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RECENT BaBaR STUDIES OF BOTTOMONIUM STATES Veronique Ziegler

1. RECENT BaBaR STUDIES OF BOTTOMONIUM STATES Veronique Ziegler SLAC National Accelerator Laboratory On behalf of the BaBar Collaboration 2011 Meeting of the Division of Particles and Fields of the American Physical Society Providence, Rhode Island, USA August 9 ─13, 2011. 2.

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RECENT BaBaR STUDIES OF BOTTOMONIUM STATES Veronique Ziegler

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  1. 1 RECENT BaBaR STUDIES OF BOTTOMONIUM STATES Veronique Ziegler SLAC National Accelerator Laboratory On behalf of the BaBar Collaboration 2011 Meeting of the Division of Particles and Fields of the American Physical Society Providence, Rhode Island, USA August 9 ─13, 2011

  2. 2 PEP-II e+e- Asymmetric Collider Running at the U(2S,3S)BaBarRUN 7 (Dec. 2007 – Apr. 2008) k CUSB k Effective k c.m. Energy (GeV) BABAR DATASETS: ~ 120 x 106Y(3S)events ~ 100 x 106Y(2S) events ~ 8.54 fb-1 above Y(4S) R-scan

  3. 3 OUTLINE • Spectroscopy circa 2008 • Radiative transitions from U(2S,3S) events using g → e+e- conversions • Search for the hb(1P) in U(3S) → p+p-hb(1P) • Evidence for the hb(1P) in U(3S) → p0hb(1P) • Present status of bottomonium spectroscopy

  4. 4 threshold (nL) where n is the principal quantum number and L indicates the bb angular momentum in spectroscopic notation (L=S, P, D,…) ? hadrons ? hadrons [Orbital Ang. Momentum between quarks] P-wave S-wave 2008 Picture of the Bottomonium Spectrum bb states below Y(3S) not yet discovered: 3 S-wave (hb), 2 P-wave (hb), 4 D-wave & possibly 4 F-wave. Among the undiscovered states was the ground state, the hb(1S), expected to be < 100 MeV/c2 below the Y(1S)

  5. 5 Radiative transition studies from inclusive spectra for converted photons

  6. Radiativebottomonium transitions from U(3S) events using g→e+e- conversions 6 arXiv:1104.5254 (submitted to PRD) SVT (5 layers) SVT supports Reconstructed Vertices Energy in C.M. frame Drift Chamber inner wall (Be) Support tube (carbon fiber) Significantly improves energy resolution [see later] Efficiency ~(0.1 – 1)%

  7. 7 Inclusive photon energy regions for U(3S) events • Resolution dominated • Small Doppler broadening

  8. 8 Inclusive photon energy regions for U(3S) events from U(3S) to U(1S)

  9. 9 Inclusive photon energy regions for U(3S) events Search for the Bottomonium Ground State hb(1S) g U(3S)→ g hb(1S) photons from calorimeter  hbsignificance < 3s

  10. Inclusive photon energy regions for U(3S) events 10 Search for the Bottomonium Ground State hb(1S) g hb significance < 3s

  11. 11 Inclusive photon energy regions for U(2S) events g hb significance < 3s ISR hb (1S)

  12. 12 Inclusive photon energy regions for U(2S) events hb significance < 3s g

  13. 13 Summary of BF measurements from U(2S,3S) radiative decays using converted photons • Precise measurements of • cbJ(nP) n=1,2→gU(mS)m=1,2 BFs • Good agreement with theory Kwong& Rosner, PRD38,279 (1988) • Measurements of BFs for • U(3S)→g cbJ(1P) transitions •  transition to cb1(1P) not seen •  in general inconsistent • with theoretical predictions ? (except Moxhay-Rosner PRD28,1132 (1983))

  14. 14 Searches for the hb(1P) State of Bottomoniumat BaBar • Essential to measure the hyperfine mass splitting for P-wave states to understand the spin dependence of qq̅ potentials for heavy quarks. • Hyperfine splitting between hb(1P) mass & spin-weighted center of gravity of the cbJ(1P) states (9899.87±0.27 MeV/c2) expected to be ~0 [confirmed for hc]. • Hyperfine mass splitting larger than 1 MeV/c2might be indicative of a vector component in the confinement potential. • BaBar searched for the hb(1P) meson in the transitions: • U(3S)p+p- hb(1P) • U(3S)p0hb(1P) (requiring a photon consistent with subsequent hbghb(1S) decay)

  15. 15 Expected Mass of the hb(1P) State Hyperfine splitting for L=1 states  M [c.o.g.(13PJ)] – M(11P1) = 9899.87 ± 0.27 MeV/c2 Search for a peak in invariant mass of systemrecoiling against p+p- or p0 U(3S) p0 pp hb(1P) cbJ(1P) hb(1S)

  16. 16 Search for the hb(1P) in the decay U(3S)p+p-hb Phys.Rev. D 84, 011104(R) background-subtracted result: hbsignal region hb ? • No hb observation: -1106 ± 2432(stat.) signal events (mass fixed at 9.9 GeV/c2) • BF(U(3S)p+p-hb)<1.0x10-4 (@90% C.L.) --suppressed by a factor >3 compared to p0 mode • First separate observation of cb1,2(2P)p+p-cb1,2(1P) transitions and BF measurements: • BF(cb1(2P)p+p-cb1,2(1P)) = (9.2±0.6±0.9)×10-3 • BF(cb2(2P)p+p-cb1,2(1P)) = (4.9±0.4±0.6)×10-3

  17. 17 Search for the hb(1P) in U(3S) pohb [420 < Eg < 540 MeV] • Analysis Strategy • Reconstruct po(g1g2) + g • Require Eg consistent with hb(1P)  ghb(1S) transition • Selection criteria on Ntracks, R2, po veto (all g candidates), pocosqh • Define po missing mass: m.m.(po)2 = (m(3S) – E*po)2 – P*po2 mrecoil(po) • Constrain mpo to improve resolution on mrecoil(po) • Npo from mg1g2 fit in each mrecoil(po) interval using modified MC po–lineshape and background Full statistics Sample ─ data ─ fit

  18. 18 Evidence for the hb(1P) in the decay U(3S) pohb background-subtracted result: arXiv:1102.4565 hb signal region uncertainty from background fit • 10814± 2813 signal events • M(hb) = 9902±4 ±2 MeV/c2(C.G.=9899.87±0.27 MeV/c2 ) • Stat. Signif. = 3.8s (√Dc2); including systematic errors = 3.3s • B(U(3S)p0hb(1P) = (4.1±1.1±0.9)10-4 < 6.110-4 (@ 90% CL) • Existence subsequently confirmed by Belle in Υ(5S)→p+p-hb(1P) (arXiv:1103.3419 (*))with combinatorial bkg. 2XBaBarU(3S) search also observe hb(2P) • 2 fit of mrecoil(po) distribution: • hb(1P) signal: Double Crystal Ballfunction • Background: 5th order polynomial • Parameters determined with hb signal region excluded (i.e. blind analysis strategy) ((*) La Thuille 2011)

  19. 19 threshold (nL) where n is the principal quantum number and L indicates the bb angular momentum in spectroscopic notation (L=S, P, D,…) ? hadrons ? hadrons [Orbital Ang. Momentum between quarks] P-wave S-wave 2011 Picture of the Bottomonium Spectrum bb states below Y(3S) not yet discovered: 2 S-wave (hb(2S,3S)) , 3 D-wave & possibly 4 F-wave. Recently discovered states including the hb(1P) and hb(2P) states

  20. 20 SUMMARY OF BaBar RESULTS • Precision measurements of radiative transitions between known bottomonium states using g → e+e- conversions • No evidence for the hb(1P) in the transition U(3S) → p+p-hb(1P) • Evidence at 3.3s level for the hb(1P) in U(3S) → p0hb(1P) decay – confirmed by Belle using U(5S) data

  21. Backup Slides

  22. 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)]

  23. BaBar integrated luminosity since startup

  24. Confirmation of the existence of the hb(1P) by Belle in e+e-→p+p- transitions at the U(5S) Observation of the hb(1P) and hb(2P) states background subtracted results • Measured hb(1,2P) mass values consistent with predictions • Observed hb production rate enhancement may be indicative of exotic process violating HQ spin-flip suppression • Resonant structures in hb(1P, 2P)seen in (5S) hb(1P, 2P)+- events (also in (5S) (nS)+-) charged exotic candidates Zb1, Zb2 arXiv:1103.3419  Consistent with BaBar measmt.

  25. background-subtracted result: Evidence for the hb(1P) in the decay U(3S) pohb arXiv:1102.4565 • 9145 ± 2804 signal events • M(hb) = 9902±4 ±1 MeV/c2 • consistent with predictions • Stat. Signif = 3.2s (i.e. √Dc2), including systematic errors = 3.0s(evaluated with the hb mass fixed at expected value of 9.9 GeV/c2) • B(U(3S)p0hb(1P) = (3.7±1.1±0.4)10-4 • B(U(3S)p0hb(1P)< 5.810-4 (@ 90% CL) • 2 fit of m.m.(po) distribution: • hb(1P) signal: Double Crystal Ball function • Background: Polynomial

  26. hb Search: Comparison of Eg Spectra for U(3S) and U(2S) Events U(2S) U(3S) Results from Y(2S) and Y(3S) analyses are consistent!

  27. hb Search: Summary of Results S. Godfrey, J.L. Rosner PRD 64 074011 (2001) BF measurements: B((3S)  ghb(1S)) = (5.1 ± 0.7)  10-4B((2S)  ghb(1S)) = (3.9 ± 1.5)  10-4 • Compatible with predictions • Combined values of mass and HF splitting: • mhb(1S) = 9390.9 ± 2.8 MeV/c2 (Ghb(1S) 10 MeV) • (m(1S) – mhb(1S)) = 69.3 ± 2.8 MeV/c2 • Unquenched lattice QCD calculations (~50-60 MeV/c2) agree better than NRQCD predictions (~40 MeV/c2)

  28. RadiativeBottomonium Transitions • Radiative transitions • Rates generally phenomenologically well-predicted • Gateway to discovery (e.g.: (nS)  ghb(1S)) • Use converted photons (g  e+e-) improve resolution (e.g.: 25  5 MeV) • Reconstruct pair of tracks, selected with c2fitter, mg, rg • Additional cuts: |cosqthrust|, Ntracks, poveto • Fit Eg* spectrum in four regions of interest • Goals: Resolve Eg* spectrum to make precision measurements

  29. Converted Photon Conclusions • Precise measurements of bottomonium transition rates in good agreement with predictions • (3S)  gb0,2(1P) rates are an exception • Further theoretical/experimental work needed • b(1S) mass measurement inconclusive • Need more data to take full advantage of converted photon technique

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