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t Fermilab
FERMILAB-CONF-05-621-E
Rare Decays at the Tevatron
Sin6ad M. Farrington (On behalf of the CDF and DO collaborations) a
aUniversity of Liverpool, Liverpool L69 7ZE, United Kingdom
The confidence level limits of the CDF and DO searches for the B , B0 -+ p+ - and B0 -+ p+p-0 rare decays
are presented.1. Introduction
In the quest to find new physics, two comple-
mentary methods are employed: direct searches,
for example searches for supersymmetric parti-
cles, and indirect searches, for example tests for
deviations from Standard Model predictions such
as branching ratios. Through both of these meth-
ods, limits may be set on new physics model pa-
rameters. The searches for the Bd, B - p+
and B0 -+ p+pg rare decays at the Tevatron
are strong indirect tests of the Standard Model.
2. Search for Bd, B - p+i-
In the Standard Model, the flavour chang-
ing neutral current decays B - p+ -- pro-
ceed through loop diagrams and are thus heav-
ily suppressed. The predicted branching ratio
of the B0 +p-- is (3.4 0.5) x 10-9 and
the Bd - +-- is further CKM suppressed to
(1.00 0.14) x 10-10 [1]. These branching ratios
are both below the sensitivity of the Tevatron ex-
periments, and so an observation of these decay
modes would be clear evidence of new physics,
independently of any model interpretation.
In new physics scenarios, the branching ratio of
B -+ p+p- could be enhanced by orders of mag-
nitude. For example, in the MSSM the branching
ratio is proportional to tan6 0. Alternatively, R-
parity violating SUSY would give rise to a tree
level diagram via a sneutrino which would in-
crease the branching ratio sufficiently for an ob-
servation at low tan, values. In mSUGRA, the
B -+ p+-- search complements direct trilepton
SUSY searches [2].
The experimental challenge of a search forB - p+p-- is the large combinatorial background
present in a hadron collider. The key elements of
the analysis are to determine the efficiencies for
observing these decays, to select discriminating
variables in order to reject background and to es-
timate the remaining background contribution.
The CDF and DO collaborations have searched
for B - p+ -- in 360pb-1 and 300pb-1 of data
respectively [3,4]. The CDF analysis searches for
opposite sign p pairs in the B and Bd mass win-
dows, while DO are limited by worse mass resolu-
tion and search for the B decay only and assume
Minimal Flavour Violation allowing B2 decays to
be neglected. Both analyses optimise the event
selection without using events in the signal region
in order to avoid introducing biases in the selec-
tion. The outcome of the search is designed to be
a branching ratio measurement or limit depend-
ing on whether a significant signal is observed.
C120 - DO Run II Preliminary
~100
(100 -B - J/y K
& 80 - = 906 35 22
60
40
20 .
8 5 5.2 5.4 5.6 5.8 6
Invariant mass (W * K ) [GeV/c2]
Figure 1. Invariant mass of control channel
(B+ -+ J/PK+) candidates.
The analysis procedure is to reconstruct the1
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Farrington, S.M. Rare decays at the Tevatron, article, January 1, 2006; Batavia, Illinois. (https://digital.library.unt.edu/ark:/67531/metadc884085/m1/1/: accessed April 26, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.