arXiv subjects

David London

Publications and source records attributed to David London.

158 records · Page 9Linked to original sources

arXiv1994

An Update of the CKM Matrix

We update the constraints on the parameters of the quark flavour mixing matrix $V_{CKM}$ in the standard model using the latest experimental and theoretical results as input. We present the 95$\%$ C.L. allowed region of the unitarity triangle and the corresponding ranges for the ratio $\vert V_{td}/V_{ts} \vert$ and for the quantities $\sin 2α$, $\sin 2β$ and $\sin^2γ$, which characterize CP-violating rate asymmetries in $B$-decays. The SM prediction for the $\bs$-$\bsb$ mixing ratio $\xs$ is also presented.

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arXiv1994

Triangles, Triangles, Triangles: CP Violation in the B System and the Measurement of Strong and Weak Phases

We present the current wisdom regarding the measurement of the CP-violating phases of the CKM unitarity triangle in $B$-meson decays. After an introduction to the SM picture of CP violation, we review direct and indirect CP violation, the role of penguins and isospin analysis, and $B\to DK$ decays. We also discuss recent work on how to use SU(3) flavor symmetry, along with some dynamical approximations, to get at the CKM weak phases. Through time-independent $B$-decay measurements alone, we show that it is possible to extract all information: the weak phases, the incalculable strong phase shifts, and the sizes of the tree, color-suppressed, and penguin contributions to these decays.

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arXiv1994

CP Violation in the B System: What's Old, What's New?

I review the many ways of obtaining information about the CKM matrix through CP violation in the $B$ system. I include direct and indirect CP violation, the role of penguins and isospin analysis, tagging, and $B\to DK$ decays. I also discuss recent developments showing how to use $SU(3)$ flavor symmetry, along with some dynamical approximations, to extract from $B$ decays to $ππ$, $πK$ and $K\kbar$ the weak CKM phases, the strong phase shifts, and the sizes of the various contributing diagrams. Finally, I briefly show what can be learned from an exact treatment of the CKM matrix. (Talk given at the 5th Conference on the Intersections of Particle and Nuclear Physics, St. Petersburg, Florida, USA, May 31-June 6, 1994.)

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arXiv1994

Measuring Strong and Weak Phases in Time-Independent B Decays

Flavor SU(3) symmetry implies certain relations among $B$-decay amplitudes to $ππ$, $πK$ and $K {\bar K}$ final states, when annihilation-like diagrams are neglected. Using three triangle relations, we show how to measure the weak CKM phases $α$ and $γ$ using time-independent rate measurements only. In addition, one obtains all the strong final-state phases and the magnitudes of individual terms describing tree (spectator), color-suppressed and penguin diagrams. Many independent measurements of these quantities can be made with this method, which helps to eliminate possible discrete ambiguities and to estimate the size of SU(3)-breaking effects.

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arXiv1994

Decays of $B$ Mesons to Two Light Pseudoscalars

The decays $B \to PP$, where $P$ denotes a pseudoscalar meson, are analyzed, with emphasis on charmless final states. Numerous triangle relations for amplitudes hold within SU(3) symmetry, relating (for example) the decays $B^+ \to π^+ π^0,~ π^0 K^+$, and $π^+ K^0$. Such relations can improve the possibilities for early detection of $CP$-violating asymmetries. Within the context of a graphical analysis of decays, relations are analyzed among SU(3) amplitudes which hold if some graphs are neglected. One application is that measurements of the rates for the above three $B^+$ decays and their charge-conjugates can be used to determine a weak CKM phase. With measurements of the remaining rates for $B$ decays to $ππ,~πK$, and $K \bar K$, one can obtain two CKM phases and several differences of strong phase shifts.

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arXiv1994

Weak Coupling Phase from Decays of Charged B Mesons to $πK$ and $ππ$

The theory of $CP$ violation based on phases in weak couplings in the Cabibbo-Kobayashi-Maskawa (CKM) matrix requires the phase $γ\equiv {\rm Arg~} V^*_{ub}$ (in a standard convention) to be nonzero. A measurement of $γ$ is proposed based on charged $B$ meson decay rates to $π^+ K^0$, $π^0 K^+$, $π^+ π^0$, and the charge-conjugate states. The corresponding branching ratios are expected to be of the order of $10^{-5}$. (submitted to Physical Review Letters)

hep-ph↗

arXiv1993

B Decays in the Standard Model and Beyond

B decays in and beyond the standard model are reviewed. I specifically discuss right-handed B decays, rare B decays, B_c decays, B_s-B_s(bar) mixing, and T violation. (Plenary talk given at the `Workshop on B Physics at Hadron Accelerators', Snowmass, Colorado, June 21-July 2, 1993.)

hep-ph↗

arXiv1993

Bounding Anomalous Gauge-Boson Couplings

In this version we have corrected some minor errors in the tables, corrected typos, and added a reference. We have also updated our comparison with earlier workers. Figures are now included as uuencoded compressed tar files.

hep-ph↗

arXiv1993

Uses and Abuses of Effective Lagrangians

Motivated by past and recent analyses we critically re-examine the use of effective lagrangians in the literature to constrain new physics and to determine the `physics reach' of future experiments. We demonstrate that many calculations, such as those involving anomalous trilinear gauge-boson couplings, either considerably overestimate loop-induced effects, or give ambiguous answers. The source of these problems is the use of cutoffs to evaluate the size of such operators in loop diagrams. In contrast to other critics of these loop estimates, we prove that the inclusion of nonlinearly-realized gauge invariance into the low-energy lagrangian is irrelevant to this conclusion. We use an explicit example using known multi-Higgs physics above the weak scale to underline these points. We show how to draw conclusions regarding the nature of the unknown high-energy physics without making reference to low-energy cutoffs.

hep-ph↗

arXiv1993

Exotic Fermions

I review the current limits on the mixing of ordinary and exotic fermions.

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arXiv1993

Leptoquarks at $eγ$ Colliders

We consider single production of leptoquarks (LQ's) at $eγ$ colliders, for two values of the centre-of-mass energy, $\sqrt{s}=500$ GeV and 1 TeV. LQ's with masses essentially up to the kinematic limit can be seen, even for couplings as weak as $O(10^{-3})$-$O(10^{-2})α_{em}$. It is possible to detect LQ's of mass greater than $\sqrt{s}$ by looking for signals of virtual LQ production in $eγ\to e q{\overline q}$.

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arXiv1992

Loops, Cutoffs and Anomalous Gauge Boson Couplings

We discuss several issues regarding analyses which use loop calculations to put constraints on anomalous trilinear gauge boson couplings (TGC's). Many such analyses give far too stringent bounds. This is independent of questions of gauge invariance, contrary to the recent claims of de Rujula et. al., since the lagrangians used in these calculations ARE gauge invariant, but the SU(2)_L X U(1)_Y symmetry is nonlinearly realized. The real source of the problem is the incorrect use of cutoffs -- the cutoff dependence of a loop integral does not necessarily reflect the true dependence on the heavy physics scale M. If done carefully, one finds that the constraints on anomalous TGC's are much weaker. We also compare effective lagrangians in which SU(2)_L X U(1)_Y is realized linearly and nonlinearly, and discuss the role of custodial SU(2) in each formulation.

hep-ph↗

arXiv1992

Loop Calculations with Anomalous Gauge Boson Couplings

Analyses which use loop calculations to put constraints on anomalous trilinear gauge boson couplings (TGC's) often give bounds which are much too stringent. The reason has nothing to do with gauge invariance, in contrast to the recent claims of de Rujula et. al., since the lagrangians used in these calculations ARE gauge invariant, with the SU(2)L X U(1)Y symmetry nonlinearly realized. We trace the true cause of the problem to the improper interpretation of cutoffs in the calculation. The point is that the cutoff dependence of a loop integral does not necessarily reflect the true dependence on the heavy physics scale M. We illustrate that, if done carefully, one finds that the true constraints on anomalous TGC's are much weaker.

hep-ph↗

arXiv1992

Light Spin-One Particles Imply Gauge Invariance

Recently, calculations which consider the implications of anomalous trilinear gauge-boson couplings, both at tree-level and in loop-induced processes, have been criticized on the grounds that the lagrangians employed are not \gwk gauge invariant. We prove that, in fact, the general Lorentz-invariant and $U(1)_\em$ invariant but {\it not} $SU_L(2)\times U_Y(1)$ invariant action is equivalent to the general lagrangian in which $SU_L(2)\times U_Y(1)$ appears but is nonlinearly realized. We demonstrate this equivalence in an explicit calculation, and show how it is reconciled with loop calculations in which the different formulations can (superficially) appear to give different answers. In this sense any effective theory containing light spin-one particles is seen to be automatically gauge invariant.

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