Quarkonia Production & Polarization at CDF

1. Quarkonia Production & Polarization at CDF Min Jeong Kim, Carnegie Mellon University (For the CDF Collaboration) International Workshop on Heavy Quarkonium 2006 @ BNL, June 27-30

2. Outline • Today’s presentation is limited to the charmonium production. • Charmonium production at Tevatron: • - prompt (direct & feeddown from heavier states) • - decay of B-hadrons • Introduce three CDF Run II analyses related to the topic of charmonium production: - A Measurement of the J/y Spin Alignment - Measurement of the y’ Polarization - Relative Production of the cc1(1P) and cc2(1P) International Workshop on Heavy Quarkonium

3. Theory Motivation • A large excess (×50) of J/y & y(2S) production compared with predictions from the Color Singlet Model (CSM); difference in the pT spectrum. [PRL 79, 572 (1997), PRD 71, 032001 (2005)] • Prediction based on the CSM: prompt J/y production should be dominated (>90%) by feeddown from cc production. However, CDF Run I measurement [PRL 79, 578 (1997)] shows that ~30% of prompt J/y production came from cc. • Nonrelativistic QCD (NRQCD) addresses the discrepancy between data and the CSM by introducing the Color Octet Mechanism with adjustable hadronization parameters that allow it to match the observed pT-dependence and amplitude of production. • Prediction based on NRQCD: the J/y mesons should be produced with transverse polarization at large pT (> 15 GeV/c). The Run I data did not show such an effect, but the amount of data in the region where the model expected to work well, were not sufficient enough to make a definite conclusion. [PRL 85, 2886 (2000)] International Workshop on Heavy Quarkonium

4. Polarization q *: angle between m+ in the J/y rest frame & J/y in the lab frame. Transverse (a = 1) Longitudinal: (a = -1) Zero polarization (a= 0) means that all 3 helicity states are equally populated. Angular distribution depends on the polarization parametera: International Workshop on Heavy Quarkonium

5. J/y Candidate Selection • Reconstruct J/y m+ m- from 800 pb-1 of data collected using the CDF central dimuon trigger: 5 ≤ pT(m+ m-) < 30 GeV/c, |y| < 0.6. • Identify muons using the COT (central outer tracker), SVX II (silicon vertex detector) and CMU (central muon system). --- Overview of CDF detector was given by M. Aoki on Tuesday.--- • Select baseline samples with pT > 1.75 GeV/c requirement to minimize biases due to trigger turn on. • Separate into prompt or B-decay candidates using the impact • parameter information of two muons: MC studies show Prompt: S≤ 8, B-decay: S > 16 International Workshop on Heavy Quarkonium

6. J/y Candidates Mass fit: double Gaussian signal plus linear background • Signal region: (M-3s, M+3s) • Lower sideband (M-13s, M-10s) is further displaced from the nominal J/y mass than upper-sideband (M+5s, M+8s), to avoid any effects from the radiative tail of J/y mass distribution. • Extract decay angular distributions from the events in signal and sideband (background) regions. • Divide candidates into 6 pT bins for polarization measurement. International Workshop on Heavy Quarkonium

7. Residual Background (Contamination) • Estimate using the sideband- • subtracted ct distributions All Events PromptGaussian B-decay Evts Assumption: prompt Gaussian signal is centered at ct = 0 and symmetric. Mis-measured Evts Introduce ct > 0.03 cut to further reduce the prompt contamination. Prompt Events B-decay Events International Workshop on Heavy Quarkonium

8. Residual Heavy Flavor Contamination Percentage B fraction fB comparison between ours and published analysis [PRD 71, 032001 (2005)]: International Workshop on Heavy Quarkonium

9. MC Templates • Getting detector trigger acceptance right is crucial: use experimentally-derived acceptance function. • Angular resolution is very important: CDF cos q*resolution < 0.01 for all pT. • Raising the muon threshold reduces cos q * range. International Workshop on Heavy Quarkonium

10. Polarization of J/y Mesons from B-decays Polarization for B-decay events should be independent of pT.  Combine 6 bins by a c2 average; aB = -0.066  0.050 Prob (c2) = 18 % aB = -0.1  0.1 (CDF Run I) aB = -0.129  0.009 (BaBar measurement adapted to the CDF environment in Run II) • Our measurement is consistent with both Run I and BaBar. • We differ from BaBar only by 1.2s. • CDF data are influenced by Bs and B-baryon contributions that are not seen at B-factories. International Workshop on Heavy Quarkonium

11. Prompt J/y Polarization Results afit is corrected for the residual heavy flavor using aB measured: International Workshop on Heavy Quarkonium

12. Systematic Studies All systematic effects are small compared to the statistical errors. • We also investigated other possible systematics: • - cos q * binning effect • - different signal and background extraction method • - run dependence (detector and trigger issues) • - dependence of different pT(m) requirements •  No significant effects are found. International Workshop on Heavy Quarkonium

13. y′Polarization • Same theoretical framework applies to prompt y′ and J/y production. • y′ is a cleaner system than J/y; no contributions from feeddown from higher states. • This analysis uses y′m+m-events from CDF central dimuon trigger. • This y′ sample has 10× more events than the Run I sample. • y′uses same analysis method just described for J/y. International Workshop on Heavy Quarkonium

14. y′ Polarization < B-decay polarization > • First measurement of aB for y′: Within statistics, it could be same as for J/y, but the central value is transverse. < prompt polarization > • Prompt polarization agrees with Run I. • Prompt alignment becomes longitudinal at high pT, just like J/y case. International Workshop on Heavy Quarkonium

15. Measurement ofs(cc2)/s(cc1) • Models of prompt charmonium production in hadronic collisions always contain significant ccJ contributions. • Measurement of the properties of ccJ production has always been an experimental challenge. • The relatively low energy photon from the ccJJ/yg, decay is difficult to measure • Calorimeter measurements give good efficiency, poor resolution • Conversion measurements give poor efficiency, good resolution • The measurement of s(cc2) / s(cc1) has been performed at several energies and beam types over the years. • Best measurements have ~100 events, 30% statistical uncertainty on the cross section ratio. • Results like 1.0±0.3 are consistent with most models. International Workshop on Heavy Quarkonium

16. ccJData Set • Here we reconstruct:ccJJ/yg, J/ym+m-, ge+e- • Same events used for polarization analysis. • Conversion reconstruction of the photon gives excellent energy (mass) resolution. • B/Prompt components are easily separated. • Simultaneous fit to the mass and flight distance distributions is used to extract the relative yields for both production mechanisms. International Workshop on Heavy Quarkonium

17. For prompt production, we measure (for pT 4-20 Gev/c) This is a new level of precision for this measurement This should provide a nice constraint on production models. CDF preliminary Results on s(cc2)/s(cc1) • Systematic uncertainties are small • for this ratio: Prompt Production • The dominant systematic uncertainty • comes from the branching fractions: International Workshop on Heavy Quarkonium

18. Conclusion • Measured alignments for prompt J/y and y′ mesons are longitudinal in higher pT region; results disagree with NRQCD predictions, but agree with Run I measurement at the highest pT point. • y′ polarization agrees with J/y pattern.  Eur. Phys. J. C 39, 163 (2005); predict longitudinal polarization for pT(J/y) > 15 GeV/c. • For convenient comparison, we restate the prompt production ratios as: International Workshop on Heavy Quarkonium

19. (Backup Slides) International Workshop on Heavy Quarkonium

20. Residual Heavy Flavor Contamination Percentage B fraction fB comparison between ours and published analysis [PRD 71, 032001 (2005)] fother = 3.6 [%] International Workshop on Heavy Quarkonium

21. Polarization Fitter • An adaptation of the c2 fitter developed for the CDF Run I measurement. • Components that get into the polarization fit: - ND : total number of events in the signal region. - Di : cos q * distribution for ND events. - NB : total number of events in the sideband regions. - Bi: cos q * distribution for NB events. - Template angular distributions from Ti (transverse) & Li (longitudinal)signalMC samples: include all the corrections due to acceptance and efficiency effects to the theoretical angular distributions. [Run II measured J/y pT spectrum from PRD 71, 032001 (2005)] - BB : residual heavy flavor contamination • 40 bins of 0.05 ( -1 < cos q * < 1): i = 0  39 International Workshop on Heavy Quarkonium

22. MC Templates Acceptance depends on the polarization; acceptance is lower in T case. Raising the pT(m) cut reduces discrimination between T & L Polarization, especially at low pT(J/y). International Workshop on Heavy Quarkonium

23. Polarization of J/y Mesons from B-decays The remaining contamination is corrected with the zero polarization assumption. International Workshop on Heavy Quarkonium

24. Prompt J/y Polarization Results hfit is corrected for the residual heavy flavor using hB measured: International Workshop on Heavy Quarkonium

25. Prompt J/y: Data/MC Comparison of Muon pT Spectrum The influence of the J/y spin alignment to the pT spectrum of muons. The polarization dependence on low-pT muon is largest at low pT(J/y) bin. m+ m- Good agreement between data and MC tuned to match the measured polarization in the lowest pT bin of J/y with muon pT cut of 1.6 GeV/c. m+ m- Prob (c2) = 27 % Prob (c2) = 68 % International Workshop on Heavy Quarkonium