3,142 research outputs found
Charm CPV and rare decays at LHCb
No full textCharm physics has been playing all along a role in particle physics, by contributing to the for-mulation of the Standard Model (SM) as it is known nowadays. The level of attention on it has tremendously increased in recent years because of the first experimental observations of the slow mixing rate of the flavour oscillations, providing definitely a full range of probes, entirely complementary to the and mesons, for mixing and - violation. In fact the charm quark is the only up-type quark that manifests flavour oscillations. Only in recent years it has been possible to collect huge and very clean samples of meson decays, several orders of magnitude larger in size than in the past, allowing also for the first time approaching the small SM expectations for -violation below the level. Thus, the dynamics of the charm quark can be probed for the presence of New Physics with negligible SM “background”, since any generic non-SM contribu-tion would naturally carry additional -violating phases, which could enhance the observable -violation relative to SM predictions. It is worth to mention that mixing can proceed in the SM through a double weak boson exchange (short distance contributions) or through inter-mediate states that are accessible to both and (long distance contributions). The potentially large long distance contributions are non–perturbative and therefore difficult to estimate from the theory, however the interplay of many and even more precise experimental measurements, that only recently approached the desired precision, along with the foreseen theoretical improvements in calculating such amplitudes, should allow constraining theoretical uncertainties in the next and far future increasing the sensitivity to possible contributions from new processes and particles at mass scales beyond the reach of direct searches. The LHCb experiment at the Large Hadron Collider is currently the main player and this brief write-up covers the most recent LHCb results on -violation in the charm sector and on the search of rare charm decays
Branching fractions and direct CP Asymmetries of charmless B decay modes at the tevatron
No full textWe present new CDF results on the branching fractions and time-integrated direct CP asymmetries for B-0 and B-s(0) decay modes into pairs of charmless charged hadrons (pions or kaons). The data-set for this update amounts to 1 fb(-1) of (p) over barp collisions at a center of mass energy 1.96 TeV. We report the first observation of the B-s(0 ->) K-pi(+) mode and a measurement of its branching fraction and direct CP asymmetry. We also observe for the first time two charmless decays of the Lambda(b)-baryon: Lambda(0)(b) -> p pi(-) and Lambda(0)(b) -> pK(-)
B physics at the Tevatron
No full textThe Fermilab Tevatron offers unique opportunities to perform measurements of the heavier b-hadrons that are not accessible at the Gamma(4S) resonance. In this paper, we describe most important heavy flavour results from D empty set and CDF Collaborations and we discuss prospects for future measurements, that could reveal New Physics before the start-up of the Large Hadron Collider (LHC)
Measurement of CP-Violation in
No full textCharm physics has played all along a central role in particle physics, however the level of attention on it has tremendously increased in the last years because of the observation of "fast" flavour oscillations and because of very recent observed hints of CP violation. While in the past these would have been unambiguously interpreted as signs of New Physics, the revisitation of theoretical expectations, prompted by the latest experimental measurements, makes the picture not clear. This brief review covers the current status of CP-violating measurements in the system, both on the experimental and theoretical side
FCNC at the Tevatron
No full textProcesses involving flavor changing neutral currents (FCNC) provide excellent signatures with which to search for evidence of new physics. They have very small branching fractions in the Standard Model since they are highly suppressed by Glashow-Iliopoulos-Maiani (GIM) mecha- nism. They occur only through higher order diagrams, and new particles contributions can provide a significant enhancements, which would be an uniquevocal signs of physics beyond the Standard Model. In this paper we present the most recent measurements on FCNC processes performed by CDF and DØ Collaborations, while last section is devote to the charm physics at CDF
Measurements of CP Asymmetries and Branching Fractions of Two-Body Charmless Decays of B0 and B0s Mesons
No full textCP and charge asymmetries at CDF
No full textWe present CDF results on the branching fractions and time-integrated direct CP asymmetries for B0 and B0s decay modes into pairs of charmless charged hadrons (pions or kaons). We report also the first observation of B0s->DsK mode and the measurement of its branching fraction
CP violation in the D0 -> pi+ pi- decay at CDF
No full textWe report a measurement of the CP violating asymmetry in D{sup 0} {yields} {pi}{sup +}{pi}{sup -} decays using approximately 215,000 decays reconstructed in about 5.94 fb{sup -1} of CDF data. We use the strong D*{sup +} {yields} D{sup 0}{pi}{sup +} decay ('D* tag') to identify the flavor of the charmed meson at production time and exploit CP-conserving strong c{bar c} pair-production in p{bar p} collisions. Higher statistic samples of Cabibbo-favored D{sup 0} {yields} K{sup -}{pi}{sup +} decays with and without D* tag are used to highly suppress systematic uncertainties due to detector effects. The result, A{sub CP}(D{sup 0} {yields} {pi}{sup +}{pi}{sup -}) = [0.22 {+-} 0.24 (stat.) {+-} 0.11 (syst.)]%, is the world's most precise measurement to date and it is fully consistent with no CP violation
Mixing and CP violation in D-0 -> K-pi(+) decays
No full textWe review the experimental methods to measure mixing and time-dependent CP violation in D-0 decays into two hadrons. While these phenomena are usually neglected for D-0 -> K-pi(+) decays, this approximation is not always justified. In particular, it produces a bias on the measurement of the parameter y(CP), when this is performed by relying on D-0 -> K-pi(+) decays as a normalisation channel, whose size is around 40% of the precision of the current world average. Finally, we estimate the sensitivity to the weak mixing phases achievable by studying D-0 -> K-pi(+) and untagged D -> K-pi(+) decays, where D stands for either of the D-0 and (D) over bar (0) mesons. Contrary to Cabibbo-suppressed D-0 -> h(+)h(-) decays, these decay channels allow to measure these phases without final-state dependent nuisance contributions from the decay amplitudes, but their sensitivity is lower by a factor of six
Observation of New Charmless Decays of Bottom Hadrons
No full textThe authors search for new charmless decays of neutral b-hadrons to pairs of charged hadrons with the upgraded Collider Detector at the Fermilab Tevatron. Using a data sample corresponding to 1 fb{sup -1} of integrated luminosity, they report the first observation of the B{sub s}{sup 0} {yields} K{sup +}{pi}{sup +} decay, with a significance of 8.2{sigma}, and measure {Beta}(B{sub s}{sup 0} {yields} K{sup -}{pi}{sup +}) = (5.0 {+-} 0.7 (stat.) {+-} 0.8 (syst.)) x 10{sup -6}. They also report the first observation of charmless b-baryon decays in the channels {Lambda}{sub b}{sup 0} {yields} p{pi}{sup -} and {Lambda}{sub b}{sup 0} {yields} pK{sup -} with significances of 6.0{sigma} and 11.5{sigma} respectively, and they measure {Beta}({Lambda}{sub b}{sup 0} {yields} p{pi}{sup -}) = (3.5 {+-} 0.6 (stat.) {+-} 0.9 (syst.)) x 10{sup -6} and {Beta}({Lambda}{sub b}{sup 0} {yields} pK{sup -}) = (5.6 {+-} 0.8 (stat.) {+-} 1.5 (syst.)) x 10{sup -6}. No evidence is found for the decays B{sup 0} {yields} K{sup +}K{sup -} and B{sub s}{sup 0} {yields} {pi}{sup +}{pi}{sup -}, and they set an improved upper limit {Beta}(B{sub s}{sup 0} {yields} {pi}{sup +}{pi}{sup -}) < 1.2 x 10{sup -6} at the 90% confidence level. All quoted branching fractions are measured using {Beta}(B{sup 0} {yields} K{sup +}{pi}{sup -}) as a reference
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