Study of the Rare Decay B --> Xs L L− at BaBar
Author : Ventzislav B. Koptchev
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Page : 368 pages
File Size : 47,47 MB
Release : 2004
Category : Beta decay
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Author : Ventzislav B. Koptchev
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Page : 368 pages
File Size : 47,47 MB
Release : 2004
Category : Beta decay
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Author : Daniel Anthony Bowerman
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Page : pages
File Size : 16,29 MB
Release : 2003
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Page : 167 pages
File Size : 30,51 MB
Release : 2006
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The rare decay B → ?ll- is the simplest manifestation of a b → dl+l- 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 → ?l+l- 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 → Kl+l- decay. Using 230 million B$ar{B}$ meson pairs collected with the BABAR detector, we have done a search for the rare decay B →?l+l- . The data was produced in e+e- collision at the Y(4S) resonance in the PEP-II collider between 1999 and 2004. Four exclusive B-meson decay modes have been reconstructed: B+ → ?+l+l- and B0 → ?0l+l- , where l+ l- is either an electron pair (e+e-) or a muon pair (?+?-). We find no evidence for a signal, and we obtain upper limits on the branching fractions ?. Assuming the isospin relation ?(B+ → ?+l+l- ) 2 x ?B+/?B0 ?(B0 → ?0l+l-), we obtain an upper limit at 90% confidence level on the lepton-flavor-averaged branching fraction of B → ?l+l- to be ?(B → ?e?) 9.2 x 10sup-8 /supat 90% C.L. We have also reconstructed two control modes Bsup+/sup→ ?sup+/supesup±/sup?sup±/sup and Bsup0/sup → ?sup0/supesup±/sup?sup±/sup and we also obtain an upper limit at 90% confidence level on the lepton-flavor-violating decay B → ?e? of ?(B → ?e?) 9.2 x 10
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Page : pages
File Size : 44,6 MB
Release : 2003
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Page : pages
File Size : 47,22 MB
Release : 2003
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The BABAR experiment operating at the PEP-II e[sup+]e[sup -] collider is designed to study CP violation effects in the B-meson system. From May 1999 to June 2002 approximately 81 fb[sup -1] of data have been collected at the[Upsilon](4S) resonance, containing (87.9[+-] 1.4) Million BB pairs. From this data sample the branching fraction for the decay B[sup 0][yields][pi][sup 0][pi][sup 0] has been extracted using a multi-dimensional maximum likelihood technique. With an efficiency of 20.4%, we find 36[sub -14-1][sup+15+1] B[sup 0][yields][pi][sup 0][pi][sup 0] events and measure the branching fraction to be[Beta](B[sup 0][yields][pi][sup 0][pi][sup 0])= (2.0[sub -0.8-0.2][sup+0.9+0.3]) x 10[sup -6] where the first error is statistical and the second systematic. The statistical significance is 3.1[sigma] and we report an upper limit of[Beta](B[sup 0][yields][pi][sup 0][pi][sup 0])
Author : Sheila McLachlin
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Page : pages
File Size : 28,97 MB
Release : 2004
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Page : 167 pages
File Size : 17,55 MB
Release : 2007
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Page : pages
File Size : 32,67 MB
Release : 2003
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The authors report on the evidence for the decays B[sup 0][yields] D[sub s][sup+][pi][sup -] and B[sup 0][yields] D[sub s][sup -] K[sup+] and the results of a search for the decays B[sup 0][yields] D*[sub s][sup+][pi][sup -] and B[sup 0][yields] D*[sub s][sup -] K[sup+] from a sample of 84 million[Upsilon](4S) decays into B meson pairs collected with the BaBar detector at the PEP II asymmetric-energy e[sup+]e[sup -] collider. The measured B[sup 0][yields] D[sub s][sup+][pi][sup -] yield has a probability of less than 10[sup -3] to be a fluctuation of the background and they measure the branching fraction[Beta](B[sup 0][yields] D[sub s][sup+][pi][sup -])= (3.2[+-] 0.9(stat.)[+-] 1.0 (syst.)) x 10[sup -5]. The measured B[sup 0][yields] D[sub s][sup -] K[sup+] yield has a probability of less than 5 x 10[sup -4] to be a fluctuation of the background and they measure the branching fraction[Beta](B[sup 0][yields] D[sub s][sup -] K[sup+])= (3.2[+-] 1.0(stat.)[+-] 1.0(syst.)) x 10[sup -5]. They also set 90% C.L. limits[Beta](B[sup 0][yields] D*[sub s][sup+][pi][sup -])
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Page : 7 pages
File Size : 42,6 MB
Release : 2003
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We present evidence for the flavor-changing neutral current decay B → K*ll− and a measurement of the branching fraction for the related process B → Kl+l−, where l+l− is either an e+e− or?+?− pair. These decays are highly suppressed in the Standard Model, and they are sensitive to contributions from new particles in the intermediate state. The data sample comprises 123 x 106?(4S) → B{bar B} decays collected with the BABAR detector at the PEP-II e+e− storage ring. Averaging over K* isospin and lepton flavor, we obtain the branching fractions?(B → Kl+l−) = (0.65{sub -0.13}{sup +0.14} ± 0.04) x 10−6?(B → K*l+l−) = (0.88{sub -0.29}{sup +0.33} ± 0.10) x 10−6, where the uncertainties are statistical and systematic, respectively. The significance of the B → Kl+l− signal is over 8?, while for B → K*l+l− it is 3.3?
Author : Christopher Thomas Potter
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Page : 223 pages
File Size : 24,46 MB
Release : 2006
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The Standard Model of particle physics predicts that the branching ratio for the rare decay B{sup 0} {yields} {tau}{sup +}{tau}{sup -} is 3.1 x 10{sup -8}, though untested models which could supersede it predict large enhancements. This dissertation describes the search for this rare decay in 210.4 fb{sup -1} of B{sup 0}{bar B}{sup 0} data collected at the {Upsilon}(4S) resonance in the Babar detector at the Stanford Linear Accelerator Center. In the analysis, one neutral B meson is fully reconstructed in a hadronic mode and recoil events which are consistent with each tau decaying in a mode {tau} {yields} {pi}{nu}, {rho}{nu}, or l{nu}{bar {nu}} are selected. There is no evidence for signal. The result is consistent with a downward fluctuation by 1.1 statistical standard deviations of the expected Standard Model background. Taking the expected background, the number of observed events and the expected statistical and systematic errors into account yields 2.7 x 10{sup -3} as the upper limit for B{sup 0} {yields} {tau}{sup +}{tau}{sup -} at the 90% confidence level.