\title{Searching for Dark Photons with the SeaQuest Spectrometer}

\author{Sho Uemura\\Los Alamos National Laboratory\\SeaQuest Collaboration}

\date{October 25, 2017}

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\begin{abstract}
    The existence of a dark sector, containing families of particles that do not couple directly to the Standard Model, is motivated as a possible model for dark matter.
    A ``dark photon'' -- a massive vector boson that couples weakly to electric charge -- is a common component of dark sector models.

    The SeaQuest spectrometer at Fermilab is designed to detect dimuon pairs produced by the interaction of a 120 GeV proton beam with a rotating set of thin fixed targets, each of thickness $\sim0.1$ nuclear interaction lengths.
    An iron-filled magnet downstream of the target, 5 meters in length, serves as a beam dump.

    The SeaQuest spectrometer is sensitive to dark photons that are mostly produced in the beam dump and decay to dimuons, and a SeaQuest search for dark sector particles was approved as Fermilab experiment E1067.
    As part of E1067, a displaced-vertex trigger was built, installed and commissioned this year.
    This trigger uses two planes of extruded scintillators to identify dimuons originating far downstream of the target, and is sensitive to dark photons that travel deep inside the beam dump before decaying to dimuons.
    This trigger will be used to take data parasitically alongside the primary SeaQuest physics program.
    In this talk I will present the displaced-vertex trigger and its performance, and projected sensitivity from future running.
	%The Heavy Photon Search (HPS) requires precision tracking and vertexing of $e^+e^-$ pairs against a high background in a difficult experimental environment.
	%The silicon vertex tracker (SVT) for HPS uses actively cooled silicon microstrip sensors with fast readout electronics.
	%To maximize acceptance and vertex resolution with a relatively small detector, the SVT operates directly downstream of the target, close to the beam line, and inside of a dipole magnet.
	%This talk presents the design and performance of the HPS SVT.
	
	%The silicon vertex tracker (SVT) operates close to the target and beamline, in vacuum and in the bore of a dipole magnet.
	%To maximize acceptance and vertex resolution with a relatively small detector, the SVT 
	%the first layer of silicon sensors is placed only 10~cm downstream of the target and 500 $\mu$m away from the beam line.
	%Much of the SVT --- the sensors, frontend readout, and ADCs --- operates in vacuum and inside the bore of a dipole magnet.
	%The HPS silicon vertex tracker employs actively cooled silicon microstrip sensors with fast readout electronics, directly downstream of a target and inside of a dipole magnet
	%A simple, small-scale version of the HPS SVT was operated on beam at Jefferson Lab in 2012; 
	%the lessons learned from that detector have been incorporated in the current SVT.

	%The Heavy Photon Search (HPS) is a new experiment at Jefferson Lab that will search for 
	%massive U(1) vector bosons (also known as heavy photons, dark photons, or $A'$)
	%of mass 20--1000 MeV that couple to electric charge with relative coupling $\alpha'/\alpha$ of $10^{-5}$--$10^{-10}$.
	%The HPS experiment is designed to produce heavy photons by electron scattering off a fixed target, and 
	%detect decays to $e^+e^-$ pairs with two signatures (invariant mass resonance and displaced decay vertex).
	%The detector is a compact, large-acceptance forward spectrometer 
	%comprising a silicon microstrip tracker for momentum measurement and vertexing and an electromagnetic calorimeter for triggering on $e^+e^-$.
	%This talk will give an overview of the HPS experiment and its current status after test, commissioning, and engineering runs.
\end{abstract}

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