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Register a new userRelativistic calculations of $R(D^{(*)})$, $R(D^{(*)}_s)$, $R(eta_c)$ and $R(J/psi)$
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Recently, the deviation of the ratios $R(D)$, $R(D^{*})$ and $R(J/psi)$ have been found between experimental data and the Standard Model predictions, which may be the hint of New Physics. In this work, we calculate these ratios within the Standard Model by using the improved instantaneous Bethe-Salpeter method. The emphasis is pad to the relativistic correction of the form factors. The results are $R(D)=0.312 ^{+0.006}_{-0.007}$, $R(D^*)= 0.249^{+0.001}_{-0.002}$, $R(D_s)=0.320 ^{+0.009}_{-0.009}$, $R(D^*_s)=0.251 ^{+0.002}_{-0.003}$, $R(eta_c)=0.384 ^{+0.032}_{-0.042}$, and $R(J/psi)=0.267 ^{+0.009}_{-0.011}$, which are consistent with predictions of other models and the experimental data. The semileptonic decay rates and corresponding form factors at zero recoil are also given.
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The experimental results on the ratios of branching fractions $mathcal{R}(D) = {cal B}(bar{B} to D tau^- bar{ u}_{tau})/{cal B}(bar{B} to D ell^- bar{ u}_{ell})$ and $mathcal{R}(D^*) = {cal B}(bar{B} to D^* tau^- bar{ u}_{tau})/{cal B}(bar{B} to D^* ell^- bar{ u}_{ell})$, where $ell$ denotes an electron or a muon, show a long-standing discrepancy with the Standard Model predictions, and might hint to a violation of lepton flavor universality. We report a new simultaneous measurement of $mathcal{R}(D)$ and $mathcal{R}(D^*)$, based on a data sample containing $772 times 10^6$ $Bbar{B}$ events recorded at the $Upsilon(4S)$ resonance with the Belle detector at the KEKB $e^+ e^-$ collider. In this analysis the tag-side $B$ meson is reconstructed in a semileptonic decay mode and the signal-side $tau$ is reconstructed in a purely leptonic decay. The measured values are $mathcal{R}(D)= 0.307 pm 0.037 pm 0.016$ and $mathcal{R}(D^*) = 0.283 pm 0.018 pm 0.014$, where the first uncertainties are statistical and the second are systematic. These results are in agreement with the Standard Model predictions within $0.2$, $1.1$ and $0.8$ standard deviations for $mathcal{R}(D)$, $mathcal{R}(D^*)$ and their combination, respectively. This work constitutes the most precise measurements of $mathcal{R}(D)$ and $mathcal{R}(D^*)$ performed to date as well as the first result for $mathcal{R}(D)$ based on a semileptonic tagging method.
We report a measurement of the ratios of branching fractions $mathcal{R}(D) = {cal B}(bar{B} to D tau^- bar{ u}_{tau})/{cal B}(bar{B} to D ell^- bar{ u}_{ell})$ and $mathcal{R}(D^{ast}) = {cal B}(bar{B} to D^* tau^- bar{ u}_{tau})/{cal B}(bar{B} to D^* ell^- bar{ u}_{ell})$, where $ell$ denotes an electron or a muon. The results are based on a data sample containing $772times10^6$ $Bbar{B}$ events recorded at the $Upsilon(4S)$ resonance with the Belle detector at the KEKB $e^+ e^-$ collider. The analysis utilizes a method where the tag-side $B$ meson is reconstructed in a semileptonic decay mode, and the signal-side $tau$ is reconstructed in a purely leptonic decay. The measured values are $mathcal{R}(D)= 0.307 pm 0.037 pm 0.016$ and $mathcal{R}(D^{ast})= 0.283 pm 0.018 pm 0.014$, where the first uncertainties are statistical and the second are systematic. These results are in agreement with the Standard Model predictions within $0.2$ and $1.1$ standard deviations, respectively, while their combination agrees with the Standard Model predictions within $1.2$ standard deviations.
Elegant experiments are being carried out, or are in preparation, to improve the precision with which the solar and atmospheric neutrino-oscillation parameters are known, and to attempt to make a first measurement of the small mixing angle $theta_{13}$. The compelling case for the development of an accelerator-based neutrino source to serve the programme of precision measurements of neutrino oscillations and sensitive searches for leptonic-CP violation that is required to follow these experiments is briefly reviewed. The Neutrino Factory, an intense high-energy neutrino source based on a stored muon beam, is widely believed to yield a precision and sensitivity superior to other proposed second-generation facilities. The alternatives are identified and the case for a critical comparison of the performance of the various options is presented. Highlights of the exciting international R&D programmes which are designed to demonstrate the feasibility of the required techniques are then reviewed. The steps that the international community is taking to produce, by the end of the decade, a full conceptual design for the facility are described. The ambition of the Neutrino Factory community is to demonstrate the feasibility of a cost-effective design such that, should forthcoming measurements show that it is required, the facility could be brought into operation in the second half of the next decade.
Recent results on the particle detector R&D for new accelerators are reviewed. Different approaches for the muon systems, hadronic and electromagnetic calorimeters, particle identification devices, and central trackers are discussed. Main emphasis is made on the detectors for the International Linear Collider and Super B-factory. A detailed description of a novel photodetector, a so called Silicon Photomultiplier, and its applications in scintillator detectors is presented.
Liquid argon detectors, with mass up to 100 kton, are being actively studied in the context of proton decay searches, neutrino astrophysics and for the next generation of long baseline neutrino oscillation experiments to study the neutrino mass hierarchy and CP violation in the leptonic sector. The proposed Giant Liquid Argon Charge Imaging ExpeRiment (GLACIER) offers a well defined conceptual design for such a detector. In this paper we present the GLACIER design and some of the R&D activities pursued within the GLACIER.
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