arXiv subjects

David London

Publications and source records attributed to David London.

At least 73 records · Page 4Linked to original sources

arXiv2013

Searching for New Physics with bbar -> sbar Bs -> V_1 V_2 Penguin Decays

We present the most general (six-helicity) angular analysis of Bs -> V_1 (-> P_1P'_1) V_2 (-> P_2P'_2) (V_i is a vector meson, and P_i, P'_i are pseudoscalars). We focus on final states accessible to both Bs and Bsbar -- these are mainly bbar -> sbar penguin decays. We also derive the most general decay amplitude, and discuss the differences between it and that used by LHCb in its analysis of Bs -> phi phi. In the standard model, all CP violation is predicted to be small, so that the simple measurement of a sizeable CP-violating observable indicates the presence of new physics. A full fit to the data is not necessary. By determining which of the CP-violating observables are nonzero, one can learn about the structure of the underlying NP. Finally, we apply the angular analysis to Bs -> K^{*0} Kbar^{*0}, and show that there are numerous CP-violating observables that remain in the untagged data sample.

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arXiv2013

New Physics in b -> s mu+ mu-: CP-Conserving Observables

We perform a comprehensive study of the impact of new-physics operators with different Lorentz structures on decays involving the b -> s mu+ mu- transition. We examine the effects of new vector-axial vector (VA), scalar-pseudoscalar (SP) and tensor (T) interactions on the differential branching ratios and forward-backward asymmetries (A_{FB}'s) of Bsbar -> mu+ mu-, Bdbar -> Xs mu+ mu-, Bsbar -> mu+ mu- gamma, Bdbar -> Kbar mu+ mu-, and Bdbar -> K* mu+ mu-, taking the new-physics couplings to be real. In Bdbar -> K* mu+ mu-, we further explore the polarization fraction f_L, the angular asymmetry A_T^{(2)}, and the longitudinal-transverse asymmetry A_{LT}. We identify the Lorentz structures that would significantly impact these observables, providing analytical arguments in terms of the contributions from the individual operators and their interference terms. In particular, we show that while the new VA operators can significantly enhance most of the asymmetries beyond the Standard Model predictions, the SP and T operators can do this only for A_{FB} in Bdbar -> Kbar mu+ mu-.

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arXiv2013

Reducing Penguin Pollution

The most common decay used for measuring 2beta_s, the phase of Bs-Bsbar mixing, is Bs -> J/psi phi. This decay is dominated by the colour-suppressed tree diagram, but there are other contributions due to gluonic and electroweak penguin diagrams. These are often referred to as "penguin pollution" (PP) because their inclusion in the amplitude leads to a theoretical error in the extraction of 2beta_s from the data. In the standard model (SM), it is estimated that the PP is negligible, but there is some uncertainty as to its exact size. Now, phi_s^{c\bar{c}s} (the measured value of 2beta_s) is small, in agreement with the SM, but still has significant experimental errors. When these are reduced, if one hopes to be able to see clear evidence of new physics (NP), it is crucial to have the theoretical error under control. In this paper, we show that, using a modification of the angular analysis currently used to measure phi_s^{c\bar{c}s} in Bs -> J/psi phi, one can reduce the theoretical error due to PP. Theoretical input is still required, but it is much more modest than entirely neglecting the PP. If phi_s^{c\bar{c}s} differs from the SM prediction, this points to NP in the mixing. There is also enough information to test for NP in the decay. This method can be applied to all Bs/Bsbar -> V1 V2 decays.

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arXiv2013

Shift in weak phase $γ$ due to CP asymmetries in $D$ decays to two pseudoscalar mesons

A difference of several tenths of a percent has been observed between the direct CP asymmetries of $D^0\to K^+K^-$ and $D^0\to π^+π^-$. It has been noted recently that CP asymmetries in such singly-Cabibbo-suppressed (SCS) decays can affect the determination of the weak phase $γ$ using the Gronau-London-Wyler method of comparing rates for $B^+ \to D K^+$ and $B^- \to D K^-$, where $D$ is a superposition of $D^0$ and $\od$ decaying to a CP eigenstate. Using an analysis of the CP asymmetries in SCS decays based on a $c \to u$ penguin amplitude with standard model weak phase but enhanced by CP-conserving strong interactions, we estimate typical shifts in $γ$ of several degrees and pinpoint measurements which would reduce uncertainties to an acceptable level.

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arXiv2012

Extracting Weak Phases Cleanly from Charmless 3-Body B Decays

In the past, it was believed that one cannot obtain clean weak-phase information from the measurement of CP-violating asymmetries in 3-body B decays. Recently it was shown that this is not true -- by expressing the decay amplitudes in terms of diagrams and using Dalitz plots, one can resolve all the difficulties and cleanly extract weak phases. In this talk I describe how this is done, and present preliminary results on the measurement of gamma using the decays B -> K pi pi and B -> K Kbar K.

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arXiv2012

Extraction of $γ$ from three-body B decays

The conventional use of two-body B decays to extract $γ$, although theoretically clean, is currently statistics-limited. On the other hand, a bulk of data on three-body B decays is available from $B$ factories. Applying the flavor-SU(3)-symmetric approach proposed in Ref.\ \cite{ReyLeLorier:2011ww} to \babar data, we find the highly promising result $γ= (81^{+4}_{-5} ({\rm avg.}) \pm 5 ({\rm std.\ dev.}))^\circ$. This establishes the use of three-body B decays as a viable alternative for the extraction of weak phases. In this preliminary analysis we have neglected several sources of uncertainties such as the effect of flavor-SU(3) breaking due to meson masses, and error correlations between input experimental parameters. A better understanding of these will improve the viability of this method.

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arXiv2012

Rescattering Contributions to rare B-Meson Decays

Several $B$ and $B_s$ decays have been observed which have been cited as evidence for exchange ($E$), penguin annihilation ($PA$) and annihilation ($A$) processes, such as $\bar b d \to \bar u u$, $\bar b s \to \bar u u$ and $\bar b u \to W^* \to \bar c s$, respectively. These amplitudes are normally thought to be suppressed, as they involve the spectator quark in the weak interaction and thus should be proportional to the $B$-meson decay constant $f_B$. However, as pointed out a number of years ago, they can also be generated by rescattering from processes whose amplitudes do not involve $f_B$, such as color-favored tree amplitudes. In this paper we investigate a number of processes such as $B^0 \to K^+ K^-$, $B_s \to π^+ π^-$, and $B^+ \to D_s^+ ϕ$, and identify promising states from which they can be generated by rescattering. We find that $E$ and $PA$-type processes are characterized respectively by amplitudes ranging from 5% to 10% and from 15% to 20% with respect to the largest amplitude from which they can rescatter. Based on this regularity, using approximate flavor SU(3) symmetry in some cases and time-reversal invariance in others, we predict the branching fractions for a large number of as-yet-unseen $B$ and $B_s$ decays in an extensive range from order $10^{-9}$ to $10^{-4}$.

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arXiv2012

B Physics: Theory Overview

This is an overview of B physics that can be done at the LHC with the purpose of searching for new physics.

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arXiv2012

New Physics in b -> s Transitions and the B_{d,s}^0 -> V_1 V_2 Angular Analysis

We suppose that there is new physics (NP) in b -> s transitions, and examine its effect on the angular distribution of B_q^0 -> V_1 V_2 (q=d,s), where V_{1,2} are vector mesons. We find that, in the presence of such NP, the formulae relating the parameters of the untagged, time-integrated angular distribution to certain observables (polarization fractions, CP-violating triple-product asymmetries, CP-conserving interference term) must be modified from their standard-model forms. This modification is due in part to a nonzero B^0_q-Bbar^0_q width difference, which is significant only for B^0_s decays. We re-analyze the B^0_s -> phi phi data to see the effect of these modifications. As (Delta Gamma_s/2)/Gamma_s ~ 10%, there are O(10%) changes in the derived observables. These are not large, but may be important given that one is looking for signals of NP. In addition, if the NP contributes to the b -> s decay, the measurement of the untagged time-dependent angular distribution provides enough information to extract all the NP parameters.

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arXiv2012

Measuring beta_s with Bs -> K0() K0bar() -- a Reappraisal

The Bs-Bsbar mixing phase, beta_s, can be extracted from Bs -> K0(*) K0bar(*), but there is a theoretical error if the second amplitude, Vub* Vus P'uc, is non-negligible. Ciuchini, Pierini and Silvestrini (CPS) have suggested measuring Puc in Bd -> K0(*) K0bar(*), and relating it to P'uc using SU(3). For their choice of the direct and indirect CP asymmetries in Bd -> K0(*) K0bar(*), they find that the error on beta_s is very small, even allowing for 100% SU(3) breaking. In this paper, we re-examine the CPS method, allowing for a large range of the Bd -> K0(*) K0bar(*) observables. We find that the theoretical error in the extraction of beta_s can be quite large, up to 18 degrees. This problem can be ameliorated if the value of SU(3) breaking were known, and we discuss different ways, both experimental and theoretical, of determining this quantity.

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arXiv2012

$B_s (\bar B_s)$ -> $D^0_{CP} K {\bar K}$: Detecting and Discriminating New Physics in $B_s$-$\bar B_s$ Mixing

If the weak phase of B_s-anti B_s mixing (2 beta_s) is found to be significantly different from zero, this is a clear signal of new physics (NP). However, if such a signal is found, we would like an unambiguous determination of 2 beta_s in order to ascertain which NP models could be responsible. In addition, in the presence of NP, the width difference ΔΓ_s between the two B_s mass eigenstates can be positive or negative, and ideally this sign ambiguity should be resolved experimentally. Finally, in order to see if the NP is contributing to Γ^s_{12} in addition to M^s_{12}, the precise measurement of |Γ^s_{12}| is crucial. In this paper, we consider several different methods of measuring B_s-anti B_s mixing using two- and three-body decays with ${\bar b} \to {\bar c} u {\bar s}$ and ${\bar b} \to {\bar u} c {\bar s}$ transitions. We find that the most promising of these is a time-dependent Dalitz-plot analysis of $B_s (\bar B_s) \to D^0_{CP} K {\bar K}$. With these decays, all of the above issues can be addressed, and the measurement of the weak phase gamma is also possible. We also note that, with all three-body decays it is possible to resolve the sign ambiguity of ΔΓ_s even without determining the CP phase phi_s.

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arXiv2012

Measuring gamma with B -> K pi pi and B -> K K Kbar Decays

We present a method for cleanly extracting the CP phase gamma from the Dalitz plots of B+ -> K+ pi+ pi-, Bd -> K+ pi0 pi-, Bd -> K0 pi+ pi-, Bd -> K+ K0 K-, and Bd -> K0 K0 Kbar0. The B -> K pi pi and B -> K K Kbar decays are related by flavor SU(3) symmetry, but SU(3) breaking is taken into account. Most of the experimental measurements have already been made -- what remains is a Dalitz-plot analysis of Bd -> K0 K0 Kbar0 (or Bd -> KS KS KS). We (very) roughly estimate the error on gamma to be ~25%. This is somewhat larger than the error in two-body decays, but it would be the first clean measurement of gamma in three-body decays. Furthermore, at the super-B factory, it is possible that gamma could be measured more precisely in three-body decays than in two-body decays.

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arXiv2011

New Physics in b -> s mu+ mu-: CP-Violating Observables

We perform a comprehensive study of the impact of new-physics operators with different Lorentz structures on CP-violating observables involving the b -> s mu+ mu- transition. We examine the effects of new vector-axial vector (VA), scalar-pseudoscalar (SP) and tensor (T) interactions on the CP asymmetries in the branching ratios and forward-backward asymmetries of Bs -> mu mu, B -> Xs mu mu, Bs -> mu mu gamma, B -> K mu mu, and B -> K* mu mu. In B -> K* mu mu, we also explore the direct CP asymmetries in the longitudinal polarization fraction f_L and the angular asymmetries A_T^{(2)} and A_{LT}, as well as the triple-product CP asymmetries A_T^{(im)} and A^{(im)}_{LT}. We find that, in almost all cases, the CP-violating observables are sensitive only to new physics which involves VA operators. The VA new physics may therefore be unambiguously identified by a combined analysis of future measurements of these CP-violating observables.

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arXiv2011

Using t -> b \bar{b} c to Search for New Physics

We consider new-physics (NP) contributions to the decay t -> b \bar{b} c. We parameterize the NP couplings by an effective Lagrangian consisting of 10 Lorentz structures. We show that the presence of NP can be detected through the measurement of the partial width. A partial identification of the NP can be achieved through the measurements of a forward-backward-like asymmetry, a top-quark-spin-dependent asymmetry, the partial rate asymmetry, and a triple-product asymmetry. These observables, which vanish in the standard model, can all take values in the 10-20% range in the presence of NP. Since |V_{tb}V_{cb}| \simeq |V_{ts} V_{cs}|, most of our results also hold, with small changes, for t -> s \bar{s} c.

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arXiv2011

SU(3) Breaking in Charmless B Decays

There are many charmless B decay pairs whose amplitudes are related by U spin (d <--> s) or flavor SU(3). The theoretical uncertainty in any analysis involving such pairs must take into account U-spin/SU(3) breaking. In the past, such considerations generally used theoretical input, but we show that this can be experimentally measured. We present lists of two- and three-body decay pairs from which the size of the breaking can be obtained. We detail the values of U-spin/SU(3) breaking given by the present experimental data. One pair -- Bd -> pi+ pi- and Bd -> pi- K+ -- exhibits large nonfactorizable breaking. We present other signals of SU(3) breaking in two- and three-body decays, and discuss further tests for nonfactorizable effects. Finally, we also point out that the pure-penguin decay Bs -> Kbar0 Kbar0 K0 is intriguing because it can be used to cleanly probe the Bs-Bsbar mixing phase.

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arXiv2011

Diagrammatic Analysis of Charmless Three-Body B Decays

We express the amplitudes for charmless three-body B decays in terms of diagrams. In addition, we show how to use Dalitz-plot analyses to obtain decay amplitudes which are symmetric or antisymmetric under the exchange of two of the final-state particles. When annihilation-type diagrams are neglected, as in two-body decays, many of the exact, purely isospin-based results are modified, leading to new tests of the standard model (SM). Some of the tests can be performed now, and we find that present data agree with the predictions of the SM. Furthermore, contrary to what was thought previously, it is possible to cleanly extract weak-phase information from three-body decays, and we discuss methods for B -> K pi pi, K K Kbar, K Kbar pi and pi pi pi.

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arXiv2011

Measuring gamma in B -> K pi pi Decays

We re-examine the question of measuring the weak phase gamma in B -> K pi pi decays. To this end, we express all B -> K pi pi amplitudes in terms of diagrams. We show that, as in B -> K pi, there exist relations between certain tree and electroweak-penguin diagrams. The imposition of these relations allows the extraction of gamma from measurements of the B -> K pi pi observables. We estimate the theoretical error in this method to be O(5%).

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arXiv2011

Searching for New Physics with B-Decay Fake Triple Products

In pure-penguin bbar -> sbar B -> V_1 V_2 decays (V_{1,2} are vector mesons), fT/fL ~= 1 has been observed (fT (fL) is the polarization fraction of transverse (longitudinal) decays). Explanations of this unexpectedly large result have been given within the standard model (SM) and with new physics (NP). In this paper, we show that these two explanations can be partially distinguished through the triple products (TP's) in these transitions. In particular, the SM predicts one of the two fake, CP-conserving TP's to be small (|A_T^{(2)}| <= 9%), while NP often gives larger values for |A_T^{(2)}|. We discuss the implications of the measurements of both fake TP's in B -> phi K* -- the present data prefer a SM explanation of fT/fL -- and provide the SM predictions for Bs -> phi phi.

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