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Prospects for hadron spectroscopy in CMS

Prospects for hadron spectroscopy in CMS. Roberto Covarelli (University-INFN of Perugia) on behalf of the CMS collaboration HADRON 2007 – Frascati – 12 Oct 2007. Outline. The CMS detector at LHC: status and planning Heavy flavor physics in CMS Efficiency studies:

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Prospects for hadron spectroscopy in CMS

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  1. Prospects for hadron spectroscopy in CMS Roberto Covarelli (University-INFN of Perugia) on behalf of the CMS collaboration HADRON 2007 – Frascati – 12 Oct 2007 Roberto Covarelli

  2. Outline • The CMS detector at LHC: status and planning • Heavy flavor physics in CMS • Efficiency studies: • J/y reconstruction performances in CMS • Heavy meson spectroscopy: • Prospect for measurement of Bc mass and lifetime • Quarkonia: • Study of cc and bb quarkonium production in heavy-ion collisions • Conclusions and more prospects… Roberto Covarelli

  3. The CMS detector at LHC Muon stations (barrel): Drift Tubes Muon stations (endcaps): Cathode Strip Chambers 4T solenoidal magnet Hadronic calorimeter Electromagnetic calorimeter Outer tracker: Silicon strips compared to a man’s size… Inner tracker: Silicon pixels Roberto Covarelli

  4. LHC data-taking plans • Official LHC startup date is mid-2008!  CMS commissioning is our primary task • Main running program: • p-p collisions at ECM = 14.0 TeV • Start-up luminosity foreseen as low as 1032 cm-2 s-1 • Low luminosity régime: L ~ 2 x 1033 cm-2 s-1 • Nominal luminosity régime: L ~ 1 x 1034 cm-2 s-1 • Heavy ion running program: • One month per year dedicated to heavy ion collisions (mainly 208Pb-208Pb at ECM = 5.5 TeV) • Design luminosity: L ~ 4 x 1026 cm-2 s-1 } Different trigger strategies being optimized Great experimental challenge: extreme detector occupancy especially in tracking volumes Roberto Covarelli

  5. Heavy flavor physics in CMS • Heavy flavor physics in CMS still a key topic: • Two areas of interest: production and decays • Competitive results can be obtained already with low luminosity • Through processes at O(mb) scale, tests of New Physics at much higher scales • Hadronic environment: needing modes with excellent resolution and background control Bs mass in Bs→ J/y f Bs mass in Bs→mm Roberto Covarelli

  6. Global tracking efficiency in the SST (muons) CMS vs. other LHC experiments • Competition with ATLAS and dedicated LHC experiments (LHCb for B-physics, ALICE for heavy ion physics) • Dedicated experiments: • are better equipped for hadron identification • have better low-pT muon trigger efficiency • CMS  will focus onmuon/di-muon triggered events: • better muon resolution in some regions, e.g. mid-rapidity • high B-field • largest silicon tracking device • ~4p acceptance (|h| < 2.5, full f coverage) • less affected by misalignment at |h| ~ 0 Roberto Covarelli

  7. J/y reconstruction Z. Yang and S. Qian, CMS-NOTE-2007/017 • An essential ingredient in studies shown here (and many more heavy flavor analyses) is J/y→m+m -reconstruction: • Large production (both prompt and from b-hadron decays) • Opposite-sign di-muon trigger • Small decay width • Detailed studies have been performed on Bs→ J/y f MonteCarlo samples to determine: • Single muon / di-muon efficiencies as functions of: • pT / |h| / separation angle between the two muons after: • Reconstruction only / level-1 (L1) / high-level trigger (HLT) decisions A field where the tracking/ muon-ID performances of CMS can be fully exploited Roberto Covarelli

  8. J/y: reconstruction efficiency • J/y • Single muons Above 90% for pT(m) > 7 GeV/c Above 60% for pT(J/y) > 20 GeV/c e vs. pT m+m -mass e vs. pT e vs. |h| e vs. |h| s = 34MeV/c2 Roberto Covarelli

  9. J/y: trigger efficiencies • Very good reconstruction + L1 trigger efficiency (10.1%) • Low default HLT efficiency (< 1%) • Muon isolation criteria redefined for di-muon HLT, in order to account for possible small  efficiency recovered New HLT (up to 3 GeV pT cut, affordable at startup luminosity) Default HLT Roberto Covarelli

  10. The Bc meson: theory X.W. Meng, J.Q. Tao and G.M. Chen, CMS-NOTE-2006/118 • Bc+(1S) ≡ bc ground state must decay via weak interaction  sole long-lived particle made of two heavy quarks • Theoretical models: • Use of non-relativistic potential models to predict mass of ground and excited states  rich spectroscopy expected m(Bc+) = (6.24 ± 0.05) GeV/c2 • Full width estimated summing over (non-interfering) final states: • b → c(~ 26%) • c → s(~ 66%) • Annihilation decays(~ 8%) t (Bc+) = (0.54 ± 0.15) ps [W. Kwong and J. Rosner, Phys.Rev. D44, 212] [E. Eichten and C. Quigg, Phys.Rev. D49, 5845] See also talk by A. Kraan this morning (heavy meson spectroscopy) [I.I. Bigi, Phys.Lett. 371B, 105] [M. Beneke and G. Buchalla, Phys.Rev. D53, 4991] Roberto Covarelli

  11. Status and LHC prospects • Bc meson observed by CDF collaboration in different decay channels, measuring: m(Bc+) = (6.2741 ± 0.0032stat ± 0.0026syst) GeV/c2 in J/y p t (Bc+) = (0.463 -0.065+0.073stat ± 0.036syst) ps in J/y ev • LHC will provide: • higher luminosity than Tevatron • larger Bc production cross-section: sBc(ECM= 14 TeV) ~ 16 sBc(ECM= 1 TeV) • Potentially much more Bc mesons collected… • In CMS analysis the Bc is searched for in the channel: Bc+→J/yp+ (J/y→m+m -) [CDF Public Note 07-07-12] [F. Abe et al. (CDF collaboration), Phys.Rev.Lett. 97, 012002] Roberto Covarelli

  12. Event generation • Signal production several generators tested: • PYTHIA 6.228 • Two dedicated Bc generators (BCVEGPY, Protvino) • Good agreement in momentum spectra between BCVEGPY and PYTHIA: the former is used for generation, the latter to estimate systematics from the theoretical model • Simulated backgrounds: • J/y from other b-hadron decays (B0, B+, Bs, Lb) • Prompt J/y production (color octet contribution included) • bb, cc→m+m -X • W, Z + jets • Generic QCD processes • Generator-level cuts simulate effects of L1 and high-level di-muon trigger: • pT (Bc) > 10 GeV/c • |h (Bc)| < 2.0 • pT (m±) > 4 GeV/c • |h (m±)| < 2.2 Roberto Covarelli

  13. Bc reconstruction • Pxy > 60 mm (proper decay length in the transverse plane) • cos(qsp) > 0.8 (angle between the Bc momentum and the vector pointing from secondary to primary vertex) • Candidate selection: • Vertex-constrained kinematic fitting • 3.0 < m(m+m -) < 3.2 GeV/c2 • Muon-electron veto on pion track • pT (p ) > 2 GeV/c • |h (p )| < 2.4 • Lxy / sLxy > 2.5 (decay length in the transverse plane; resolution estimated from signal MC events) MonteCarlo rescaled to 1 fb-1 data Roberto Covarelli

  14. Mass and lifetime estimation • Signal and background expected yields in 1 fb-1: • Mass fit (simple Gaussian): • Lifetime fit (exponential convolved to a resolution function): • No bias observed • Expected statistical uncertainties m(Bc+) = (6.402 ± 0.002stat) GeV/c2 m(Bc+)gen = 6.400 GeV/c2 ct (Bc+) = (149 ± 13stat) mm ct (Bc+)gen = 150 mm Roberto Covarelli

  15. Systematics and result • Systematic sources considered (in order of fractional uncertainty): • Tracker / muon chamber misalignment (impact on momentum scale, momentum resolution and vertex determination) • Limited MC statistics • Theoretical models (generator yield comparisons) • Cut variations • Total expected uncertainties (in 1 fb-1): m(Bc+) = (x.xxx ± 0.002stat ± 0.015syst) GeV/c2 t (Bc+) = (x.xxx ± 0.044stat ± 0.010syst) ps • Foreseen improvements: • Efficiency / systematic estimation from data (using the large B+→J/y K+ control sample) large uncertainty from misalignment is totally from a worst-case scenario. In real data momentum scale can be determined from other samples Roberto Covarelli

  16. Quarkonia in heavy ion collisions M. Bedjidian, O. Kodolova CMS-NOTE-2006/089 • QCD predicts quark deconfinement at a critical temperature Tc ~ 180 MeV possible formation of Quark-Gluon Plasma (QGP) • How to detect it? • QGP could screen the color binding potential, preventing heavy quarks from forming bound states  measurable suppression of quarkonia yields • Results from previous experiments: • NA38: measured J/y production suppressed w.r.t. Drell-Yan  explained by nuclear absorption of quarks • NA50: first evidence in Pb-Pb collisions  departure from nuclear absorption scheme of a factor 0.77 ± 0.04 • RHIC: takingPb-Pb data at ECM = 200 GeV • Recent theoretical studies show that J/y could survive at temperatures as high as 1.5Tc  out of range for RHIC? • What about other quarkonia (e.g. Y)? [T. Matsui and H. Satz, Phys.Lett. B178, 416] [M.C. Abreu et al. (NA50 collaboration), Phys.Lett. B450, 456] [F. Karsch, D. Kharzeev, H.Satz, Phys.Lett. B637, 75] Roberto Covarelli

  17. Event generation (I) • Due to the very low quarkonium production vs. Pb-Pb total inelastic cross-section, full simulation (e.g. using HIJING) is not an option • Detailed input on signal and background production needed, as well as good simulation of detector response: • Signal production: J/y,y’,Y, Y’, Y”→m+m - • Backgrounds considered: • Muons from soft hadrons (p±/K±) produced in the collisions, generated in two different multiplicity scenarios: dN ±/dh|h=0 = 5000 (high) ordN ±/dh|h=0 = 2500 (low) • Muons from open c- and b-hadron pair production: large cross-sections but lower probability of a muon pair (PYTHIA) Roberto Covarelli

  18. Event generation (II) • Simulation of detector response: • Muon tables used to simulate trigger efficiency • Di-muon reconstruction efficiency studied vs. background type, pT and h • Resulting mass resolution for y and Y used as smearing in MC generation • h acceptance accounted for (1.3% for J/y, 26% for Y) Ymass: s = 86MeV/c2 J/y mass: s = 35MeV/c2 Roberto Covarelli

  19. Invariant mass distributions • Mass regions: • 2.0 < M < 4.5 GeV/c2 (y) • 8.5 < M < 11.0 GeV/c2 (Y) • MC rescaled to 0.5 nb-1 integrated luminosity • S/B greatly improved by requiring both muons to be in the barrel region (|h | < 0.8) but smaller yields • Same-sign di-muons used to subtract combinatorial bkg Roberto Covarelli

  20. Event yields and systematics • Expected event yields and S/B ratios in 0.5 nb-1: • Systematic uncertainties due to use of “fast” MonteCarlo (weighting method) estimated by adding in quadrature errors from limited statistics • about 20% for J/y, 25% for Y • Other systematic sources, to be evaluated: • “fast” vs. full MC comparison • limitations in detector description • dependence on impact parameter Roberto Covarelli

  21. Conclusions • CMS prospects in hadron spectroscopy have been illustrated with particular focus on two measurements: • Bc mass and lifetime: • Competitive results with Tevatron can be obtained with 1 fb-1 data-taking using the channel Bc+→ J/yp+: m(Bc+) = (x.xxx ± 0.002stat ± 0.015syst) GeV/c2 t (Bc+) = (x.xxx ± 0.044stat ± 0.010syst) ps • Quarkonium production in heavy ion collisions: • In 0.5 nb-1 (one month) of heavy ion data-taking 140000 to 180000 J/yand 20000 to 25000 Y mesons will be selected, allowing one to study production suppression and further analysis, e.g. in correlation with the centrality of the collision and the transverse momentum of the resonance Roberto Covarelli

  22. Other prospects • CMS is particularly sensitive to channels involving di-muons, as far as hadron spectroscopy (and in general heavy flavor physics) is concerned, due to its excellent tracking / muon system Bs→mm • Many other measurements can be foreseen with 1 fb-1 data: • Study of Lb(*) (Lb→ L J/y) • Confirmation of Sb(*) observations from CDF • Xb , Wb and other doubly-heavy baryons • CMS capabilities yet to be studied … t→ mmm CMS: lot of room for hadron spectroscopy Roberto Covarelli

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