arXiv subjects

N. Sherrill

Publications and source records attributed to N. Sherrill.

18 recordsLinked to original sources

arXiv2025

Flavor-changing signatures of spacetime-symmetry violations

This proceedings contribution discusses Lorentz and CPT violation in the context of charged-lepton flavor-changing processes. Particular emphasis is placed on coherent muon-to-electron conversion in muonic atoms. Data collected by the SINDRUM~II experiment at the Paul Scherrer Institute is used to extract constraints on mass dimension $d=5$ electromagnetic and $d=6$ quark-lepton effects. The Mu2e experiment at Fermilab and COMET experiment at the Japan Proton Accelerator Complex are projected to improve constraints by up to two orders in magnitude.

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arXiv2025

Limits on New Lorentz-violating Bosons

We obtain novel constraints on new scalar fields interacting with Standard Model fermions through Lorentz-violating couplings, bridging searches for scalar particles and Lorentz-symmetry tests. These constraints arise from torsion-balance experiments, magnetometer searches, and an excessive energy loss in Red Giant stars. Torsion-balance experiments impose stringent constraints, benefitting from large macroscopic sources including the Sun and Earth. Magnetometer-based searches, which detect pseudo-magnetic fields through spin precession, offer additional limiting power to low-mass scalar fields. Meanwhile, observations of Red Giant stars place strong limits on additional energy loss mechanisms, extending these constraints to higher scalar mass ranges and a wider range of Lorentz-violating couplings. Combining data from laboratory experiments and astrophysical observations, this approach strengthens constraints on Lorentz-violating interactions and paves the way for future investigations into physics beyond the Standard Model.

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arXiv2025

Flavor-changing Lorentz and CPT violation in muonic atoms

Flavor-changing signatures of Lorentz and CPT violation involving muon-electron conversions in muonic atoms are studied using effective field theory. Constraints on coefficients for Lorentz violation at parts in $10^{-12}$ GeV$^{-1}$ for flavor-changing electromagnetic muon decays and parts in $10^{-13}$ GeV$^{-2}$ for flavor-changing 4-point quark-lepton interactions are extracted using existing data from the SINDRUM II experiment at the Paul Scherrer Institute. Estimates are provided for sensitivities attainable in the forthcoming experiments Mu2e at Fermilab and COMET at the Japan Proton Accelerator Complex.

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arXiv2024

The azimuthal correlation between the leading jet and the scattered lepton in deep inelastic scattering at HERA

The azimuthal correlation angle, $\Delta\phi$, between the scattered lepton and the leading jet in deep inelastic $e^{\pm}p$ scattering at HERA has been studied using data collected with the ZEUS detector at a centre-of-mass energy of $\sqrt{s} = 318 \;\mathrm{GeV}$, corresponding to an integrated luminosity of $326 \;\mathrm{pb}^{-1}$. A measurement of jet cross sections in the laboratory frame was made in a fiducial region corresponding to photon virtuality $10 \;\mathrm{GeV}^2 < Q^2 < 350 \;\mathrm{GeV}^2$, inelasticity $0.04 < y < 0.7$, outgoing lepton energy $E_e > 10 \;\mathrm{GeV}$, lepton polar angle $140^\circ < \theta_e < 180^\circ$, jet transverse momentum $2.5 \;\mathrm{GeV} < p_\mathrm{T,jet} < 30 \;\mathrm{GeV}$, and jet pseudorapidity $-1.5 < \eta_\mathrm{jet} < 1.8$. Jets were reconstructed using the $k_\mathrm{T}$ algorithm with the radius parameter $R = 1$. The leading jet in an event is defined as the jet that carries the highest $p_\mathrm{T,jet}$. Differential cross sections, $d\sigma/d\Delta\phi$, were measured as a function of the azimuthal correlation angle in various ranges of leading-jet transverse momentum, photon virtuality and jet multiplicity. Perturbative calculations at $\mathcal{O}(\alpha_{s}^2)$ accuracy successfully describe the data within the fiducial region, although a lower level of agreement is observed near $\Delta\phi \rightarrow \pi$ for events with high jet multiplicity, due to limitations of the perturbative approach in describing soft phenomena in QCD. The data are equally well described by Monte Carlo predictions that supplement leading-order matrix elements with parton showering.

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arXiv2024

Probing CPT invariance with top quarks at the LHC

The first model-independent sensitivity to CPT violation in the top-quark sector is extracted from ATLAS and CMS measurements of the top and antitop kinematical mass difference. We find that the temporal component of a CPT-violating background field interacting with the top-quark vector current is restricted within the interval $[-0.13,0.29]$ GeV at 95% confidence level.

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arXiv2023

Measurement of jet production in deep inelastic scattering and NNLO determination of the strong coupling at ZEUS

A new measurement of inclusive-jet cross sections in the Breit frame in neutral current deep inelastic scattering using the ZEUS detector at the HERA collider is presented. The data were taken in the years 2004 to 2007 at a centre-of-mass energy of $318\,\text{GeV}$ and correspond to an integrated luminosity of $347\,\text{pb}^{-1}$. Massless jets, reconstructed using the $k_t$-algorithm in the Breit reference frame, have been measured as a function of the squared momentum transfer, $Q^2$, and the transverse momentum of the jets in the Breit frame, $p_{\perp,\text{Breit}}$. The measured jet cross sections are compared to previous measurements and to perturbative QCD predictions. The measurement has been used in a next-to-next-to-leading-order QCD analysis to perform a simultaneous determination of parton distribution functions of the proton and the strong coupling, resulting in a value of $\alpha_s(M_Z^2) = 0.1142 \pm 0.0017~\text{(experimental/fit)}$ ${}^{+0.0006}_{-0.0007}~\text{(model/parameterisation)}$ ${}^{+0.0006}_{-0.0004}~\text{(scale)}$, whose accuracy is improved compared to similar measurements. In addition, the running of the strong coupling is demonstrated using data obtained at different scales.

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arXiv2022

Search for effective Lorentz and CPT violation using ZEUS data

Lorentz and CPT symmetry in the quark sector of the Standard Model are studied in the context of an effective field theory using ZEUS $e^{\pm} p$ data. Symmetry-violating effects can lead to time-dependent oscillations of otherwise time-independent observables, including scattering cross sections. An analysis using five years of inclusive neutral-current deep inelastic scattering events corresponding to an integrated HERA luminosity of $372\; \text{pb}^{-1}$ at $\sqrt{s} = 318$ Gev has been performed. No evidence for oscillations in sidereal time has been observed within statistical and systematic uncertainties. Constraints, most for the first time, are placed on 42 coefficients parameterising dominant CPT-even dimension-four and CPT-odd dimension-five spin-independent modifications to the propagation and interaction of light quarks.

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arXiv2022

Electromagnetic Flavor-Changing Lepton Decays from Lorentz and CPT Violation

Lorentz- and CPT-violating effects initiating two-body electromagnetic flavor-changing decays of charged leptons are studied in the framework of Lorentz-violating effective field theory. An analysis of data from experiments at the Paul Scherrer Institute and at the Stanford Linear Accelerator measuring the branching ratios of these decays provides 576 constraints on independent flavor-changing effects in the charged-lepton sector, consistent with no Lorentz and CPT violation at the level of parts in $10^{-13}$ GeV$^{-1}$ to $10^{-9}$ GeV$^{-1}$.

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arXiv2022

Snowmass 2021 White Paper: Electron Ion Collider for High Energy Physics

Electron Ion Collider (EIC) is a particle accelerator facility planned for construction at Brookhaven National Laboratory on Long Island, New York by the United States Department of Energy. EIC will provide capabilities of colliding beams of polarized electrons with polarized beams of proton and light ions. EIC will be one of the largest and most sophisticated new accelerator facilities worldwide, and the only new large-scale accelerator facility planned for construction in the United States in the next few decades. The versatility, resolving power and intensity of EIC will present many new opportunities to address some of the crucial and fundamental open scientific questions in particle physics. This document provides an overview of the science case of EIC from the perspective of the high energy physics community.

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arXiv2021

Measuring the stability of fundamental constants with a network of clocks

The detection of variations of fundamental constants of the Standard Model would provide us with compelling evidence of new physics, and could lift the veil on the nature of dark matter and dark energy. In this work, we discuss how a network of atomic and molecular clocks can be used to look for such variations with unprecedented sensitivity over a wide range of time scales. This is precisely the goal of the recently launched QSNET project: A network of clocks for measuring the stability of fundamental constants. QSNET will include state-of-the-art atomic clocks, but will also develop next-generation molecular and highly charged ion clocks with enhanced sensitivity to variations of fundamental constants. We describe the technological and scientific aims of QSNET and evaluate its expected performance. We show that in the range of parameters probed by QSNET, either we will discover new physics, or we will impose new constraints on violations of fundamental symmetries and a range of theories beyond the Standard Model, including dark matter and dark energy models.

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arXiv2021

QSNET, a network of clocks for measuring the stability of fundamental constants

The QSNET consortium is building a UK network of next-generation atomic and molecular clocks that will achieve unprecedented sensitivity in testing variations of the fine structure constant, $α$, and the electron-to-proton mass ratio, $μ$. This in turn will provide more stringent constraints on a wide range of fundamental and phenomenological theories beyond the Standard Model and on dark matter models.

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arXiv2019

Lorentz-Violating Running of Coupling Constants

We compute the full vacuum polarization tensor in the minimal QED extension. We find that its low-energy limit is dominated by the radiatively induced Chern-Simons-like term and the high-energy limit is dominated by the c-type coefficients. We investigate the implications of the high-energy limit for the QED and QCD running couplings. In particular, the QCD running offers the possibility to study Lorentz-violating effects on the parton distribution functions and observables such as the hadronic R ratio.

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arXiv2018

Phenomenology of Relativistic $\mathbf{3} \to \mathbf{3}$ Reaction Amplitudes within the Isobar Approximation

Further progress in hadron spectroscopy necessitates the phenomenological description of three particle reactions. We consider the isobar approximation, where the connected part of the $\mathbf{3}\to\mathbf{3}$ amplitude is first expressed as a sum over initial and final pairs, and then expanded into a truncated partial wave series. The resulting unitarity equation is automatically fulfilled by the $B$-matrix solution, which is an integral equation for the partial wave amplitudes, analogous to the $K$-matrix parameterization used to describe $\mathbf{2}\to\mathbf{2}$ amplitudes. We study the one particle exchange and how its analytic structure impacts rescattering solutions such as the triangle diagram. The analytic structure is compared to other parameterizations discussed in the literature. We briefly discuss the analogies with recent formalisms for extracting $\mathbf{3}\to\mathbf{3}$ scattering amplitudes in lattice QCD.

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arXiv2018

What is the right formalism to search for resonances? II. The pentaquark chain

We discuss the differences between several partial-wave analysis formalisms used in the construction of three-body decay amplitudes involving fermions. Specifically, we consider the decay Lambda_b -> psi p K- , where the hidden charm pentaquark signal has been reported. We analyze the analytical properties of the amplitudes and separate kinematical and dynamical singularities. The result is an amplitude with the minimal energy dependence compatible with the S-matrix principles.

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arXiv2018

Khuri-Treiman equations for $ππ$ scattering

The Khuri-Treiman formalism models the partial-wave expansion of a scattering amplitude as a sum of three individual truncated series, capturing the low-energy dynamics of the direct and cross channels. We cast this formalism into dispersive equations to study $ππ$ scattering, and compare their expressions and numerical output to the Roy and GKPY equations. We prove that the Khuri-Treiman equations and Roy equations coincide when both are truncated to include only $S$- and $P$-waves. When higher partial waves are included, we find an excellent agreement between the Khuri-Treiman and the GKPY results. This lends credence to the notion that the Khuri-Treiman formalism is a reliable low-energy tool for studying hadronic reaction amplitudes.

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arXiv2018

Vector Meson Photoproduction with a Linearly Polarized Beam

We propose a model based on Regge theory to describe photoproduction of light vector mesons. We fit the SLAC data and make predictions for the energy and momentum transfer dependence of the spin-density matrix elements in photoproduction of $ω$, $ρ^0$ and $ϕ$ mesons at $E_γ\sim 8.5$ GeV, which are soon to be measured at Jefferson Lab.

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arXiv2017

What is the right formalism to search for resonances?

Hadron decay chains constitute one of the main sources of information on the QCD spectrum. We discuss the differences between several partial wave analysis formalisms used in the literature to build the amplitudes. We match the helicity amplitudes to the covariant tensor basis. Hereby, we pay attention to the analytical properties of the amplitudes and separate singularities of kinematical and dynamical nature. We study the analytical properties of the spin-orbit (LS) formalism, and some of the covariant tensor approaches. In particular, we explicitly build the amplitudes for the B -> psi pi K and B -> Dbar pi pi decays, and show that the energy dependence of the covariant approach is model dependent. We also show that the usual recursive construction of covariant tensors explicitly violates crossing symmetry, which would lead to different resonance parameters extracted from scattering and decay processes.

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arXiv2017

Features of $πΔ$ Photoproduction at High Energies

Hybrid/exotic meson spectroscopy searches at Jefferson Lab require the accurate theoretical description of the production mechanism in peripheral photoproduction. We develop a model for $πΔ$ photoproduction at high energies ($5 \leq E_{\text{lab}} \leq 16~\text{GeV}$) that incorporates both the absorbed pion and natural-parity cut contributions. We fit the available observables, providing a good description of the energy and angular dependencies of the experimental data. We also provide predictions for the photon beam asymmetry of charged pions at $E_{\text{lab}} = 9~\text{GeV}$ which is expected to be measured by GlueX and CLAS12 experiments in the near future.

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