Charmless and Penguin Decays at CDF Page: 2 of 7
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1 Introduction: the penguin role
Since the relevance of the penguin amplitudes was well established by the CLEO
experiment about ten years ago , penguin-dominated processes become more and
more attractive despite their theoretical complexity and experimental rareness. The
possibility to access to New Physics (NP) through new virtual particles in the loops
makes them an opportunity to be exploited rather than a limitation.
Non-leptonic two-body charmless decays of neutral B mesons, with their sen-
sitivity to penguin amplitudes, play a major role. They can be used to determine
the values of the CKM related quantities, which may differ from the ones extracted
from tree-level dominated processes, possibly indicating non-Standard Model contri-
butions. Comparison between <y determinations from charmed tree-dominated de-
cays and from charmless B0 -* h+h'- probes possible presence of NP in the pen-
guin amplitude. Similarly, comparison of the mixing phase between the tree-process
B- * J/45 and the penguin B2 0 0 charmless mode could allow to disentangle NP
contribution in mixing and decay.
Usually optimal sensitivity is obtained through a full tagged and time-dependent
analysis (as the case of B2 -* J/#b above). However, this requires significant statis-
tics of decays that are typically rare. Nevertheless, several strategies have been pro-
posed that do not require identification of production flavor and provide already some
sensitivity to NP contributions from measurements of averaged branching fractions,
polarization amplitudes and time-integrated CP-asymmetries.
The CDF experiment provides a joint access to large samples of B0 and B2 mesons,
which allows to study charmless decays into charged final-state particles. This has
been explored since the early 2000's with a pioneering and very rewarding program
(for instance [2, 3]); here, the latest measurements of the B2 0 0 decay and an
overview of the results of the B0) -* h+h'- analysis are reported, discussing finally
some prospects. All conjugate modes are implied and branching fractions are CP-
averages; for each result, the first uncertainty is statistical and the second one is the
2 Charmless B decays in hadron collisions
CDF is a multipurpose solenoidal spectrometer with calorimeters and muon detectors,
located at one of the two interaction points of the Tevatron collider. The good
performances of the Tevatron (peak luminosity ~ 4 x 1032 cm-2 s-1) and the high
data-taking efficiency allow to store on tape about 50 pb-' of data every week.
Despite the higher production rate of B mesons with respect to the B-factories
(0(103) more), the production cross section for a bb quarks pair at 1.96 TeV (the
Tevatron center of mass energy) is a permille fraction of the total. Thus, a highly-
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Dorigo, Mirco & Collaboration, for the CDF. Charmless and Penguin Decays at CDF, article, December 1, 2010; Batavia, Illinois. (https://digital.library.unt.edu/ark:/67531/metadc840514/m1/2/: accessed March 20, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.