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Exclusive Decays: Evidence for b → sγ Process

Evidence for the b → sγ process using exclusive B → K*(892)γ decays was found in 1993. Recent data advancements, such as more than 800 times larger data on Y(4S) by Babar and Belle, and LHCb data collection, make exclusive decays an ideal tool to search for new physics. Various observables like Branching Fraction, Direct CP Violation, Time-dependent CP Violation, Isospin Violation, and Up-Down Asymmetry can be studied through exclusive decays.

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Exclusive Decays: Evidence for b → sγ Process

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  1. bsg Exclusive Decays Akimasa Ishikawa (Tohoku University)

  2. Evidence for bsg • CLEO found an evidence for bsg process using exclusive BK*(892)g decays in 1993 with only 1.38fb-1 data on Y(4S). More than 20 years has passed from the evidence and now….

  3. Now we are here • Now we (Babar and Belle) have more than 800 times larger data of 1144fb-1 (433fb-1+711fb-1) on Y(4S) than data with which CLEO found an evidence for bsg. • Further, LHCb collected 3fb-1 at 7TeV and 8TeV at pp collisions. • sbb = 7.7mb for pTbb> 5GeV and 2.5 < h < 4.0 at 7TeV Copious numbers of B hadrons are available.

  4. Ideal tool to search for new physics • Exclusive bsg decays can be used to measure • Branching fraction (BF) • Fragmentation of Xs • Direct CP Violation (ACP) • To Search for New phase • Time dependent CP Violation (SCP) • For B0fCPg modes • to search for right handed current/new phase • CPV is suppressed by O(ms/mb) • Isospin Violation (D0+ or AI) • Spectator dependent operator • Up-Down Asymmetry (AUD) • For BK1gKppg • To search for right handed current • New physics makes |AUD| value smaller than the SM • Photon Polarization from conversion (no groups measure yet) • To search for right handed current

  5. Observed Exclusive Decays • Now we observed • BK*(892)gin 1993 • BK2*(1430)g in 2000 • BKfg in 2004 • BKhg in 2005 • BK1(1270)gin 2005 • BpLgin 2007 • BKh’g in 2010 Only 40% are exclusively known!

  6. Direct CPV • In the SM, bsg process is dominated by single EW penguin diagram, and further weak phase in Vts is suppressed by O(l2), so direct CPV in bsg is small. • E.g. ACP(BK*(892)g) = -0.6±0.4% • If new physics contribution to bsg has sizable amplitude and weak (+strong) phase, direct CPV could appear. • Is the difference of direct CPV btw B0 and B+ interesting/sensitive NP also for exclusive decays? • Benzke, Lee, Neuber and Paz propose it for inclusive decays as a sensitive probe for new physics. • Matsumori, Sanda, Keum

  7. Direct CPV in BK*(892)g • LHCb reported ACP with 1fb-1 • Only with K*0K+p- • W.A. consistent with nullasymmetry predicted in the SM • -0.6±0.4 % • exp error 3times larger than theo • LHCb 1fb-1 3fb-1 • Belle 78fb-1 711fb-1 • Matsumori, Sanda, Keum

  8. Isospin Violation • Isospin Violation can be calculated in the SM. • +5.0 ~ +10 % • +2.7±0.8 % • If new physics has isospin breaking contributions, such as spectator dependent diagrams, D0- could be deviated from the SM value • Even sign of Isospin Violation flips • Kagan, Neubert • Matsumori, Sanda, Keum

  9. Isospin Violation in BK*(892)g • Babar and Belle measured isospin violation • thanks to high reconstruction efficiency for Ks and p0 involved modes at e+e- machine • Consistent with SM Predictions • +5.0 ~ +10 % • +2.7±0.8 % • Kagan, Neubert • Matsumori, Sanda, Keum

  10. Time dependent CPV • In the SM, photon emitted from b is predominantly left handed. Time dependent CPV in BfCPg is small due to small interference • If new physics has right handed current, time dependent CPV emerges by interference. • Gluon emission bsggprocesses make SSM larger than naive calculation?? Atwood, Gronau, Soni Atwood, Gershon, Hazumi,Soni SSM ~ O(0.1) Grinstein, Grossman, Ligeti, Pirjol Grinstein, Pirjol Matsumori, Sanda Ball, Zwicky

  11. Preliminary Time Dependent CPV in BKhg 711fb-1 • Recently Belle reported measurement of time dependent CPV in BKhg with full data • Measured values are out of physical boundary but consistent with null CPV. SM prediction

  12. Summary of time dependent CP Violation • Four decay modes are used to search for time dependentCPV. • fCP = Ksp0(K*0), Ksh, Ksr, Ksf • All are consistent with null with stat errors.

  13. Up Down Asymmetry Gronau, Grossman, Pirjol, Ryd • Polarization of photon can be extracted from the BK1g(Kpp)gprocess by measuring up down asymmetry (photon polarization from K1 polarization). • Angle q btw photon and normal vector to K1 decay plane. • Interference btw rK and K*p generates imaginary part. •  modes involving p0 gives larger AUD • Need theoretical calculation of the amplitudes

  14. Up Down Asymmetry in BKppg • LHCb observed AUD with 3fb-1 in BK+p-p+g • With 13876±153 signal events • Measure AUD with 4 bins of MKpp • No resonance separation • 5.2s significance from null polarization • No interpretation to photon polarization yet

  15. bdg Exclusive Decays Given title is bsg exclusive decays but I would add bdg

  16. bdg Decays • The bdg is suppressed by Vtd • About 30 times smaller than bsg( |Vtd/Vts|2 ) • Need very good PID detector and EM Calorimeter • The observables to search for NP are the same as the bsg but NP contribution could be different. • Branching fraction (BF) • Direct CP Violation (ACP) • Time dependent CP Violation (SCP) • IsospinViolation (Dr) • Up-Down Asymmetry (AUD) • Photon Polarization from conversion (no groups measure yet)

  17. Observation of bdg • Belle had observed bdg process using exclusive B(r, w)g with 357fb-1 data in 2006

  18. |Vtd/Vts|, ACP and Dr • |Vtd/Vts| can be measured from the ratio of BF of B (r,w)g and BK*g • Consistent with the SM • Direct CPV in Br+gconsistent with null • DrIsospin Violation large? • 2~3sdeviation • + 4 +14 -7 % • - 10±6 % • - 5.4±3.9 % if f3 = 60deg • - 4.6±7 % Ali, Lunghi Lyon, Zwicky Ball, Jones, Zwicky Beneke, Feldmann, Seidel

  19. Time Dependent CPV in B0r0g • Only Belle had measured time dependent CPV in B0r0g • 48±14signal events are used for fits. • Though signal yield is smaller than B0Ksp0g, fraction of events used for time dependent fit is larger thanks to easier vertex reconstruction with r0p+p- • The results are consistent with null asymmetry

  20. Summary • Many studies of bsg are performed in more than 20 years to search for new physics. • No hint of new physics yet. • New window bdg was opened since2006. • A hint in Isospin Asymmetry?? • Some analyses in bsgand all analyses in bdgare still statistical error dominant • Need higher luminosity experiments •  Belle II and LHCbupgrade • Some theoretical predictions are different btw groups. • Isospin violation • Time dependent CPV • Hope the predictions improved in coming several years.

  21. backup

  22. CCP = - ACP

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