21,544 research outputs found
CP violation and CKM phases from angular distributions for decays into admixtures of CP eigenstates
We investigate the time-evolutions of angular distributions for decays
into final states that are admixtures of CP-even and CP-odd configurations. A
sizable lifetime difference between the mass eigenstates allows a probe
of CP violation in time-dependent untagged angular distributions. Interference
effects between different final state configurations of , determine the Wolfenstein parameter from
untagged data samples, or -- if one uses as an additional
input -- the notoriously difficult to measure CKM angle . Another
determination of is possible by using isospin symmetry of strong
interactions to relate untagged data samples of
and . We note that the untagged angular
distribution for provides interesting information about
electroweak penguins.Comment: 19 pages, LaTeX, no figure
Observing Direct CP Violation in Untagged B-Meson Decays
Direct CP violation can exist in untagged B-meson decays to self-conjugate,
three-particle final states; it would be realized as a population asymmetry in
the untagged decay rate across the mirror line of the Dalitz plot of the
three-body decay. We explore the numerical size of this direct CP-violating
effect in a variety of B-meson decays to three pseudoscalar mesons; we show
that the resulting asymmetry is comparable to the partial rate asymmetry in the
analogous tagged decays, making the search for direct CP violation in the
untagged decay rate, for which greater statistics accrue, advantageous.Comment: 31 pages, REVTeX4, 1 eps figure, references added, typos corrected,
version to appear in PR
Using untagged B^0 -> D K_S to determine gamma
It is shown that the weak phase gamma=arg(-V_{ud}V^*_{ub}V_{cb}V_{cd}^*) can
be determined using only untagged decays B/Bbar--> D K_S. In order to reduce
the uncertainty in gamma, we suggest combining information from B^{+-}-->
DK^{+-} and from untagged B^0 decays, where the D meson is observed in common
decay modes. Theoretical assumptions, which may further reduce the statistical
error, are also discussed.Comment: 18 pages, same as published versio
In Pursuit of New Physics with B_s Decays
The presence of a sizeable CP-violating phase in B_s^0-B_s^0-bar mixing would
be an unambiguous signal of physics beyond the Standard Model. We analyse
various possibilities to detect such a new phase considering both tagged and
untagged decays. The effects of a sizeable width difference Delta Gamma between
the B_s mass eigenstates, on which the untagged analyses rely, are included in
all formulae. A novel method to find this phase from simple measurements of
lifetimes and branching ratios in untagged decays is proposed. This method does
not involve two-exponential fits, which require much larger statistics. For the
tagged decays, an outstanding role is played by the observables of the
time-dependent angular distribution of the B_s -> J/psi [-> l^+ l^-] \phi [->
K^+K^-] decay products. We list the formulae needed for the angular analysis in
the presence of both a new CP-violating phase and a sizeable Delta Gamma, and
propose methods to remove a remaining discrete ambiguity in the new phase. This
phase can therefore be determined in an unambiguous way.Comment: minor changes, lattice prediction of Delta Gamma updated, appears in
PR
Coherent Vector Meson Photoproduction with Nuclear Breakup in Relativistic Heavy Ion Collisions
Relativistic heavy ions are copious sources of virtual photons. The large
photon flux gives rise to a substantial photonuclear interaction probability at
impact parameters where no hadronic interactions can occur. Multiple
photonuclear interactions in a single collision are possible. In this letter,
we use mutual Coulomb excitation of both nuclei as a tag for moderate impact
parameter collisions. We calculate the cross section for coherent vector meson
production accompanied by mutual excitation, and show that the median impact
parameter is much smaller than for untagged production. The vector meson
rapidity and transverse momentum distribution are very different from untagged
exclusive vector meson production.Comment: 14 pages, including 4 figure
CP violation and the CKM angle from angular distributions of untagged decays governed by
We demonstrate that time-dependent studies of angular distributions for
decays caused by quark-level transitions extract
cleanly and model-independently the CKM angle . This CKM angle could be
cleanly determined from untagged decays alone, if the lifetime difference
between the mass eigenstates and is sizable. The
time-dependences for the relevant tagged and untagged observables are given
both in a general notation and in terms of linear polarization states and
should exhibit large CP-violating effects. These observables may furthermore
provide insights into the hadronization dynamics of the corresponding exclusive
decays thereby allowing tests of the factorization hypothesis.Comment: 14 pages, LaTeX, no figure
Direct CP Violation in Untagged B-Meson Decays
Direct CP violation can exist in untagged, neutral B-meson decays to certain
self-conjugate, hadronic final states. It can occur if the resonances which
appear therein permit the identification of distinct, CP-conjugate states -- in
analogy to stereochemistry, we term such states ``CP-enantiomers.'' These
states permit the construction of a CP-odd amplitude combination in the
untagged decay rate, which is non-zero if direct CP violation is present. The
decay B\to \pi^+\pi^-\pi^0, containing the distinct CP-conjugate states \rho^+
\pi^- and \rho^- \pi^+, provides one such example of a CP-enantiomeric pair. We
illustrate the possibilities in various multi-particle final states.Comment: 8 pages, ReVTeX 4.
Distinguishing Word Senses in Untagged Text
This paper describes an experimental comparison of three unsupervised
learning algorithms that distinguish the sense of an ambiguous word in untagged
text. The methods described in this paper, McQuitty's similarity analysis,
Ward's minimum-variance method, and the EM algorithm, assign each instance of
an ambiguous word to a known sense definition based solely on the values of
automatically identifiable features in text. These methods and feature sets are
found to be more successful in disambiguating nouns rather than adjectives or
verbs. Overall, the most accurate of these procedures is McQuitty's similarity
analysis in combination with a high dimensional feature set.Comment: 11 pages, latex, uses aclap.st
Finding predominant word senses in untagged text
In word sense disambiguation (WSD), the heuristic of choosing the most common sense is extremely powerful because the distribution of the senses of a word is often skewed. The problem with using the predominant, or first sense heuristic, aside from the fact that it does not take surrounding context into account, is that it assumes some quantity of handtagged data. Whilst there are a few hand-tagged corpora available for some languages, one would expect the frequency distribution of the senses of words, particularly topical words, to depend on the genre and domain of the text under consideration. We present work on the use of a thesaurus acquired from raw textual corpora and the WordNet similarity package to find predominant noun senses automatically. The acquired predominant senses give a precision of 64% on the nouns of the SENSEVAL- 2 English all-words task. This is a very promising result given that our method does not require any hand-tagged text, such as SemCor. Furthermore, we demonstrate that our method discovers appropriate predominant senses for words from two domainspecific corpora
Exploring Decays in the Presence of a Sizable Width Difference
The decays allow a theoretically clean
determination of , where is the -
mixing phase and the usual angle of the unitarity triangle. A sizable
decay width difference was recently established, which
leads to subtleties in analyses of the branching
ratios but also offers new "untagged" observables, which do not require a
distinction between initially present or mesons. We
clarify these effects and address recent measurements of the ratio of the
, branching ratios. In
anticipation of future LHCb analyses, we apply the SU(3) flavour symmetry of
strong interactions to convert the -factory data for , decays into predictions of the
observables, and discuss strategies for the
extraction of , with a special focus on untagged observables and
the resolution of discrete ambiguities. Using our theoretical predictions as a
guideline, we make simulations to estimate experimental sensitivities, and
extrapolate to the end of the planned LHCb upgrade. We find that the interplay
between the untagged observables, which are accessible thanks to the sizable
, and the mixing-induced CP asymmetries, which require tagging,
will play the key role for the experimental determination of .Comment: 21 pages, 7 figures, matches published versio
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