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تسجيل مستخدم جديدProperties and Decays of the $B_c^+$ meson
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تأليف
Lucio Anderlini
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ﻻ يوجد ملخص باللغة العربية
Recent studies of properties and decays of the $B_c^+$ meson by the LHC experiments are presented. Mass and lifetime measurements are discussed and some of the many new observed decays are reported.
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The lifetime of the $B_c^+$ meson is measured using semileptonic decays having a $J!/!psi$ meson and a muon in the final state. The data, corresponding to an integrated luminosity of $2mathrm{~fb^{-1}}$, are collected by the LHCb detector in $pp$ col
lisions at a centre-of-mass energy of $8,mathrm{TeV}$. The measured lifetime is $$tau = 509 pm 8 pm 12 mathrm{~fs},$$ where the first uncertainty is statistical and the second is systematic.
In this paper, we study the lepton number violation processes of $B_c$ meson induced by possible doubly-charged scalars. Both the three-body decay channels and the four-body decay channels are considered. For the former, $Brtimesleft(frac{s_Delta h_{
ij}}{M_Delta^2}right)^{-2}$ is of the order of $10^{-7}sim 10^{-9}$, and for the later channels, $Brtimesleft(frac{s_Delta h_{ij}}{M_Delta^2}right)^{-2}$ is of the order of $10^{-12}sim 10^{-20}$, where $s_Delta$, $h_{ij}$, $M_Delta$ are the constants related to the doubly-charged boson.
We study the semileptonic decays of $B_c$ meson to S-wave charmonium states in the framework of relativistic independent quark model based on an average flavor-independent confining potential $U(r)$ in the scalar-vector harmonic form $U(r)=frac{1}{2}
(1+gamma^0)(ar^2+V_0)$, where ($a$, $V_0$) are the potential parameters.The form factors for $B_c^+to eta_c /psi e^+ u_e$ transitions are studied in the physical kinematic range. Our predicted branching ratios (BR) for transitions to ground state charmonia are found comparatively large $sim $ $10^{-2}$, compared to those for transitions to radially excited 2S and 3S states. Like all other mpdel predictions, our predicted BR are obtained in the hierarchy: BR($B_c^+to eta_c /psi (3S)$) $<$ BR($B_c^+to eta_c/ psi (2S)$) $<$ BR($B_c^+to eta_c /psi (1S)$). The longitudinal ($Gamma_L$) and transverse polarization ($Gamma_T$) for $B_c to psi(ns)$ decay modes are predicted in the small and large $q^2$ - region as well as in the whole physical region. The ratios for such transitions are obtained $frac {Gamma_L}{Gamma_T} < 1$ throughout the kinematic range which means the $B_c^+$ meson transitions to vector meson charmonium states take place predominantly in transverse polarization mode. The theoretical predictions on these transitions could be tested in the on-going and forthcoming experiments at LHCb.
In this work, we discuss exclusive semileptonic $B_c$-meson decays: $B_cto eta_c(J/psi)l u$ and $B_cto D(D^*)l u$ in the framework of the relativistic independent quark(RIQ) model based on an average flavor independent confining potential in equally
mixed scalar-vector harmonic form. We calculate the invariant form factors representing decay amplitudes from the overlapping integrals of meson wave functions derivable in the RIQ model. To evaluate the lepton mass effects in the semileptonic decays, we first study the $q^2$-dependence of the form factors in the accessible kinematic range of $q^2$ involved in the decay process in its $e^-$ and $tau^-$ mode separately. Similar studies on helicity amplitudes, $q^2-$spectra for different helicity contributions, and total $q^2$-spectra for each decay process are carried out separately in their $e^-$ and $tau^-$ modes. We predict the decay rates/ branching fractions, forward-backward asymmetry, and the asymmetry parameter in reasonable agreement with other model predictions, which can hopefully be tested in future experiments at the Tevatron and LHC. We also predict the observable $R$ which corresponds to the ratio of branching fractions for the decay process in its $e^-$ mode to its corresponding value in the $tau^-$ mode. Our results are comparable to another standard model(SM) predictions which highlight the failure of the lepton flavor universality hinting at new physics beyond SM for the explanation of the observed deviation of observable $R$ value from the corresponding SM predictions.
The difference in total widths between the $B_c^+$ and $B^+$ mesons is measured using 3.0fb$^{-1}$ of data collected by the LHCb experiment in 7 and 8 TeV centre-of-mass energy proton-proton collisions at the LHC. Through the study of the time evolut
ion of $B_c^+ rightarrow J/psi pi^+$ and $B^+rightarrow J/psi K^+$ decays, the width difference is measured to be $$ DeltaGamma equiv Gamma_{B_c^+} - Gamma_{B^+} = 4.46 pm 0.14 pm 0.07mm^{-1}c,$$ where the first uncertainty is statistical and the second systematic. The known lifetime of the $B^+$ meson is used to convert this to a precise measurement of the $B_c^+$ lifetime, $$tau_{B_c^+} = 513.4 pm 11.0 pm 5.7fs,$$ where the first uncertainty is statistical and the second systematic.
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