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[en] We study the photon-triggered light and heavy meson production in both p+p and A+A collisions. We find that a parton energy loss approach that successfully describes inclusive hadron attenuation in nucleus-nucleus reactions at RHIC can simultaneously describe well the experimentally determined photon-triggered light hadron fragmentation functions. Using the same framework, we generalize our formalism to study photon-triggered heavy meson production. We find that the nuclear modification of photon-tagged heavy meson fragmentation functions in A+A collision is very different from that of the photon-tagged light hadron case. While photon-triggered light hadron fragmentation functions in A+A collisions are suppressed relative to p+p, photon-triggered heavy meson fragmentation functions can be either enhanced or suppressed, depending on the specific kinematic region. The anticipated smaller energy loss for b-quarks manifests itself as a flatter photon-triggered B-meson fragmentation function compared to that for the D-meson case. We make detailed predictions for both RHIC and LHC energies. We conclude that a comprehensive comparative study of both photon-tagged light and heavy meson production can provide new insights in the details of the jet quenching mechanism.
[en] The KEDR detector is a universal magnetic detector designed for studying the c- and b-quarks and two-photon physics, and is employed at the VEPP-4M e+ e− collider. A specific feature of the experiment is the measurement of absolute beam energy using two methods: the resonant depolarization and the faster but less precise Compton backscattering of laser photons. This allowed a large series of measurements to be performed, in which the accuracy of determination of such fundamental parameters of particles as mass and total and leptonic widths was improved.
[en] The phenomenon of CP violation and its explanation are of vital interest in our understanding of the structure of matter and perhaps of the excess of matter over anti-matter in the universe. The mixing between quark generations, represented by the CKM matrix, has been suggested as the mechanism responsible for CP violation and particle/anti-particle oscillation observed in neutral K mesons. The elements of the CKM matrix describe the phenomena of CP violation, particle/anti-particle oscillation and inter-generational transitions. All these phenomena were also predicted for hadrons containing the b quark. Since that prediction, particle/anti-particle oscillation has been observed in Bd mesons, however, no evidence has yet been seen for CP violation in the B sector. All the phenomena related to the CKM mixing matrix in the b sector can be summarized in a (unitarity triangle'. Once the sides and angles of this triangle have all been measured, whether or not they form a triangle will determine if the CKM prescription is the correct description of CP violation. We will report about the status of particle oscillation in the B sector as well as on recent attempt to observe asymmetries in the decay of neutral B mesons
[en] The determination of |Vub| from inclusive semileptonic B decays is limited by uncertainties in modeling the decay distributions in b → u(ell)ν transitions. The largest uncertainties arise from the limited knowledge of the appropriate b quark mass and Fermi momentum to use in the parameterization of the shape function. This paper presents a new method in which these shape function parameters are constrained by the same data used to measure |Vub|. The method requires measurements of the momenta of both the charged lepton and the neutrino in semileptonic B decays. From these quantities two complementary observables can be constructed, one for discriminating between b → u(ell)ν transitions and background and the other for constraining the shape function. Using this technique the uncertainties in |Vub| from the shape function may be significantly reduced
[en] We report on a measurement of the Bd0 mixing frequency and the calibration of an opposite-side flavor tagger in the D0 experiment. Various properties associated with the b quark on the opposite side of the reconstructed B meson are combined using a likelihood-ratio method into a single variable with enhanced tagging power. Its performance is tested with data, using a large sample of reconstructed semileptonic B → μD0 X and B → μD* X decays, corresponding to an integrated luminosity of approximately 1 fb-1. The events are divided into groups depending on the value of the combined tagging variable, and an independent analysis is performed in each group. Combining the results of these analyses, the overall effective tagging power is found to be (varepsilon)(prime)D2 = (2.48 ± 0.21-0.06+0.08)%. The measured Bd0 mixing frequency Δmd = 0.506 ± 0.020 (stat) ± 0.016 (syst) ps-1 is in good agreement with the world average value
[en] Known perturbative expressions for the decay rates of 115 GeV Higgs particle into either two gluons or a b bar b pair are shown to exhibit renormalization-scale (μ) dependence that is largely removed via renormalization-group or Padeprime-approximant estimates of these rates' next order contributions. The extrema in μ characterizing both rates, as determined from fully known orders of perturbation theory, are very nearly equal to corresponding μ-insensitive rates obtained via estimation of their next order contributions, consistent with 'minimal-sensitivity' expectations
[en] Current errors on vertbarVubvertbar are dominated by model dependence. For inclusive decays, the model dependence comes from the Fermi motion of the b quark. By combining the endpoint photon and lepton spectra from the inclusive decays B rarrow Xsγ and B rarrow Xuellbar ν, it is possible to remove this model dependence. We show how to combine these rates including the resummation of the end-point logs at next to leading order. The theoretical errors on vertbarVubvertbar on the order of 10% are possible. We also give a brief discussion on comparing different extractions
[en] We discuss the polar angle decay distribution in the decay of on-shell and off-shell polarized (W, Z) gauge bosons into massive quark pairs. In particular for the off-shell decays in it is important to keep the masses of the charm and bottom quarks at their finite values since the scale of the problem is not set by m2 W,Z but by the offshellness of the gauge boson which varies in the range (m 1 + m 2)2 ≤ q 2 ≤ (m H − m W,Z )2.
[en] The simplest extension of the supersymmetric standard model--the addition of one singlet superfield--can have a profound impact on the Higgs and its decays. We perform a general operator analysis of this scenario, focusing on the phenomenologically distinct scenarios that can arise, and not restricting the scope to the narrow framework of the NMSSM. We reexamine decays to four b quarks and four τ's, finding that they are still generally viable, but at the edge of LEP limits. We find a broad set of Higgs decay modes, some new, including those with four gluon final states, as well as more general six and eight parton final states. We find the phenomenology of these scenarios is dramatically impacted by operators typically ignored, specifically those arising from D-terms in the hidden sector, and those arising from weak-scale colored fields. In addition to sensitivity of mz, there are potential tunings of other aspects of the spectrum. In spite of this, these models can be very natural, with light stops and a Higgs as light as 82 GeV. These scenarios motivate further analyses of LEP data as well as studies of the detection capabilities of future colliders to the new decay channels presented
[en] We begin to analyze and contrast the predictions for the decay b → sl+l- in the Left-Right Symmetric Model (LMR) with those of the Standard Model (SM). In particular, we show that the forward-backward asymmetry of the lepton spectrum can be used to distinguish the SM from the simplest manifestation of the LRM