Heavy Photon Search Experiment

About the HPS Experiment

The Heavy Photon Search Group at SLAC is collaborating with physicists at Jefferson Lab, Fermilab, UNH and UCSC in two experiments aimed at discovering a hidden-sector, heavy photon. Such a particle would have mass in the range 0.1 to 1.0 GeV, couple weakly to electrons, and decay to e ⁺ e ^- . It would be produced by electron bremstrahlung on a heavy target, and be identified as a narrow e ⁺ e ^- resonance. Weak couplings of this heavy photon to electrons account for it having not yet been discovered and can give rise to separated vertices in its decay, providing a spectacular signature. Heavy photons have become a hot topic recently because they may explain high energy electrons and positrons in cosmic rays, and be intimately linked to dark matter annihilation or decay.

The first experiment is the APEX experiment, which has been conditionally approved at Jlab, and which has already completed a test run this past Summer. The experiment makes use of two large spectrometers in Jlab's experimental Hall A to search for a heavy photon. If successful, several more data taking runs will be scheduled in 2010-2012.

The second experiment is the Heavy Photon Search experiment (HPS). In January 2011, the Thomas Jeferson National Accelerator Facility's Program Advisory Committee (PAC37) reviewed the scientific motivations for and the technical feasibility of HPS, and approved Stage I of the HPS proposal, the HPS Test Run, and urged it be scheduled before the end of 6 GeV running. They also granted approval for Stage II, the full HPS experiment, contingent on the success of the test run. Our SLAC group, in collaboration with others, has just submitted a proposal to Jefferson Laboratory and hopes for approval this Fall. The experiment will use LHC style readout of silicon microstrip detectors for tracking and vertex reconstruction of e ⁺ e ^- pairs and a PbWO₄ crystal calorimeter to deal with the extremely high trigger rates expected.