Quarkonium production in p-p and A-A collisions: ALICE status report

E. Scomparin (INFN-Torino, Italy)for the ALICE Collaboration

Fermilab, May 18-21, 2010

Introduction

• ALICE (A Large Heavy-Ion Collision Experiment):the dedicated heavy-ion experiment at the LHC

• Main focus on Pb-Pb collisions QGP studies up to the nominal LHC luminosity, 51026 cm-2s-1

• p-p collisions are a crucial aspect of the physics program• Reference for heavy-ion collision studies• Genuine p-p physics• Maximum luminosity limited to ~3 1030 cm-2s-1

due to pile-up in TPC• Faster detectors (e.g. muon spectrometer) may stand a higher luminosity

Running conditions appropriate for quarkonium studies(both charmonium and bottomonium)

The ALICE experiment

Quarkonium production can be studied at both central and forward y

Still to be completedPHOS: 3/5EMCAL: 4/12TRD: 7/18

ZDC

Quarkonium measurement in ALICE (1)• Quarkonia can be measured at BOTH central (|y|<0.9) and forward (2.5<y<4) rapidity

• Central barrel (e+e- decay mode) Tracking+PID in ITS+TPC+TRD

• e- reconstruction efficiency 80-90% for pT>0.5 GeV/c• mis-identification ~ 1%

TRD

Quarkonium measurement in ALICE (2)

• TPC substantially helps in hadron rejection, at small momenta

• Overall TPC+TRD e- reconstruction efficiency ~75%

85 m3 - NeC2O2N2 gas mixture 557,568 readout channels Maximum drift time = 92 msMany (>90) 3D points (+dE/dx) per track

Quarkonium measurement in ALICE (3)

Front absorber (10 I)Muon filter (7.2 I)

• Cathode Pad Chambers for tracking (1.08106 channels)• Resistive Plate Chambers for trigger (2.1 104 channels)

for muon selection

• Beam shield to protect muon detectors

Muon spectrometer

Quarkonium measurement in ALICE (4)• Trigger logic:

• pT cut (with various thresholds >0.5 GeV/c)• Select particles pointing to the interaction region

• Muon trigger very effective in rejecting• Hadronic contribution• Soft (background related) component

• Distance of closest approach (DCA) to the vertex for tracks in the muon spectrometer

DCA(cm) DCA(cm)

PYTHIA7 TeV

No triggerrequirement

With triggerrequirement

MuonsHadronsTotal

PYTHIA7 TeV

pp7 TeV

No triggerWith trigger

ALICE PerformanceWork in Progress

J/ acceptances

Central rapidity (|y|<0.9)

• As an example, consider pp collisions at √s =7 TeV

Forward rapidity (2.5<y<4)

No trigger cutTrigger cut pT=0.5 GeV/cTrigger cut pT=1 GeV/c

Physics performance, PbPb collisions,central rapidity

• Simulations for the 2010 running conditions (√s = 2.76 ATeV) still in progress. For the nominal LHC conditions:

• First estimates for the 2010 PbPb run: ~10000 J/, ~70

J/ physics accessible, may need trigger

J/ ~ 30 MeV, ~ 80 MeV

Physics performance, PbPb collisions,forward rapidity

• Again, detailed simulation at √s = 2.76 ATeV still not ready• At nominal energy and luminosity, for 106 s running time

J/ (2S) (1S) (2S) (3S)

7105 2104 7103 2103 1103

Integrated yields (no medium effects except shadowing)

centralJ/ ~ 70 MeV

~ 100 MeV

Resonance separationis possible

• Centrality dependence of J/ and yields can be studied• Worse situation for (2S)

Enough for QGP physics ?

• Many crucial predictions can be settled at the LHC

(3S) b(2P)(2S)

b(1P)

(1S)

Digal et al., Phys.Rev. D64(2001) 094015

• Hyerarchy of suppression for both charmonia and bottomonia ?• Observation of melting?

• Charmonia enhancement due to thermal production at the phase boundary ? (CC = 10RHIC, Volume = 3RHIC)

Andronic et al., Phys. Lett. B652(2007) 259

pp collisions, central rapidity

• ALICE is luminosity limited, due mainly to pile-up in the TPC, to 3 1030 cm-2s-1 240 kHz interaction rate• Data taking rate limited to ~1kHz (a few 100 Hz in Pb-Pb)

• Need electron trigger (level 1,2) to provide a reduction factor ~200 (under study)

J/ efficiency with single-e L1 trigger

• pp first run at 7 TeV (109 MB event sample)

• No trigger a few 102 J/• With L1 trigger a few 105 J/ !

• Statistics would increase by a factor 7-10 with full TRD installed

pp collisions, forward rapidity• At nominal LHC energy (107 s run, L= 3 1030 cm-2s-1)

• Spectrum dominated by correlated background (low multiplicity, the uncorrelated contribution is small)

S [x103] S/B S/√(S+B)

J/ 2800 12 1600

’ 75 0.6 170

• It will be possible to study J/ pT differential distribution with reasonable statistics up to 20 GeV/c

• First pp run at 7 TeV• Depending on the maximum luminosity chosen for ALICE, and assuming, tentatively, LHC=0.12

• L= 3 1029 cm-2s-1 (beginning) 104 J/ month-1

• L= 3 1030 cm-2s-1 105 J/ month-1

Other charmonia resonances: c

• C J/+ (pp collisions at midrapidity)• Photon conversion: opposite sign tracks associated to a V0, with cuts on the angle (<0.1 rad) and mass (<0.15 GeV/c2)

m=m(e+e- )-m(e+e-)

• Electron triggering crucial also for this signal• Expected statistics from first run: ~2000 c

Bottomonium production

• Forward rapidity, nominal √s and luminosity, 107 s running time

S [x103] S/B S/√(S+B)

27 10.4 157

’ 6.8 3.4 73

’’ 4.2 2.4 55

• Good statistics allows a detailed study of differential distributions and polarization

• Central rapidity, triggering is mandatory for a meaningful statistics

• Measurement feasible also in the first run at 7 TeV

Quarkonia polarization, forward y

(J/ bck subtr)(J/ + bck)

• Bias on the evaluation of the J/ polarization due to the background is not very large (as expected)

• with 200K J/, the error on J/ is < 0.02

J/

• With the available statistics we can evaluate the polarization with a statistical error between 0.05–0.11

= 0

• Statistical errors, for the pT dependence of the polarization, vary between 0.03 -0.2

ALICE expected statistics in 1 year ~ 3 times CDF statistics (Run I, 3 yr)

J/ from B hadrons

• Feasible in the central barrel, thanks to the very good impact parameter resolution (r < 60m for pT>1 GeV/c)

T

Jxy p

mLX /

T

Txy p

pLL

with

results corresponding to4109 MB events

(7/18 TRD)

• Forward detection more difficult• 3-muon events• upgrade with Si tracker in front of muon spectrometer

First quarkonia signals in ALICE

Muon-chamberalignment ongoing

ALICEwork in progress

Forward rapidity Central rapidity

After a few weeks running at 7 TeV, quarkonia signals start to pop out

Luminosity now increasing.....

...expect physics results soon!

Conclusions

• ALICE: an experiment conceived for heavy-ion running, but with good pp capabilities

• Luminosity limited (TPC) to L~31030 cm-2s-1 , but enough for most charmonium/bottomonium related signals

• Crucial detectors for quarkonia measurement in good shape from the beginning of the LHC run at 7 TeV

• TRD to be completed asap

First quarkonium signals (J/) have been observed: physics results expected soon

Starts from ||<0.9 (not y)10 TeV differential distributions (CDF extrapolation)

MUON ARM

ITS

TPC

TRD

TOFPHOS

EMCAL

PMD, V0

HMPID

ACORDE

ZDC