Harvard ATLAS Group
Harvard ATLAS group, led by Profs. Melissa Franklin, John Huth, and Masahiro Morii, conduct a broad research program using the high-energy proton-proton collisions created by the Large Hadron Collider. The group has been responsible for the initial construction and the later upgrade of the ATLAS end-cap muon spectrometer, and continues to play a leading role in its trigger and the data-acquisition systems. The group members take on many challenging data-analysis projects, including precision measurements of the Standard Model processes, studies of the properties of the Higgs boson, and searches for new particles predicted by new theories beyond the Standard Model. In anticipation of the LHC's luminosity upgrade, the group is contributing to the upgrade of the ATLAS Inner Tracker.
Post-doctoral Positions Available
We are hiring two post-doctoral scholars to work with Profs. Franklin and Morii on ATLAS. The positions are advertised in Academic Jobs Online and InspireHEP.
Faculty
Graduate Students
Ongoing Detector Projects
People involved and a short explanation of the project.
People involved and a short explanation of the project.
PI: Masahiro Morii
Students and postdocs: Kees Benkendorfer, Laura Bruce, Michael Farrington
The ATLAS Inner Tracker (ITk) upgrade aims to replace the current inner tracking system of ATLAS with a new all-silicon detector. We are targeting installation in ~2030, in time for the high-luminosity upgrade of the LHC (HL-LHC). The new detector will have finer granularity than the current inner tracker, which will be necessary to distinguish tracks in the high-pileup, high-multiplicity environment of the HL-LHC. The design, intended to minimize the amount of non-sensing material in the system, pushes the state of the art of particle detector construction, thereby presenting many challenges and opportunities for students to learn.
ITk is divided into two subsystems: silicon strips, and silicon pixels. The Harvard group is focused on the silicon strips. Our group has recently contributed to detector integration at CERN, the detector control system (DCS), and the data acquisition (DAQ) software. The team's hardware work is conducted in a cleanroom at CERN, and the software work is done remotely.
Ongoing Physics Analyses
People involved and a short explanation of the physics.
PI: Melissa Franklin.
Graduate students: Alexis Mulski, Ismail Elmengad
PI: Masahiro Morii
Students and postdocs: Laura Bruce, Aidan Chambers, Knut Zoch
We searched for heavy new particles with lifetimes between 10 ps and 10 ns using events that contain at least one displaced vertex and a displaced muon. The analysis used partial Run 3 data (2022-24). The analysis completed with a Phys. Lett. B paper, which is the basis of Laura's Ph.D. thesis.
People involved and a short explanation of the physics.
PI: Masahiro Morii
Students and postdocs: Kees Benkendorfer, Knut Zoch
The existence of BSM physics at high scales can affect physical observations at lower scales --- an example is the existence of the W boson, which mediates beta decay even though it is too heavy to be produced directly by the energy of nuclear transitions. If we frame the Standard Model (SM) as a low-energy effective theory that lacks a full description of physics at higher energies, we can systematically categorize most possible effects of higher-scale physics on the production rates of SM particles through a framework called Standard Model Effective Field Theory (SMEFT). A large and growing program is underway to measure SMEFT parameters at the LHC.
One process that is highly sensitive to many EFT parameters is ttZ --- the production of a top-antitop pair in association with a Z boson. This is a naturally high-energy process, which makes it very sensitive to effects from high-scale particles. We aim to enhance the EFT sensitivity even further by performing measurements in a regime where the tops recoil off of the Z and are highly boosted. This analysis will be the first measurement of ttZ production at 13.6 TeV, and in addition to the EFT interpretation, we aim to provide useful differential observables to be used for Monte Carlo developments.
PI: Masahiro Morii
Students: Aidan Chambers, Santiago Cane
Recent Publications
Selected ATLAS publications our group members have produced.
| Title | Journal citation | Publication date | arXiv reference |
|---|---|---|---|
Search for massive, long-lived particles in events with displaced vertices and displaced muons in pp collisions at sqrt(s) = 13.6 TeV with the ATLAS experiment | Phys. Lett. B 878 (2026) 140509 | July 2026 | arXiv:2603.01991 [hep-ex] |
Search for resonant leptoquark production via lepton-jet signatures in pp collisions at sqrt(s) = 13 TeV and sqrt(s) = 13.6 TeV with the ATLAS detector | JHEP 12(2025)180 | December 2025 | arXiv:2507.03650 [hep-ex] |
Search for displaced leptons in sqrt(s) = 13 TeV and 13.6 TeV pp collisions with the ATLAS detector | Phys. Rev. D 112 (2025) 012016 | July 2025 | arXiv:2410.16835 [hep-ex] |
Search for long-lived charged particles using large specific ionisation loss and time of flight in 140 fb−1 of pp collisions at √s = 13 TeV with the ATLAS detector | JHEP 07(2025)140 | July 2025 | arXiv:2502.06694 [hep-ex] |
Measurement of the total and differential cross-sections of ttW production in pp collisions at sqrt(s) = 13 TeV with the ATLAS detector | JHEP 05(2024)131 | May 2024 | arXiv:2401.05299 [hep-ex] |
A search for R-parity-violating supersymmetry in final states containing many jets in pp collisions at sqrt{s} = 13 TeV with the ATLAS detector | JHEP 05(2024)003 | May 2024 | arXiv:2401.16333 [hep-ex] |
Search for top-philic heavy resonances in pp collisions at sqrt(s) = 13 TeV with the ATLAS detector | Eur. Phys. J. C 84:157 | February 2024 | arXiv:2304.01678 [hep-ex] |
Search for heavy, long-lived, charged particles with large ionisation energy loss in pp collisions at √s = 13 TeV using the ATLAS experiment and the full Run 2 dataset | JHEP 06(2023)158 | June 2023 | arXiv:2205.06013 [hep-ex] |
Observation of four-top-quark production in the multilepton final state with the ATLAS detector | Eur. Phys. J. C 83:496 | June 2023 | arXiv:2303.15061 [hep-ex] |
Measurement of Higgs boson decay into b-quarks in associated production with a top-quark pair in pp collisions at √s = 13 TeV with the ATLAS detector | JHEP 06(2022)097 | June 2022 | arXiv:2111.06712 [hep-ex] |
Measurement of the tttt production cross section in pp collisions at √s = 13 TeV with the ATLAS detector | JHEP 11(2021)118 | November 2021 | arXiv:2106.11683 [hep-ex] |
Search for Displaced Leptons in √s = 13 TeV pp Collisions with the ATLAS Detector | Phys. Rev. Lett. 127:051802 | July 2021 | arXiv:2011.07812 [hep-ex] |
A search for the decays of stopped long-lived particles at √s = 13 TeV with the ATLAS detector | JHEP 07(2021)173 | July 2021 | arXiv:2104.03050 [hep-ex] |