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Polarized radiative L b decays at LHCb

Polarized radiative L b decays at LHCb. Outline. Theoretical motivations Angular distributions Observables L b production at LHC Selection of L b  L (x) g events at LHCb Status and perspectives. Theoretical motivations. L b  L (X) g  p k. L b  L(1115) g  p p. g.

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Polarized radiative L b decays at LHCb

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  1. Polarized radiative Lb decays at LHCb Federica Legger

  2. Outline • Theoretical motivations • Angular distributions • Observables • Lb production at LHC • Selection of Lb L(x) g events at LHCb • Status and perspectives

  3. Theoretical motivations • Lb L(X) g •  pk • Lb L(1115) g •  p p g g b s k b s u Lb L d d Lb u p u u d d u u • Electromagnetic penguin b  s g • In the SM the photon is predicted to be left-handed, but could have a right-handed component in LR symmetric models; • Effective Hamiltonian at LO in as: left right

  4. Photon polarization measurements Exp. status Theor. Refs. e+e- conversion First measurements of K* polarization in B->K*l+l- by Belle/Babar Grossman, Pirjol, JHEP06, 029 (2000) Melikov, Nikitin, Simula, PLB 442, 381 (1998) Latest world average sin2b = 0.0 ± 0.3 Atwood, Gronau, Soni, PRL 79, 185 (1997) B-B interference B factories Difficult to disentangle resonance structure (BaBar, hep/0507031) Gronau, Pirjol, PRD 66, 054008 (2002) Higher K* resonances Gronau, Grossman, Pirjol, PRL 88, 051802 (2002) Charmonium res. interference No results so far... Knecht, Schietinger, PLB 634, 403 (2006) Mannel, Recksiegel, JPG: NPP 24, 979 (1998) Exploit ang. correlations between polarized initial state and final state. Under study at LHCb LHCb b-baryons Hiller, Kagan, PRD 65, 074038 (2002)

  5. Polarized Lb L(1115) g decays • Angular distributions for Lb (L(1115)  pp) g: depend on photon polarization and constrain • PB = Lb polarization • ap = weak decay parameter Evtgen distribution Hiller, Kagan, Phys Rev D65, 074038 (2002)

  6. Observables for Lb L(1115) g • 2 indipendent measurements for r, or • Lb polarization measurement: • a discrepancy with the value measured in semileptonic Lb  Lc l n X decays would indicate the presence of non-standard right-handed b  c currents • Direct CP violation at NLO: O(1%) in SM but 10% if NP! • r probes the ratio of CP even contributions to NLO Hamiltonian

  7. L(X) resonances • From the experimental point of view the decay Lb L(1115) g is quite hard to observe (ct = 7.89 cm) • Can we increase the statistics by using heavier L resonances? 1520 L spin = 1/2 L spin = 3/2 1670 1690 1600 L(X) parameters (PDG 2004) + BR(Lb L(X) g) (slide 16)

  8. Helicity formalism for Lb L(px) g • Need angular distributions  helicity formalism • Lb polarization • Polarization density matrix : • Helicity amplitudes • Lb L(X) g • L(X)  px +  ½ -  -½ Jacob, Wick, Ann Phys 7, 404 (1959)

  9. Results : JL = 1/2 • Photon angular distribution depends on photon helicity parameter ag,1/2which is related to |r| • Proton angular distribution flat because of P conservation Helicity formalism HQET

  10. Results : JL = 3/2 • L helicity can now assume the values: ±1/2, ±3/2 • 4 helicity amplitudes

  11. Helicity formalism : JL = 3/2 • Decay probability:

  12. Photon angular distribution • Similar dependence to spin 1/2 L resonances • but now a depends on the asymmetry of Lb baryons produced with different helicities

  13. Assumptions • Photon helicity is independent of the helicity of the final state L formed in the hadronization process • Because of parity conservation in strong interactions, the ratio of L baryons produced with helicity 3/2 and 1/2 = ratio of L baryons produced with helicity -3/2 and -1/2

  14. Results : JL = 3/2 • Photon angular distribution dependence can be factorized with the photon helicity parameter ag,1/2and strong parameter  • no theoretical predictions for … • but we can extract it from the proton angular distribution

  15. Possible scenarios for h • L(X) with helicity 3/2 dominates   » 1 • same amount of 1/2 and 3/2 helicity    1 • L(X) with helicity 1/2 dominates   « 1 SM prediction ag,3/2  - ag,1/2ap,3/2  1 ag,3/2 ap,3/2  0 ag,3/2  ag,1/2ap,3/2  -3 • |r| can be probed by measuring ag,3/2 and 

  16. Lb production at LHC: • bb cross section in pp collision = 500 mb • 10% of produced bb hadronize in B hadrons • Lb dominates (90%) • Lb produced with transversal polarization • Predictions are PB~ 20% • ATLAS plans to measure it with a statistical precision better than 1% • BR (Lb L(1115) g ) = 4.15 · 10-5 • BR (Lb L(1520) g ) = 1.30 · 10-5 • BR (Lb L(1670) g ) = 0.70 · 10-5 • BR (Lb L(1690) g ) = 0.70 · 10-5 n Lb p1 p2 Ajaltouni, Conte, Leitner,‘‘Λb into Λ-vector decays’’,Phys Lett B, 614 (2005) Feasibility of Beauty Baryon Polarization Measurement in Lb J/Y L decay channel by ATLAS – Atlas note Calculations based on Hiller (2002)+PDG2004

  17. Data sample & Tools • Lb L(1115) gpol = long, full300k evts • Lb L(1670) gpol = long, full300k evts • Lb L(1670) gpol = transv, full300k evts • Lb L(1670) gphsp, full300k evts • bb inclusive (DC04-v2) 39M evts • DaVinci v12r16 • No particular method to optimize cuts values: • PT, IPS (with respect to all primaries) cuts on final states • Mass window = 4s for resonances with intrinsic width • Cut values chosen to kill bb events while maintaining higher possible efficiencies

  18. BY (T) 0 - 0.2 - 0.4 - 0.6 - 0.8 - 1.0 - 1.2 2 8 0 4 6 z (m) Upstream track TT Long track T track Downstream track VELO Velo track T2 T3 T1 L(1115)  p p • ct = 7.89 cm • About 14% of L interact before decay or decay after LHCb spectrometer  lost • 305000 (generated)  262464 (DoI) L candidates (associated to MC truth)

  19. Vertex fit for Lb L(1115) g • L(1115) vertex: • refit the L vertex • explain • apply cut on L mass and unconstrained chi square • Lb vertex = L(1115) + photon • fit: PV + the L direction • Choose the PV with minimum chi square p L p PV g

  20. Charged tracks selection (L(1115)) LONG • DLL p-p > 6 • DLL p-k > 4 • PT > 1600 MeV • sIPS > 4 DOWN • DLL p-p > 10 • DLL p-k > 8 • PT > 2500 MeV • sIPS > 3 UP • DLL p-p > 6 • DLL p-k > 0 • PT > 500 MeV • sIPS > 4 p: LONG • PT > 350 MeV • sIPS > 4 UP • PT >250MeV • sIPS > 4 DOWN • PT > 350 MeV • sIPS > 3 p: • Hard DLL and PT cuts on protons to suppress background • Slow momentum pions

  21. L(1115) selection LL • 2 < 6 • Dm < 6 MeV • PT >500MeV • sIPS > 4 • FS > 4 UL • 2 < 2 • Dm < 27 MeV • PT >500MeV • sIPS > 4 • FS > 5 s = 1.2 MeV s = 2.8 MeV DD • 2 < 2 • Dm < 11 MeV • PT > 2000 MeV • sIPS > 3 • FD > 300 mm LD • 2 < 2 • Dm < 6 MeV • PT > 1500 MeV

  22. Lb (L(1115)  p p)g LL • PT > 2500 MeV • 2 < 2 • Dm < 300 MeV • (Lb) < 0.15 UL • PT >500MeV • 2 < 2 • Dm < 300 MeV • (Lb) < 0.15 Lb selection DD • PT > 2000 MeV • 2 < 1 • Dm < 300 MeV • (Lb) < 0.15 LD • PT > 1000 MeV • 2 < 1 • Dm < 300 MeV • (Lb) < 0.15 • PT > 3200 MeV/c (LL) • PT > 3400, 3800 MeV/c for UL, DD, LD • PT (in Lb direction)  [2250,3000] MeV/c g selection

  23. Efficiencies for Lb L(1115) g • etot = 0.011% • no events selected in 39M bb incl • Yield = 747/ year • B/S < 42 @ 90 % CL BR measurement x 10-4 s = 78.1 MeV 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1

  24. Lb L(1670)g selection • g : • PT > 2600 MeV • 1600 MeV < PT (in Lb direction) < 2800 MeV • L(1670) : • 2 < 6, Dm < 100 MeV • PT > 1500 MeV • sIPS > 4 • Lb : • Dm < 200 MeV • FS > 2; • PT > 2000 MeV • (Lb) < 0.01 • Protons: • Only Long tracks • DLL p-p > 5 • DLL p-K > 0 • Exclusive DLL selection • PT > 600 MeV • sIPS > 3 • Kaons: • Only Long tracks • DLL K-p > 5 • DLL K-p> 0 • Exclusive DLL selection • PT > 600 MeV • sIPS> 3  p PV Lb

  25. Efficiencies for Lb L(1670) g After HLT Generic TDR, after L0 x L1 • Phase space • etot = 0.225% • Annual yield:2515 • long. pol • etot = 0.224% • Annual yield:2507 • trans. pol • etot = 0.228% • Annual yield:2553 • no events selected in 39M bb incl. • B/S = 18.2 @ 90% CL Bs fg, etot = 0.220 % Bd K* g, etot = 0.156 % s = 69.4 MeV Bs,d f/K* g, s = 64 MeV

  26. Photon polarization • Lb L(1670) g selected evts. (transversally polarized) • efficiency corrected (from unpolarized decays) ag,1/2

  27. Statistical sensitivity on |r| Lb L(1670) g Lb L(1115) g • Still far from the SM expected value, but interesting if NP is present! • LHCb could be the first to measure the photon polarization in b-> sg transitions

  28. Conclusions • Selection for Lb L(1115) g and Lb L(1670) g ready • BR studies feasible • Angular asymmetries studies ongoing: • promising photon polarization measurement • Can we separate the L(1670) and the L(1690)? • Still observing these resonances could give indications on their production mechanism... • LHCb note(s) in preparation

  29. Backup slides Federica Legger

  30. Photon polarization (eff. correction) • Lb L(1670) g (phase space) efficiency • Lb L(1670) g (transversally polarized)

  31. Lb (L(1670)  p K)g bb incl signal bb incl signal Charged tracks: • Protons: • Only Long tracks • DLL p-p > 5 • DLL p-k > 0 • Exclusive DLL • Kaons • Only Long tracks • DLL K-p > 5 • DLL K-p> 0 • Exclusive DLL false p true p false K true K

  32. Lb (L(1670)  p K)g bb incl signal bb incl signal Charged tracks: • Protons: • PT > 600 MeV • sIPS > 3 • Kaons • PT > 600 MeV • sIPS> 3 bb incl signal bb incl signal

  33. Lb (L(1670)  p K)g g selection: • PT > 2600 MeV/c • PT (with respect to Lb direction) [1600,2800] MeV/c bb incl signal

  34. Lb (L(1670)  p K)g bb incl signal bb incl signal L(1670) selection: • 2 < 6 • Dm < 100 MeV • PT > 1500 MeV • sIPS > 4 Lbselection: • Dm < 200 MeV • FS > 2 • PT > 2000 MeV • (Lb) < 0.0165 bb incl signal bb incl signal  p PV Lb

  35. Lb L(1115) g : DLL cuts bb incl signal bb incl signal bb incl signal false p true p false p true p false p true p

  36. Lb L(1115) g : PT cuts (p and p) bb incl signal bb incl signal bb incl signal bb incl signal bb incl signal bb incl signal

  37. Lb L(1115) g : IPS cuts (p and p) bb incl signal bb incl signal bb incl signal bb incl signal bb incl signal bb incl signal

  38. Lb L(1115) g : FD cuts (L) bb incl signal bb incl signal bb incl signal bb incl signal bb incl signal bb incl signal bb incl signal bb incl signal

  39. KF unconstrained fit 2 L(1115) 2 (DD) 2 (LL) signal (true L) bb incl (true L) bb incl (fake L) • Separated cut on chi2 and L mass 2 (LD) 2 (LU)

  40. Lbglobal fit 2 signal (Fake PV) signal (true PV) Fake PV true PV 2 (LL) 2 (DD) Fake PV true PV Fake PV true PV 2 (LU) 2 (LD) • Global fit distinguishes fake from true PVs

  41. Lb L(1115) g : PT cuts (Lb, g) bb incl signal bb incl signal bb incl signal bb incl signal bb incl signal bb incl signal bb incl signal bb incl signal

  42. Lbmass resolution (true tracks) Mean = 5606 MeV/c2 Mean = 5606 MeV/c2 Mean = 5601 MeV/c2 Mean = 5601 MeV/c2 • Mass peak: 20 MeV offset due to photon calibration • s90 MeV

  43. Photon polar angle res. (sel evts) Lb L(1115) g Lb L(1670) g

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