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Title: A Search for the Rare Decay B->tau+tau- at the BaBar Experiment

Abstract

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.

Authors:
;
Publication Date:
Research Org.:
Stanford Linear Accelerator Center (SLAC)
Sponsoring Org.:
USDOE
OSTI Identifier:
877222
Report Number(s):
SLAC-R-805
TRN: US0700252
DOE Contract Number:
AC02-76SF00515
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
43 PARTICLE ACCELERATORS; B MESONS; BRANCHING RATIO; DECAY; FLUCTUATIONS; PHYSICS; RESONANCE; STANDARD MODEL; STANFORD LINEAR ACCELERATOR CENTER; Experiment-HEP,HEPEX

Citation Formats

Potter, Christopher Thomas, and /Oregon U. A Search for the Rare Decay B->tau+tau- at the BaBar Experiment. United States: N. p., 2006. Web. doi:10.2172/877222.
Potter, Christopher Thomas, & /Oregon U. A Search for the Rare Decay B->tau+tau- at the BaBar Experiment. United States. doi:10.2172/877222.
Potter, Christopher Thomas, and /Oregon U. Tue . "A Search for the Rare Decay B->tau+tau- at the BaBar Experiment". United States. doi:10.2172/877222. https://www.osti.gov/servlets/purl/877222.
@article{osti_877222,
title = {A Search for the Rare Decay B->tau+tau- at the BaBar Experiment},
author = {Potter, Christopher Thomas and /Oregon U.},
abstractNote = {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.},
doi = {10.2172/877222},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Tue Mar 07 00:00:00 EST 2006},
month = {Tue Mar 07 00:00:00 EST 2006}
}

Technical Report:

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  • We present a search for the decay B{sup -} {yields} {tau}{sup -} {bar {nu}}{sub {tau}} in a sample of 88.9 x 10{sup 6} B{bar B}pairs recorded with the BABAR detector at the SLAC B-Factory. One of the two B mesons from the {Upsilon}(4S) is reconstructed in a hadronic or a semileptonic final state and the decay products of the other B in the event are analyzed for consistency with a B{sup -} {yields} {tau}{sup -} {bar {nu}}{sub {tau}} decay. We find no evidence of a signal and set an upper limit on the branching fraction of {Beta}(B{sup -} {yields} {tau}{supmore » -} {bar {nu}}{sub {tau}}) < 4.2 x 10{sup -4} at the 90% confidence level.« less
  • We present the results of a search for the decay B{sup 0}{yields}{tau}{sup +}{tau}{sup -} in a data sample of (232{+-}3)x10{sup 6} {upsilon}(4S){yields}BB decays using the BABAR detector. Certain extensions of the standard model predict measurable levels of this otherwise rare decay. We reconstruct fully one neutral B meson and seek evidence for the signal decay in the rest of the event. We find no evidence for signal events and obtain B(B{sup 0}{yields}{tau}{sup +}{tau}{sup -})<4.1x10{sup -3} at the 90% confidence level.
  • The flavour changing neutral current (FCNC) process,more » $B^+$ → $K^+ τ^+ τ^-$ highly suppressed in the Standard Model (SM). This decay is forbidden at tree level and only occurs at lowest order via one-loop diagrams.$B^+$ → $K^+ τ^+ τ^-$ thus has the potential to provide a stringent test of the SM and a fertile ground for new physics searches. Contributions due to virtual particles in the loop allow one to probe, at relatively low energies, new physics at large mass scales. We search for the rare FCNC process $B^+$ → $K^+ τ^+ τ^-$ using data collected by the BaBaR detector at the SLAC National Accelerator Laboratory. The BaBaR data sample corresponds to a total integrated luminosity, at the energy of the Τ(4S) resonance, of 424.4 $fb^-1$ and 471 million $$B\bar{B}$$ pairs. For this search, hadronic $$B_{tag}$$ reconstruction is employed, where one B is exclusively reconstructed via one of many possible hadronic modes. The remaining decay products in an event are then attributed to the signal B, on which the search for $B^+$ → $K^+ τ^+ τ^-$ is performed. Each τ is required to decay leptonically, into either an electron or a muon and the lepton neutrinos. Furthermore, a multi-variate analysis technique (neural network) is used to select for signal events and suppress dominant background modes. No significant signal is observed. The resulting branching fraction is measured to be $$\beta(B^+$$ → $K^+ τ^+)$ = $$1.31^{0:66}_{-0:61}$$(stat.) $$^{+0:35}_{-0:25}$$(sys.) x 10$$^{-3}$$, which is consistent with zero at the 1.9σ level, with an upper limit of 2.25 x 10$$^{-3}$$, at the 90% confidence level.« less
  • We present the results of a search for the decay B{sup 0} {yields} {tau}{sup +}{tau}{sup -} in a data sample of (232 {+-} 3) x 10{sup 6} {Upsilon}(4S) {yields} B{bar B} decays using the BABAR detector. Certain extensions of the Standard Model predict measurable levels of this otherwise rare decay. We reconstruct fully one neutral B meson and seek evidence for the signal decay in the rest of the event. We find no evidence for signal events and obtain {Beta}(B{sup 0} {yields} {tau}{sup +}{tau}{sup -}) < 3.2 x 10{sup -3} at the 90% confidence level.
  • The rare decay B → πℓℓ - is the simplest manifestation of a b → dℓ +- 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 → πℓ +- 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 +- decay. Using 230 million Bmore » $$\bar{B}$$ meson pairs collected with the BABAR detector, we have done a search for the rare decay B →πℓ +- . 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 + → π ++- and B 0 → π 0+- , where ℓ + - is either an electron pair (e +e -) or a muon pair (μ +μ -). We find no evidence for a signal, and we obtain upper limits on the branching fractions β. Assuming the isospin relation β(B + → π ++- ) 2 x τB +/ τB 0 β(B 0 → π 0+-), we obtain an upper limit at 90% confidence level on the lepton-flavor-averaged branching fraction of B → πℓ +- to be β(B → πeμ) < 9.2 x 10 -8 at 90% C.L. We have also reconstructed two control modes B +→ π +e ±μ ± and B 0 → π 0e ±μ ± and we also obtain an upper limit at 90% confidence level on the lepton-flavor-violating decay B → πeμ of β(B → πeμ) < 9.2 x 10 -8 at 90% C.L. This is the first search for these rare decays at the current B-Factory experiments. This limit is an improvement by four orders of magnitude with respect to the previous experimental limit, and about a factor three above Standard Model predictions.« less