About

James Rohlf is a professor in the Department of Physics at Boston University, with research interests centered on particle physics at the energy frontier. His work includes significant contributions to the discovery of the W and Z bosons at CERN, where he played an integral and pioneering role, especially in the identification of the first events and measurements of their mass and spin. Since 1993, he has been involved with the CMS experiment at CERN, helping develop advanced digital electronics for detector readout and participating in numerous physics analyses, including the discovery of the Higgs boson. Rohlf's academic background includes a Ph.D. in Physics from Caltech, earned in 1980, with prior degrees from UCLA and the University of Minnesota. His doctoral thesis involved pioneering experiments on jets and tests of Quantum Chromodynamics at Fermilab, which laid the foundation for sophisticated simulation techniques in the field. During his graduate studies, he contributed to the first experiment to trigger on hadron jets with a calorimeter and worked on the discovery of the Upsilon (4S) resonance at Cornell. His research has consistently focused on experimental particle physics, utilizing innovative analysis techniques and developing cutting-edge detector technology. Rohlf's extensive career reflects a deep engagement with high-energy physics experiments aimed at understanding the fundamental particles and forces of nature.

Research topics

• Physics
• Nuclear physics
• Particle physics
• Quantum mechanics
• Mathematics
• Optics
• Statistics
• Astrophysics

Selected publications

• 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.

• Luminosity determination using Z boson production at the CMS experiment

  HAL (Le Centre pour la Communication Scientifique Directe) · 2024 · 7 citations

  • Physics
  • Particle physics
  • Nuclear physics

  of integrated luminosity, thus facilitating the efficiency and rate measurement as a function of time and instantaneous luminosity. Using the ratio of the efficiency-corrected numbers of Z bosons, the precisely measured integrated luminosity of one data set is used to determine the luminosity of another. For the first time, a full quantitative uncertainty analysis of the use of Z bosons for the integrated luminosity measurement is performed. The uncertainty in the extrapolation between two data sets, recorded in 2017 at low and high instantaneous luminosity, is less than 0.5%. We show that the Z boson rate measurement constitutes a precise method, complementary to traditional methods, with the potential to improve the measurement of the integrated luminosity.

  DOI

• 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.

  DOI

• Search for long-lived particles decaying to final states with a pair of muons in proton-proton collisions at $$ \sqrt{s} $$ = 13.6 TeV

  arXiv (Cornell University) · 2024 · 6 citations

  • Physics
  • Particle physics
  • Nuclear physics

  A bstract An inclusive search for long-lived exotic particles (LLPs) decaying to final states with a pair of muons is presented. The search uses data corresponding to an integrated luminosity of 36.6 fb − 1 collected by the CMS experiment from the proton-proton collisions at $$ \sqrt{s} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msqrt> <mml:mi>s</mml:mi> </mml:msqrt> </mml:math> = 13.6 TeV in 2022, the first year of Run 3 of the CERN LHC. The experimental signature is a pair of oppositely charged muons originating from a secondary vertex spatially separated from the proton-proton interaction point by distances ranging from several hundred μ m to several meters. The sensitivity of the search benefits from new triggers for displaced dimuons developed for Run 3. The results are interpreted in the framework of the hidden Abelian Higgs model, in which the Higgs boson decays to a pair of long-lived dark photons, and of an R -parity violating supersymmetry model, in which long-lived neutralinos decay to a pair of muons and a neutrino. The limits set on these models are the most stringent to date in wide regions of lifetimes for LLPs with masses larger than 10 GeV.

  DOI

• Measurement of simplified template cross sections of the Higgs boson produced in association with W or Z bosons in the H $\to$ $\mathrm{b\bar{b}}$ decay channel in proton-proton collisions at $\sqrt{s}$ = 13 TeV

  arXiv (Cornell University) · 2023 · 2 citations

  • Physics
  • Particle physics
  • Nuclear physics

  Differential cross sections are measured for the standard model Higgs boson produced in association with vector bosons (W, Z) and decaying to a pair of b quarks. Measurements are performed within the framework of the simplified template cross sections. The analysis relies on the leptonic decays of the W and Z bosons, resulting in final states with 0, 1, or 2 electrons or muons. The Higgs boson candidates are either reconstructed from pairs of resolved b-tagged jets, or from single large distance parameter jets containing the particles arising from two b quarks. Proton-proton collision data at $\sqrt{s}$ = 13 TeV, collected by the CMS experiment in 2016-2018 and corresponding to a total integrated luminosity of 138 fb$^{-1}$, are analyzed. The inclusive signal strength, defined as the product of the observed production cross section and branching fraction relative to the standard model expectation, combining all analysis categories, is found to be $\mu$ = 1.15$^{+0.22}_{-0.20}$. This corresponds to an observed (expected) significance of 6.3 (5.6) standard deviations.

  DOI

• Search for new physics using effective field theory in 13 TeV <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>p</mml:mi><mml:mi>p</mml:mi></mml:math> collision events that contain a top quark pair and a boosted <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>Z</mml:mi></mml:math> or Higgs boson

  HAL (Le Centre pour la Communication Scientifique Directe) · 2023 · 7 citations

  • Physics
  • Particle physics
  • Nuclear physics

  A data sample containing top quark pairs ($t\overline{t}$) produced in association with a Lorentz-boosted $Z$ or Higgs boson is used to search for signs of new physics using effective field theory. The data correspond to an integrated luminosity of $138\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ of proton-proton collisions produced at a center-of-mass energy of 13 TeV at the LHC and collected by the CMS experiment. Selected events contain a single lepton and hadronic jets, including two identified with the decay of bottom quarks, plus an additional large-radius jet with high transverse momentum identified as a $Z$ or Higgs boson decaying to a bottom quark pair. Machine learning techniques are employed to discriminate between $t\overline{t}Z$ or $t\overline{t}H$ events and events from background processes, which are dominated by $t\overline{t}+\text{jets}$ production. No indications of new physics are observed. The signal strengths of boosted $t\overline{t}Z$ and $t\overline{t}H$ production are measured, and upper limits are placed on the $t\overline{t}Z$ and $t\overline{t}H$ differential cross sections as functions of the $Z$ or Higgs boson transverse momentum. The effects of new physics are probed using a framework in which the standard model is considered to be the low-energy effective field theory of a higher energy scale theory. Eight possible dimension-six operators are added to the standard model Lagrangian, and their corresponding coefficients are constrained via fits to the data.

  DOI

Frequent coauthors

• J. Li

  University of Antwerp

  41 shared

• C. Dozen

  Institute of Nuclear Physics of Lyon

  33 shared

• G. Hamel de Monchenault

  Université Paris-Saclay

  31 shared

• Olena Karacheban

  University of Antwerp

  30 shared

• P. Simkina

  Université Paris-Saclay

  28 shared

• V. Lohezic

  CEA Paris-Saclay

  28 shared

• S. Goy López

  Unidades Centrales Científico-Técnicas

  27 shared

• J. Alcaraz Maestre

  A. Alikhanyan National Laboratory

  27 shared