A Search for the Rare Decay [B Meson to Two Photons]


Book Description

This thesis describes a search for the rare radiative decay of a B meson to two photons. where the charged congugate mode is implied throughout. These decays are highly suppressed in the Standard Model where the branching fraction is expected to be of order 10^-8. In some new physics scenarios this could be enhanced by up to an order of magnitude to 10^-7. Therefore an observation of a significant signal above the Standard Model prediction could be a sign of new physics. The search for this rare decay was performed using the data collected with the BaBar detector at the SLAC National Accelerator Laboratory PEP-II storage ring operating at the Upsilon(4S) resonance. The analysis uses a dataset with an integrated luminosity of 425.7 fb-1 corresponding to 467 million BB pairs. A signal yield of 21.3 +12.8 -11.8 events with a significance of 1.88 sigma was measured using an unbinned extended maximum likelihood fit. An upper limit on the branching fraction is set at the 90% confidence level of less than 3.2 times 10^-7. This is about two times more stringent than the best upper limit of less than 6.2 times 10^-7 published by the Belle collaboration.







A Search for the Rare Decay B° to D{sub S} Rho−


Book Description

The authors report on a search for the decay B° --> D{sub s}?− in a sample of 90 x 106?(4S) decays into B meson pairs collected between 1999 and 2001 with the BABAR detector at the PEP-II asymmetric-energy e+e− collider. No significant excess of signal events above the expected background is observed. The authors set a 90% C.L. limit on the branching fraction B(B° --> D{sub s}+?−) 1.9 x 10−5. Assuming a flavor SU(3) symmetry relation between the decays B° -- D{sub s}+?− and B° --> D+?−, they set a limit on the ratio of CKM-suppressed to CKM-favored amplitudes r(D?)




A Search for the Rare Decay B -] Pi Ll−


Book Description

This thesis presents a search for the rare B meson decay B -> pi ll− (l=e or mu) using 428 fb−1 of data collected at the Upsilon(4S) resonance by the BaBar detector at the PEP-II asymmetric energy ee− storage rings located located at SLAC National Accelerator Laboratory in Menlo Park, California. Four exclusive modes are studied: B+ -> pi+ e+e−, B+ -> pi+ mu+mu−, B0 -> pi0 e+e−, and B0 -> pi0 mu+mu−. Branching fraction upper limits at the 90% confidence level are presented for the exclusive modes B+ -> pi+ mu+mu− and B0 -> pi0 mu+mu−, and the combined mode B -> pi mu+mu−.




Search for the Rare Decay B {u2192} ?l+l- in the BaBar Experiment


Book Description

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







A Search for the Rare Decay B[sup 0] to D[sub S][sup +] Rho[sup -].


Book Description

The authors report on a search for the decay B[sup 0] --> D[sub s][sup +][rho][sup -] in a sample of 90 x 10[sup 6] [Upsilon](4S) decays into B meson pairs collected between 1999 and 2001 with the BABAR detector at the PEP-II asymmetric-energy e[sup +]e[sup -] collider. No significant excess of signal events above the expected background is observed. The authors set a 90% C.L. limit on the branching fraction B(B[sup 0] --> D[sub s][sup +][rho][sup -]) 1.9 x 10[sup -5]. Assuming a flavor SU(3) symmetry relation between the decays B[sup 0] -- D[sub s][sup +][rho][sup -] and B[sup 0] --> D[sup +][rho][sup -], they set a limit on the ratio of CKM-suppressed to CKM-favored amplitudes r(D[rho])




A Search for the Rare Decay $B\rightarrow\gamma\gamma$


Book Description

We report the result of a search for the rare decay B° 2![gamma][gamma] in 426 fb−1 of data, corresponding to 226 million B°{bar B}° pairs, collected on the [Upsilon](4S) resonance at the PEP-II asymmetric-energy ee− collider using the BABAR detector. We use a maximum likelihood fit to extract the signal yield and observe 2112{sup +13} signal events with a statistical signficance of 1.9 [sigma]. This corresponds to a branching fraction [Beta](B° 2![gamma][gamma]) = (1.7 ± 1.1(stat.) ± 0.2(syst.)) x 10−7. Based on this result, we set a 90% confidence level upper limit of [Beta](B° 2![gamma][gamma])




Search for the Rare Decay B to Pi L+ L-


Book Description

The authors have performed a search for the flavor-changing neutral-current decays B →?ll−, where l+l− is either e+e− or?+?−, using a sample of 230 million?(4S) → B{bar B} decays collected with the BABAR detector. They observe no evidence of a signal and measure the upper limit on the isospin-averaged branching fraction to be?(B →?l+l−)




The Search for the Rare Decay B to A0+pi0


Book Description

A search for the decay B{+-} {yields} a{sub 0}{sup {+-}}{pi}{sup 0} with the a{sub 0}{sup +} decaying to an {eta} and a {pi}{sup +} was carried out at the Stanford Linear Accelerator Center using the BABAR detector coupled with the PEP-II collider. The analysis used a data sample comprised of approximately 252 million B{bar B} pairs collected at the {Upsilon}(4S) resonance. No signal was observed and a 90% confidence level upper limit on the branching fraction was set at 1.32 x 10{sup -6}.