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Division of Physics Mathematics and Astronomy

David Hitlin's Home Page

Contact Information

Office: 367 LauritsenMail Stop: 356-48Telephone: (626) 395 6694Mobile: (626) 484 0222Fax: (626) 395 8728email: hitlin@caltech.eduHEP Administrator: Leona KershawPhone: (626) 395 4515email:

Working closely with Frank Porter for many years, I have probed the flavor sector of the Standard Model by making increasingly precise measurements of the production and decay properties of heavy quarks and leptons. These experiments, carried out over the last several decades with the Mark II (at SPEAR), Mark III, Crystal Ball, BES-II, SLD and BABAR detectors, have been crucial in establishing the validity of the Standard Model flavor sector ansatz. In particular, our measurement of the CP asymmetry in B0 decays at BABAR was cited in the award of the 2008 Nobel Prize to Kobayashi and Maskawa.

Our current program comprises two novel and extremely sensitive probes of physics beyond the Standard Model: the Mu2e experiment at Fermilab, a search for evidence of charged lepton flavor violation in muon-to-electron conversion and the nascent LDMX experiment at SLAC, a very sensitive search for hidden sector dark matter particles. We also continue analysis of BABAR data, as much of the sample remains unique.

Mu2e is a new experiment at Fermilab whose aim is the discovery of charged lepton flavor violation via the process of muon to electron conversion. Mu2e has a sensitivity four orders of magnitude greater than the limits set by existing experiments, bringing it into the regime of CLFV predictions of many Standard Model extensions.

We are working on the design and construction of the crystal calorimeter system of Mu2e. We have responsibilities in the area of calorimeter geometry, photosensor development, crystal and readout specification and testing, modeling, the calibration system and the online and data analysis systems.

We are also beginning effort on the next phase of Mu2e which will have an additional order of magnitude more sensitivity.

The Mu2e Conceptual Design Report

The Mu2e Technical Design Report

Mu2e Run 1 Sensitivity Update

Mu2e-II Snowmass Report

Given the stringent limits that now exist on GeV-scale dark matter, the mass region between 1 MeV and 1 GeV has now become a focus for sensitive new dark matter searches. Dark matter in this mass range can be efficiently produced in accelerator experiments; LDMX (the Light Dark Matter eXperiment) has been proposed to run at the new LESA beam line at SLAC, using 4 GeV, and eventually, 8 GeV electrons.

LDMX has a straightforward apparatus design, utilizing existing technologies to avoid a lengthy development phase, and to allow the experiment to begin when the LESA beamline is complete. The experiment has unrivaled sensitivity to many types of dark matter force carriers; it will be able to test a great variety of dark matter models down to the thermal relic limit.

We are working on the design and construction of the large hadronic veto calorimeter and the LYSO active target.

The Light Dark Matter eXperiment

The BABAR experiment took data at the PEP-II asymmetric B Factory at SLAC from 1999 to 2008.
The experiment first demonstrated the existence of a CP-violating asymmetry in the decays of B0 mesons. BABAR continues to produce forefront results; it has published 600 papers on many aspects of heavy quark and tau lepton physics.

The Physics of the B Factories

BABAR is now in its archival analysis phase. Caltech has a number of important analyses in progress on searches for dark photons, neutral heavy leptons and mesons with exotic quark signatures.


Nobel medal (chocolate coin version)

The 2008 Nobel Prize was awarded to Makoto Kobayashi and Toshihide Maskawa (one half), and to Yoichiro Nambu (one half). Former SLAC Director Jonathan Dorfan and I were invited by Kobayashi-san to attend the award ceremonies, along with our KEK colleagues, in recognition (cited in the Nobel press release) of the contributions of BABAR and Belle in proving the relevance of the CKM phase as the source of CP violation in the Standard Model.

Particle Data Group

Obituary of C.S. Wu

US postage stamp

This page last updated on February 17, 2023
© 2002-2023 David Hitlin
Babar characters trademark and copyright L. de Brunhoff