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Tim Gershon

Publications and source records attributed to Tim Gershon.

At least 19 recordsLinked to original sources
arXiv2026

Method to study $CP$ violation in $B_s^0\to K_S K^\pm \pi^\mp$ decays

The $B_s^0\to K_S K^\pm \pi^\mp$ decays are of interest to test the Standard Model and search for new sources of $CP$ violation. A full study of these decays requires a tagged decay-time-dependent Dalitz-plot analysis performed simultaneously in the two final states. Such an analysis has never previously been performed. The method to carry out such an analysis, relating the amplitudes for decays to resonances in the two final-states to each other, is set out and its feasibility is demonstrated using pseudoexperiments. The sensitivity to the weak phase difference, $\phi_s^{\rm eff}$, between $B_s^0 \to K_S K^*(892)^0$ decays with and without $B_s^0$-$\bar{B}_s^0$ mixing is studied. Good precision on $\phi_s^{\rm eff}$ is found to be achievable with a dataset corresponding to LHCb Runs 1-3, with further improvement expected with datasets to be collected in future. The method is implemented in the Laura++ Dalitz-plot analysis package, and can be applied to other multibody decays with multiple final states.

hep-ph↗
arXiv2025

More visualisation of decay-time-dependent asymmetries in multibody B-meson decays

Methods have been proposed recently to weight data in order to allow visualisation of CP-violation effects in transitions of neutral B mesons to multibody final states that are not CP-eigenstates. These are useful since integration of the unweighted data over the phase space would otherwise wash out the effects of interest. A similar method, elaborated upon here, with a different weighting function can also be used to visualise CP-conserving $B_{(s)}^0$--$\overline{B}{}_{(s)}^0$ oscillations, rather than the CP-violating asymmetries. Together with the other weighting functions, this new method could be useful, for example, to demonstrate the accuracy of the calibration of the flavour tagging algorithms that are crucial for analyses such as the measurement of the CP-violating phase in $B_s^0 \to J/\!\psi\phi$ decays. Their application to the formalism in common use for such decays is explicitly demonstrated.

hep-ph↗
arXiv2024

Visualisation of $CP$-violation effects in decay-time-dependent analyses of multibody $B$-meson decays

Decay-time-dependent $CP$-violation effects in transitions of neutral $B$ mesons to $CP$-eigenstates can be visualised by oscillations in the asymmetry, as a function of decay time, between decay yields from mesons tagged as initially having $\overline{B}$ or $B$ flavour. Such images, for example for $B^0 \to J/\psi K^0_{\rm S}$ decays where the magnitude of the oscillation is proportional to $\sin(2\beta)$ with $\beta$ being an angle of the Cabibbo--Kobayashi--Maskawa Unitarity Triangle, provide a straightforward illustration of the underlying physics. Until now there has been no comparable method to provide visualisation for the case of decays to multibody final states that are not $CP$-eigenstates, where interference between $CP$-even and -odd amplitudes provides additional physics sensitivity. A method is proposed to weight the data so that the terms of interest can be projected out and used to obtain asymmetries that visualise the relevant effects. Application of the weighting to $B^0_s$ decays, where effects due to non-zero width difference are not negligible, provides a novel method to observe $CP$ violation in interference between mixing and decay without tagging the production flavour.

hep-ph↗
arXiv2021

Testing the Standard Model with CP-asymmetries in flavour-specific non-leptonic decays

Motivated by recent indications that the rates of colour-allowed non-leptonic channels are not in agreement with their Standard Model expectations based on QCD factorisation, we investigate the potential to study CP asymmetries with these decays. In the Standard Model, these flavour-specific decays are sensitive to CP violation in $B^0_{(s)}$--$\bar{B}^0_{(s)}$ mixing, which is predicted with low uncertainties and can be measured precisely with semileptonic decays. If there are beyond Standard Model contributions to the non-leptonic decay amplitudes, there could be significant enhancements to the CP asymmetries. Measurements of these quantities therefore have potential to identify BSM effects without relying on Standard Model predictions that might be affected by hadronic effects. We discuss the experimental prospects, and note the excellent potential for a precise determination of the CP asymmetry in $\bar{B}_s \to D_s^+ \pi^-$ decays by the LHCb experiment.

hep-ph↗
arXiv2018

Tetraquarks and pentaquarks

Greig Cowan and Tim Gershon describe new types of matter called tetraquarks and pentaquarks, and discuss the outlook for understanding these particles.

physics.pop-ph↗
arXiv2017

Laura++ : a Dalitz plot fitter

The Dalitz plot analysis technique has become an increasingly important method in heavy flavour physics. The Laura++ fitter has been developed as a flexible tool that can be used for Dalitz plot analyses in different experimental environments. Explicitly designed for three-body decays of heavy-flavoured mesons to spinless final state particles, it is optimised in order to describe all possible resonant or nonresonant contributions, and to accommodate possible CP violation effects.

hep-ex↗
arXiv2017

Current challenges and future prospects for $\gamma$ from $B\to D hh^\prime$ decays

Decays of the type $B\to D hh^\prime$, where a $b$~hadron decays to a neutral charm meson that can be an admixture of $D^0$ and $\overline{D}{}^0$ states together with two light particles that are typically a kaon and a pion, have demonstrated potential to enable precise determinations of the angle $\gamma$ of the CKM Unitarity Triangle. The current status and future prospects of these measurements are reviewed.

hep-ex↗
arXiv2014

Probing CP violation in $B^0_s \rightarrow K^{0}_{\rm S} \pi^{+}\pi^{-}$ decays

The three-body charmless hadronic decay $B^0_s \rightarrow K^{0}_{\rm S} \pi^{+}\pi^{-}$ provides a number of novel possibilities to search for CP violation effects and test the Standard Model of particle physics. These include fits to the Dalitz-plot distributions of the decay-time-integrated final state, decay-time-dependent (but without initial state flavour tagging) fits to the Dalitz-plot distribution, as well as full decay-time-dependent and flavour tagged fits. The relative sensitivities of these different approaches are investigated.

hep-ph↗
arXiv2013

Flavour physics in the LHC era

These lectures give a topical review of heavy flavour physics, in particular \CP violation and rare decays, from an experimental point of view. They describe the ongoing motivation to study heavy flavour physics in the LHC era, the current status of the field emphasising key results from previous experiments, some selected topics in which new results are expected in the near future, and a brief look at future projects.

hep-ex↗
arXiv2011

Overview of the CKM Matrix

The current status of the determination of the elements of the Cabibbo-Kobayashi-Maskawa quark-mixing matrix is reviewed. Tensions in the global fits are highlighted. Particular attention is paid to progress in, and prospects for, measurements of CP violation effects.

hep-ex↗
arXiv2010

Delta Gamma_d: A Forgotten Null Test of the Standard Model

The recent measurement of an anomalous like-sign dimuon asymmetry by the D0 collaboration has prompted theoretical speculation on possible sources of physics beyond the Standard Model that may affect lifetimes and lifetime differences in neutral B meson systems. One observable that deserves closer attention is the width difference in the B_d system, Delta Gamma_d. Since the Standard Model prediction for this quantity is well below 1%, it serves as a "null test" whereby the measurement of a larger value would cleanly reveal the presence of new physics. Methods to measure Delta Gamma_d at current and future experiments are reviewed and an attractive new approach is proposed.

hep-ph↗
arXiv2009

Prospects for the Measurement of the Unitarity Triangle Angle gamma from B0 to DK+pi- Decays

The potential for a precise measurement of the Unitarity Triangle angle $γ$ in future experiments from the decay $B^0 \to DK^{*0}$ is well-known. It has recently been suggested that the sensitivity can be significantly enhanced by analysing the $B^0 \to DK^+π^-$ Dalitz plot to extract amplitudes relative to those of the flavour-specific decay $B^0 \to D_2^{*-}K^+$. An extension to this method which includes the case where the neutral $D$ meson is reconstructed in suppressed final states is presented. The sensitivity to $γ$ is estimated using this method and compared to that obtained using the $B^0 \to DK^{*0}$ decay alone. Experimental effects, such as background contamination, are also considered. This approach appears to be a highly attractive addition to the family of methods that can be used to determine $γ$.

hep-ph↗
arXiv2009

Double Dalitz Plot Analysis of the Decay B^0 -> D K+ Pi-, D -> Ks Pi+ Pi-

It is shown that it is possible to perform a model-independent extraction of the CKM Unitarity Triangle angle $\gamma$ using only the decays $B^0\to D K^+\pi^-$ with $D\to K^0_S\pi^+\pi^-$ and $B^0\to D K^+\pi^-$ with flavour-specific $D$ decays. The proposed method can also utilise the $B^0\to D K^+\pi^-$ data with CP-eigenstate decays of the D meson in a model-independent way.

hep-ph↗
arXiv2009

On the Measurement of the Unitarity Triangle Angle gamma from B^0 -> DK^{*0} Decays

The decay B^0 -> DK^{*0} is well-known to provide excellent potential for a precise measurement of the Unitarity Triangle angle gamma in future experiments. It is noted that the sensitivity can be significantly enhanced by studying the amplitudes relative to those of the flavour-specific decay B^0 -> D_2^{*-}K^+, which can be achieved by analyzing the B^0 -> Dπ^-K^+ Dalitz plot.

hep-ph↗
arXiv2008

A Method to Measure cos(2beta) Using Time-Dependent Dalitz Plot Analysis of B0 -> D_CP pi+ pi-

We present a feasibility study of a method to measure the cosine of twice the CKM Unitarity Triangle angle beta using a time-dependent Dalitz plot analysis of B0 -> D pi+ pi- decays, where the neutral D meson is reconstructed in decays to CP eigenstates. We show that this method can be used at the B factories to make a measurement of cos(2beta) that is competitive with, or more precise than, other techniques using different quark-level transitions, while sin(2beta) can be measured to an accuracy more precise than any existing measurement using b -> c ubar d transitions. Furthermore, this technique has great potential to be employed at LHCb.

hep-ph↗
arXiv2008

New Physics at a Super Flavor Factory

The potential of a Super Flavor Factory (SFF) for searches of New Physics is reviewed. While very high luminosity B physics is assumed to be at the core of the program, its scope for extensive charm and tau studies are also emphasized. The possibility to run at the Upsilon(5S) is also very briefly discussed; in principle, this could provide very clean measurements of B_s decays. The strength and reach of a SFF is most notably due to the possibility of examining an impressive array of very clean observables. The angles and the sides of the unitarity triangle can be determined with unprecedented accuracy. These serve as a reference for New Physics (NP) sensitive decays such as B^+ ->tau^+ nu and penguin dominated hadronic decay modes, providing tests of generic NP scenarios with an accuracy of a few percent. Besides, very precise studies of direct and time dependent CP asymmetries in radiative B decays and forward-backward asymmetry studies in B-> X_s l^+ l^- and numerous null tests using B, charm and tau decays are also likely to provide powerful insights into NP. The dramatic increase in luminosity at a SFF will also open up entirely new avenues for probing NP observables, e.g. by allowing sensitive studies using theoretically clean processes such as B -> X_s nu nubar. The SFF is envisioned to be a crucial tool for essential studies of flavor in the LHC era, and will extend the reach of the LHC in many important ways.

hep-ph↗