1 / 36

BOTTOMONIUM RESULTS FROM BABAR

BOTTOMONIUM RESULTS FROM BABAR Veronique Ziegler (SLAC) Representing the BaBar Collaboration CharmEx 2009, Bad Honnef, Germany, Aug. 10-12 2009 OVERVIEW Observation of the Bottomonium Ground State, h b (1S), in U (3S) → g h b (1S) Decay

liam
Télécharger la présentation

BOTTOMONIUM RESULTS FROM BABAR

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. BOTTOMONIUM RESULTS FROM BABAR Veronique Ziegler (SLAC) Representing the BaBar Collaboration CharmEx 2009, Bad Honnef, Germany, Aug. 10-12 2009

  2. OVERVIEW • Observation of the Bottomonium Ground State, hb(1S), in U(3S) → g hb(1S) Decay • Confirmation of the Observation of the hb(1S) in U(2S) → g hb(1S) Decay • Rb Scan above the U(4S)

  3. 6580 DIRC Charged particle ID by means of velocity measurement DCH Angles and positions of charged tracks just outside the beam pipe Charged tracks momentum dE/dx for PID (1.5 T) 3.1 GeV 9.03 GeV [Y(4S)] 8.65 GeV [Y(3S)] 8.10 GeV [Y(2S)]

  4. k k k BaBar RUN 7 (Dec. 2007 – Apr. 2008)PEP-II e+e- Asymmetric Collider Running at the U(2S,3S)… Effective BABAR DATASETS: ~ 120 x 106Y(3S) events ≈ 20 X previous dataset (CLEO) ~ 100 x 106Y(2S) events ≈ 11 X previous dataset (CLEO) ~ 8.54 fb-1 above Y(4S) ≈ 30 X previous datasets (CLEO, CUSB) R-scan 4

  5. (nL) where n is the principal quantum number and L indicates the bb angular momentum in spectroscopic notation (L=S, P, D,…) Current Picture of the Bottomonium Spectrum threshold hadrons hadrons [Orbital Ang. Momentum between quarks] P-wave S-wave

  6. The hb(1S) State (11S0)

  7. Expected hb Production Mechanism The U(nS) states are produced in hadronic interactions or from a virtual photon in e+e− annihilation One of the expected production mechanisms of the hb(n’S) is by M1 (i.e. SS) transition from the U(nS) states [n’≤n]

  8. The Search for thehbat BaBar • Decays of hb not known  Search for hb signal in inclusive photon spectrum i.e. Search for the radiative transition Y(3S)→ghb(1S) • In c.m. frame: • For hb mass m = 9.4 GeV/c2 monochromatic line in Eg spectrum at 915 MeV, i.e. look for a bump near 900 MeV in inclusive photon energy spectrum from data taken at the U(3S) √s = c.m. energy = m(Y(3S)) m = m(hb)

  9. ANALYSIS STRATEGY • Look for a bump near 900 MeV in the inclusive photon spectrum • Large background • Non-peaking components • Peaking components • Reduce the background • Selection Criteria • Optimization of Criteria • Optimization Check • Fitting Procedure • One-dimensional fit to the Eg distribution • Obtain lineshapes of the various components • Binned Maximum Likelihood Fit

  10. DATA SETS • Y(3S) On-peak data • Full data sample: L = 28.6 fb-1 • 122 x 106 Y(3S) events • Analysis sample: L = 25.6 fb-1 • 109 x 106 Y(3S) events • expect ~ 20 x 103 Y(3S) g hb events • Test sample: L = 2.6 fb-1 • 11 x 106 Y(3S) events • expect ~ 2 x 103 Y(3S) g hb events • Use since no reliable event generator for Y(3S) background photon simulation • Y(3S) & Y(4S) Off-peak data: L = 2.4 & 43.9 fb-1 L = Integrated Luminosity (used for optimization of selection criteria) much smaller than expected background (used for background studies)

  11. The Inclusive Photon Spectrum • Use ~9% of the Full U(3S) Data Sample Look for a bump near 900 MeV in the inclusive photon spectrum Non-Peaking background components: ~1/10 Y(3S) Analysis Sample Large background from cbJ(2P) decay (next slide)

  12. The Inclusive Photon Spectrum cbJ(2P) → g U(1S) (Peaking) background parametrization: PDF: 3 Crystal Ball functions relative peak positions and yield ratios are taken from PDF Peaking background components (1): U(3S)  cb0(2P)g softE(g soft) = 122 MeV  U(1S) g hard E(g hard) = 743 MeV U(3S)  cb1(2P)g softE(g soft) = 99 MeV  U(1S) g hard E(g hard) = 764 MeV U(3S)  cb2(2P)g softE(g soft) = 86 MeV  U(1S) g hard E(g hard) = 777 MeV U(3S)  cbJ(2P)g soft (J=0,1,2)  U(1S) g hard ~1/10 Analysis Sample

  13. The Inclusive Photon Spectrum Expected Signal • Very important to determine both lineshape and yield Depending on hb mass, the peaks may overlap!  Radiative return to theU(1S) , e+e-→ gISR U(1S) (Peaking) background parametrization: • Estimate the expected yield using Y(4S) Off-Peak data [high statistics, no other peaking background near ISR signal], and extrapolating the yield to Y(3S) On-Peak data ~1/10 Analysis Sample Peaking background component: Radiative return from Y(3S) to Y(1S): e+e-→ gISR Y(1S) [ Eg = 856 MeV ] ISR

  14. Crystal Ball lineshape obtained from simulated events M.C. U(3S)g hbSignal Parametrization • Fix signal Crystal Ball parameters from zero-width MC • Fix the S-wave Breit-Wigner width to 10 MeV • Fit the data with 5, 15, 20 MeV widths to study systematic errors

  15. Fit Result Full data sample L = 25.6 fb-1  (109 ± 1) x 106 Y(3S) events cbJ(2P) ~70000 events/ 5 MeV 15

  16. All backgrounds subtracted 19152 ± 2010 events The Observation of thehb • cbJ Peak Yield : 821841 ± 2223 • gISR Y(1S) Yield : 25153 (fixed) • hb Yield : 19152 ± 2010 • R(ISR/cbJ) ~ 1/33 • R(hb/cbJ) ~ 1/43 Non-peaking Background subtracted gISR hb

  17. No significant change ! STUDY OF SYSTEMATIC UNCERTAINTIES • Vary ISR yield by ± 1s (stat  5% syst) dN = 180, dEg =0.7 MeV • Vary ISR PDF parameters by ± 1sdN = 50, dEg =0.3 MeV • Vary Signal PDF parameters by ± 1s dN = 98, dEg =0.1 MeV • Vary cbJ peak PDF parameters by ± 1s dN = 642, dEg =0.3 MeV • Fit with BW width fixed to 5, 15, 20 MeV dN = 2010, dEg=0.8 MeV • Systematic uncertainty in the hb mass associated with the g energy calibration shift obtained from the fit to the cb peak dEg=2.0 MeV * Study of Significance • Vary BW width • Vary all parameters independently • Vary all parameters in the direction resulting in lowest significance main source of systematic uncertainty in the hb yield 17

  18. Summary of Results • Signal Yield : • Estimate of Branching Fraction (expected transition rate): • Mass of the hb(1S): • Peak in g energy spectrum at • Corresponds to hb mass • The hyperfine (U(1S)-hb(1S)) mass splitting is

  19. The Search for thehb in U(2S) → g hb(1S) Decay

  20. The Search for the hb in U(2S) → g hb(1S) Decay Eg ~ 600 MeV Eg ~ 400 ± 80MeV Data Sample ~ 100 x 106U(2S) events Similar analysis strategy in U(2S)→g hbas for U(3S)→g hb

  21. Comparison of Eg Spectra Non-peaking Background subtracted U(3S) spectrum Comparison with Y(3S) g hb Analysis: ☛ Better photon energy resolution at lower energy  better separation between peaks ☛ More random photon background at lower energy  less significance at similar BF U(2S) spectrum 21

  22. Summary of hb Results • hb mass: • Hyperfine splitting: • Combined mass is m(hb(1S)) = 9390.4± 3.1 MeV/c2 • resulting in a hyperfine splitting of 69.9 ± 3.1 MeV/c2

  23. Comparison of hb Results with Predictions Compatible with predictions for hindered M1 transitions taking into account relativistic corrections S. Godfrey, J.L. Rosner PRD64, 074011 (2001) Branching Fraction Values

  24. x □unquenched supercoarse ■unquenched coarse □ unquenched fine ▲unquenched coarse ∆ unquenched fine Comparison of hb Results with Predictions • Bottomonium spectrum has been computed in effective field theory of (potential) nonrelativistic QCD; in the next-to-leading logarithmic (NLL) approximation the Hyperfine splitting for charmonium, M(J/y)-M(hc)=104 MeV [B.A. Kniehl, et.al., Phys. Rev.Lett. 92, 242001 (2004)] is consistent with the experimental value, M(J/y)-M(hc)=117.7±1.3 MeV [CLEO] • For bottomium, non-perturbative contribution to Hyperfine splitting expected to be smaller than for charmonium • Nonrelativistic QCD NLL prediction: M(U(1S))-M(hb)=39±11(th)+9-8(das)MeV (das(MZ)=0.118±0.003) • Need proper description of QCD non-perturbative long distance effects... • Lattice QCD: unquenched prediction, M(U(1S))-M(hb)=61±14 MeV [A. Gray, et.al., Phys. Rev. D72, 094507 (2005)] Agrees well with BaBar measurement, M(U(1S))-M(hb)=80±10 MeV [T-W. Chiu, et.al., Phys. Rev.Lett. B651, 171 (2007)] * A.Penin [arXiv:0905.429v1] and private conversation with M. Karliner Hyperfine Splitting * A. Gray, et.al., Phys. Rev. D72, 094507 (2005) HFS (MeV)

  25. Rb Scan above theU(4S)

  26. cross section for 0th order cross section for Energy Scan above the U(4S) • Motivation • Search for bottomonium states that do not behave as two-quark states (in analogy to Y(4260), Y(4350) and Y(4660) exotic states); such states would have a mass above the U(4S) and below 11.2 GeV. • Procedure • Precision scan in √s from 10.54 to 11.20 GeV • 5 MeV steps collecting ~25 pb-1 at each step (3.3 fb-1 total) • 600 pb-1 scan in energy range 10.96 to 11.10 GeV in 8 steps with unequal energy spacing (investigation of U(6S)) • Measurement • Inclusive hadronic cross section • Search for unexpected structures in Rb(s)

  27. s s Clear structures corresponding to the bb opening thresholds Energy Scan above the U(4S): Results Inclusive hadronic cross section measurement (PRL 102,012001 (2009)) Consistent with coupled channel predictions

  28. U(5S) and U(6S) Mass and Width Measurement Fit with non-resonant amplitude & flat component added coherently with two interfering relativistic Breit-Wigner functions Incoherent superposition of Gaussians and bckgr. • Compared to CLEO & CUSB, • BaBar has: • >30 x more data • 4 x smaller energy steps • Much more precise definition of shape s 28

  29. - First observation of the hb(1S) bottomonium ground state in the decay U(3S) → g hb(1S) SUMMARY - Confirmation from U(2S) →g hb(1S) - Combined mass is m(hb(1S)) = 9390.4 ± 3.1 MeV/c2 and hyperfine splitting DMHFS = 69.9 ± 3.1 MeV/c2 - Precision scan of Rb in the energy range 10.54 < √s < 11.20 GeV yields parameters for U(5S) and U(6S), which differ from the PDG averages (also confirmed by Belle 's exclusive studies)

  30. BACK-UP SLIDES

  31. Bottomonium Transitions • U(nS) resonances undergo: • Hadronic transitions via p0, h, w, pp emission • Electric dipole transitions • Magnetic dipole transitions -- Allowed transition: • Electromagnetic transitions between the levels can be calculated in the quark model  important tool in understanding the bottomonium internal structure

  32. Hyperfine splitting Fine splitting S = 1 S = 0 Mass Splittings in Heavy Quarkonia Triplet-Singlet mass splitting of quarkonium states Mass splitting of triplet nP quarkonium states: cc,b(n3P0), cc,b(n3P1), cc,b(n3P2) Non-relativistic approximation = 0 for L≠ 0 (→ 0 for r → 0), if long-range spin forces are negligible ≠ 0 for L=0 U(1S)-hb(1S) mass splitting meast.key test of applicability of perturbative QCD to the bottomonium system 6

  33. QCD Calculations of the ηb mass and branching fraction • Recksiegel and Sumino, Phys. Lett. B 578, 369 (2004) [hep-ph/0305178] • Kniehl et al., PRL 92 242001 (2004) [hep-ph/0312086] • Godfrey and Isgur, PRD 32, 189 (1985) • Fulcher, PRD 44, 2079 (1991) • Eichten and Quigg, PRD 49, 5845 (1994) [hep-ph/9402210] • Gupta and Johnson, PRD 53, 312 (1996) [hep-ph/9511267] • Ebert et al., PRD 67, 014027 (2003) [hep-ph/0210381] • Zeng et al., PRD 52, 5229 (1995) [hep-ph/9412269] e+e-→gISRY(1S) Calculations 

  34. SUMMARY OF hb MEASUREMENTS from Y(3S) CLEO arXiv: hep-ph/0412158

  35. Segmented array of 6580 Thallium-doped CsI crystals 16 to 17.5 radiation lengths deep (Rad. L. >1.85 cm) energy & position resolution: The ElectroMagneticCalorimeter Designed to detect electromagnetic showers over the energy range from 20 MeV to 4GeV • Also used to: • detect KL’s • identify electrons e+ (3.1 GeV) e- (8.65 GeV)

More Related