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Semileptonics at LHCb , and the prospects for V ub

Semileptonics at LHCb , and the prospects for V ub. Robert W. Lambert on behalf of the LHCb Collaboration. Acknowledgements. Thanks to the LHC and the rest of the LHCb collaboration Specifically extra thanks to my colleagues:

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Semileptonics at LHCb , and the prospects for V ub

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  1. Semileptonics at LHCb, and the prospects for Vub Robert W. Lambert on behalf of the LHCb Collaboration HQ&L, Oct 2010

  2. Acknowledgements • Thanks to the LHC and the rest of the LHCb collaboration • Specifically extra thanks to my colleagues: • Marina Artuso, Phillip Urquijo, Kim Vervink, Liming Zhang for direct contributions to this talk HQ&L, Oct 2010

  3. Outline • LHC and LHCb • Semileptonics and challenges • Progress towards Vcb and Vub • A little on afs HQ&L, Oct 2010

  4. LHC • The LHC is surpassing earlier predictions • We hope for 50 pb-1 by the end of the year Online Luminosity Estimate LHC now achieves>1pb-1 per fill! HQ&L, Oct 2010

  5. LHCb • LHCb is a dedicated, precision, b-physics experiment • High statistics: we’re in the forward region, and at LHC HQ&L, Oct 2010

  6. Being Timely • Proper Time: LHCb Velo precise down to 35 fs! (MC) HQ&L, Oct 2010

  7. Being Precise • Particle ID: separation handled by dedicated subdetectors • Two RICHes, Calorimetry and Muon system RICH 1 (Vertical) RICH 2 (Horizontal) TT MAGNET T1-T3 HQ&L, Oct 2010

  8. Semileptonic decays • LHCb can reconstruct charmed and charmless B-decays • Backgrounds from open charm and other light mesons • Since Vcb>>Vub, then the charmed are the first to be seen… • To measure the q2 we also need to reconstruct the neutrino... HQ&L, Oct 2010

  9. Neutrino Reconstruction • Use kinematics to calculate the neutrino momentum • Two ambiguous solutions, the lower momentum has lower error Fit low HQ&L, Oct 2010

  10. bb cross-section CERN-PH-EP-2010-029arxiv:1009.2731 • Second LHCb paper, L=(15.0±1.5)nb-1 • sbb from semileptonic decays of the form • ln(IP) distribution used to discriminate prompt contribution HQ&L, Oct 2010

  11. bb cross-section CERN-PH-EP-2010-029arxiv:1009.2731 • Second LHCb paper, L=(15.0±1.5)nb-1 • sbb from semileptonic decays of the form • Scale to full rapidity: See ConorFitzpatrick’s talk (yesterday) HQ&L, Oct 2010

  12. Vub • Theoretically interesting: constrains UT and form factors • LHCb can also probe Vub in the Bs system BaBar2010 arxiv:1005.3288 B→pln HQ&L, Oct 2010

  13. Vcb • Vcb is an early-data proxy for Vub, and is the main background • Like Vub, need two external inputs: BR and/or Form Factors HQ&L, Oct 2010

  14. Vcb • Vcb is an early-data proxy for Vub, and is the main background • However, very little is known in this sector • Form factors are expected to differ in q2 shape ? BaBar2010 arxiv:1005.3288 B→pln Bs->Xc(*)ln HQ&L, Oct 2010

  15. Vcb • Vcb is an early-data proxy for Vub, and is the main background • However, very little is known in this sector • Form factors are expected to differ in q2 shape • And The exclusive Ds(*)(*) branching ratios are not well known • … plus one measurement from D (2009) (my copy ofthe PDG 2008) PRL 102, 051801 HQ&L, Oct 2010

  16. D** branching ratios • Measurements of and will constrain • LHCb is investigating… Phys. Rev. D 32, 189–231 (1985) HQ&L, Oct 2010

  17. Vcb • Choose a set of form-factors for the LHCb MC (HQET2/ISGW2) • Set the relative branching ratios from D/D*/D**, ~2.5:~6:~1 • 0.8 pb-1 examined so far, should become powerful in 50 pb-1 Ds Ds* Ds** Prompt mKKpSB MC Ds Ds* Ds** HQ&L, Oct 2010

  18. An aside: prospects for afs HQ&L, Oct 2010

  19. afs hep-ex 1005.2757 • Great attention thanks to the recent D result • Dominated by detector and background asymmetries • They measured: • 3.2 s from SM! fs vs. See PeterRatoff’s talk (tomorrow) fs HQ&L, Oct 2010

  20. afs • At LHCb systematics will dominate exclusive measurements • Particularly detector and production asymmetries • We can measure: • Since the detector asym.cancels for the same final states fs vs. MC fs HQ&L, Oct 2010

  21. afs • We have already collected thousands of relevant decays • We expect to have sufficient statistics after 100 pb-1 ~100k Ds in 5 fb-1 Estimate 100k Ds in 0.1 fb-1 HQ&L, Oct 2010

  22. Conclusions • LHCb has a broad but precise physics program • We expect 50 pb-1 this year, which makes us competitive with the b-factories and TeVatron • Good prospects for the near future: • Vcb, form factors, D**/D*/D ratios • Gs, Gd, Gs/Gd • Hopefully also: • Dms, Dmd • fs&fd • Next year: • DAfs and Vub Theory input encouraged! HQ&L, Oct 2010

  23. End • Backups are often required HQ&L, Oct 2010

  24. Semileptonic Prospects DAfs 100 pb-1 50 pb-1 Dms Dmd Gs/Gd Gs, Gd 10 pb-1 Form factors Vub 1 pb-1 ratios fsfd [D, D*, D**] BranchingRatios <0.1 pb-1 bb cross-section CERN-PH-EP-2010-029 HQ&L, Oct 2010

  25. Being Timely • Proper Time: LHCb Velo precise down to 35 fs! (MC) HQ&L, Oct 2010

  26. Being Exclusive • Our forte: exclusive, reconstructed, b-decays • In particular, time-dependent measurements ~100k Ds in 5 fb-1 Estimate 100k Ds in 0.1 fb-1 HQ&L, Oct 2010

  27. The simple formula 10-3 -> 10 -5 HQ&L, Oct 2010

  28. The simple formula Very Complicated • Polluting asymmetries are much larger than afs • Detector asymmetrydc ~(10-2) • Production asymmetrydp~(10-2) • Background asymmetrydb~(10-3) 10-3 -> 10 -5 10 -2 10 -2 10 -3 HQ&L, Oct 2010

  29. Detector Asymmetry, dc Asymmetry from Long Muon Tracks Reconstructed in MC • Magnet divides +/- charge, allowing +/- asymmetry • by reversing magnet in D0: dc reduced from 3% -> ~0.1% Left Right Left Right +ve -ve -ve +ve -1 HQ&L, Oct 2010

  30. Detector Asymmetry, dc 120 K-, p . 100 K+, p 80 hadronic cross-section / mb 60 40 20 0 0.1 1 10 100 1000 momentum in lab frame P / GeV c lab Kaon interaction cross-section • Matter detector  hadronic interactions are asymmetric • Dominant systematic at order 1% Resultant charge asymmetry (MC) PDG K- p K+ p Kaon PDG cross-section Monte Carlo -1 HQ&L, Oct 2010

  31. Production Asymmetry, dp • LHC is a proton-proton collider: not CP-symmetric • LHCb is at high rapidity where production asymm. are largest • There is never a simple control channel to measure dp Explicitly asymmetric at LHC dp(B0 and B0) Monte Carlo Valence Quark Scattering HQ&L, Oct 2010

  32. The clever method • Take Bs/Bd with the same final states ( =KKp m) • All production asymmetry is in x2/x3, just throw it away • Measure the difference between Bs and Bd HQ&L, Oct 2010

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