arXiv subjects

David London

Publications and source records attributed to David London.

At least 127 records · Page 7Linked to original sources

arXiv2004

Measuring New-Physics Parameters in B Penguin Decays

We examine new-physics (NP) effects in B decays with large b -> s penguin amplitudes. Decays involving b -> d penguins are assumed to be unaffected. We consider a model-independent parametrization of such NP. We argue that NP strong phases are negligible relative to those of the standard model. This allows us to describe the NP effects in terms of a small number of effective amplitudes A_NP^q (q=u,d,s,c) and corresponding weak phases Phi_q. We then consider pairs of neutral B decays which are related by flavour SU(3) in the standard model. One receives a large b -> s penguin component and has a NP contribution; the other has a b -> d penguin amplitude and is unaffected by NP. The time-dependent measurement of these two decays allows the {\it measurement} of the NP parameters A_NP^q and Phi_q. The knowledge of these parameters allows us to rule out many NP models and thus partially identify the new physics.

hep-ph↗

arXiv2004

CP Violation in B -> rho pi: New Physics Signals

A Dalitz-plot analysis of Bd(t) -> rho pi -> pi+ pi- pi0 decays allows one to obtain the CP-violating phase α. In addition, one can extract the various tree (T) and penguin (P) amplitudes contributing to these decays. By comparing the measured value of |P/T| with the theoretical prediction, one can detect the presence of physics beyond the standard model.

hep-ph↗

arXiv2004

Testing the Standard Model with Bs-> K^+ K^- Decays

In the limit of flavor SU(3) symmetry, the amplitudes for Bd->pi^+π^- and Bs-> K^+ K^- are related to one another. Taking the values of the weak phases beta and gamma from independent measurements, the ratio Rds=BR(Bs-> K^+K^-)/BR(Bd->pi^+ pi^-) and the two Bd->pi^+pi^- CP asymmetries Adir and Amix depend on only two quantities. By measuring these three observables, one can test for the presence of physics beyond the standard model. In this paper, using present data, and including theoretical uncertainties due to SU(3) breaking, we perform such an analysis. The experimental errors are still very large, but with improved measurements from Babar, Belle and CDF this will be a useful method to search for new physics.

hep-ph↗

arXiv2004

CP Violation in the B System: Measuring New-Physics Parameters

I review CP violation in the standard model (SM). I also describe the predictions for CP violation in the B system, along with signals for physics beyond the SM. I stress the numerous contributions of Pat O'Donnell to this subject. Finally, I discuss a new method for measuring new-physics parameters in B decays. This knowledge will allow us to partially identify any new physics which is found, before its direct production at high-energy colliders.

hep-ph↗

arXiv2004

Dynamical CP Violation in the Early Universe

Following earlier ideas of Dolgov, we show that the asymmetrical dynamical evolution of fields in the early Universe provides a new source for CP violation. This can lead to baryogenesis without any additional CP-violating interactions. The magnitude of this CP violation is time-dependent. In particular, it vanishes (or is very small) in the late Universe after the fields have relaxed (or are in their final approach) to their vacuum values. We provide an explicit example in which our mechanism is realized.

hep-ph↗

arXiv2004

Obtaining CKM Phase Information from B Penguin Decays

We discuss a method for extracting CP phases from pairs of B decays which are related by flavor SU(3). One decay (B0 -> M1 M2) receives a significant bbar -> dbar penguin contribution. The second (B' -> M1' M2') has a significant bbar -> sbar penguin contribution, but is dominated by a single amplitude. CP phase information is obtained using the fact that the B' -> M1' M2' amplitude is related by SU(3) to a piece of the B0 -> M1 M2 amplitude. The leading-order SU(3)-breaking effect (~25%) responsible for the main theoretical error can be removed. For some decay pairs, it can be written in terms of known decay constants. In other cases, it involves a ratio of form factors. However, this form-factor ratio can either be measured experimentally, or eliminated by considering a double ratio of amplitudes. In all cases, one is left only with a second-order effect, ~5%. We find twelve pairs of B decays to which this method can be applied. Depending on the decay pair, we estimate the total theoretical error in relating the B' -> M1' M2' and B0 -> M1 M2 amplitudes to be between 5% and 15%. The most promising decay pairs are Bd -> pi+ pi- and Bu+ -> K0 pi+, and Bd -> D+ D- and Bd -> Ds+ D- or Bu+ -> Ds+ D0bar.

hep-ph↗

arXiv2004

Bounds on New Physics from B -> V1 V2 Decays

We consider the possibility that physics beyond the standard model contributes to the decays B -> V1 V2, where V1 and V2 are vector mesons. We show that a time-dependent angular analysis of B -> V1 V2 decays provides many tests for this new physics (NP). Furthermore, although one cannot solve for the NP parameters, we show that this angular analysis allows one to put bounds on these parameters. This can be useful in estimating the scale of NP, and can tell us whether any NP found directly at future high-energy colliders can be responsible for effects seen in B -> V1 V2 decays.

hep-ph↗

arXiv2003

Extracting γfrom Bd(t) -> D()+ D()- and Bd -> Ds()+ D()- Decays

We show that the CP phase γcan be obtained from measurements of Bd(t) -> D(*)+ D(*)- and Bd -> Ds(*)+ D(*)-. These decays are related by flavor SU(3) in the limit where spectator-quark contributions are small. If the pseudoscalar-pseudoscalar decays Bd(t) -> D+ D- and Bd -> Ds+ D- are used, the leading-order SU(3)-breaking effect is f_Ds/f_D. The dependence on decay constants can be removed by using a double ratio involving two helicity states of the vector-vector decays Bd(t) -> D*+ D*- and Bd -> Ds*+ D*-. In this case the theoretical error arising from all sources is in the range 5-10%.

hep-ph↗

arXiv2003

Triple-Product Correlations in B -> V1 V2$ Decays and New Physics

In this paper we examine T-violating triple-product correlations (TP's) in B -> V1 V2 decays. TP's are excellent probes of physics beyond the standard model (SM) for two reasons: (i) within the SM, most TP's are expected to be tiny, and (ii) unlike direct CP asymmetries, TP's are not suppressed by the small strong phases which are expected in B decays. TP's are obtained via the angular analysis of B -> V1 V2. In a general analysis based on factorization, we demonstrate that the most promising decays for measuring TP's in the SM involve excited final-state vector mesons, and we provide estimates of such TP's. We find that there are only a handful of decays in which large TP's are possible, and the size of these TP's depends strongly on the size of nonfactorizable effects. We show that TP's which vanish in the SM can be very large in models with new physics. The measurement of a nonzero TP asymmetry in a decay where none is expected would specifically point to new physics involving large couplings to the right-handed b-quark.

hep-ph↗

arXiv2003

CP Violation Beyond the Standard Model

I review CP-violating signals of physics beyond the standard model in the B system. I examine the prospects for finding these effects at future colliders, with an emphasis on hadron machines.

hep-ph↗

arXiv2003

Obtaining the Full Unitarity Triangle from B -> pi K Decays

We present a method of obtaining the entire unitarity triangle from measurements of B -> pi K decay rates alone. Electroweak penguin amplitudes are included, and are related to tree operators. Discrete ambiguities are removed by comparing solutions with independent experimental data. The theoretical uncertainty in this method is rather small, in the range 5--10%.

hep-ph↗

arXiv2003

Signals of New Physics using angular analysis in B -> V1 V2 decays

We show that an angular analysis of B -> V1 V2 decays yields numerous tests for new physics in the decay amplitudes. Many of these new-physics observables are nonzero even if the strong phase differences vanish. For certain observables, neither time-dependent measurements nor tagging is necessary. Should a signal for new physics be found, one can place a lower limit on the size of the new-physics parameters, as well as bound its effect on the measurement of the B^0--Bbar^0 mixing phase.

hep-ph↗

arXiv2003

Determining weak phases using B->D^*V Decays

We describe how the angular analysis of vector-vector final states in B decays provides theoretically clean techniques for determination of CP violating phases. The quantity $\sin^2 (2β+ γ)$ can be cleanly obtained from the time dependent study of decays such as B_d(t)->D^{*\pm} ρ^\mp, D^{*\pm} a_1^{\mp} etc. Similarly, one can use B_s(t)-> D_s^{*\pm} K^{*\mp} to extract $\sin^2 γ$. A time independent study of the charged decay mode B^\pm-> D^{*0}(\bar D^{*0}) K^{*\pm} can also be used to extract gamma.

hep-ph↗

arXiv2003

T violation in $B \to V V$ Decays in the SM and Beyond

In this talk, we describe T-violating triple-product correlations (TP's) in $B \to V_1 V_2$ decays. We point out that TP's in the SM are generally tiny. It is only in a few decays with excited vector mesons in the final state that measurable TP's may be obtained. On the other hand, TP's in models beyond the SM can be large, and hence TP correlations are excellent probes of new physics.

hep-ph↗

arXiv2003

New Physics and B -> V1 V2 Decays

I discuss several techniques for observing new physics using measurements of B -> V1 V2 decays. Within the standard model, all CP-violating triple-product correlations (TP's) involving light vector mesons are expected be very small or to vanish. However, these TP's can be large in models with new physics (NP). If a time-dependent angular analysis of B -> V1 V2 can be performed, there are numerous additional tests for NP in the decay amplitudes. Should a signal for NP be found, one can place constraints on the NP parameters.

hep-ph↗

arXiv2002

Lepton Polarization and Forward-Backward Asymmetries in b -> s tau+ tau-

We study the spin polarizations of both tau leptons in the decay b -> s tau+ tau-. In addition to the polarization asymmetries involving a single tau, we construct asymmetries for the case where both polarizations are simultaneously measured. We also study forward-backward asymmetries with polarized tau's. We find that a large number of asymmetries are predicted to be large, >~ 10%. This permits the measurement of all Wilson coefficients and the b-quark mass, thus allowing the standard model (SM) to be exhaustively tested. Furthermore, there are many unique signals for the presence of new physics. For example, asymmetries involving triple-product correlations are predicted to be tiny within the SM, O(10^{-2}). Their observation would be a clear signal of new physics.

hep-ph↗

arXiv2002

New-Physics Effects on Triple-Product Correlations in Lambda_b Decays

We adopt an effective-lagrangian approach to compute the new-physics contributions to T-violating triple-product correlations in charmless Lambda_b decays. We use factorization and work to leading order in the heavy-quark expansion. We find that the standard-model (SM) predictions for such correlations can be significantly modified. For example, triple products which are expected to vanish in the SM can be enormous (~50%) in the presence of new physics. By measuring triple products in a variety of Lambda_b decays, one can diagnose which new-physics operators are or are not present. Our general results can be applied to any specific model of new physics by simply calculating which operators appear in that model.

hep-ph↗

arXiv2002

b Physics Beyond the Standard Model

I review the signals for New Physics in CP-violating measurements in B and Lambda_b decays. I also discuss ways of identifying this New Physics, should such a signal be found.

hep-ph↗