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Rare Decays

Rare Decays. and their sensitivity to New Physics. Klassiker:. hep-ph / 0108037. mSUGRA Parameter:. Light chargino bounds from LEP, Radiative EWSB. LSP not neutral. hep-ph / 0108037. < 5.8 · 10 -8 95% CL. arXiv:0712.1708 to PRL. 2 fb -1. < 9.3 · 10 -8 95% CL. D0 Note 5344-Conf (2007).

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Rare Decays

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  1. Rare Decays and their sensitivity to New Physics

  2. Klassiker: hep-ph/0108037 mSUGRA Parameter:

  3. Light chargino bounds from LEP, Radiative EWSB LSP not neutral hep-ph/0108037

  4. < 5.8·10-895% CL arXiv:0712.1708 to PRL 2 fb-1 < 9.3·10-895% CL D0 Note 5344-Conf (2007)

  5. Problem: Untergrundunterdrückung Invariante Masse keine ausreichende Diskriminate Multivariate Analyse

  6. Bs Impact Parameter Lifetime of B Muon Pion Likelihood (LL) DOCA between muons Muon Impact Parameter Sign. Muon Kaon Likelihood (LL) Isolation Geometry Likelihood PID Likelihood signal bb inclusive b b BcJ/ 

  7. 3-dim. Binning: • 4 Bins in Geometry LL • 3 Bins in PID LL • 5 Bin in invarianter Masse signal bb inclusive Untergrund Ereignisse/Bin Signalereignisse/Bin (BR) Sensitivität

  8. BR excluded at 90 % CL, i.e. only background is observed BR observed or discovered. Exclude the interesting region between 10-8 and SM with little Lumi (~0.5 fb-1) Observe (discover) SM BR with 3 (5) after ~2 (~6) fb-1

  9. Events after preselection cuts in 600 (60) MeV mass window

  10. Radiative bs decays • Standard Model bs (bs): • LH s-quark (RH s-quark) • LH (RH) photons BSM physics (SUSY, LR Models) could lead to appreciable RH  component photon helicity probes BSM physics • Probing photon helicity: • (Photon conversion) • Time dependent ACP: • Parity-odd triple correlations between photon and 2 out of 3 hadrons in B (K+p+p-) decays • b(X)

  11. B0sFg Erste Beobachtung von Bs (Ball et al.) [1] hep-ph/0607258 [2] arXiv:hep-ex/0607071v1

  12. Why this decay ? sensitive to NP

  13. What do we expect at LHCb ? Expected for one year of measurement ( 2 fb-1 ) • have to fight background • very good PID necessary, 0 rejection • proper time resolution (Time dependent CPV  g polarization) • high trigger efficiency • good offline selection

  14. Reconstruction and Selection g K- SV K+ F PV Selection mainly based on • two body kinematics • geometrical cuts on pp-interaction PV and B-decay SV Selection criteria maximize  with  = S: signal evts B: background evts

  15. Some selection criteria… • Photon selection • 2 body kinematics hard ET(g) • spectrum • from numerous p0 decay soft g • Require ET(g) > 2.8 GeV • On the way to the  • Charged tracks must NOT • come from PV (t of B) • K+K- should come from SV

  16. Some selection criteria… • On the way to the B • pB = p+ pg should point to PV • use qB ( allow rather large qB as the SV resolution is not good because of K’s !) flight path SV qB reconstructed p PV

  17. Background… K+ B qH F K- • large background fromB0sFp0 und BK*0 • use vector meson polarization • helicity of F = 0 for B0sFp0 • F = 1 for B0sFg • define helicity angle qH • sin2qHdistribution for signals • cos2qHdistribution for • correlated bkg • flat for combinatorial bkg

  18. And finally one gets… B0K0*g B0K0*g • Expect 68k signal events for 2 fb-1 with B/S < 0.6 Bsfg • Expect 11.5k signal events for 2 fb-1 with B/S < 0.6 • red: true events • blue : comb. bkg.

  19. g Polarization • g from bsg predominantly left-handed (SM: V-A • coupling of W boson) • e.g. in MSSMg can be largely right-handed • ( doesn’t effect incl. radiative decay rate predicted by • SM) • helicity measurement via time-dependent CP asymmetry, …

  20. g Polarization amplitudes Relative amount of „wrong photon polarization“ Weak phases (CP odd)

  21. Time dependent decay rate Standard Model:

  22. CP Asymmetry The CP asymmetry From the time dependent decay rate one gets The measurement of AD determines the fraction of ‘different-polarized’ photons ! LHCb Toy study: for 2 fb-1

  23. Interesting observable: Muon forward-backward Asymmetry Asymmetrie:

  24. hep-ph/9910221 „Zero crossing point:“

  25. Generator Studie: 6.5 M Ereignisse. Change in order to which Wilson coefficients are calculated.

  26. M2 mass distributiuon Forward backward asymmetry SM SM SUGRA SUGRA Upper/lower lines C7 < 0 / C7 > 0 MIA SUSY MIA SUSY MIA SUSY C10 >0 (lower lines = pure short distance components) MIA = Flavor violating SUSY, mass insertion approx. A. Ali et al. hep-ph/9910221

  27. Non-resonant background: Upper limit: BR < 4  10-7 173075 events / 2 fb-1 irreducible Asymmetry In kinematischer Region II erwartet man gleiche Afb wie für K*ll

  28. Q2 Verteilung für Daten-Set von 2 fb-1: signal Untergrund (fluktuiert), flach in M Bemerkung: Nicht-resonanter Untergrund wird vernachlässigt. Signal Ereignisse: 37001200 Untergund: 1100 250 (non-res ignoriert)

  29. 2 fb-1 AFB (s0) = 0.46 (s0) = 0.27 (10 fb-1) s=m2 [GeV2] Statistische Signifikanz des Zero-Crossing Punktes: (aus 10000 toy Experimenten) Kein Untergrund: 0.41 GeV2 Mit Untergrund (kein non-res): 0.46 GeV2 / 0.27 GeV2 Standardmodell: s02 = 4.2  0.6 GeV2 Systematische Effekte sind bisher noch nicht untersucht !!

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