LHCb

Abstract:

A test of the benchmark QED process e⁺e^- → γγ(γ) is reported, using the data collected with the DELPHI detector at LEP 2. The data analysed were recorded at centre-of-mass energies ranging from 161 GeV to 208 GeV and correspond to a total integrated luminosity of 656.4 pb^-1. The Born cross-section for the process e ⁺e^- → γγ(γ) was determined, confirming the validity of QED at the highest energies ever attained in electron-positron collisions. Lower limits on the parameters of a number of possible deviations from QED, predicted within theoretical frameworks expressing physics beyond the Standard Model, were derived. © Springer-Verlag/ Società Italiana di Fisica 2004.

Abstract:

Using events in which one of two neutral B mesons from the decay of an Y(4S) resonance is fully reconstructed, we set limits on the difference between the decay rates of the two neutral B mass eigenstates and on CP, T, and CPT violation in B0B̄0 mixing. The reconstructed decays, comprising both CP and flavor eigenstates, are obtained from 88 million Y(4S)→BB̄ decays collected with the BABAR detector at the PEP-II asymmetric-energy B Factory at SLAC. We determine six independent parameters governing oscillations (Δm,ΔΓ/Γ), CPT and CP violation (Re z,Im z), and CP and T violation (Im λCP,|q/p|), where λCP characterizes B0 and B̄0 decays to states of charmonium plus KS0 or KL0. The results are sgn(Re λCP)ΔΓ/ Γ=-0.008±0.037(stat.)±0.018(syst.)[-0.084,0.068], |q/p|=1.029±0.013(stat.)±0.011(syst.)[1.001,1.057], (Re λCP|λCP|)Re z=0.014±0.035(stat.) ±0.034(syst.)[-0.072,0.101], Im z=0.038±0.029(stat.)±0.025 (syst.)[-0.028,0.104]. The values inside square brackets indicate the 90% confidence-level intervals. The values of Im λCP and Δm are consistent with previous analyses and are used as cross checks. These measurements are in agreement with standard model expectations.

Abstract:

The branching fractions of the decays B0 → K*0 γ and B+ → K*+ γ are measured using a sample of 88 × 106BB̄ events collected with the BABAR detector at the PEP-II asymmetric-energy e +e- collider. We find B(B0 → K* γ) = [3.92 ± 0.20(stat) ± 0.24(syst)] × 10 -5, B(B+ → K*+ γ) = [3.87 ± 0.28(stat) ± 0.26(syst)] × 10-5. Our measurements also constrain the direct CP asymmetry to be -0.074 < A(B → K* γ) < 0.049 and the isospin asymmetry to be -0.046 < Δ0-̈ < 0.146, both at the 90% confidence level.