1. Federica Legger Polarized radiative  b decays at LHCb

2. 2 Outline Theoretical motivations Angular distributions Observables  b production at LHC Selection of  b   (x)  events at LHCb Status and perspectives

3. 3 Theoretical motivations  b    p  s d  u b d u bb   b   (X)   p k s d u b d u bb  u u p k Electromagnetic penguin b  s  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  s : leftright

4. 4 Photon polarization measurements Melikov, Nikitin, Simula, PLB 442, 381 (1998) Grossman, Pirjol, JHEP06, 029 (2000) Atwood, Gronau, Soni, PRL 79, 185 (1997) Mannel, Recksiegel, JPG: NPP 24, 979 (1998) LHCb B factories Knecht, Schietinger, PLB 634, 403 (2006) Gronau, Pirjol, PRD 66, 054008 (2002) B-B interference First measurements of K* polarization in B->K*l+l- by Belle/Babar e + e - conversion Exp. statusTheor. Refs. Latest world average sin2  = 0.0 ± 0.3 Higher K* resonances Difficult to disentangle resonance structure (BaBar, hep/0507031) Gronau, Grossman, Pirjol, PRL 88, 051802 (2002) Charmonium res. interference No results so far... b-baryons Hiller, Kagan, PRD 65, 074038 (2002) Exploit ang. correlations between polarized initial state and final state. Under study at LHCb

5. 5 Polarized  b   (1115)  decays Angular distributions for  b  (  (1115)  p  )  depend on photon polarization and constrain Hiller, Kagan, Phys Rev D65, 074038 (2002) P B =  b polarization  p = weak decay parameter Evtgen distribution

6. 6 2 indipendent measurements for r, or  b polarization measurement: a discrepancy with the value measured in semileptonic  b   c l 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 Observables for  b   (1115) 

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

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

9. 9 Results : J  = 1/2 Photon angular distribution depends on photon helicity parameter   which is related to |r| Proton angular distribution flat because of P conservation Helicity formalism HQET

10. 10 Results : J  = 3/2  helicity can now assume the values: ±1/2, ±3/2 4 helicity amplitudes

11. 11 Helicity formalism : J  = 3/2 Decay probability:

12. 12 Similar dependence to spin 1/2  resonances but now  depends on the asymmetry of  b baryons produced with different helicities Photon angular distribution

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

14. 14 Photon angular distribution dependence can be factorized with the photon helicity parameter   and strong parameter  no theoretical predictions for  … but we can extract it from the proton angular distribution Results : J  = 3/2

15. 15  (X) with helicity 3/2 dominates   » 1 same amount of 1/2 and 3/2 helicity    1  (X) with helicity 1/2 dominates   « 1 Possible scenarios for    3/2  -   1/2  p  3/2  1   3/2    1/2  p  3/2  -3   3/2   p  3/2  0 |r| can be probed by measuring   3/2 and  SM prediction

16. 16  b production at LHC: bb cross section in pp collision = 500  b  10% of produced bb hadronize in B hadrons  b dominates (  90%)  b produced with transversal polarization Predictions are P B ~ 20% ATLAS plans to measure it with a statistical precision better than 1% BR (  b   (1115)  = 4.15 · 10 -5 BR (  b   (1520)  = 1.30 · 10 -5 BR (  b   (1670)  = 0.70 · 10 -5 BR (  b   (1690)  = 0.70 · 10 -5 p1p1 p2p2 bb n Ajaltouni, Conte, Leitner, ‘‘ Λ b into Λ-vector decays ’’, Phys Lett B, 614 (2005) Feasibility of Beauty Baryon Polarization Measurement in  b  J  decay channel by ATLAS – Atlas note Calculations based on Hiller (2002)+PDG2004

17. 17 Data sample & Tools DaVinci v12r16 No particular method to optimize cuts values: PT, IPS (with respect to all primaries) cuts on final states Mass window = 4  for resonances with intrinsic width Cut values chosen to kill bb events while maintaining higher possible efficiencies  b   (1115)  pol = long, full300k evts  b   (1670)  pol = long, full  300k evts  b   (1670)  pol = transv, full  300k evts  b   (1670)  phsp, full  300k evts bb inclusive (DC04-v2) 39M evts

18. 18  (1115)  p  c  = 7.89 cm About 14% of  interact before decay or decay after LHCb spectrometer  lost 305000 (generated)  262464 (DoI) T1 T2T3 VELO TT T track Upstream track Long track Downstream track Velo track B Y (T) z (m) - 0.2 - 0.4 - 0.6 - 0.8 - 1.0 - 1.2 0 0 2 46 8  candidates (associated to MC truth)

19. 19 Vertex fit for  b   (1115)   (1115) vertex: refit the  vertex explain apply cut on  mass and unconstrained chi square  b vertex =  (1115) + photon fit: PV + the  direction Choose the PV with minimum chi square p    PV

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

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

22. 22  b  (  (1115)  p  )  LL PT > 2500 MeV  2 < 2  m < 300 MeV  (  b ) < 0.15 UL PT > 500 MeV  2 < 2  m < 300 MeV  (  b ) < 0.15 LD PT > 1000 MeV  2 < 1  m < 300 MeV  (  b ) < 0.15 PT > 3200 MeV/c (LL) PT > 3400, 3800 MeV/c for UL, DD, LD PT (in  b direction)  [2250, 3000] MeV/c  selection  b selection DD PT > 2000 MeV  2 < 1  m < 300 MeV  (  b ) < 0.15

23. 23 Efficiencies for  b   (1115)   tot = 0.011 % no events selected in 39M bb incl Yield = 747 / year B/S < 42 @ 90 % CL  = 78.1 MeV 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 x 10 -4 BR measurement

24. 24  b   (1670)  selection Protons: Only Long tracks DLL p-  > 5 DLL p-K > 0 Exclusive DLL selection PT > 600 MeV sIPS > 3 Kaons: Only Long tracks DLL K-  > 5 DLL K-p  > 0 Exclusive DLL selection PT > 600 MeV sIPS  > 3  PT > 2600 MeV 1600 MeV < PT (in  b direction) < 2800 MeV  (1670) :  2 < 6,  m < 100 MeV PT > 1500 MeV sIPS > 4  b :  m < 200 MeV FS > 2; PT > 2000 MeV  (  b ) < 0.01 PV  bb p

25. 25 Efficiencies for  b   (1670)  Phase space  tot = 0.225 % Annual yield: 2515 long. pol  tot = 0.224 % Annual yield: 2507 trans. pol  tot = 0.228 % Annual yield: 2553 no events selected in 39M bb incl. B/S = 18.2 @ 90% CL TDR, after L0 x L1 B s   ,  tot = 0.220 % B d  K* ,  tot = 0.156 % After HLT Generic B s,d   /K* ,  = 64 MeV  = 69.4 MeV

26. 26 Photon polarization  b   (1670)  selected evts.  transversally polarized) efficiency corrected (from unpolarized decays)  

27. 27 Statistical sensitivity on |r| 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-> s  transitions  b   (1115)  b   (1670) 

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

29. Federica Legger Backup slides

30. 30 Photon polarization (eff. correction)  b   (1670)   transversally polarized)  b   (1670)   phase space) efficiency

31. 31  b  (  (1670)  p K)  Charged tracks: false p true p Protons: Only Long tracks DLL p-  > 5 DLL p-k > 0 Exclusive DLL Kaons Only Long tracks DLL K-  > 5 DLL K-p  > 0 Exclusive DLL false K true K bb incl signal bb incl signal

32. 32  b  (  (1670)  p K)  Charged tracks: bb incl signal bb incl signal Protons: PT > 600 MeV sIPS > 3 Kaons PT > 600 MeV sIPS  > 3 bb incl signal bb incl signal

33. 33  b  (  (1670)  p K)   selection: PT > 2600 MeV/c PT (with respect to  b direction)  [1600, 2800] MeV/c bb incl signal

34. 34  b  (  (1670)  p K)   (1670) selection: bb incl signal  2 < 6  m < 100 MeV PT > 1500 MeV sIPS > 4 bb incl signal bb incl signal bb incl signal  b  selection:  m < 200 MeV FS > 2 PT > 2000 MeV  (  b ) < 0.0165 PV  bb p

35. 35  b   (1115)  DLL cuts bb incl signal bb incl signal bb incl signal false p true p false p true p false p true p

36. 36  b   (1115)  PT cuts (p and  ) bb incl signal bb incl signal bb incl signal bb incl signal bb incl signal bb incl signal

37. 37  b   (1115)  IPS cuts (p and  ) bb incl signal bb incl signal bb incl signal bb incl signal bb incl signal bb incl signal

38. 38  b   (1115)  FD cuts (  ) 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. 39 KF unconstrained fit  2  (1115)  2 (LL)  2 (LD)  2 (LU) Separated cut on chi2 and  mass signal (true  ) bb incl (true  ) bb incl (fake  )  2 (DD)

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

41. 41  b   (1115)  PT cuts (  b,  ) 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. 42  b  mass resolution (true tracks) Mean = 5606 MeV/c 2 Mean = 5601 MeV/c 2 Mean = 5606 MeV/c 2 Mass peak: 20 MeV offset due to photon calibration  90 MeV

43. 43 Photon polar angle res. (sel evts)  b   (1115)   b   (1670) 