Charmless and Penguin Decays at CDF Page: 3 of 7
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discriminating signature is needed to distinguish relevant events of b-physics. This is
provided by the characteristic long lifetime of b-hadrons: they are typically produced
with transverse momentum of a few GeV, thus flying about 0.5 mm in the detector
and resulting in secondary vertices displaced from the pp collision point. Triggering
on those vertices is challenging. First, it requires a high resolution tracking detector;
this is given by double-sided silicon microstrips arranged in five cylindrical layers and
an open cell drift chamber with 96 sense wires, all immersed in a 1.4 T solenoidal
magnetic field . Second, it needs to read out all the silicon detector (212 000 chan-
nels) and do pattern recognition and track fitting online. In CDF this is done by the
Silicon Vertex Trigger in 25 ps with a resolution of the track impact parameter (IP),
48 pm, comparable with off-line measurements . A sample enriched with b-flavor
particles is then provided by a specific three-level trigger, based on the requirement
of two displaced tracks (i. e., with IP larger than 0(120 pm)) with opposite charge.
3 B - ## Polarization
The B - ## decay proceeds through a b - sss quark level process, whose domi-
nant SM diagram is the b - s penguin. The rich dynamics of decay of pseudoscalar
meson in two vector particles involves three different amplitudes corresponding to the
polarization states. Hence, the B2 - # channel is attractive to test the theoretical
predictions for these polarization amplitudes , which have shown several discrepan-
cies with measurements of similar penguin decays , raising considerable attention
on the so-called "polarization puzzle".
The first evidence for the B2 - # decay has been reported by CDF in 2005 with
8 events in a data sample corresponding to integrated luminosity of 180 pb-' .
An updated analysis recently improved the measurement of branching fraction using
2.9 fb-r of data and allows the world's first decay polarization measurement .
We reconstruct the B2 - J/45 decay in the same dataset, and use this decay as a
normalization for the branching ratio measurement and as a control sample for the
Signal candidates are reconstructed by detecting - K+K- and J/y -* p+
decays and are formed by fitting four tracks to a common vertex. Combinatorial
background is reduced by exploiting several variables sensitive to the long lifetime
and relatively hard PT spectrum of B mesons. The requirements on the discriminat-
ing variables are optimized by maximizing S/ S + B, where the signal (S) is derived
from a Monte Carlo (MC) simulation and the background (B) is represented by ap-
propriately normalized data sampled from the sideband mass regions. Two sources of
background are expected for both B2 - # and B2 - J/4#: a dominant and smooth
combinatorial background and a physics component, which is given by B0 - OK*O
(B0 - J/PK*O) decays in the case of B - # (B J/4) and it is estimated
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Dorigo, Mirco & Collaboration, for the CDF. Charmless and Penguin Decays at CDF, article, December 1, 2010; Batavia, Illinois. (digital.library.unt.edu/ark:/67531/metadc840514/m1/3/: accessed October 15, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.