arXiv subjects
Publications and source records attributed to Tim Gershon.
Flavour will play a crucial role in understanding physics beyond the Standard Model. Progress in developing a future programme to investigate this central area of particle physics has recently passed a milestone, with the completion of the conceptual design report for SuperB, a very high luminosity, asymmetric e+e- collider. This article summarizes the important role of SuperB in understanding new physics in the LHC era.
In light of the results from the B factories, which clearly show that the Cabibbo-Kobayashi-Maskawa mechanism is the dominant source of the observed CP violation in K and B physics, only small deviations due to sources of CP violation beyond the Standard Model are likely. Therefore, in the quest for New Physics, null tests of the Standard Model become increasingly important. Motivated by these considerations, we describe a number of approximate null tests of the Standard Model. These tests provide several theoretically clean approaches to searching for new physics in the B system. We find that in many cases, the requisite sensitivity can only be achieved with an International Super B Factory, with luminosity around 10^36 cm^-2 s^-1.
The status of $B$ physics, CP violation and related measurements at the time of the Beauty 2006 conference are summarized. Particular attention is given to the exciting prospects that lie ahead, at the commencement of the LHC era, and beyond.
In radiative B decays to final states containing one spin zero meson, one spin one meson and a photon, the photon polarization can be measured from the angular distribution of the final state. The P-odd, C-even components of this distribution lead to triple correlation asymmetries that are very sensitive to new physics as they are likely to receive only tiny contributions from the Standard Model. There are also (CP-conserving) forward-backward asymmetries to which there may be SM contributions of a few percent; nevertheless there is a data driven means to overcome the SM ``pollution''. These latter observables can be used to search for a class of New Physics which does not necessarily possess a new CP-odd phase, and wherein the current structure is different from the left-handed electroweak theory of the Standard Model. The mode $B^\pm \to K^\pm ϕγ$ is particularly useful due to the relatively large branching ratio and its distinctive final state but there are dozens of such final states in the decays of $B_u$, $B_d$ and $B_s$ mesons where the analysis is applicable. In many cases, after the decay of the spin one resonance, several of these channels lead to only charged mesons and a photon in the final state, so they may well be accessible in a hadronic environment in addition, of course, to $e^+ e^-$ (Super) $B$ Factories. In passing we also briefly explain why the CP-conserving forward-backward asymmetries in $B \to P V γ$ decays is a more reliable signal of new physics compared to the (CP-conserving) transverse polarization in $B \to V_1 V_2$ modes even though, of course, the latter may be somewhat more abundant.
We describe a new method to measure the angle $ϕ_1$ of the CKM Unitarity Triangle using amplitude analysis of the multibody decay of the neutral $D$ meson produced via $\bar{B} \to D h^0$ colour-suppressed decays. The method employs the interference between $D^0$ and $\bar{D}^0$ to directly extract the value of $2ϕ_1$, and thus resolve the ambiguity between $2ϕ_1$ and $π-2ϕ_1$ in the measurement of $\sin(2ϕ_1)$ using $\bar{B}^0 \to J/ ψ\ks$. We present a feasibility study of this method using Monte Carlo simulation.
We show that in a decay of the form B_d or B_s-> P_1 P_2 gamma (where P_1 and P_2 are pseudoscalar mesons), through a flavor changing dipole transition, time dependent oscillations can reveal the presence of physics beyond the Standard Model. If P_1 and P_2 are CP eigenstates (e.g. as in B_d -> K_S pi0 gamma), the oscillation is independent of the resonance structure. Thus data from resonances as well as from nonresonant decays can be included. This may significantly enhance the sensitivity to new physics of the method. If P_1 is a charged particle, and P_2 its anti-particle (e.g. as in B_d -> pi+ pi- gamma), one has the additional advantage that both the magnitude and the weak phase of any new physics contribution can be determined from a study of the angular distribution. These signals offer excellent ways to detect new physics because they are suppressed in the Standard Model. We also show that the potential contamination of these signals originating from the Standard Model annihilation diagram gives rise to photons with, to a very good approximation, the same helicity as the dominant penguin graph and thus causes no serious difficulty.
The most precise current determination of the Unitarity Triangle angle $ϕ_3$ is presented. It is obtained using the decay $B^+ \to D^{(*)} K^+$, with Dalitz plot analysis of the subsequent $D \to K_S π^+π^-$ decay. The result is $ϕ_3 = 68^\circ ^{+14^\circ}_{-15^\circ} \stat \pm 13^\circ \syst \pm 11^\circ \model$.
We point out that in decays of the type $B^- \to D^* K^-$, where the neutral $D^*$ meson is an admixture of $D^{*0}$ and $\bar{D}^{*0}$, there is an effective strong phase difference of $π$ between the cases that the $D^*$ is reconstructed as $Dπ^0$ and $Dγ$. We consider the consequences for measurements of $ϕ_3$ using these modes, some of which are profound and beneficial.
We note that in decays of the type $B^0 \to P^0P^0X^0$, where $P^0$ and $X^0$ represent any CP eigenstate spin-0 neutral particles, the final state is a CP eigenstate. We consider the possibilities for studying time-dependent CP violation in decays of this type at $B$ factories with high luminosity, with particular attention to $B^0 \to \ks \ks \ks$. We also comment on some cases where $X^0$ has non-zero spin, and decays of the type $B^0 \to P^0 Q^0 X^0$, where the three final state particles are different spin-0 CP eigenstates.