Christopher Hill
VerifiedOhio State University · Physics
Active 1959–2026
About
Christopher Hill is a Professor in the Department of Physics at The Ohio State University. He holds an AB in Physics & Philosophy from Dartmouth College (1994), an MS in Physics from the University of California, Davis (1998), and a PhD in Physics from the University of California, Davis (2001). His areas of expertise include High Energy Experiment. His research focuses on experimental physics within high energy physics, contributing to the understanding of fundamental particles and forces. He has been recognized for his work with awards such as the Breakthrough Prize in Fundamental Physics in 2025 and is a Fellow of the American Physical Society since 2016.
Research topics
- Physics
- Nuclear physics
- Particle physics
- Computer Science
- Optics
- Astrophysics
- Algorithm
- Artificial Intelligence
- Mechanics
- Geography
- Quantum mechanics
- Astronomy
- Operating system
Selected publications
Afterpulse Prediction for the SUB-Millicharge ExperimenT (SUBMET)
Progress of Theoretical and Experimental Physics · 2026-01-22
articleOpen accessAbstract The SUB-Millicharge ExperimenT (SUBMET) investigates an unexplored parameter space of millicharged particles with mass $m_\chi <$ 1.6 GeV/c$^2$ and charge $Q_\chi < 10^{-3}e$. The detector consists of an Eljen-200 plastic scintillator coupled to a Hamamatsu Photonics R7725 photomultiplier tube (PMT). PMT afterpulses, delayed pulses produced after an energetic pulse, have been observed in the SUBMET readout system, especially following primary pulses with a large area. We present a prediction method for afterpulse rates based on measurable parameters, which reproduces the observed rate with approximately 20% precision. This approach enables a better understanding of afterpulse contributions and, consequently, improves the reliability of background predictions.
Progress of Theoretical and Experimental Physics · 2025-11-18 · 1 citations
articleOpen accessAbstract We present a detailed description of the detector design for the SUB-Millicharge ExperimenT (SUBMET), developed to search for millicharged particles. The experiment probes a largely unexplored region of the charge–mass parameter space, focusing on particles with mass $m_\chi < 1.6\,\rm {GeV}/c^2$ and electric charge $Q < 10^{-3}e$. The detector has been optimized to achieve high sensitivity to interactions of such particles while maintaining effective discrimination against background events. We provide a comprehensive overview of the key detector components, including scintillation modules, photomultiplier tubes, and the mechanical support structure. Furthermore, we present the results of weight and seismic analyses, which validate the structural integrity and operational safety of the detector under various conditions.
Physical Review Letters · 2025-08-20 · 2 citations
articleOpen accessWe report on a search for elementary particles with charges much smaller than the electron charge using a data sample of proton-proton collisions provided by the CERN Large Hadron Collider in 2023-24, corresponding to an integrated luminosity of 124.7 fb^{-1} at a center-of-mass energy of 13.6 TeV. The analysis presented uses the completed Run 3 milliQan bar detector to set the most stringent constraints to date for particles with charges ≤0.24 e and masses ≥0.45 GeV.
Review of top quark mass measurements in CMS
OSTI OAI (U.S. Department of Energy Office of Scientific and Technical Information) · 2025 · 8 citations
- Particle physics
- Physics
- Nuclear physics
The top quark mass is one of the most intriguing parameters of the standard model (SM). Its value indicates a Yukawa coupling close to unity, and the resulting strong ties to Higgs physics make the top quark mass a crucial ingredient for understanding essential aspects of the electroweak sector of the SM. This review offers the first comprehensive overview of the top quark mass measurements performed by the CMS Collaboration using the data collected at centre-of-mass energies of 7, 8, and 13 TeV. Moreover, a detailed description of the top quark event reconstruction is provided and dedicated studies of the dominant uncertainties in the modelling of the signal processes are discussed. The interpretation of the experimental results on the top quark mass in terms of the SM Lagrangian parameter is challenging and is a focus of an ongoing discussion in the theory community. The CMS Collaboration has performed two main types of top quark mass measurements, addressing this challenge from different perspectives: highly precise ‘direct’ measurements, based on reconstructed top quark decay products and relying exclusively on Monte-Carlo simulations, as well as ‘indirect’ measurements, where the simulations are employed to determine parton-level cross sections that are compared to fixed-order perturbative calculations. Recent mass extractions using Lorentz-boosted top quarks open a new avenue of measurements based on top quark decay products contained in a single particle jet, with promising prospects for accurate theoretical interpretations.
Scientific program for the Forward Physics Facility
The European Physical Journal C · 2025-04-17 · 15 citations
reviewOpen accessAbstract The recent direct detection of neutrinos at the LHC has opened a new window on high-energy particle physics and highlighted the potential of forward physics for groundbreaking discoveries. In the last year, the physics case for forward physics has continued to grow, and there has been extensive work on defining the Forward Physics Facility and its experiments to realize this physics potential in a timely and cost-effective manner. Following a 2-page Executive Summary, we first present the status of the FPF, beginning with the FPF’s unique potential to shed light on dark matter, new particles, neutrino physics, QCD, and astroparticle physics. We then summarize the current designs for the Facility and its experiments, FASER2, FASER $$\nu $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>ν</mml:mi> </mml:math> 2, FORMOSA, and FLArE.
Differential cross section measurements for the production of top quark pairs and of additional jets using dilepton events from pp collisions at $$ \sqrt{s} $$ = 13 TeV
OSTI OAI (U.S. Department of Energy Office of Scientific and Technical Information) · 2025 · 8 citations
- Physics
- Particle physics
- Nuclear physics
A bstract Differential cross sections for top quark pair ( $$ \textrm{t}\overline{\textrm{t}} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>t</mml:mi> <mml:mover> <mml:mi>t</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> </mml:math> ) production are measured in proton-proton collisions at a center-of-mass energy of 13 TeV using a sample of events containing two oppositely charged leptons. The data were recorded with the CMS detector at the CERN Large Hadron Collider and correspond to an integrated luminosity of 138 fb − 1 . The differential cross sections are measured as functions of kinematic observables of the $$ \textrm{t}\overline{\textrm{t}} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>t</mml:mi> <mml:mover> <mml:mi>t</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> </mml:math> system, the top quark and antiquark and their decay products, as well as of the number of additional jets in the event. The results are presented as functions of up to three variables and are corrected to the parton and particle levels. When compared to standard model predictions based on quantum chromodynamics at different levels of accuracy, it is found that the calculations do not always describe the observed data. The deviations are found to be largest for the multi-differential cross sections.
Search for exotic decays of the Higgs boson to a pair of pseudoscalars in the $\mu\mu$bb and $\tau\tau$bb final states
2024
- Physics
- Particle physics
- Nuclear physics
A search for exotic decays of the Higgs boson (H) with a mass of 125 GeV to a pair of light pseudoscalars $\mathrm{a}_1$ is performed in final states where one pseudoscalar decays to two b quarks and the other to a pair of muons or $\tau$ leptons. A data sample of proton-proton collisions at $\sqrt{s}$ = 13 TeV corresponding to an integrated luminosity of 138 fb$^{-1}$ recorded with the CMS detector is analyzed. No statistically significant excess is observed over the standard model backgrounds. Upper limits are set at 95% confidence level (CL) on the Higgs boson branching fraction to $\mu\mu$bb and to $\tau\tau$bb, via a pair of $\mathrm{a}_1$s. The limits depend on the pseudoscalar mass $m_{\mathrm{a}_1}$ and are observed to be in the range (0.17-3.3) $\times$ 10$^{-4}$ and (1.7-7.7) $\times$ 10$^{2}$ in the $\mu\mu$bb and $\tau\tau$bb final states, respectively. In the framework of models with two Higgs doublets and a complex scalar singlet (2HDM+S), the results of the two final states are combined to determine model-independent upper limits on the branching fraction $\mathcal{B}$(H $\to$ $\mathrm{a}_1\mathrm{a}_1$ $\to$ $\ell\ell$bb) at 95% CL, with $\ell$ being a muon or a $\tau$ lepton. For different types of 2HDM+S, upper bounds on the branching fraction $\mathcal{B}$(H $\to$ $\mathrm{a}_1\mathrm{a}_1$) are extracted from the combination of the two channels. In most of the Type II 2HDM+S parameter space, $\mathcal{B}($H $\to$ $\mathrm{a}_1\mathrm{a}_1$) values above 0.23 are excluded at 95% CL for $m_{\mathrm{a}_1}$ values between 15 and 60 GeV.
Performance of CMS muon reconstruction from proton-proton to heavy ion collisions
OSTI OAI (U.S. Department of Energy Office of Scientific and Technical Information) · 2024 · 3 citations
- Physics
- Nuclear physics
- Particle physics
Abstract The performance of muon tracking, identification, triggering, momentum resolution, and momentum scale has been studied with the CMS detector at the LHC using data collected at √( s NN ) = 5.02 TeV in proton-proton (pp) and lead-lead (PbPb) collisions in 2017 and 2018, respectively, and at √( s NN ) = 8.16 TeV in proton-lead (pPb) collisions in 2016. Muon efficiencies, momentum resolutions, and momentum scales are compared by focusing on how the muon reconstruction performance varies from relatively small occupancy pp collisions to the larger occupancies of pPb collisions and, finally, to the highest track multiplicity PbPb collisions. We find the efficiencies of muon tracking, identification, and triggering to be above 90% throughout most of the track multiplicity range. The momentum resolution and scale are unaffected by the detector occupancy. The excellent muon reconstruction of the CMS detector enables precision studies across all available collision systems.
Physical Review Letters · 2024 · 96 citations
- Physics
A search is reported for near-threshold structures in the J/ψJ/ψ invariant mass spectrum produced in proton-proton collisions at sqrt[s]=13 TeV from data collected by the CMS experiment, corresponding to an integrated luminosity of 135 fb^{-1}. Three structures are found, and a model with quantum interference among these structures provides a good description of the data. A new structure is observed with a local significance above 5 standard deviations at a mass of 6638_{-38}^{+43}(stat)_{-31}^{+16}(syst) MeV. Another structure with even higher significance is found at a mass of 6847_{-28}^{+44}(stat)_{-20}^{+48}(syst) MeV, which is consistent with the X(6900) resonance reported by the LHCb experiment and confirmed by the ATLAS experiment. Evidence for another new structure, with a local significance of 4.7 standard deviations, is found at a mass of 7134_{-25}^{+48}(stat)_{-15}^{+41}(syst) MeV. Results are also reported for a model without interference, which does not fit the data as well and shows mass shifts up to 150 MeV relative to the model with interference.
Physics Letters B · 2023 · 75 citations
- Computer Science
- Physics
- Algorithm
Measurements are presented of the Bs0→μ+μ− branching fraction and effective lifetime, as well as results of a search for the B0→μ+μ− decay in proton-proton collisions at s=13TeV at the LHC. The analysis is based on data collected with the CMS detector in 2016–2018 corresponding to an integrated luminosity of 140fb−1. The branching fraction of the Bs0→μ+μ− decay and the effective Bs0 meson lifetime are the most precise single measurements to date. No evidence for the B0→μ+μ− decay has been found. All results are found to be consistent with the standard model predictions and previous measurements.
Frequent coauthors
- 2198 shared
M. Titov
Institut de Recherche sur les Lois Fondamentales de l'Univers
- 2185 shared
G. Hamel de Monchenault
Université Paris-Saclay
- 2121 shared
A. Rosowsky
Institut de Recherche sur les Lois Fondamentales de l'Univers
- 2044 shared
M. Besançon
CEA Paris-Saclay
- 2013 shared
M. Lethuillier
Institute of Nuclear Physics of Lyon
- 1936 shared
A. Meyer
Deutsches Elektronen-Synchrotron DESY
- 1879 shared
J. Andreä
Institut Pluridisciplinaire Hubert Curien
- 1858 shared
C. Collard
Institut Pluridisciplinaire Hubert Curien
Education
- 2001
PhD, Physics
University of California Davis
Awards & honors
- Breakthrough Prize in Fundamental Physics (2025)
- Fellow of the American Physical Society (2016)
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