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

1. Quarkonium studies in p+p andPb+Pb collisions with CMS – Torsten Dahms (on behalf of CMS) – CERN ReteQuarkonii Thematic Day, IPN Orsay February 9th, 2010

2. Quarkonia production at the LHC The 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 μb−1 (400 mb−1) • Starting February/March 2010 with p+p collisions at √s = 7 TeV with peak luminosities up to1032 cm−2s−1 until 1 fb−1of 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−1Pb+Pb instantaneous luminosity  Quarkonium states will be produced at very high rates

3. A transverse slice of the CMS barrel CalorimetersECAL PbWO4HCAL Plastic Sci/Steel sandwich Si TrackerSilicon micro-stripsand pixels Muon BarrelDrift Tube Chambers (DT)Resistive Plate Chambers (RPC)

4. CMS phase-space coverage • CMS: full φ and almost full η acceptance at the LHC • charged tracks and muons: |η| < 2.4 • electrons and photons: |η| < 3 • jets, energy flow: |η| < 6.7 (plus |η| > 8.3 for neutrals, with the ZDC) • excellent granularityand resolution • very powerfulHigh-Level-Trigger ZDC CASTOR HF HF CASTOR ZDC

5. J/ψ detection and dimuon mass resolutionin CMS • CMS is ideal to measure quarkoniain the dimuon decay channel: • large rapidity coverage (|η|<2.4) • 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

6. Inclusive differential J/ψcross sections in p+p collisions • The observed J/ψ yield results from: • direct production • decays from ψ’ and 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/ψ yield is extracted by fitting the dimuon mass distribution, separating the signal peak from the underlying background continuum p+p √s = 14 TeV(3 pb−1) CMS simulation CMS PAS BPH-07-002 prompt

7. Inclusive differential J/ψ cross sections CMS simulation CMS PAS BPH-07-002 A CMS simulation CMS PAS BPH-07-002 p+p at 14 TeV3 pb−1  ~ 75 000 J/ψ 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

8. Feed-down from B meson decays 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 B fraction fit J/ψ pT : 9–10 GeV/c CMS simulation CMS PAS BPH-07-002 CMS simulation CMS PAS BPH-07-002 Systematic error dominated byluminosity and polarization uncertainties

9. Quarkonium production in Pb+Pb collisions dNch/dη = 3500 Υ  μμ− CMS simulation

10. Barrel + endcaps: muons in |h| < 2.4  Barrel: both muons in |h| < 0.8 Acceptance pT (GeV/c) ϒ→μ+μ−: acceptance and mass resolution Pb+Pb √sNN = 5.5 TeV(0.5 nb−1) σ = 54 MeV/c2  • 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 • 1 month Pb+Pb at 5.5 TeV with average luminosity of 4×1026 cm−2s−1 0.5 nb−1 ’ CMS simulation CMS PTDR Addendum 1 ’’ CMS simulation CMS simulation

11. pT (GeV/c) h 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 Υ due to high mass • but for J/ψ’s this sets a relatively high threshold on the pT • The low pT J/ψ acceptance is better at forward rapidity Pb+Pb √sNN = 5.5 TeV(0.5 nb−1) barrel + endcaps (|η|<2.4) σJ/ψ = 35 MeV/c2 J/ψ Acceptance barrel +endcaps CMS simulation CMS PTDR Addendum 1 barrel pT (GeV/c)

12. The High Level Trigger Pb+Pb at 5.5 TeV design luminosity • 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 jets ×35 ×35 • CMS PTDR Addendum 1

13. pT reach of quarkonia measurements 0.5 nb−1 : 1 month at 4×1026 cm−2s−1 Expected rec. quarkonia yields: J/ψ : ~ 180 000 Υ : ~ 26 000 Statistical accuracy (with HLT) ofΥ’ / Υ ratio vs. pTshould be goodenough to rule out some models ● produced in 0.5 nb−1 ■rec. if dN/dh ~ 2500 ○ rec. if dN/dh ~ 5000 J/ψ CMS simulation CMS PTDR Addendum 1 Pb+Pb √sNN = 5.5 TeV Υ CMS simulation CMS PTDR Addendum 1 CMS simulation CMS PTDR Addendum 1

14. 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 simulation CMS PTDR Addendum 1 CMS simulation CMS PTDR Addendum 1

15. 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/ψ; ~90 MeV for the Υ, over ||<2.4 Good S/B and separation of Υ(1S), Υ(2S) and Υ(3S) • Expected p+p rates are high enough to collect J/ψ and Υ dimuons up topT ~ 40 GeV/c in a few days at 7 TeV • Expected Pb+Pb rates at √sNN = 5.5 TeV:180 000 J/ψ and 26 000 Υ(1S) per 0.5 nb−1 (one month) Studies of Upsilon suppression as signal of QGP formation • J/ψ and Υ polarization, and χc → J/ψ + γ studies require larger samples

16. A first look at “real” data

17. Start of the LHC: First CollisionsMonday 23rd November CMS Experiment at the LHC, CERN Date Recorded: 2009-11-23 19:21 CET Run/Event: 122314/1514552 Candidate Collision Event Events recorded: All CMS ON 900GeV: ~400k 2.36 TeV: ~20k

18. 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

19. Eta and Phi η φ CMS 2009 Preliminary Uncorrected CMS 2009 Preliminary • Data: N(η)/N(π0) = 0.020 ± 0.003 • MC: N(η)/N(π0) = 0.021 ± 0.003

20. Muons: A Dimuon Event at 2.36 TeV pT(μ1) = 3.6 GeV, pT(μ2) = 2.6 GeV, m(μμ)= 3.03 GeV

21. Dimuon event at 2.36 TeV • 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)

22. Backup

23. Some numbers

24. Why to study Quarkonia at the LHC? y’ cc 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/ψ and Υ with increasing temperature • 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

25. 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 = A2x p+p p+p equivalent ∫ L dt = 20 pb-1 1 event limit at 0.05 pb (p+p equiv.)

26. 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

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

28. dimuon trigger g* g away side associated hadrons 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 inφ Z0+jet