The Heavy Photon Search Test Detector
Creators: name: Battaglieri, Marco
name: Boyarinov, Sergey
name: Bueltmann, Stephen
name: Burkert, Volker
name: Celentano, Andrea
name: Charles, Gabriel
name: Cooper, William
name: Cuevas, Chris
name: Dashyan, Natalia
name: DeVita, Raffaella
name: Desnault, Camille
name: Deur, Alexandre
name: Egiyan, Hovanes
name: Elouadrhiri, Latifa
name: Essig, Rouven
name: Fadeyev, Vitaliy
name: Field, Clive
name: Freyberger, Arne
name: Gershtein, Yuri
name: Gevorgyan, Nerses
name: Girod, Francois-Xavier
name: Graf, Norman
name: Graham, Mathew
name: Griffioen, Keith
name: Grillo, Alexander
name: Guidal, Michel
name: Haller, Gunther
name: Adrian, Per Hansson
name: Herbst, Ryan
name: Holtrop, Maurik
name: Jaros, John
name: Kaneta, Scott
name: Khandaker, Mahbub
name: Kubarovsky, Alexey
name: Kubarovsky, Valery
name: Maruyama, Takashi
name: McCormick, Jeremy
name: Moffeit, Ken
name: Moreno, Omar
name: Neal, Homer
name: Nelson, Timothy
name: Niccolai, Silvia
name: Odian, Al
name: Oriunno, Marco
name: Paremuzyan, Rafayel
name: Partridge, Richard
name: Phillips, Sarah
name: Rauly, Emmanuel
name: Raydo, Benjamin
name: Reichert, Joseph
name: Rindel, Emmanuel
name: Rosier, Philippe
name: Salgado, Carlos
name: Schuster, Philip
name: Sharabian, Youri
name: Sokhan, Daria
name: Stepanyan, Stepan
name: Toro, Natalia
name: Uemura, Sho
name: Ungaro, Maurizio
name: Voskanyan, Hakop
name: Walz, Dieter
name: Weinstein, Larry
name: Wojtsekhowski, Bogdan
Publisher: name: arXiv
Year: 2014
Subjects: subject: Instrumentation and Detectors (physics.ins-det)
subject: High Energy Physics - Experiment (hep-ex)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: The Heavy Photon Search (HPS), an experiment to search for a hidden sector photon in fixed target electroproduction, is preparing for installation at the Thomas Jefferson National Accelerator Facility (JLab) in the Fall of 2014. As the first stage of this project, the HPS Test Run apparatus was constructed and operated in 2012 to demonstrate the experiment's technical feasibility and to confirm that the trigger rates and occupancies are as expected. This paper describes the HPS Test Run apparatus and readout electronics and its performance. In this setting, a heavy photon can be identified as a narrow peak in the e$^+$e$^-$ invariant mass spectrum, above the trident background or as a narrow invariant mass peak with a decay vertex displaced from the production target, so charged particle tracking and vertexing are needed for its detection. In the HPS Test Run, charged particles are measured with a compact forward silicon microstrip tracker inside a dipole magnet. Electromagnetic showers are detected in a PbW0$_{4}$ crystal calorimeter situated behind the magnet, and are used to trigger the experiment and identify electrons and positrons. Both detectors are placed close to the beam line and split top-bottom. This arrangement provides sensitivity to low-mass heavy photons, allows clear passage of the unscattered beam, and avoids the spray of degraded electrons coming from the target. The discrimination between prompt and displaced e$^+$e$^-$ pairs requires the first layer of silicon sensors be placed only 10~cm downstream of the target. The expected signal is small, and the trident background huge, so the experiment requires very large statistics. Accordingly, the HPS Test Run utilizes high-rate readout and data acquisition electronics and a fast trigger to exploit the essentially 100% duty cycle of the CEBAF accelerator at JLab.
description: Revised version to match published version, 16 pages, 18 figures, published in Nuclear Instruments and Methods in Physics Research Section A, editor: Per Hansson Adrian