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EPS 2003 Conference Aachen, Germany Eugeni Graugés (U.B) for the BaBar Collaboration Radiative Penguin BaBar B  K *  B  , B   and B.

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Presentation on theme: "EPS 2003 Conference Aachen, Germany Eugeni Graugés (U.B) for the BaBar Collaboration Radiative Penguin BaBar B  K *  B  , B   and B."— Presentation transcript:

1 EPS 2003 Conference Aachen, Germany Eugeni Graugés (U.B) for the BaBar Collaboration Radiative Penguin BaBar B  K *  B  , B   and B  X s  1

2 Flavour Changing Neutral Current decay processes The SM forbids them at tree level Do occur via loop processes involving heavy particles (W,top). Inclusive final states: theoretically cleaner, but with experimentally difficult background suppression Exclusive final states: large theoretical uncertainties from hadronic form factors, but clearer experimental signatures Radiative Penguin Decays 2

3 Their SM predictions can be changed dramatically if there is new physics! (Huth hep-ph/ ) since new particles (Higgs and SUSY) can enhance their otherwise small SM decay rates: >> Branching Fraction for B  X s  (E  >1.6 GeV in B rest frame): B (B  X s  ) = (3.60 ± 0.30)·10 -4 Gambino & Misiak, Nuc. Phys. B611, 338 (2001) B (B      ) = (0.85 ± 0.34)·10 -6 Ali & Parkhomenko, Eur. Phys. J. C.23, 89 (2002) B (B      ) = (0.49 ± 0.18)·10 -6 hep-ph/ >> B (B   )/ B (B  K*  ) is proportional to |V td | 2 /|V ts | 2 The exclusive process      with a Branching Ratio predicted to be B (B     ) = (7.1 ± 2.5)·10 -5 (Bosch & Buchalla hep-ph/ ) have a small A CP (~ 1%) which is very sensitive to non-SM extra contributions that might cause CP-violating charge asymmetries as high as 20% SM predictions & New Physics Potential 3 CKM Unitariety Triangle

4 Event Selection 4 Isolated High Energy  (1.5 < E  * < 3.5 GeV ) Shower lateral profile consistent with EM shower Veto if combined with other  in event makes  0 /  (those not vetoed are a significant background) K Identification K Rejection Use DIRC Reverse Kaon ID criteria Useful for B   to reject B  K *  events  →  *(K +  - )  Fish-Eye view Not to scale

5 Continuum Background Rejection 5 The qq,(q=u,d,s,c) “underneath” the bb Exploit the B-decay isotropy vs the “jet-like” topology of qq events Use B properties and shape variables wrt to  : decay angle,  z, flavour tag, cos  Thrust, energy flow. Cuts on combination of variables (Fisher Discriminant or Neural Network). NN plot on control sample and off-resonance data: CMS

6 Exclusive processes 6 Reconstruct B meson using the final state products: B  K *  B   (  Advantage: use kinematic signature for B decays Express energy and momentum conservation as m ES  E *2 beam -P *2 B  E=E * B -E * beam (*=CMS frame)   

7 Finding these events is experimentally very challenging: Low branching ratios ~1 x Large continuum background (ISR +   ). Neural Net fed with multiple variables is use to effectively remove the background  resonance is much wider (149 MeV) than K* B   (  Large B background from    has to be removed.  E resolution limited by  energy measurement Irreducible background from     7

8 B(B 0   0  ) < 1.2·10 90%CL B(B ±     ) < 2.1·10 90% CL B(B 0   ) < 1.0·10 90% CL A total of 78 fb -1 data are used B   /  Results (hep-ex/ submitted to PRL) A multi-dimensional maximum likelihood fit is used to extract signal yields. No Evidence of signal, upper limits are set: 8 B 0   0 ,  0   +  - B ±   ± ,  ±   +   B 0  ,    +  -   Preliminary

9 |V td |/|V ts | limit from B   /  Assuming (isospin symmetry) B(B   ) = B(B ±   ±  ) = 2 x B(B 0   0  ) Then the upper limit obtained B(B   ) < Using (Ali & Parkhomenko Eur. Phys. J. C.23, 89 (2002)) B(B   )/B(B  K *  ) = |V td /V ts | 2  2 |1+  R| (1-m  2 /M B 2 ) 3 /(1-m K* 2 /M B 2 ) 3 And assuming  =0.76±0.10,  R=0.0±0.2; |V td |/|V ts 90% CL B   limit Preliminary

10 Inclusive Processes 10 HQET: Quark-Hadron Duality B(b -> s  ) = B(B -> X s  ) s b  b Xs B  Identify  from B  X s , but With the signal  selected there is still ~10 3 more background than Signal. Challenge is to reduce bkg while minimizing stat.+sys.+model errors Two approaches: Fully Inclusive Semi Inclusive B -> X s  BB qq

11 BXsBXs 11 Semi-InclusiveFully Inclusive Background Rejection  (Exclusive States)Lepton tags Efficiency3%1% Fraction of Xs states: 50% 100% qq bkg estimationSideband subtractionOff-resonance data BB bkg estimation Monte Carlo (peaking) Sideband sub. (non-pk) M. Carlo – data validated X-feed bkg estimation Monte Carlo (peaking) Sideband sub. (non-pk) No X-feed Spectral Resolution  Mxs ~ 5 MeV  E~100 MeV Model DependenceXs, K*/Xs, M xs cutEE

12 B(B  X s  ) = (3.88 ± 0.36 (stat) ± 0.37 (syst) (model))·10 -4 Fully Inclusive B  X s  Data BB expected events Integrated to obtain Branching Fraction Preliminary Data sample 54 fb -1 Signal events integrated between 2.1 and 2.7 GeV to extract branching fraction   [2.1; 2.7] GeV Dominant Stat error due to ~6fb -1 off- resonance used for continuum subtraction Dominant Syst error from BB subtraction (   and  from B decays can fake  )   X d  events subtracted using theory prediction: (4.0±1.6)% ( Continuum Back. subtracted) hep-ex/

13 Semi-Inclusive B  X s   exclusive states) = K + /K 0 s +up to 3  (1  0 ), 12 states Observe discrepancy in JETSET simulation of Xs fragmentation. Efficiency from Monte Carlo weighted to correct discrepancy Correct for undetected modes M ES (GeV) 1.4 < M Xs < 1.6 GeV =2.35  0.04 (stat.)  0.04(sys.)  =0.37  0.09 (stat.)  0.07(sys.)  0.10(th.) GeV (Using Ligeti et.al PRD 60, (1999)) & m b =4.79  0.08 (stat.)  0.10(sys.)  0.10(th.) GeV (Ligeti et al. Phys. Review D 60, , 1999) E  in B reference system Preliminary

14 B(B  X s  ) = (4.3 ± 0.5 (stat) ± 0.8 (syst) ± 1.3 (model) )·10 -4 Semi-Inclusive B  X s  Branching fraction extracted from fit to the spectrum 14 - Fix m b =4.79 and fit using spectrum Kagan & Neubert Euro.Phys. J. C 7,5(1999) Preliminary Data sample 20 fb-1

15  measurements 15 - Preliminary

16 BaBar is measuring with high statistics and precision: B  K *  (20 fb -1 ) B(B 0  K *0  ) = (4.23 ± 0.40 (stat) ± 0.22 (syst))·10 -5 B(B ±  K ±  ) = (3.83 ± 0.62 (stat) ± 0.22 (syst))· < A CP < 90% CL Upper limits on B   /   (78 fb -1 ) B(B 0   0  ) < 1.2·10 90%CL B(B ±   ±  ) < 2.1·10 90% CL B(B 0   ) < 1.0·10 90% CL Branching Fraction and  spectrum for B  X s  inclusive B(B  X s  ) = (3.88 ± 0.36 (stat) ± 0.47 (syst) (model))·10 -4 (54 fb -1 ) semiexcl. = 2.35 ± 0.04 (stat) ± 0.04 (syst) GeV (20 fb -1 ) semiexcl. B(B  X s  ) = (4.3 ± 0.5 (stat) ± 0.8 (syst) ± 1.3 (model) )·10 -4 (20 fb -1 ) Conclusions

17 17 Backup Slides

18 B  K *(892)  (PRL 88:101805, 2002) 18 B(B 0  K *0  ) = (4.23 ± 0.40 (stat) ± 0.22 (syst))·10 -5 B(B ±  K *±  ) = (3.83 ± 0.62 (stat) ± 0.22 (syst))·10 -5 B(B  K*  )-B(B  K*  ) B(B  K*  )+B(B  K*  ) < A CP < 90% CL Data analyzed = 20 fb -1 B 0  K 0*  K 0*  K +  - B ±  K ±*  K ±*  K ±   B 0  K 0*  K 0*  K s 0   B ±  K ±*  K ±*  K s 0  ± A CP = Only the modes     s   ,         and        Are used to compute the CP-violating Charge asymmetry.

19 B   /  Upper 90% CL BaBar BELLE CLEO Theory (Ali&Parkomenko) B(B 0   0  ) < 1.2·10 -6 < 2.6·10 -6 < 17·10 -6 = (0.49±0.18)·10 -6 B(B ±   ±  ) < 2.1·10 -6 < 2.7·10 -6 < 13·10 -6 = (0.90±0.34)·10 -6 B(B 0   ) < 1.0·10 -6 < 4.4·10 -6 < 9.2·10 -6 = (0.49±0.18)· Preliminary

20  PEPII is a B factory running at energies around the  (4s) resonance.(E CM =10.6GeV)  Its asymmetry in beam energies 9.0 GeV and 3.1 GeV) allows the measurement of time-dependent CP violating asymmetries in the decay of neutral B mesons  with a boost  = 0.56 in the LAB frame)  " B meson decay channels interesting to study CP violation have small branching ratios (10 -4 ) Several tens of million of neutral B meson pairs needed to measure CP asymmetries with 10% error Luminosities of to cm -2 s -1 B Factory

21 The detector SVT: 5 double side layers, 97% efficiency, 15 mm z hit resolution DCH : 40 axial and stereo layers Tracking:  (p T )/p T = 0.13 %  p T %, s(z 0 ) = 1 GeV/c DIRC: 144 quartz bars EMC: 6580 CsI(Tl) crystals  E /E = 2.3 %  E -1/4  1.9 % IFR: 19 RPC layers, muon and K L id

22 Data Sample Data taken at the Y(4S): RUN1 ~ 20fb -1 RUN2 ~ 61 fb -1 RUN3 ~ 35 fb -1 so far 22

23 No monocromatic  spectrum because of b motion within B meson Photon Energy Spectrum 23 Experimentally hard to suppress background at low  energy  Lower energy cut on the  energy in all the experimental measurements We use Kagan and Neubert's (Euro. Phys, Jour. C7,5, 1999) HQET next-to-leading order  spectrum Eg. E  >2.2GeV corresponds to ~ 80% of all the spectrum From moments analysis of  spectrum  extraction of HQET parameters. From first moment of  spectrum   (Ligeti et al. Phys. Review D 60, , 1999) measures the energy of the light degrees of freedom Hurth hep-ph/

24 B  X s  Branching Ratios 24 S. Playfer, CKM workshop II Preliminary

25 B  K *  Branching Ratios 25 Theoretical speculation of 10% isospin breaking (Kagan & Neubert hep- ph/ ) can be tested soon Preliminary B 0  K 0*  B ±  K ±*  S. Playfer, CKM workshop II


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