Quarkonium studies in p+p andPb+Pb collisions with CMS

– Torsten Dahms (on behalf of CMS) –CERN

ReteQuarkonii Thematic Day, IPN OrsayFebruary 9th, 2010

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Quarkonia production at the LHCThe LHC will provide p+p and Pb+Pb collisions at high energies and luminosities (“latest plan” according to Chamonix 2010 meeting):

• In November/December 2009 proton beams were collided at√s = 900 GeV (2.36 TeV) during which CMS recorded an integrated luminosity of about 10 bμ −1 (400 mb−1)

• Starting February/March 2010 with p+p collisions at √s = 7 TeV with peak luminosities up to 1032 cm−2s−1 until 1 fb−1 of integrated luminosity has been collected (18 − 24 months)

• Corresponding Pb+Pb collision energy will be √sNN = 2.8 TeV

(beam time in Fall 2010)

• Running at higher energies up to 14 TeV only after a longer shutdown(≥ 2013?)

• The Pb+Pb runs will then occur at 5.5 TeV per NN collision, with4×1026 cm−2s−1 Pb+Pb instantaneous luminosity

Quarkonium states will be produced at very high rates

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A transverse slice of the CMS barrel

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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CMS phase-space coverage

• CMS: full and almost full acceptance at the LHCφ η• charged tracks and muons: | | < 2.4η• electrons and photons: | | < 3η• jets, energy flow: | | < 6.7 (plus | | > 8.3 for neutrals, with the ZDC)η η

• excellent granularityand resolution• very powerful

High-Level-Trigger

HF HF

CAST

OR

CAST

OR

ZDC

ZDC

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J/ψ detection and dimuon mass resolutionin CMS

• CMS is ideal to measure quarkoniain the dimuon decay channel:– large rapidity coverage (| |<2.4)η– excellent dimuon mass resolution

• Good muon momentum resolution:– matching between the tracks in the muon

chambers and in the silicon tracker– strong solenoidal magnetic field (3.8 T)

• Because of the increasing material thickness traversed by the muons, the dimuon mass resolution changes with pseudo-rapidity, from ~15 MeV at ~0 to ~40 MeV at ~2.2

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Inclusive differential J/ψcross sections in p+p collisions

• The observed J/ yield results from:ψ– direct production– decays from ’ and ψ χc states

– decays from B hadrons (non-prompt)

• CMS will measure the inclusive, prompt, and non-prompt productioncross sections

• CMS should collect several 104 J/ eventsin a matter of days at 1031 cm−2s−1 (∫L dt = 1 pb−1 at 14 TeV)

• The J/ yield is extracted by fitting the dimuon mass distribution, ψseparating the signal peak from the underlying background continuum

prompt

p+p √s = 14 TeV(3 pb−1)CMS simulationCMS PAS BPH-07-002

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Inclusive differential J/ψ cross sections

A : convolution between the detector acceptanceand the trigger and reconstruction efficiencies, which depend on the assumed polarization

corr : needed if MC description of trigger and offline efficiencies does not match “reality”

Competitive with Tevatron results after only 3 pb−1

A

CMS simulationCMS PAS BPH-07-002 p+p at 14 TeV

3 pb−1 ~ 75 000 J/ψ

€

dσ

dpTJ /ψ

⋅Br(J /ψ → μ +μ−) =NJ /ψfit

Ldt∫ ⋅ΔpTJ /ψ ⋅A ⋅λcorr

CMS simulationCMS PAS BPH-07-002

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Feed-down from B meson decaysAn unbinned maximum likelihood fit is made, in pT bins, to determine the non-prompt fraction, fB, using the dimuon mass and the pseudo proper decay length

Systematic error dominated byluminosity and polarization uncertainties

B fraction fit

J/ pψ T : 9–10 GeV/c

CMS simulationCMS PAS BPH-07-002

CMS simulationCMS PAS BPH-07-002

€

l xy =Lxy

J/ ψM J/ ψ

PTJ/ ψ

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Quarkonium production in Pb+Pb collisions

μΥ μ μμ−

dNch/d = η3500

CMS simulation

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ϒ→μ+μ−: acceptance and mass resolution

• CMS has a very good acceptance for dimuons in the Upsilon mass region• The dimuon mass resolution allows us

to separate the three Upsilon states:~ 54 MeV within the barrel and~ 86 MeV when including the endcaps• 1 month Pb+Pb at 5.5 TeV with average

luminosity of 4×1026 cm−2s−1 0.5 nb−1

CMS simulation

CMS simulation

Pb+Pb √sNN = 5.5 TeV(0.5 nb−1)

σ = 54 MeV/c2

Barrel: both muons in |h| < 0.8

Barrel + endcaps: muons in |h| < 2.4

pT (GeV/c)

Acce

ptan

ce

’

’’

CMS simulationCMS PTDR Addendum 1

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J/ψ→μ+μ−: acceptance and mass resolution• 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:– No acceptance problem for due to high massΥ– but for J/ ’s this sets a relatively high threshold on the pψ T

• The low pT J/ acceptance is better at forward rapidityψ

barrel +endcaps

barrel

pT (GeV/c)

J/ψ

Acce

ptan

ce

p T (G

eV/c

)

h

barrel + endcaps(| |<2.4)ησJ/ψ = 35 MeV/c2

Pb+Pb √sNN = 5.5 TeV(0.5 nb−1)

CMS simulationCMS PTDR Addendum 1

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The High Level Trigger

• CMS High Level Trigger:12 000 CPUs of 1.8 GHz ~ 50 Tflops!

• Executes “offline-like” algorithms

• p+p design luminosity L1 trigger rate: 100kHz• Pb+Pb collision rate: 3 kHz (peak = 8 kHz)

p+p 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 / second• 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 considerable factors

ET reach ×2

×35

×35

jets

Pb+Pb at 5.5 TeVdesign luminosity

CMS PTDR Addendum 1

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pT reach of quarkonia measurements

● produced in 0.5 nb−1

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

J/ψ

Υ

0.5 nb−1 : 1 month at 4×1026 cm−2s−1

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

Statistical accuracy (with HLT) of’ / ratio vs. pΥ Υ T should be good

enough to rule out some models

Pb+Pb √sNN = 5.5 TeV

CMS simulationCMS PTDR Addendum 1

CMS simulationCMS PTDR Addendum 1

CMS simulationCMS PTDR Addendum 1

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ϒ production in ultra-peripheralPb+Pb collisions

• CMS will also measure Upsilon photo-production, occurring in collisions with impact parameters larger than the Pb nuclear radii

• This will allow us to study the gluon distribution function in the Pb nucleus

• Around 500 events are expected after 0.5 nb−1, adding the e+e− and μ+μ− decay channels using neutron tagging in the ZDCs

CMS simulationCMS PTDR Addendum 1

CMS simulationCMS PTDR Addendum 1

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Summary (of the expectations)

• CMS has a high granularity silicon tracker, a state-of-the-art ECAL, large muon stations, powerful DAQ and HLT systems, etc. excellent capabilities to study quarkonium production, in p+p and Pb+Pb• Dimuon mass resolutions:

~30 MeV for the J/ ; ~90 MeV for the , over ||<2.4ψ Υ Good S/B and separation of (1S), (2S) and (3S)Υ Υ Υ• Expected p+p rates are high enough to collect J/ and dimuons up toψ Υ

pT ~ 40 GeV/c in a few days at 7 TeV

• Expected Pb+Pb rates at √sNN = 5.5 TeV:180 000 J/ and 26 000 (1S) per 0.5 nbψ Υ −1 (one month) Studies of Upsilon suppression as signal of QGP formation• J/ and polarization, and ψ Υ χc → J/ + studies require larger samplesψ γ

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A first look at “real” data

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Start of the LHC: First CollisionsMonday 23rd November

CMS Experiment at the LHC, CERNDate Recorded: 2009-11-23 19:21 CETRun/Event: 122314/1514552 Candidate Collision Event

Events recorded: All CMS ON900GeV: ~400k2.36 TeV: ~20k

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First Di-photon Distribution in CMS

• Data and MC comparison (uncorrected distributions)• Almost identical S/B, mass and width

compatible• M(π0) is low in both data and MC - Mostly

due to the readout threshold (100 MeV/Crystal) and conversions

Using “out of the box” corrections

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Data: N( )/N(η π0) = 0.020 ± 0.003

MC: N( )/N(η π0) = 0.021 ± 0.003

Eta and Phi

η CMS 2009 Preliminary Uncorrected

φ CMS 2009 Preliminary

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Muons: A Dimuon Event at 2.36 TeVpT(μ1) = 3.6 GeV, pT(μ2) = 2.6 GeV,m( )= 3.03 GeVμμ

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• Expected one J/ → ψ μ+μ− event in 500k min. bias events at √s = 2.36 TeV• Got one J/ → ψ μ+μ− candidate in 20k events

• S/B ratio: 16/1 in [3.0,3.2] GeV/c2 region (background: ~ 0)

Dimuon event at 2.36 TeV

Backup

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Some numbers

Bμμ × σPbPb ( b)μ

J/ψ ’ψ Υ ’Υ ”Υ

48 900 880 300 80 44

dNch/d |η =0η , Δη

S/B

N(J/ )ψ S/B N( )Υ N( ’Υ)

N( ”Υ)

2500, | |< 2.4η 1.2 184 000 0.12 26 000 7 300 4 400

2500, | |< 0.8η 4.5 11 600 0.97 6 400 2 00 1 200

5000, | |< 2.4η 0.6 146 000 0.07 20 300 5 900 3 500

5000, | |< 0.8η 2.8 12 600 0.52 6 000 1 800 1 100

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Why to study Quarkonia at the LHC?

In Pb+Pb collisions:• Debye screening in deconfined phase leads

to melting of quarkonia when screening length exceeds binding radius

• Binding energy depends on quarkonium state and feed down from higher states lead to sequential suppression of J/ and ψ

with increasing temperatureΥ• It is important to measure quarkonium

yields in Pb+Pb collisions as function of pT and collision centrality

In p+p collisions:• Base line for heavy ion collisions• Cross section measurements• Polarization

y’

cc

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Hard Probes at the LHC

• 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

• ∫ L dt = 0.5 nb-1 (1 month, 50% run eff.)

• Hard cross sections: Pb+Pb = A2 x p+p

p+p equivalent ∫ L dt = 20 pb-1

1 event limit at 0.05 pb (p+p equiv.)

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Impact of the HLT on the pT reach of RAA

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

Pb-Pb (PYQUEN) 0.5 nb-1

HLT

Important measurement to compare with parton energy loss models and derivethe initial parton density and the medium transport coefficient

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Jet ET reach and fragmentation functions

Jet spectra up to ET ~ 500 GeV (Pb+Pb, 0.5 nb-1, HLT-triggered)

Detailed studies of medium-modified (quenched) jet fragmentation functions

min. bias

HLT Gluon radiation:large angle (out-of-cone) vs. small angle emission

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γ, γ*, and Z tagging of jet production

Unique possibility to calibrate jet energy loss (and FF) with back-to-back gauge bosons (large cross sections and excellent detection capabilities).

Heavy quark dimuon (dominant) background can be rejected by a secondary vertex cut.Resolutions: 50 mm in radius and 20 mm in φ

Z0+jet

dimuon trigger

associated hadrons

g g*away side