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Search for the Rare Decay B to pi l+l- in the BaBar Experiment

Description: The rare decay B {yields} {pi}{ell}{sup +}{ell}{sup -} is the simplest manifestation of a b {yields} d{ell}{sup +}{ell}{sup -} flavor-changing neutral current (FCNC) process. This type of process only proceeds through penguin loop or box diagrams and is sensitive to physics at the electroweak scale. It can be used to constrain parameters of the Standard Model and its extensions. B {yields} {pi}{ell}{sup +}{ell}{sup -} events have not yet been observed; the branching fraction is expected to be an order of magnitude smaller than the measured branching fraction for the similar B {yields} K{ell}{sup +}{ell}{sup -} decay. Using 230 million B{bar B} meson pairs collected with the BABAR detector, we have done a search for the rare decay B {yields} {pi}{ell}{sup +}{ell}{sup -}. The data was produced in e+e? collision at the {Upsilon}(4S) resonance in the PEP-II collider between 1999 and 2004. Four exclusive B-meson decay modes have been reconstructed: B{sup +} {yields} {pi}{sup +}{ell}{sup +}{ell}{sup -} and B{sup 0} {yields} {pi}{sup 0}{ell}{sup +}{ell}{sup -}, where {ell}{sup +}{ell}{sup -} is either an electron pair (e{sup +}e{sup -}) or a muon pair ({mu}{sup +}{mu}{sup -}). We find no evidence for a signal, and we obtain upper limits on the branching fractions {Beta}. Assuming the isospin relation {Beta}(B{sup +} {yields} {pi}{sup +}{ell}{sup +}{ell}{sup -}) 2 x {sup {tau}}B{sup +}/{sup {tau}}B{sup 0} {Beta}(B{sup 0} {yields} {pi}{sup 0}{ell}{sup +}{ell}{sup -}), we obtain an upper limit at 90% confidence level on the lepton-flavor-averaged branching fraction of B {yields} {pi}{ell}{sup +}{ell}{sup -} to be {Beta}(B {yields} {pi}e{mu}) < 9.2 x 10{sup -8} at 90% C.L. We have also reconstructed two control modes B{sup +} {yields} {pi}{sup +}e{sup {+-}}{mu}{sup {-+}} and B{sup 0} {yields} {pi}{sup 0}e{sup {+-}}{mu}{sup {-+}} and we also obtain an upper limit at 90% confidence level on the lepton-flavor-violating decay B {yields} {pi}e{mu} of {Beta}(B ...
Date: July 17, 2007
Creator: Ofte, Ingrid & U., /Bergen
Partner: UNT Libraries Government Documents Department

Results on Searches for New Physics at B Factories

Description: We summarize recent results on B{sup +} {yields} {tau}{sup +}{nu}{sub {tau}} setting constraints on the charged Higgs mass, discuss the CP puzzle in B {yields} K{pi} decays and present searches for a light neutral Higgs in radiative {Upsilon}(2S) and {Upsilon}(3S) decays. Rare decays are processes with branching fractions of {Omicron}(10{sup -4}) or smaller. Typically, they arise if amplitudes of higher-order processes (penguin loops, box diagrams) become dominant because tree amplitudes are suppressed in the Standard Model (SM). Additional suppression comes from small CKM couplings and helicity conservation. Contributions of New Physics (NP) processes may become significant modifying the prediction with respect to those in the SM. Thus, rare decays provide an interesting hunting ground for NP searches that are complementary to direct searches at the LHC.
Date: December 2, 2011
Creator: Eigen, Gerald & U., /Bergen
Partner: UNT Libraries Government Documents Department

B, D and K Decays

Description: The present report documents the results of Working Group 2: B, D and K decays, of the workshop on Flavor in the Era of the LHC, held at CERN from November 2005 through March 2007. With the advent of the LHC, we will be able to probe New Physics (NP) up to energy scales almost one order of magnitude larger than it has been possible with present accelerator facilities. While direct detection of new particles will be the main avenue to establish the presence of NP at the LHC, indirect searches will provide precious complementary information, since most probably it will not be possible to measure the full spectrum of new particles and their couplings through direct production. In particular, precision measurements and computations in the realm of flavor physics are expected to play a key role in constraining the unknown parameters of the Lagrangian of any NP model emerging from direct searches at the LHC. The aim of Working Group 2 was twofold: on one hand, to provide a coherent, up-to-date picture of the status of flavor physics before the start of the LHC; on the other hand, to initiate activities on the path towards integrating information on NP from high-p{sub T} and flavor data. This report is organized as follows. In Sec. 1, we give an overview of NP models, focusing on a few examples that have been discussed in some detail during the workshop, with a short description of the available computational tools for flavor observables in NP models. Sec. 2 contains a concise discussion of the main theoretical problem in flavor physics: the evaluation of the relevant hadronic matrix elements for weak decays. Sec. 3 contains a detailed discussion of NP effects in a set of flavor observables that we identified as 'benchmark channels' for NP ...
Date: March 7, 2008
Creator: Artuso, M.; Asner, D.M.; Ball, P.; Baracchini, E.; Bell, G.; Beneke, M. et al.
Partner: UNT Libraries Government Documents Department

A Measurement of the Semileptonic Branching Fraction of the B_s Meson

Description: We report a measurement of the inclusive semileptonic branching fraction of the B{sub s} meson using data collected with the BABAR detector in the center-of-mass energy region above the {gamma}(4S) resonance. We use the inclusive yield of {phi} mesons and the {phi} yield in association with a high-momentum lepton to perform a simultaneous measurement of the semileptonic branching fraction and the production rate of B{sub s} mesons relative to all B mesons as a function of center-of-mass energy. The inclusive semileptonic branching fraction of the B{sub s} meson is determined to be {Beta}(B{sub s} {yields} {ell}{nu}X) = 9.5{sub -2.0}{sup +2.5}(stat){sub -1.9}{sup +1.1}(syst)%, where {ell} indicates the average of e and {mu}.
Date: June 12, 2012
Creator: Lees, J.P.; Poireau, V.; Tisserand, V.; Garra Tico, J.; Grauges, E.; Martinelli, M. et al.
Partner: UNT Libraries Government Documents Department

SuperB Progress Report: Detector

Description: This report describes the present status of the detector design for SuperB. It is one of four separate progress reports that, taken collectively, describe progress made on the SuperB Project since the publication of the SuperB Conceptual Design Report in 2007 and the Proceedings of SuperB Workshop VI in Valencia in 2008.
Date: February 14, 2012
Creator: Grauges, E.; /Barcelona U., ECM; Donvito, G.; Spinoso, V.; /INFN, Bari /Bari U.; Manghisoni, M. et al.
Partner: UNT Libraries Government Documents Department

Observation of the Decay B- --> Ds(*) K- l- nubar

Description: We report the observation of the decay B{sup -} {yields} D{sub s}{sup (*)+} K{sup -}{ell}{sup -}{bar {nu}}{sub {ell}} based on 342 fb{sup -1} of data collected at the {Upsilon}(4S) resonance with the BABAR detector at the PEP-II e{sup +}e{sup -} storage rings at SLAC. A simultaneous fit to three D{sub s}{sup +} decay chains is performed to extract the signal yield from measurements of the squared missing mass in the B meson decay. We observe the decay B{sup -} {yields} D{sub s}{sup (*)+} K{sup -}{ell}{sup -}{bar {nu}}{sub {ell}} with a significance greater than five standard deviations (including systematic uncertainties) and measure its branching fraction to be {Beta}(B{sup -} {yields} D{sub s}{sup (*)+} K{sup -}{ell}{sup -}{bar {nu}}{sub {ell}}) = [6.13{sub -1.03}{sup +1.04}(stat.) {+-} 0.43(syst.) {+-} 0.51({Beta}(D{sub s}))] x 10{sup -4}, where the last error reflects the limited knowledge of the D{sub s} branching fractions.
Date: August 12, 2011
Creator: del Amo Sanchez, P.; Lees, J.P.; Poireau, V.; Prencipe, E.; Tisserand, V.; /Annecy, LAPP et al.
Partner: UNT Libraries Government Documents Department