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Outline:

• The CMS detector and its capabilities for heavy quarkonia

• Expected performances for quarkonia studies

Heavy quarkonia perspectives with Heavy-Ions in CMS

Pedro Ramalhete, on behalf of CMS

CERN / LHCC 2007–0095 March 2007

Editor: David d’Enterriato be pub. in J. Phys. G

QWG 2007, DESY, Hamburg, October 19, 2007

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Phase space coverage of the CMS detector

CMS (with HF, CASTOR, ZDC) + TOTEM: almost full η acceptance at the LHC ! charged tracks and muons: |η| < 2.5, full φ electrons and photons: |η| < 3, full φ jets, energy flow: |η| < 6.7 (plus η > 8.3 for neutrals), full φ excellent granularity and resolution very powerful and flexible High-Level-Trigger

CAST

OR

TOTEM

HFHF

= -8 -6 -4 -2 0 2 4 6 8

ZDC

5.2 < |η| < 6.6

η > 8.3 neutrals

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h±, e±, , ± measurement in the barrel (|| < 2.5)

Si Tracker + ECAL + muon-chambers

Si TrackerSilicon micro-stripsand pixels

CalorimetersECAL PbWO4

HCAL Plastic Sci/Steel sandwich

Muon BarrelDrift Tube Chambers (DT)Resistive Plate Chambers (RPC)

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In a deconfined phase the QCD binding potential is screened and the heavy quarkonia states are “dissolved”. Different heavy quarkonium states have different binding energies and, hence, are dissolved at successive thresholds in energy density or temperature of the medium. Their suppression pattern is a thermometer of the produced QCD matter.

Latti

ce Q

Qba

r fre

e en

ergy

T

Why is quarkonia suppression interesting?

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The feed-down from higher states leads to “step-wise” J/ and suppression patterns. It is very important to measure the heavy quarkonium yields produced in Pb-Pb collisions at the LHC energies, as a function of pT and of collision centrality.

state J/ c

' (1s) b

(2s) b' (3s)

Mass [GeV} 3.096 3.415 3.686 9.46 9.859 10.023 10.232 10.355B.E. [GeV] 0.64 0.2 0.05 1.1 0.67 0.54 0.31 0.2

Td/Tc --- 0.74 0.15 --- --- 0.93 0.83 0.74 1.10 0.74 0.15 2.31 1.13 0.93 0.83 0.74

A “smoking gun” signature of QGP formation

’

c

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Drell-Yan dimuons are not affected by the dense medium they cross

reference process

The yield of J/ mesons per DY dimuon is “slightly smaller” in p-Pb collisions than inp-Be collisions; and is strongly suppressedin central Pb-Pb collisions

Interpretation: strongly bound ccbar pairs (our probe) are “anomalously dissolved” by the deconfined medium created in central Pb-Pb collisions at SPS energies

p-Be

p-Pb

centralPb-Pb

J/ suppression in heavy-ion collisions at the SPS

J/ normal nuclear absorption curveexp(-L abs)

reference data

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The ’ suppression pattern in S-U and in Pb-Pb shows a significantly stronger drop than expected from the “normal extrapolation” of the p-A data

abs ~ 20 mb

’

The “change of slope” at L ~ 4 fm is quite significant and looks very abrupt...

’

’ suppression in heavy-ion collisions at the SPS

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Hard Probes at LHC energies

• Experimentally & theoretically controlled probes of the early phase in the collision

• Very large cross sections at the LHC• CMS is ideally suited to measure them

• Pb-Pb instant. luminosity: 1027 cm-2s-1

• ∫ Lumi = 0.5 nb-1 (1 month, 50% run eff.)• Hard cross sections: Pb-Pb = A2 x pp

pp-equivalent ∫ Lumi = 20 pb-1

1 event limit at 0.05 pb (pp equiv.)

jet

Z0+jet+jet

prompt

h/h

pp s = 5.5 TeV

1 event

J

1 b

1 nb

1 pb

M. Ballitjin, C. Loizides, G. Roland, CMS note AN-2006/099

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The High Level Trigger

ET reach x2

x35

x35

jets

Pb-Pb at 5.5 TeVdesign luminosity

• CMS High Level Trigger: 12 000 CPUs of 1.8 GHz ~ 50 Tflops !• Executes faster versions of “offline algorithms” (on full events)

• pp design luminosity L1 trigger rate: 100 kHz• Pb-Pb collision rate: < 8 kHz pp L1 trigger rate Pb-Pb collision rate run HLT codes on all Pb-Pb events

• Pb-Pb event size: ~2.5 MB (up to ~9 MB)• Data storage bandwidth: 225 MB/s 10–100 Pb-Pb events/s• HLT reduction factor: 3000 Hz → 100 Hz• Average HLT time budget per event: ~4 s

• Using the HLT, the event samples of hard processes are statistically enhanced by very large factors

M. Ballitjin, C. Loizides, G. Roland, CMS note AN-2006/099

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Impact of the HLT on the pT reach of the RAA

Nuclear modification factor = AA-yield / pp-yield = “QCD medium” / “QCD vacuum”

C. Roland et al., CMS note AN-2006/109

Pb-Pb (PYQUEN) 0.5 nb-1

Important measurement to compare with parton energy loss models and derivethe initial parton density, dNg/dy, and the medium transport coefficient, ⟨q⟩^

HLT

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So far, only the dimuon decay channel has been considered.The physics performance has been evaluated with the 4 T field (2 T in return yoke) and requiring a good track in the muon chambers. The good momentum resolution results from the matching of the muon tracks to the tracks in the silicon tracker.

Quarkonia studies in CMS

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Pb-Pb → + X event in CMS

dNch/d = 3500

Pb-Pb event simulated using the official CMS software framework (developed for pp)

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→ : acceptances and mass resolutions

CMS has a very good acceptance for dimuons in the Upsilon mass region

The dimuon mass resolution allows usto separate the three Upsilon states:~ 54 MeV within the barrel and~ 86 MeV when including the endcaps

Barrel: both muons in || < 0.8

Barrel + endcaps: muons in || < 2.4

pT (GeV/c)

Acce

ptan

ce

O. Kodolova, M. Bedjidian, CMS note 2006/089

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J/ → : acceptances and mass resolutions

barrel +endcaps

O. Kodolova, M. Bedjidian, CMS note 2006/089

barrel

• The material between the silicon tracker and the muon chambers (ECAL, HCAL, magnet’s iron) prevents hadrons from giving a muon tag but impose a minimum muon momentum of 3.5–4.0 GeV/c. This is no problem for the Upsilons, given their high mass, but sets a relatively high threshold on the pT of the detected J/’s.

• The low pT J/ acceptance is better at forward rapidities.• The dimuon mass resolution is 35 MeV, in the full region.

barrel +endcaps

pT (GeV/c)

J/

Acce

ptan

ce

p T (G

eV/c

)

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pT reach of quarkonia measurements (for 0.5 nb-1)

O. Kodolova, M. Bedjidian, CMS note 2006/089

J/

● produced in 0.5 nb-1

■ rec. if dN/d ~ 2500○ rec. if dN/d ~ 5000

Expected rec. quarkonia yields:J/ : ~ 180 000 : ~ 26 000

Statistical accuracy (with HLT) of expected’ / ratio versus pT model killer...

Nucl. Phys. B492 (1997) 301–337

curves from

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production in Ultra-Peripheral Pb-Pb Collisions

D. d’Enterria, A. Hees, CMS note AN-2006/107

• CMS will also study Upsilon photo-production, which occurs when the electromagnetic fields of the 82 protons of each nuclei interact with each other• This measurement (based on neutron tagging in the ZDCs) allows us, in particular, to study the gluon distribution function in the Pb nucleus• Around 500 events are expected after 0.5 nb-1, adding the ee and decay channels

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Summary

• The CMS detector has excellent capabilities to study the dense QCD matter produced in very-high-energy heavy-ion collisions, through the use of hard probes such as high-ET (fully reconstructed) jets and heavy quarkonia

• With a high granularity inner tracker (full silicon, analog readout), a state-of-the-art crystal ECAL, large acceptance muon stations, and a powerful DAQ & HLT system, CMS has the means to measure charged hadrons, jets, photons, electron pairs, dimuons, quarkonia, Z0, etc!

• This opens the door to high-quality measurements that so far lived only in the realm of dreams (maybe even including the study of c → J/ using the ECAL)