1. Radiative B Decays (an Experimental Overview) E.H. Thorndike University of Rochester CLEO Collaboration FPCP May 18, 2002

2. The Observables  Rates for exclusive decays. eg, B  K * (892)   Rate for inclusive decay b  s  (actually  B  X s  )  CP asymmetry, inclusive decays  CP asymmetry, exclusive decays  Photon energy spectrum in inclusive decays B  X s   Same observables for b  d 

3. What do you learn?  Rate for exclusive decays Experimentally easiest. B  K * (892)  first penguin seen(1993). Form factors not known, so not good for “New Physics”.  Rate for inclusive decays Loops, w &t, so sensitive to other heavy things in loop (i.e. “New Physics”) Reliably calculated with SM and with “New Physics” ] excellent for revealing or limiting “New Physics”.  CP asymmetry Expected to be very small in SM. 10-20% in some “New Physics”. Inclusive more reliably calculated than exclusives, but if big in either, New Physics.

4. What do you learn? – cont’d  Photon energy spectrum in b  s  Insensitive to New Physics ( b  s  is 2-body, a line) Depends on quark mass and Fermi momentum Can give B light cone shape function (useful for obtaining |V ub | from b  u l inclusive). Can help determine HQET OPE expansion parameters (needed for obtaining |V cb | from b  c l inclusive).  b  d  Initial interest will be in determing |V td | (but watch out for long distance effects, and for additional CKM factors from c - and u - quark loops).

5. The Experimental Problems  MUST suppress continuum.  MUST subtract continuum.  To push spectrum down below 2.2 GeV, must handle backgrounds from other B decay processes.

6. Outline for Rest of Talk  Branching Fractions for Exclusive Decays  Branching Fraction for Inclusive Decays  CP Asymmetries  Photon Energy Spectrum  b  d 

7. Discovery of Penguins CLEO -1993

8. B  K *  (BaBar)  Run I (22.7 M BB) H Tanaka Moriond 2002

9. B  K *  (Belle)

10. B  K *  Branching Fractions BK*o BK*o  B-K*- B-K*-  CLEO ’934.0 + 1.7 + 0.85.7 + 3.1 + 1.1 CLEO ’004.55 + 0.70 + 0.343.76 + 0.86 + 0.28 BaBar ’024.23 + 0.40 + 0.223.83 + 0.62 + 0.22 Belle (prelim)4.08 + 0.34 + 0.264.92 + 0.57 + 0.38 average4.21 + 0.25 + 0.264.32 + 0.38 + 0.30 (All numbers, X10 -5 )

11. B  K * 2 (1430)  Branching Fractions CLEO ’001.66 + 0.56 + 0.13 x 10 -5 Belle (prelim)1.50 + 0.56 + 0.12 x 10 -5 Other Exclusives (Belle) B +  K +      x   K * o    x   K +  o  x   K +      (NR) < 0.9 x  

12. Continuum Suppression for Inclusives -CLEO  Leptons: If event has lepton (e or  ), use   l, E l for additional continuum suppression.  Weight: For each event with a high energy , determine probability that it is b  s , rather than continuum background. Weight each such event, according to probability.  Event shape variables: R 2, S , R’ 2, cos  ’, cone energies within 20 o, 30 o of  direction and -  direction. Into neural net, 8 inputs, 1 output.  “Pseudoreconstruction”: Search events for combinations of particles that look like B->X s . For X s use K + or K o s, and 1-4  (at most 1  o ).  Calculate  If event has  2 B <20, use  2 B, |cos  tt | for additional suppression.

13. CLEO, PRL 87, 251807 (2001) Photon energy spectra (weights per 100 MeV)  Top shows the On Y(4S) and the scaled Off-resonance spectra.  Bottom shows the difference and the spectrum estimated from B decay processes other than b  s  and b  d .

14. B ( b  s  ) CLEO ‘95 ALEPH ‘98 Belle ‘01 CLEO ‘01 2.0 GeV 2.2 GeV ?? GeV 2.2 GeV Theory Buras,Misiak, et al Hep-ph/0203135 x10 -4

15. CP Asymmetry  NOTE sign convention  FOLLOW sign convention (so far, everyone seems to have.) B  K*(892)  CLEO, ‘00+0.08 + 0.13 + 0.03 BaBar, ‘02-0.044 + 0.076 + 0.012 Belle, new+0.032 + 0.069 + 0.020 Average+0.009 + 0.048 + 0.018 CLEO, ‘01 Inclusive -0.079+0.108+0.022 (0.965 A (b  s  )+0.02 A (b  d  ))

16. Photon Energy Spectrum- the B Backgrounds   ’s from  o  ,   , that have escaped the  o /  veto.  The big one (90% of total).  Measure  o,  yields, treating  o (  ) as if it were a , all cuts as for b  s  analysis. Use Monte Carlo to determine  o /  veto efficiency.   ’s from other sources     o ,  ’   o , radiative   decay,   , a 1  , final state radiation. b  u processes, b  s  g processes.  They’re small, and with modest effort to have Monte Carlo event generator ok, one can trust the Monte Carlo.  K long, interactions in calorimeter.  Determine contribution from lateral distribution in calorimeter (E9/E25).

17. CLEO (PRL 87, 251807 (2001)) Observed laboratory frame photon energy spectrum (weights/100 MeV) for ON minus scaled OFF minus B backgrounds, the putative b  s  plus b  d  signal.

18. Moments of the Spectrum  CLEO obtains moments in the B rest frame, for E  (rest frame) > 2.0 GeV:  HQET plus OPE allows inclusive observables to be written as double expansions in powers of  s and 1/M B to order  o  2 s and 1/M 3 B C 2 and C 7 are Wilson coefficients and  o is the one-loop QCD  function. The 1/M 3 B parameters are estimated from dimensional considerations to be (0.5GeV) 3.  Using the first CLEO obtains  The expression for the second moment converges slowly in 1/MB, and so CLEO made no attempt to extract parameters from it. 

19. Convolute with light cone shape function. b  s  (parton level) B  X s  (hadron level) B  lightquark shape function, SAME (to lowest order in  QCD /m b ) for b  s   B  X s  and b  u l  B  X u l. b  u l (parton level ) B  X u l (hadron level)

20. BaBar limit by far the best  [(1-  ) 2 +  2 ] 1/2 < 1.6 (Tanaka, Moriond ’02) Still, not an improvement in limit on |V td | over that from B s - s mixing. b  d   So far nothing on inclusive. Only upper limits on exclusives.  Expect B (B   +  ) = 2 x B (B   o  ) = 2 x B (B    ) B Pairs (Million) B (B   +  ) 2 x B (B   o  ) 2 x B (B    ) CLEO ‘009.7133418 Belle ‘01111021--- BaBar prelim 632.83.0--- Branching Fraction Upper Limits (10 -6 )

21. Summary and Conclusions I  b  s   Exclusive branching fractions.  Not of great fundamental interest, but by identifying a larger fraction of the makeup of B  X s   decays, one will reduce some systematic errors on the branching fraction for the inclusive process b  s . Belle progress on this front.  b  s  inclusive branching fraction.  Experiment agrees with SM theory, places strong restrictions on New Physics.  But really only one good measurement. Babar and Belle should get to work! They will need to: 1.Accept photons down to 2.0 GeV, or lower. (2.2 GeV is no longer good enough) 2.Take a reasonable amount of data below the Y(4S) resonance. (continuum subtraction MUST be done with DATA.)

22. Summary and Conclusions II  CP asymmetry  No hint of a non-zero value.  Limits place weak restrictions on New Physics.  Plenty of room for improvement.  Asymmetry for inclusive wanted (Babar, Belle??)  b  s  photon energy spectrum  Has helped provide precise determination of |V cb | from the inclusive semileptonic decay branching fractions, and (more important) a good determination of |V ub | from the lepton endpoint yield in b  u l, with DEFENSIBLE ERRORS. Will be key for future determinations of |V ub | from inclusive b  u l.  Improvements in spectrum very desirable.  b  d   So far, nothing on inclusive, only upper limits on exclusives.  Not yet an improvement in limit on |V td | over that from mixing.  Stay tuned.