Direct CP and Rare Decays @ B A B AR BEAUTY 05 - Assisi Jamie Boyd Bristol University On behalf of...

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Transcript of Direct CP and Rare Decays @ B A B AR BEAUTY 05 - Assisi Jamie Boyd Bristol University On behalf of...

  • Slide 1
  • Direct CP and Rare Decays @ B A B AR BEAUTY 05 - Assisi Jamie Boyd Bristol University On behalf of the B A B AR collaboration
  • Slide 2
  • June 2005Jamie Boyd2 Overview Direct CP overview Analysis techniques Experimental results Time integrated B K (*) / B ( ) h / B K S K S K Time Dependent B / B Conclusion
  • Slide 3
  • June 2005Jamie Boyd3 -- Af=a1+a2Af=a1+a2 AfAf a1a1 CP A f =a 1 +a 2 ++ a1a1 Direct CP violation Direct CPV is when the Decay Amplitude for a process is different than the Amplitude of the CP conjugate process This can happen if we have 2 interfering amplitudes with different weak phases ( ) and different strong phases () (the weak phase changes sign under CP whereas the strong phase is unchanged) a2a2 AfAf a2a2 AfAfAfAf
  • Slide 4
  • June 2005Jamie Boyd4 s K+K+ -- B0B0 Direct CP violation For 2 amplitudes: So for large direct CPV we need Two amplitudes to have similar magnitudes |A 1 | ~ |A 2 | Large weak & strong phase differences Expected for some charmless B decays where we have a penguin amplitude & (Cabbibo & (sometimes color) suppressed) tree amplitude For some modes New Physics in the penguin loop can change the expected direct CPV s K+K+ -- B0B0
  • Slide 5
  • June 2005Jamie Boyd5 Direct CPV: experimental issues S C Can measure time-integrated & time-dependent Direct CPV Time Integrated Measure A CP Experimentally simple for charged B decays or self tagging neutral B decays Time dependent asymmetry in B 0 f CP given by: Direct CPV if C0 (| f |1) Experimentally fit to t of tagged events Bf Bf N(Bf ) N(Bf ) Bf Bf N(Bf ) + N(Bf )
  • Slide 6
  • June 2005Jamie Boyd6 Analysis techniques - Kinematics p* B is c. m. momentum of B E* = E* B E* BEAM Energy of the B Candidate in c. m. frame Energy of the beam in c.m. frame Exploit kinematic constraints from beam energies to form 2 kinematic variables. m ES signal resolution ~ 3 MeV/c 2 dominated by beam energy spread E signal resolution ~ 10-50 MeV depending on number of neutrals in final state E can also be used for particle id (PID) as calculate with pion mass hypothesis so kaon peak is shifted.
  • Slide 7
  • June 2005Jamie Boyd7 Analysis techniques - Particle Id (PID) Good K/ separation (>2.5) for momentum < 4 GeV/c This comes from Cherenkov detector (DIRC) combined with dE/dX from drift chamber Combine sub-detector information in ML fit to give greatest discrimination
  • Slide 8
  • June 2005Jamie Boyd8 Analysis techniques - Backgrounds Need to extract a tiny signal (BF~10 -6 ) from a huge background Background dominated by light quark continuum (u,d,s,c) This background is more jet like than isotropic B decays Use event shapes (combined with Fisher or Neural Net) to reduce this background Also have background from other B decays Signal extracted using unbinned maximum likelihood fits to event shape, E, m ES, PID, +
  • Slide 9
  • June 2005Jamie Boyd9 B 0 K + (Observation of Direct CPV in B decays) Self tagging flavour of the B from the charge of the K ML Fit uses input variables m ES, E, Fisher, C +, C - c PDFs separately for +ve, -ve tracks from PID D* control sample Fit result 4.2 , syst. included BABAR B0K+B0K+ B0K+B0K+ signal enhanced background subtracted A K bkg = 0.001 +/- 0.008 PRL 93, 131801 (2004) Important cross check 9
  • Slide 10
  • June 2005Jamie Boyd10 B + K + 0 & B + + 0 Extended ML fit to ~41k B h 0 candidates Input m ES, E, Fisher, C, and expected yields and asymmetries for B-backgrounds B, B K & BK* Preliminary results B + K + 0 B + K + 0 - In SM naively expect A CP (B + K + 0 ) ~ A CP (B 0 K + ) N = 672 39, BF = (12.0 0.7 0.6)x10 -6, A CP = 0.06 0.06 0.01 B + + 0 B + + 0 - In SM expect A CP (B + + 0 ) ~ 0 N=379 41, BF = (5.8 0.6 0.4)x10 -6, A CP = -0.01 0.10 0.02 B+K+0B+ +0B+K+0B+ +0 B+K+0B+K+0 B+ +0B+ +0 PRL 94, 181802 (2005) background subtracted
  • Slide 11
  • June 2005Jamie Boyd11 B + K* + 0 Large CPV expected from tree/penguin interference B + K* + 0, K* + K + 0 B + K* + 0, K* + K + 0 (challenging as 2 0 in final state) Analysis done using a quasi-twobody approximation 0.8
  • June 2005Jamie Boyd22 BaBar experiment Detector of Internally Reflected Cherenkov light 1.5T solenoid ElectroMagnetic Calorimeter Drift CHamber Instrumented Flux Return e + (3.1GeV) e - (9GeV) Measures momentum of charged particles + dE/dx (p T )/P T =0.13%P T 0.45% Identifies particles by their Cherenkov radiation: K- separation>3.4 for P