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Quarkonium Production at Hadron Colliders

Quarkonium Production at Hadron Colliders. Matthew Jones Purdue University. Outline. B hadron cross sections Detectors and analysis methods Resolving the mysteries from Run I cross sections at the Tevatron Early measurements with J/ ψ An experimentalist’s view of production models

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Quarkonium Production at Hadron Colliders

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  1. Quarkonium Production at Hadron Colliders Matthew Jones Purdue University TRIUMF Quarkonium Workshop

  2. Outline • B hadron cross sections • Detectors and analysis methods • Resolving the mysteries from Run I • cross sections at the Tevatron • Early measurements with J/ψ • An experimentalist’s view of production models • PromptJ/ψ and ϒ cross sections • polarization measurements • Previous methods and results • Towards a new analysis paradigm • New measurement from CDF • Status of the LHC experiments • Capabilities and early results • Future measurements? TRIUMF Quarkonium Workshop

  3. The Experiments: Tevatron Run I DØ Detector CDF Detector • 1.5 Tesla solenoid • Upgrades: • Silicon vertex detector • Additional steel absorber • Increased muon coverage • No magnetic field for tracker • U-LAr calorimeter • Good muon coverage TRIUMF Quarkonium Workshop

  4. Inclusive leptons Use pTrel to select b-component Lepton + D Naturally enhanced b-component Inclusive J/ψ Use lifetime to measure b-fraction Exclusive B reconstruction B+J/ψK+, B0sJ/ψφ B Cross Section Measurements TRIUMF Quarkonium Workshop

  5. B Cross Section “crisis”? Experiments are more or less consistent with each other. Factor of ~2.5 excess Perturbative QCD unable to describe heavy quarks? TRIUMF Quarkonium Workshop

  6. An Early Clue... b-quark cross section, integrated above pTmin, obtained from a model relating pT(b) to pT(μ). from renormalization scale, μ0. More or less consistent with NLO QCD... Exhibits typical “excess” over NLO QCD. TRIUMF Quarkonium Workshop

  7. B Production and Decay TRIUMF Quarkonium Workshop

  8. Common Issues B decay products • PDF’s: MRSD0 or MRSA’ • Acceptances calculated using exact NLO calculation by Nason, Dawson & Ellis. • Quark mass, mb & renormalization scale μ0 • Peterson fragmentation with • Hadronization fractions: • B decay models: QQ  EvtGen • Decay tables? Can’t factor these into uncorrelated parts. TRIUMF Quarkonium Workshop

  9. Non-perturbative inputs • Fragmentation parameters were tuned to LEP data and LL Monte Carlo  • Correlated with parton shower and decay table • More soft gluon emission • More B** states • NNLO calculations/parton shower • co-linear gluon emission shouldn’t be counted twice. • Consistent treatments: CTEQ6M + FONLL + matched fragmentation functions... Smaller p/harder pT(B) JHEP05(1998)007 / JHEP07(2004)033 TRIUMF Quarkonium Workshop

  10. ∫ L dt ~ 40 pb-1 Di-muon trigger, pT(μ) > 1.5 GeV/c No lower limit on pT(J/ψ) b fraction measured using pseudo-proper decay time Positive for b decays Efficiencies measured using a 4 GeV/c single-muon trigger. Results in a data-driven pT(B) spectrum: constrains acceptance in other analyses. Newer Measurements: Hb J/ψ X Phys. Rev. D71, 032001 (2005). Consistent... TRIUMF Quarkonium Workshop

  11. Cross Section Summary Consistent treatment of and fragmentation function. All are correlated with hadronization fractions... (B+J/ψK+ is 100% correlated.) TRIUMF Quarkonium Workshop

  12. Quarkonium Production Einhorn & Ellis: Phys. Rev. D12, 2007 (1975). Glover, Martin & Stirling: Z. Phys. C38 (1988) 473. Comparison with UA1 at Or not… TRIUMF Quarkonium Workshop

  13. Quarkonium Production CDF Run I: Phys. Rev. Lett. 69 (1992) 3704. With only 2.6 pb-1… • Growing discrepancy: • Need to measure bottom and charm components separately • Not an issue in the ϒ system TRIUMF Quarkonium Workshop

  14. Run I Quarkonia Cross Sections Phys. Rev. Lett. 75 (1995) 4358. Phys. Rev. Lett. 79 (1997) 572. • Excess observed in both prompt J/ψ and ϒ cross sections • Need for additional production mechanisms… • Color octet vs color singlet models? • Color evaporation model? • Other QCD factorization schemes? Direct + feed-down from decays Direct TRIUMF Quarkonium Workshop

  15. Newer Run I Measurements • Cross sections compared with NRQCD: Phys. Rev. Lett. 75, 4358 (1995). Braaten, Fleming & Leibovich: Phys. Rev. Lett. 74, 3327 (1995). Phys. Rev. Lett. 88, 161802 (2002). TRIUMF Quarkonium Workshop

  16. A Naïve Experimentalist’s View • Color singlet model: • pairs with correct quantum numbers overlap with ϒ or wavefunction • Does not describe the cross section at leading order; large changes at NLO? • Polarization? • Color evaporation model: • Any pair below open beauty threshold coalesces to form an ϒ • Normalization okay, but maybe not the shape of the cross section • NRQCD: rigorous effective theory • Long distance matrix elements need to be tuned to data; loses predictive power • Polarization? • kT factorization approach: • Appealing analog to equivalent photon approximation • Gauge invariance? Assumptions about feed-down from decays? • Polarization? Polarization should be a useful observable… TRIUMF Quarkonium Workshop

  17. “Polarization” Transverse: Longitudinal: Phys. Rev. Lett. 88, 161802 (2002). Longitudinal Transverse TRIUMF Quarkonium Workshop

  18. ϒ Polarization in Run I • No strong polarization observed in ϒ(1S) decays... • What happens at high pT? • Feed-down from χb states? • Expect better comparison with ϒ(2S) and ϒ(3S)? CDF Run I: Phys. Rev. Lett. 88, 161802 (2002). NRQCD: Phys. Rev. D63, 071501(R) (2001). kT-factorization: JETP Lett. 86, 435 (2007). NNLO*: Phys. Rev. Lett. 101, 152001 (2008). TRIUMF Quarkonium Workshop

  19. ϒ Polarization from DØ in Run II (2008) DØ Run II: Phys. Rev. Lett. 101, 182004 (2008). CDF Run I: Phys. Rev. Lett. 88, 161802 (2002). NRQCD: Phys. Rev. D63, 071501(R) (2001). kT-factorization: JETP Lett. 86, 435 (2007). NNLO*: Phys. Rev. Lett. 101, 152001 (2008). • Not sure what to make of this… • Inconsistent with any model • Inconsistent with CDF result • Different rapidity coverage? TRIUMF Quarkonium Workshop

  20. Fixed Target Experiments? • J/ψ polarization measurements in fixed-target experiments apparently inconsistent • Consistent picture might emerge when taking into account the full 3-d nature of the angular distributions TRIUMF Quarkonium Workshop

  21. Suggested New Paradigm • Not really new… just forgotten. • Faccioli, et al remind us… Phys. Rev. Lett. 102, 151802 (2009). • General spin-1 state: • Angular distribution when decaying to fermions: … • A pure state cannot have all simultaneously. • Incoherence due to feed-down from multiple sources? • Choice of reference frame is important. • Collins-Soper frame may be more appropriate. TRIUMF Quarkonium Workshop

  22. Transverse: Longitudinal: Measuring just λθis not enough But an arbitrary rotation will preserve the transverse/longitudinal shape... TRIUMF Quarkonium Workshop

  23. Need for full polarization analysis • The templates for dN/dΩ are more complicated than simply 1 ± cos2θ. • Need to measure λθ, λφ and λθφ simultaneously. • Invariant under rotations: TRIUMF Quarkonium Workshop

  24. New CDF Analysis • Goals: • Measure all three parameters simultaneously • Measure in Collins-Soper and S-channel helicity frame • Test self-consistency by calculating rotationally invariant combinations of λθ, λφ and λθφ • Minimize sensitivity to modeling the ϒ(nS) resonance line shape • Explicit measurement of angular distribution of di-muon background TRIUMF Quarkonium Workshop

  25. The CDF II Detector Central Muon Upgrade CMP Central Muon Extension CMX 0.6<|η|<1 6 layers of double-sided silicon SVX-II • Two triggers used: • CMUP (4 GeV) + CMU (3 GeV) • CMUP (4 GeV) + CMX (3 GeV) • Both require: • opposite charge • 8 < m(μ+μ-) < 12 GeV/c2 Drift chamber 1.4 Tesla field COT • Integrated luminosity: 6.7 fb-1 • Sample size: 550,000 ϒ(1S) • 150,000 ϒ(2S) • 76,000 ϒ(3S) Central Muon System CMU |η|<0.6 TRIUMF Quarkonium Workshop

  26. Analysis Method • Reconstruct μ+μ- candidates, boost into rest frame, calculate decay angles (cosθ,φ) • Analyze in both S-channel helicity and Collins-Soper frames • Factor acceptance and angular distribution: • A(cosθ,φ) from high statistics Monte Carlo • w(cosθ,φ; λθ, λφ,λθφ ) from angular distribution • Performed binned likelihood fit to observed distribution of (cosθ,φ) to determine λθ, λφ,λθφ. • Binning is large compared with angular and pT resolution TRIUMF Quarkonium Workshop

  27. Analysis Method • Trigger and reconstruction efficiencies measured using J/ψμ+μ- and B+J/ψK+ control samples • Geometric acceptance calculated using full detector simulation • Two component fit: • signal + background TRIUMF Quarkonium Workshop

  28. The Background is Complicated • Dominant background: correlated production • Triggered sample is very non-isotropic • pT(b) spectrum falls rapidly with pT • Angular distribution evolves rapidly with pT and m(μ+μ-) • Very simple toy Monte Carlo: the background might peak right under the ϒ(nS) signals in some pT ranges. 5-6 GeV/c 6-7 GeV/c 4-5 GeV/c m(μ+μ- ) TRIUMF Quarkonium Workshop

  29. New Approach • Use muon impact parameter to isolate a background-enhanced (displaced) sample • Complimentary sample (prompt) contains most of the ϒ(nS) signal. • Impact parameter requirement must not bias angular distributions • Fit to invariant mass distribution: • Measure fraction of ϒ(nS) signal present in displaced sample • Fit to displaced sample + prompt sidebands: • Measures ratio of prompt/displaced backgrounds • Not biased by signal line shape model • Allows us to predict the level of prompt background under the ϒ(nS) • Two component fit to (cosθ,φ) distribution • Determines λθ, λφ,λθφfor signal and background • Purely empirical parameterization of background – helpful to add additional term TRIUMF Quarkonium Workshop

  30. Background Proxy Sample • Measure fraction of signal in displaced sample: This fit measures the fraction of the ϒ signal that is present in the displaced sample (1-4%) TRIUMF Quarkonium Workshop

  31. Background Proxy Sample • Measure prompt scale factor: The ratio of prompt/secondary distributions is almost constant. Simultaneous fit to displaced sample and ϒ sidebands. Avoids possible bias from modeling theϒline shape. Quadratic scale factor function considered in systematic studies. TRIUMF Quarkonium Workshop

  32. Angular distributions in sidebands • The sub-sample containing a displaced track (|d0| > 150 μm) is a good description of the background under the ϒ(nS): • Prompt (histogram) and displaced (error bars) angular distributions match in the sidebands. • We use the displaced muon sample to constrain the angular distribution of background under the ϒ(nS) peaks. TRIUMF Quarkonium Workshop

  33. Fits to signal + background • The fit provides a good description of the angular distribution in both background and in signal + background mass bins. Only background Signal + background TRIUMF Quarkonium Workshop

  34. Fitted Parameters Signal and background have very different angular distributions. Background is highly “polarized” but the signal is not. mass bin numbers TRIUMF Quarkonium Workshop

  35. Consistency Tests It can be shown that the expression is the same in all reference frames. We observe that indeed it is. TRIUMF Quarkonium Workshop

  36. Frame Invariance Tests • Differences generally consistent with expected size of statistical fluctuations • Differences used to quantify systematic uncertainties on λθ, λφ and λθφ TRIUMF Quarkonium Workshop

  37. Results for ϒ(1S) state • λθ • λφ • λθφ • What about the ϒ(2S) and ϒ(3S) states? • λθ • λφ • λθφ TRIUMF Quarkonium Workshop

  38. Results for ϒ(2S) state • λθ • λφ • λθφ • Looks quite isotropic, even at high pT… • λθ • λφ • λθφ TRIUMF Quarkonium Workshop

  39. First measurement of ϒ(3S) spin alignment • λθ • λφ • λθφ • No evidence for significant polarization. Statistical Stat+syst. • λθ • λφ • λθφ TRIUMF Quarkonium Workshop

  40. Comparison with previous results Agrees with previous CDF publication from Run I • NRQCD – Braaten & Lee, Phys. Rev. D63, 071501(R) (2001) • kT – Baranov & Zotov, JETP Lett. 86, 435 (2007) TRIUMF Quarkonium Workshop

  41. Comparison with previous results • Does not agree with result from DØ at the 4.5σ level • Different rapidity coverage? • Subtraction of highly polarized background? • NRQCD – Braaten & Lee, Phys. Rev. D63, 071501(R) (2001) • kT – Baranov & Zotov, JETP Lett. 86, 435 (2007) TRIUMF Quarkonium Workshop

  42. NRQCD predictions for ϒ(1S) polarization need input for feed-down from χbJ(nP)states. 3.3 and 2.3σ effects... Might not be called an “observation” by today’s rigorous standards. But these states dilute the longitudinal polarization predicted by NRQCD... Feed-down? Phys. Rev. Lett. 84, 2094 (2000) B Production & Decay Subgroup

  43. New results from the LHC TRIUMF Quarkonium Workshop

  44. Upsilon Production: CMS • Early running: low luminosity  low trigger rates, low pT thresholds. • Current trigger conditions: • Un-prescaleddi-muon triggers: TRIUMF Quarkonium Workshop

  45. ϒ(nS) Production Cross Section 3 pb-1 result: Phys. Rev. D83, 112004 (2011). dσ/dy increased by factor of 2.2 TRIUMF Quarkonium Workshop

  46. CMS: Suppression in PbPb Collisions Phys. Rev. Lett. 107 (2011) 052302. • Suppression of 2S and 3S: • Inconsistent with equality at the 1% level. • What is the form of the potential at high temperature? TRIUMF Quarkonium Workshop

  47. CMS Converted Photons • Excellent mass resolution but efficiencies can be hard to quantify… CDF Result – 1.1 fb-1 Phys. Rev. Lett. 98, 232001 (2007) CMS-DP-2011-006 TRIUMF Quarkonium Workshop

  48. Production at ATLAS CERN-PH-EP-2011-083 • Inner detector • Compare with CMS: • Consistent with CMS cross section measurement. TRIUMF Quarkonium Workshop

  49. Results from LHCb • Probes a very different region of rapidity • Some overlap with CMS • Lots of interesting results… arXiv:1109.0963 TRIUMF Quarkonium Workshop

  50. LHCb: P-wave charmonium LHCb-CONF-2011-020 • Unknown polarization state is a general issue with χcJ production. TRIUMF Quarkonium Workshop

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