~2.6M channels 1698 sensitive vol. (72 ladders) ITS total: 2.2k alignable sensitive volumes 13k degrees of freedom ~50k cosmic µ for alignment collected since end of May, using Pixel trigger Typical event display Distribution of clusters in the 6 layers

43 ALICE Inner Tracking System alignment with cosmics Preliminary results for SPD (Pixels): Track to track (top vs bottom) distance in transv. plane before alignment after alignment (s = 55 m m (vs 40 m m in simul. without misalignment) Track to extra clusters distance in transv. plane before alignment after alignment σ = 21 m m (vs 15 m m in simul. without misalignment) These results indicate a residual misalignment (after realignment with cosmics) of < 10 µm, to be compared to a detector position resolution of 12 µm in rφ

44 ALICE (Di) Muon Spectrometer dipole magnet muon chambers muon absorber muon filter

45 All cosmic tracks

46 First interactions on Sept 12 Circulating beam 2 stray particle causing an interaction in the ITS

47 Combined Momentum Resolution in ALICE Central Barrel ALICE physics performance report resolution ~ 3% at 100 GeV/c excellent performance in hard region! dnch/dy~5000

48 Particle Identification in ALICE TPC TRD From test beam data: at 2 GeV and 90 % e eff 105 rejection

49 Backup slides

50 expected charged particle rapidity density at LHC depending on evolution of saturation scale get dnch/d = J.L.Albacete [hep ph] within kt factorization framework

51 expected evolution of QGP fireball at LHC after fast thermalization hydrodynamic expansion of fireball and cooling T / 1=3 hadronization starts at when Tc is reached (165 MeV) duration hadronization: # degrees of freedom drops by factor 3.5 > volume has to grow accordingly > 3 4 fm/c (this is independent of order of phase transition) initial NAA determines final multiplicity estimate (Eskola) dnch/d = 2600 task of heavy ion program at LHC overall several 10 k hadrons produced 'macroscopic state' K. Eskola et al. hep ph/

52 rapid hadrochemical equilibration at phase boundary Known since years: two body collisions are not sufficient to bring multi strange baryons into equilibrium. The density of particles varies rapidly with T near the phase transition. Multi particle collisions are strongly enhanced at high density and lead to chem. equilibrium very near to Tc. Lattice QCD calcs. F. Karsch et al. P. Braun Munzinger, J. Stachel, C. Wetterich Phys. Lett. B596 (2004) 61 nucl th/

53 chemical freeze out takes place at Tc rate of change of density due to multiparticle collisions n(t)nin M example: for small b, reactions such as KKK Nbar bring multi strange baryons close to equilibrium. Equilibration time T 60! All particles freeze out within a very narrow temperature window close to Tc. P. Braun Munzinger, J. Stachel, C. Wetterich Phys. Lett. B596 (2004) 61 nucl th/

54 54 / N L O p Q C D w t h a p r o p ri a e F High pt Spectra in p p Collisions (II)

55 radiation fails, is scattering the solution for heavy quarks? recently shown by Korinna Zapp (U. Heidelberg) that scattering also important for parton energy loss; implementation in nonperturbative approach SCI jet quenching model (K. Zapp, G. Ingelman, J. Rathsman, J. Stachel, PLB637 (2006) 179 apply same approach to c and b 0 10% centr. =5.2 mb to match pion data charm contribution indeed suppressed as much as pions but adding beauty data are not reproduced need improved heavy quark data to come with RHIC upgrades or even earlier from ALICE

56 comparison of model predictions to RHIC data: centrality dependence and rapidity distribution P. Braun Munzinger, K. Redlich, J. Stachel, Nucl. Phys. A789 (2007) 334 nucl th/ nucl ex/ pp open charm cross section FONLL Cacciari et al., PRL 95 (2005) cc = b good agreement, no free parameters but need for good open charm measurement obvious (this is a lesson for LHC as well!)

57 systematics of charm cross section compared to NLO pqcd pqcd cross section consistent with data (modulo discrepancy between STAR and PHENIX) only in spectra at higher pt some deviation

58 First hits and tracks in ALICE muon arm June 2008 Run (seg 010) event 79