1 / 63

Upsilon Polarization Studies: Insights from CDF and Beyond

This seminar presents a comprehensive overview of Upsilon polarization research conducted at Fermilab, detailing the evolution of charm and bottomonium observations from early experiments to advanced techniques like NRQCD and kT-factorization. Highlights include discussions on the CDF Detector's findings from Run I and II, polarization measurements of Upsilon states, and the implications of these results on theoretical models. The seminar emphasizes the challenges faced in understanding polarization dynamics, including discrepancies between experimental observations and theoretical predictions.

jaeger
Download Presentation

Upsilon Polarization Studies: Insights from CDF and Beyond

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Upsilon Polarization at CDF Matthew Jones Purdue University Fermilab W&C Seminar

  2. Brookhaven, 1968 PDP-6 – 36 bit processor Fermilab W&C Seminar

  3. First observation of charmonium Fermilab W&C Seminar

  4. Second observation of charmonium SLAC Mark I BNL E-598 Fermilab W&C Seminar

  5. Bottomonium Fermilab E288: CFS collaboration Fermilab W&C Seminar

  6. Over 30 years later… CESR/CUSB (1980’s) BB threshold PEP II/BaBar (2008) Fermilab W&C Seminar

  7. Quarkonium Production Einhorn & Ellis: Phys. Rev. D12, 2007 (1975). Glover, Martin & Stirling: Z. Phys. C38, 473 (1988). Comparison with UA1 at Or not… Fermilab W&C Seminar

  8. Color-Singlet Production Model • Production/decay via : • Production at hadron colliders: • Definite prediction for polarization! Fermilab W&C Seminar

  9. Color Evaporation Model • pairs produced with must eventually form a bound state. Halzen - Phys. Lett. B 69, 105 (1977) Fritzsch- Phys. Lett. B 67, 217 (1977) • Unable to predict polarization… Fermilab W&C Seminar

  10. The CDF Detector in Run Ia Fermilab W&C Seminar

  11. 1992 measurement: No prompt/secondary separation Assumptions: Fraction from B decays? Feed-down from excited states? J/ψ Cross Section – Run Ia PRL 69, 3704 (1992) Fermilab W&C Seminar

  12. Muon upgrades: CMX (|η|<1) + CMP (|ηmax| ~ 0.4) Muon triggers: Level 1 trigger: Muon stubs Level 2 trigger: Association with tracks The CDF Detector in Run Ib Fermilab W&C Seminar

  13. 1997 measurement: Silicon detector allows measurement of prompt fraction Excess and shape not explained by Structure functions Production in B decays Feed-down from states J/ψ Cross Section – Run Ib PRL 79, 572 (1997) X 30 Fermilab W&C Seminar

  14. 1995 measurement: No feed-down from B decays Also a significant excess! Run I ϒ(nS)Cross Section PRL 75, 4358 (1995) |y| < 0.4 Direct + feed-down from decays Direct Fermilab W&C Seminar

  15. Non-Relativistic QCD Caswell & Lepage – Phys. Lett. 167B, 437 (1986) Bodwin, Braaten & Lepage – Phys. Rev. D 51, 1125 (1995) • Expansion in powers of and • Factorization hypothesis applied to ϒ: • Color-octet terms are important! pQCD NRQCD matrix elements Fermilab W&C Seminar

  16. Octet Sum Singlet NRQCD + Color-Octet Models • Matrix elements tuned to accommodate Tevatron results • Apparently not needed to explain J/ψ cross section measurements from HERA: Cho & Leibovich, PRD 53, 6203 (1996). • Predicted transverseϒpolarization for Fermilab W&C Seminar

  17. “Polarization” Transverse: Longitudinal: Phys. Rev. Lett. 88, 161802 (2002). Longitudinal Fit yield in 8 bins of cosθ* Transverse Fermilab W&C Seminar

  18. Another Approach: “kT factorization” “un-integrated gluon density” Initial state gluon polarization related to kT • No need for color-octet terms… • Some criticism of the method (not gauge invariant) • Predicted longitudinal ϒpolarization for Fermilab W&C Seminar

  19. Higher-order QCD calculations • Partial calculation including terms up to … • Large increase in cross section compared with LO calculation • No need for color-octet contributions • Predicts longitudinalϒpolarization for Artoisenet, et al – Phys. Rev. Lett. 101, 152001 (2008). Fermilab W&C Seminar

  20. ϒ(1S) 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). Fermilab W&C Seminar

  21. Tevatron Run II The end! New CDFϒ(nS) polarization Preliminary CDFϒ(1S) polarization DØ ϒ(1S), ϒ(2S) polarization CDFψ(2S) cross section CDF J/ψ, ψ(2S) polarization (CDF Run Iϒ(1S) polarization) Run I Fermilab W&C Seminar

  22. ϒ Polarization from DØ in Run II 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? Fermilab W&C Seminar

  23. Suggested New Paradigm • 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. Fermilab W&C Seminar

  24. 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 Fermilab W&C Seminar

  25. Transverse: Longitudinal: Transverse/Longitudinal Insufficient But an arbitrary rotation will preserve the transverse/longitudinal shape... Fermilab W&C Seminar

  26. 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: Fermilab W&C Seminar

  27. Helicity (HX) – J/ψmomentum vector in C.M. frame of colliding beams (natural for production in gluon fragmentation) Gottfried-Jackson (GJ) – Direction of beam momentum in J/ψrest frame (better suited for spin transferred from initial hadron) Collins-Soper (CS) – Bisector of beam momentum vectors in J/ψrest frame (~C.M. frame of colliding partons) Which polarization axis? Fermilab W&C Seminar

  28. Could it be possible? S-channel helicity frame Fermilab W&C Seminar

  29. Could it be possible? Collins-Soper frame Fermilab W&C Seminar

  30. New CDF Analysis • Goals: • Use both central and forward muon systems • 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-muonbackground Fermilab W&C Seminar

  31. 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 Fermilab W&C Seminar

  32. Analysis Method • Previous analysis techniques do not generalize well to fits in both cosθ and φ. • Instead, we factor the acceptance and angular distribution: • A(cosθ,φ) from high statistics Monte Carlo • w(cosθ,φ; λθ, λφ,λθφ ) from angular distribution • Use binned likelihood fit to observed distribution of (cosθ,φ) to determine λθ, λφ,λθφ. • Bins are large compared to angular and pTresolution • Bins are small compared to variations in w(cosθ,φ) Fermilab W&C Seminar

  33. 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 Fermilab W&C Seminar

  34. 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: peaking backgrounds may be present in some pT ranges. 5-6 GeV/c 6-7 GeV/c 4-5 GeV/c m(μ+μ- ) Fermilab W&C Seminar

  35. A New Approach – by example Phys. Rev. Lett. 106, 121804 (2011) • lifetime analysis: • We do not fit m(J/ψK+) in bins of ct(J/ψK+)… • Instead, we expect the background decay time distribution to be independent of mass • Mass sidebands constrain its shape Fermilab W&C Seminar

  36. 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 Fermilab W&C Seminar

  37. 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%) Fermilab W&C Seminar

  38. 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. Fermilab W&C Seminar

  39. 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. Fermilab W&C Seminar

  40. 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 Fermilab W&C Seminar

  41. Fitted Parameters Signal and background have very different angular distributions. Background is highly “polarized” but the signal is not. mass bin numbers Fermilab W&C Seminar

  42. Consistency Tests It can be shown that the expression is the same in all reference frames. We observe that indeed it is. Fermilab W&C Seminar

  43. Frame Invariance Tests • Differences generally consistent with expected size of statistical fluctuations • Differences used to quantify systematic uncertainties on λθ, λφ and λθφ Fermilab W&C Seminar

  44. Results for ϒ(1S) state • λθ • λφ • λθφ • What about the ϒ(2S) and ϒ(3S) states? • λθ • λφ • λθφ Fermilab W&C Seminar

  45. Results for ϒ(2S) state • λθ • λφ • λθφ • Looks quite isotropic, even at high pT… • λθ • λφ • λθφ Fermilab W&C Seminar

  46. First measurement of ϒ(3S) spin alignment • λθ • λφ • λθφ • No evidence for significant polarization. Statistical Stat+syst. • λθ • λφ • λθφ Fermilab W&C Seminar

  47. Comparison with Models • Previous predictions for in the S-channel helicity frame: Fermilab W&C Seminar

  48. 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) Fermilab W&C Seminar

  49. Comparison with previous results • Does not agree with result from DØ at about 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) Fermilab W&C Seminar

  50. Comparisons with newer calculations CDF Run II preliminary – 6.7 fb-1 Nucl. Phys. B 214, 3 (2011) summary: • NLO NRQCD – Gong, Wang & Zhang, Phys. Rev. D83, 114021 (2011) • Color-singlet NLO and NNLO* - Artoisenent, et al. Phys. Rev. Lett. 101, 152001 (2008) NLO NRQCD with color-octet matrix elements Significant uncertainty due to feed-down from states (conservative assumptions) NLO color- singlet Fermilab W&C Seminar

More Related