arXiv subjects

D. London

Publications and source records attributed to D. London.

At least 19 recordsLinked to original sources

arXiv2013

Implications of LHCb measurements and future prospects

During 2011 the LHCb experiment at CERN collected 1.0 fb-1 of sqrt{s} = 7 TeV pp collisions. Due to the large heavy quark production cross-sections, these data provide unprecedented samples of heavy flavoured hadrons. The first results from LHCb have made a significant impact on the flavour physics landscape and have definitively proved the concept of a dedicated experiment in the forward region at a hadron collider. This document discusses the implications of these first measurements on classes of extensions to the Standard Model, bearing in mind the interplay with the results of searches for on-shell production of new particles at ATLAS and CMS. The physics potential of an upgrade to the LHCb detector, which would allow an order of magnitude more data to be collected, is emphasised.

hep-ex↗

arXiv2005

The Discovery Potential of a Super B Factory

The Proceedings of the 2003 SLAC Workshops on flavor physics with a high luminosity asymmetric e+e- collider. The sensitivity of flavor physics to physics beyond the Standard Model is addressed in detail, in the context of the improvement of experimental measurements and theoretical calculations.

hep-ph↗

arXiv2004

Probing New Physics via an Angular Analysis of 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. Unlike direct CP asymmetries, 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 on their effect on the measurement of the phase of B0--Bbar0 mixing.

hep-ph↗

arXiv2002

New Physics in B -> J/Psi K^*

Direct CP violation in B -> J/Psi K is a clean test for new physics. However, the direct CP asymmetry will vanish if the new-physics amplitude has the same strong phase as the standard-model amplitude. We show that this type of new physics can still be detected via an angular analysis of the sister decay mode B -> J/Psi K^*. Time-dependent measurements and tagging are not necessary. Should new physics be found, this angular analysis can be used to obtain information about the size of the new-physics parameters.

hep-ph↗

arXiv2001

Extracting Weak Phase Information from B -> V_1 V_2 Decays

We describe a new method for extracting weak, CP-violating phase information, with no hadronic uncertainties, from an angular analysis of B -> V_1 V_2 decays, where V_1 and V_2 are vector mesons. The quantity $\sin^2 (2 \phi_1 + \phi_3)$ (\phi_1=\beta and \phi_3=\gamma) can be cleanly obtained from the study of decays such as B_d^0(t) -> D^{*\pm} \rho^\mp, D^{*\pm} a_1^{\mp}, D^{*0} K^{*0}, etc. Similarly, one can use B_s^0(t) -> D_s^{*\pm} K^{*\mp} or even B\pm -> D^{*0}K^*\pm to extract $\sin^2 \phi_3$. There are no penguin contributions to these decays. It is possible that $\sin^2 (2\phi_1 + \phi_3)$ will be the second function of CP phases, after $\sin 2\phi_1$, to be measured at B-factories.

hep-ph↗

arXiv2001

Searching for New Physics via CP Violation in B -> pi pi

We show how B -> pi pi decays can be used to search for new physics in the b -> d flavour-changing neutral current. One needs one piece of theoretical input, which we take to be a prediction for P/T, the ratio of the penguin and tree amplitudes in Bd -> pi+ pi-. If present, new physics can be detected over most of the parameter space. If α(ϕ_2) can be obtained independently, measurements of B+ -> pi+ pi0 and Bd/Bd(bar) -> pi0 pi0 are not even needed.

hep-ph↗

arXiv2000

What if the Mass Difference $ΔM_s$ is around 18 Inverse Picoseconds?

Present experiments in pursuit of the mass difference in the Bs-Bs(bar) system have put a lower bound on this quantity of $ΔM_s > 14.9 ps^{-1}$ (at 95% C.L.). The same experiments also yield a local minimum in the log-likelihood function around $ΔM_s = 17.7 ps^{-1}$, which is $2.5σ$ away from being zero. Motivated by these observations, we investigate the consequences of a possible measurement of $ΔM_s = 17.7 \pm 1.4 ps^{-1}$, in the context of both the standard model and supersymmetric models with minimal flavor violation. We perform a fit of the quark mixing parameters in these theories and estimate the expected ranges of the CP asymmetries in B decays, characterized by $α$, $β$ and $γ$, the interior angles of the CKM-unitarity triangle. Based on this study, we argue that, if indeed $ΔM_s$ turns out to be in its currently-favored range, this would disfavor a large class of supersymmetric models. Indeed, of all the models examined here, the best fit to the data occurs for the standard model.

hep-ph↗

arXiv2000

Supersymmetric Large Extra Dimensions Are Small and/or Numerous

Recently, a scenario has been proposed in which the gravitational scale could be as low as the TeV scale, and extra dimensions could be large and detectable at the electroweak scale. Although supersymmetry is not a requirement of this scenario, it is nevertheless true that its best-motivated realizations arise in supersymmetric theories (like M theory). We argue here that supersymmetry can have robust, and in some instances fatal, implications for the expected experimental signature for TeV-scale gravity. The signature of the supersymmetric version of the scenario differs most dramatically from what has been considered in the literature because mass splittings within the gravity supermultiplet in these models are extremely small, implying in particular the existence of a very light spin-one superpartner for the graviton. We compute the implications of this graviphoton, and show that it can acquire dimension-four couplings to ordinary matter which can strongly conflict with supernova bounds.

hep-ph↗

arXiv2000

Searching for New Physics via CP Violation in B -> pi pi

It is well known that one can use B -> pi pi decays to probe the CP-violating phase α. In this paper we show that these same decays can be used to search for new physics. This is done by comparing two weak phases which are equal in the standard model: the phase of the t-quark contribution to the b -> d penguin amplitude, and the phase of Bd-Bd(bar) mixing. In order to make such a comparison, we require one piece of theoretical input, which we take to be a prediction for |P/T|, the relative size of the penguin and tree contributions to Bd -> pi^+ pi^-. If independent knowledge of αis available, the decay Bd(t) -> pi^+ pi^- alone can be used to search for new physics. If a full isospin analysis can be done, then new physics can be found solely through measurements of B -> pi pi decays. The most promising scenario occurs when the isospin analysis can be combined with independent knowledge of α. In all cases, the prospects for detecting new physics in B -> pi pi decays can be greatly improved with the help of additional measurements which will remove discrete ambiguities.

hep-ph↗

arXiv2000

Supersymmetric Effects on Isospin Symmetry Breaking and Direct CP Violation in $B \to ργ$

We argue that one can search for physics beyond the standard model through measurements of the isospin-violating quantity $Δ^{-0} \equiv Γ(B^- \to ρ^- γ)/2Γ(B^0 \to ρ^0 γ)-1$, its charge conjugate $Δ^{+0}$, and direct CP violation in the partial decay rates of $B^\pm \to ρ^\pm γ$. We illustrate this by working out theoretical profiles of the charge-conjugate averaged ratio $Δ\equiv {1 \over 2}(Δ^{+0} +Δ^{-0})$ and the CP asymmetry $A_{CP}(B^\pm \to ρ^\pm γ)$ in the standard model and in some variants of the minimal supersymmetric standard model. We find that chargino contributions in the large $\tan β$ region may modify the magnitudes and flip the signs of $Δ$ and $A_{CP}(B^\pm \to ρ^\pm γ)$ compared to their standard-model values, providing an unmistakeable signature of supersymmetry.

hep-ph↗

arXiv2000

T-Odd Triple-Product Correlations in Hadronic b Decays

We study T-violating triple-product asymmetries in the quark-level decay b -> s u u(bar) within the standard model (SM). We find that only two types of triple products are non-negligible. The asymmetry in p_u . [s_u x s_u(bar)] or p_u(bar) . [s_u x s_u(bar)] can be as large as about 5%. It can be probed in B -> V_1 V_2 decays, where V_1 and V_2 are vector mesons. And the asymmetry in s_b . [p_u x p_s] can be in the range 1%--3%. One can search for this signal in the decay Λ_b -> Λπ^+ π^- or in B^* -> X_s X, where X_s and X then each decay into two mesons. All other triple-product asymmetries are expected to be small within the SM. This gives us new methods of searching for new physics.

hep-ph↗

arXiv2000

Is it possible to Measure the Weak Phase of a Penguin Diagram?

The $b\to d$ penguin amplitude receives contributions from internal $u$, $c$ and $t$-quarks. We show that it is impossible to measure the weak phase of any of these penguin contributions without theoretical input. However, a single assumption involving the hadronic parameters makes it possible to obtain the weak phase and test for the presence of new physics in the $b\to d$ flavour-changing neutral current.

hep-ph↗

arXiv2000

B-Decay CP Asymmetries, Discrete Ambiguities and New Physics

The first measurements of CP violation in the $B$ system will likely probe $\sin 2α$, $\sin 2β$ and $\cos 2γ$. Assuming that the CP angles $α$, $β$ and $γ$ are the interior angles of the unitarity triangle, these measurements determine the angle set $(α,β,γ)$ except for a twofold discrete ambiguity. If one allows for the possibility of new physics, the presence of this discrete ambiguity can make its discovery difficult: if only one of the two candidate solutions is consistent with constraints from other measurements in the $B$ and $K$ systems, one is not sure whether new physics is present or not. We review the methods used to resolve the discrete ambiguity and show that, even in the presence of new physics, they can usually be used to uncover this new physics. There are some exceptions, which we describe in detail. We systematically scan the parameter space and present examples of values of $(α,β,γ)$ and the new-physics parameters which correspond to all possibilities. Finally, we show that if one relaxes the assumption that the bag parameters $\BBd$ and $\BK$ are positive, one can no longer definitively establish the presence of new physics.

hep-ph↗

arXiv1999

Exploring CP Violation with B_d -> D K_s Decays

We (re)examine CP violation in the decays B_d -> D K_s, where D represents D^0, D(bar), or one of their excited states. The quantity $\sin^2(2β+ γ)$ can be extracted from the time-dependent rates for $B_d(t) -> {\bar D}^{**0} K_s$ and $B_d(t) -> D^{**0} K_s$, where the $D^{**0}$ decays to $D^{(*)+}π^-$. If one considers a non-CP-eigenstate hadronic final state to which both D(bar) and D^0 can decay (e.g. $K^+π^-$), then one can obtain two of the angles of the unitarity triangle from measurements of the time-dependent rates for $B_d(t) -> (K^+π^-)_{D K_s}$ and $B_d(t) -> (K^-π^+)_{D K_s}$. There are no penguin contributions to these decays, so all measurements are theoretically clean.

hep-ph↗

arXiv1999

Inverse neutrinoless double beta decay (and other Delta L=2 processes)

I review the prospects for the detection of Delta L=2 processes at future colliders. Except in contrived models, the process e- e- -> W- W- is unobservable at future linear colliders unless $\sqrt{s} \gsim 2$ TeV, due to constraints from neutrinoless double beta decay. As there are no analogous constraints on the Majorana mass of the $ν_μ$, mu- mu- -> W- W- could be observed at a muon collider with considerably lower $\sqrt{s}$. One can also consider esoteric processes such as gamma gamma -> mu+ mu+ W- W-. Such processes may be observable if $\sqrt{s} \gsim 4$ TeV.

hep-ph↗

arXiv1999

Looking for New Physics in Bd-Bd(bar) Mixing

There are variety of methods which directly test for the presence of new physics in the b -> s flavour-changing neutral current (FCNC), but none which cleanly probe new physics in the b -> d FCNC. One possible idea is to compare the weak phase of the t-quark contribution to the b -> d penguin, which is $-β$ in the SM, with that of Bd-Bd(bar) mixing ($-2β$ in the SM). In this talk I show that, in fact, it is impossible to measure the weak phase of the t-quark penguin, or indeed any penguin contribution, without theoretical input. However, if one makes a single assumption involving the hadronic parameters, it is possible to obtain the weak phase. I discuss how one can apply such an assumption to the time-dependent decays $Bd(t) -> K0 K0(bar)$ and $Bs(t) -> ϕK_s$ in order to detect new physics in the b -> d FCNC.

hep-ph↗

arXiv1999

Searching for New Physics in the b->d FCNC using B_s^0(t)->ϕK_s and B_d^0(t)->K^0\bar{K}^0

Time-dependent measurements of the decays B_s^0(t)-->ϕK_s and B_d^0(t) --> K^0 \bar{K}^0 can be used to compare the weak phases of B_d^0-\bar{B}_d^0 mixing and the t-quark contribution to the b->d penguin. Since these two phases are equal in the standard model, any discrepancy would be a sign of new physics, specifically in the b->d flavour-changing neutral current (FCNC). The method can be applied to other pairs of decays, such as B_s^0(t)--> J/ΨK_s and B_d^0(t)--> J/Ψπ^0.

hep-ph↗

arXiv1999

Can One Measure the Weak Phase of a Penguin Diagram?

The b -> d penguin amplitude receives contributions from internal u, c and t-quarks. We show that it is impossible to measure the weak phase of any of these penguin contributions without theoretical input. However, it is possible to obtain the weak phase if one makes a single assumption involving the hadronic parameters. With such an assumption, one can test for the presence of new physics in the b -> d flavour-changing neutral current by comparing the weak phase of B_d^0-{\bar B}_d^0 mixing with that of the t-quark contribution to the b -> d penguin.

hep-ph↗