Hot quarkonium spectral functions from QCD sum rules and MEM
Perspectives for quarkonium production in CMS
description
Transcript of Perspectives for quarkonium production in CMS
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Perspectives for quarkonium production in CMS
Carlos Lourenço, on behalf of CMS QWG 2008, Nara, Japan, December 2008
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A transverse slice through the CMS “barrel”
Muon BarrelDrift Tube ChambersResistive Plate Chambers
Si TrackerSilicon pixelsand micro-strips
CalorimetersECAL PbWO4
HCAL Plastic Sci / Steel sandwich
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The CMS phase space coverage
CMS + TOTEM: full φ and almost full η acceptance at the LHC charged tracks and muons: |η| < 2.5 electrons and photons: |η| < 3 jets, energy flow: |η| < 6.7 (plus η > 8.3 for neutrals, with the ZDC)
HFHF
= -8 -6 -4 -2 0 2 4 6 8
excellent granularity and resolutionvery powerful
High-Level-Trigger
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The CMS assembly: a “LEGO” design
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Quarkonium production at LHC energies
• The LHC will provide pp and Pb-Pb collisions at high energies and luminosities
• Early times will be with pp collisions at 10 TeV (or maybe less) with instantaneous luminosities between 1030 and 1031 cm-2s-1 (or maybe less)
• Depending on the machine performance, at some moment the energy will be increased to 14 TeV and the luminosity to 1034 cm-2s-1
• The Pb-Pb runs will occur at 5.5 TeV per NN collision, with 1027 cm-2s-1 Pb-Pb instantaneous luminosity
• Quarkonium states will be produced with very high rates
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J/ detection and dimuon mass resolution in CMS
• CMS is ideally suited to measure quarkonium in the dimuon decay channel:• large rapidity coverage (||<2.5)• excellent dimuon mass resolution
• The good dimuon mass resolution is due to the good muon momentum resolution, which results from the matching between the tracks in the muon chambers and in the silicon tracker
• 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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•The observed J/ yield results from:• direct production• decays from ’ and c states• decays from B hadrons
•CMS will measure the inclusive, prompt and non-prompt (B decays)production cross sections
•In 1 or 2 days at 1031 cm-2s-1
(1 pb-1 of integrated luminosity),CMS will collect ~ 25 000 J/ events
•The J/ yield is extracted by fitting the dimuon mass distribution, separating the signal peak from the underlying background continuum
Inclusive differential J/ cross sections
CMS simulation
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Inclusive differential J/ cross section
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dσ
dpTJ /ψ
⋅Br(J /ψ → μ +μ−) =NJ /ψfit
Ldt∫ ⋅ΔpTJ /ψ ⋅A ⋅λcorr
A : convolution between the detector acceptanceand the trigger and reconstruction efficiencies, which depend on the assumed polarization
corr : needed if MC does not match “reality”
pp at 14 TeV3 pb-1 ~ 75 000 J/
CMS simulation
A
Competitive with Tevatron results after only 3 pb-1
CMS simulation
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An 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
Feed-down from B meson decays
B fraction fit
J/ pT : 9–10 GeV/c
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l xy =LxyJ/ψMJ/ψ
PTJ/ψ
CMS simulation
CMS simulation
Systematic error dominated byluminosity and polarization uncertainties
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Quarkonium production in Pb-Pb collisions
dNch/d = 3500
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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
CMS simulation
CMS simulation
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J/ → : acceptances and mass resolutions
barrel +endcaps
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
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p T (G
eV/c
)
CMS simulation
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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 “offline-like” algorithms
• pp design luminosity L1 trigger rate: 100 kHz• Pb-Pb collision rate: 3 kHz (peak = 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 / 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
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pT reach of quarkonia measurements
J/
● produced in 0.5 nb-1
■ rec. if dN/d ~ 2500○ rec. if dN/d ~ 5000
0.5 nb-1 : 1 month at 4x1026 cm2s-1
Expected rec. quarkonia yields:J/ : ~ 180 000 : ~ 26 000
Statistical accuracy (with HLT) of’ / ratio vs. pT should be good enough to rule out some models
CMS simulation
CMS simulation
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production in Ultra-Peripheral Pb-Pb Collisions
• CMS will also measure Upsilon photo-production, occurring when the Pb nuclei fly through each other
• 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 ee and decay channels using neutron tagging in the ZDCs
CMS simulation CMS simulation
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Summary
•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 pp and Pb-Pb
•Dimuon mass resolutions: ~30 MeV for the J/; ~90 MeV for the , over ||<2.4 Good S/B and separation of (1S), (2S) and (3S)
•Expected pp rates: 25’000 J/ and 7’000 per pb-1 (1 or 2 days at 1031 cm-2s-1) J/ and dimuons up to pT ~ 40 GeV/c in a few days
•Expected Pb-Pb rates: 180’000 J/ and 25’000 (1S) per 0.5 nb-1 (one month) Studies of Upsilon suppression as signal of QGP formation
•J/ and polarization, and c → J/ studies require larger samples
Further information can be found in:http://cms.cern.ch/iCMS/ (“B-physics” and “Heavy-Ions” Physics Analysis Groups)http://www.slac.stanford.edu/spires/find/hep/www?j=JPHGB,G34,N143http://www.slac.stanford.edu/spires/find/hep/www?j=JPHGB,G34,2307
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LHC proton beam in CMS, on September 10
CMS recorded several splash events when the proton beam was steered onto the collimators; halo muons were observed once beam started passing through CMS
Detectors flooded by few hundred thousand muons resulting from 109 protons (one bunch) simultaneous hitting a collimator
Correlation between the energies collected in the HCAL and ECAL calorimeters from several
“beam-collimator collisions”
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“splash event”
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“halo muons event”
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Cosmic muons in CMS
CMS recorded almost 300 million cosmic muons in one month of 24 / 7 runningat full magnetic field and with all detectors operational
A cosmic muon that traversed the barrel muon systems, the barrel calorimeters, and the silicon strip and pixel trackers
Improved track quality in the strip trackeras the nominal design geometry is replaced by
versions aligned with cosmic muons
See http://www.cern.ch/cms-project-cmsinfo/ for more information
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The 2010 QWG meeting will see the first CMS quarkonium results…