A
bstract
This report details the capabilities of LHCb and its upgrades towards the study of kaons and hyperons. The analyses performed so far are reviewed, elaborating on the prospects for some key ...decay channels, while proposing some new measurements in LHCb to expand its strangeness research program.
Using an effective-theory approach, we analyze the impact of B(Bs→μ+μ−) in constraining new-physics models that predict modifications of the Z-boson couplings to down-type quarks. Under motivated ...assumptions about the flavor structure of the effective theory, we show that the bounds presently derived from B(Bs→μ+μ−) on the effective Z-boson couplings are comparable (in the case of minimal flavor violation) or significantly more stringent (in the case of generic partial compositeness) with respect to those derived from observables at the Z peak.
We present a set of recommendations for the presentation of LHC results on searches for new physics, which are aimed at providing a more efficient flow of scientific information between the ...experimental collaborations and the rest of the high energy physics community, and at facilitating the interpretation of the results in a wide class of models. Implementing these recommendations would aid the full exploitation of the physics potential of the LHC.
The RK measurement by LHCb suggests non-standard lepton non-universality (LNU) to occur in b→sℓ+ℓ− transitions, with effects in muons rather than electrons. A number of other measurements of b→sℓ+ℓ− ...transitions by LHCb and B-factories display disagreement with the SM predictions and, remarkably, these discrepancies are consistent in magnitude and sign with the RK effect. Non-standard LNU suggests non-standard lepton flavor violation (LFV) as well, for example in B→Kℓℓ′ and Bs→ℓℓ′. There are good reasons to expect that the new effects may be larger for generations closer to the third one. In this case, the Bs→μe decay may be the most difficult to reach experimentally. We propose and study in detail the radiative counterpart of this decay, namely Bs→μeγ, whereby the chiral-suppression factor is replaced by a factor of order α/π. A measurement of this mode would be sensitive to the same physics as the purely leptonic LFV decay and, depending on experimental efficiencies, it may be more accessible. A realistic expectation is a factor of two improvement in statistics for either of the Bd,s modes.
We present a new method for extracting excited states from a single two-point correlation function calculated on the lattice. Our method simply combines the correlation function evaluated at ...different time slices so as to “subtract” the leading exponential decay (ground state) and to give access to the first excited state. The method is applied to a quenched lattice study (volume=243×64, β=6.2, a−1=2.55 GeV) of the first excited state of the nucleon using the local interpolating operator O=ɛabcuaTCγ5dbuc. The results are consistent with the identification of our extracted excited state with the Roper resonance N′(1440). The switching of the level ordering with respect to the negative-parity partner of the nucleon, N*(1535), is not seen at the simulated quark masses and, basing on crude extrapolations, is tentatively expected to occur close to the physical point.
We discuss a number of strategies to reduce the BR(Bs to l+ l- gamma)theoretical error, and make such a measurement a new probe of the interactionsthat are interesting in the light of present-day ...flavor discrepancies. Inparticular, for low di-lepton invariant mass we propose to exploit the closeparenthood between BR(Bs to l+ l- gamma) and the measured BR(Bs to phi (to K+K-) gamma). For high q^2, conversely, we exploit the fact that the decay isdominated by two form-factor combinations, plus contributions from broadcharmonium that we model accordingly. We construct the ratio R_gamma, akin toR_K and likewise sensitive to lepton-universality violation. Provided the tworates in this ratio are integrated in a suitable region that minimisesbremsstrahlung contributions while maximising statistics, the ratio is veryclose to unity and the form-factor dependence cancels to an extent that makesit a new valuable probe of lepton-universality violating contributions in theeffective Hamiltonian. We finally speculate on additional ideas to extractshort-distance information from resonance regions, which are theoreticallyinteresting but statistically limited at present.
as an electroweak precision test Guadagnoli, D; Isidori, G
Physics letters. B,
07/2013, Letnik:
724, Številka:
1-3
Journal Article
Recenzirano
Using an effective-theory approach, we analyze the impact of B (B s a mu + mu -) in constraining new-physics models that predict modifications of the Z-boson couplings to down-type quarks. Under ...motivated assumptions about the flavor structure of the effective theory, we show that the bounds presently derived from B (B s a mu + mu -) on the effective Z-boson couplings are comparable (in the case of minimal flavor violation) or significantly more stringent (in the case of generic partial compositeness) with respect to those derived from observables at the Z peak.
The Bs to mu mu gamma decay offers sensitivity to a wider set of effectiveoperators than its non-radiative counterpart Bs to mu mu, and a set that isinteresting in the light of present-day ...discrepancies in flavour data. On theother hand, the direct measurement of the Bs to mu mu gamma decay poseschallenges with respect to the Bs to mu mu one. We present a novel strategy tosearch for Bs to mu mu gamma decays in the very event sample selected for Bs tomu mu searches. The method consists in extracting the Bs to mu mu gammaspectrum as a "contamination" to the Bs to mu mu one, as the signal window forthe latter is extended downward with respect to the peak region. We providearguments for the actual practicability of the method already on Run-2 data ofthe LHC.
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