20,958 research outputs found

    CP violation and CKM phases from angular distributions for BsB_s decays into admixtures of CP eigenstates

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    We investigate the time-evolutions of angular distributions for BsB_s decays into final states that are admixtures of CP-even and CP-odd configurations. A sizable lifetime difference between the BsB_s mass eigenstates allows a probe of CP violation in time-dependent untagged angular distributions. Interference effects between different final state configurations of BsDs+DsB_s\to D^{*+}_s D^{*-}_s, J/ψϕJ/\psi \phi determine the Wolfenstein parameter η\eta from untagged data samples, or -- if one uses Vub/Vcb|V_{ub}|/|V_{cb}| as an additional input -- the notoriously difficult to measure CKM angle γ\gamma. Another determination of γ\gamma is possible by using isospin symmetry of strong interactions to relate untagged data samples of BsK+KB_s\to K^{\ast+} K^{\ast-} and BsK0K0B_s\to K^{\ast0} \overline{K^{\ast0}}. We note that the untagged angular distribution for Bsρ0ϕB_s\to\rho^0 \phi provides interesting information about electroweak penguins.Comment: 19 pages, LaTeX, no figure

    Observing Direct CP Violation in Untagged B-Meson Decays

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    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

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    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

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    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

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    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 γ\gamma from angular distributions of untagged BsB_s decays governed by bˉcˉusˉ\bar b\to\bar c u\bar s

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    We demonstrate that time-dependent studies of angular distributions for BsB_s decays caused by bˉcˉusˉ\bar b\to\bar cu\bar s quark-level transitions extract cleanly and model-independently the CKM angle γ\gamma. This CKM angle could be cleanly determined from untagged BsB_s decays alone, if the lifetime difference between the BsB_s mass eigenstates BsLB_s^L and BsHB_s^H 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 BsB_s decays thereby allowing tests of the factorization hypothesis.Comment: 14 pages, LaTeX, no figure

    Direct CP Violation in Untagged B-Meson Decays

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    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

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    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

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    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 BsDs()±KB_s \to D_s^{(*)\pm} K^\mp Decays in the Presence of a Sizable Width Difference ΔΓs\Delta\Gamma_s

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    The BsDs()±KB_s \to D_s^{(*)\pm} K^\mp decays allow a theoretically clean determination of ϕs+γ\phi_s+\gamma, where ϕs\phi_s is the Bs0B^0_s-Bˉs0\bar B^0_s mixing phase and γ\gamma the usual angle of the unitarity triangle. A sizable BsB_s decay width difference ΔΓs\Delta\Gamma_s was recently established, which leads to subtleties in analyses of the BsDs()±KB_s \to D_s^{(*)\pm} K^\mp branching ratios but also offers new "untagged" observables, which do not require a distinction between initially present Bs0B^0_s or Bˉs0\bar B^0_s mesons. We clarify these effects and address recent measurements of the ratio of the BsDs±KB_s\to D_s^\pm K^\mp, BsDs±πB_s\to D_s^\pm\pi^\mp branching ratios. In anticipation of future LHCb analyses, we apply the SU(3) flavour symmetry of strong interactions to convert the BB-factory data for BdD()±πB_d\to D^{(*)\pm}\pi^\mp, BdDs±πB_d\to D_s^{\pm}\pi^\mp decays into predictions of the BsDs()±KB_s \to D_s^{(*)\pm} K^\mp observables, and discuss strategies for the extraction of ϕs+γ\phi_s+\gamma, 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 ΔΓs\Delta\Gamma_s, and the mixing-induced CP asymmetries, which require tagging, will play the key role for the experimental determination of ϕs+γ\phi_s+\gamma.Comment: 21 pages, 7 figures, matches published versio
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