\title{Direct Search for Dark Photons with the SeaQuest Spectrometer}
 
\author{Sho Uemura, Kun Liu and Ming Liu \\Los Alamos National Laboratory\\SeaQuest Collaboration}
 
\date{April 14, 2018}
 
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\begin{abstract}
%SeaQuest/E1067 is a direct search for dark sector particles using the SeaQuest spectrometer at Fermilab.
%The SeaQuest experiment studies nuclear dependent Drell-Yan dimuon production using the high intensity 120~GeV proton beam from the Main Injector on thin fixed targets.
%An iron-filled magnet downstream of the target, 5 meters in length, serves as the focusing magnet and beam dump.
%Proton-nucleus collisions, mostly in the beam dump, can produce dark photons and dark Higgs through Drell-Yan like $q+\bar{q}$ (or $g+g$) fusion processes.
%These will decay to pairs of charged particles that can be detected in the SeaQuest spectrometer.

%A displaced-vertex trigger was built, installed, and commissioned in 2017.
%This trigger, which operates parasitically with the primary SeaQuest physics program, is sensitive to dark photons or dark Higgs with mass above the dimuon threshold that travel deep inside the beam dump before decaying.
%It recorded one week of production data during the last run of the E906 experiment, and will continue to take data during the upcoming E1039 experiment.
%We present the displaced-vertex trigger upgrade and its performance, the current status of the dark photon search from 2017 data, and projected sensitivity from future running.


%The SeaQuest experiment has been in operation since 2011 and is designed to study nuclear dependent Drell-Yan productions in the dimuon channel using the high intensity 120GeV proton beam from the Main Injector on various thin nuclear targets (about $\sim0.1$ nuclear interaction length each).
%It provides an ideal setting for dark photon and dark Higgs search in a parameter space of great interest.
%In this energy, through kinetic mixing, the postulated low-mass  ($ \sim < 10GeV$)  dark photon (and/or dark Higgs) particles could be produced in the Drell-Yan like $q+\bar{q}$ (or $g+g$) fusion processes in high energy proton + nucleus collisions, mostly in the beam dump ($p+Fe$) and decay into dimuons (or di-electrons).
%For this search, a dedicated displaced-vertex trigger detector was built, installed and commissioned with upgraded DAQ in 2017. 
%This trigger uses two planes of extruded scintillators to identify dimuons originating far downstream of the target, and is sensitive to dark photons (dark Higgs) that travel deep inside the beam dump before decaying to dimuons.
%We successfully took one week worth of production data parasitically with the E906 experiment in 2017.
%We will continue taking additional data parasitically alongside the upcoming SeaQuest polarized proton target physics program (E1039) for several years.
%In this talk we will present the latest status of the preliminary dark photon search from 2017 data and also discuss future opportunity.

SeaQuest/E1067 is a direct search for dark sector particles using the SeaQuest spectrometer at Fermilab.
In the context of dark sector searches, SeaQuest operates as a proton beam dump where a high intensity 120~GeV proton beam is absorbed in the 5-meter length of an iron-filled magnet.
Dark photons can be produced through meson decays, proton bremsstrahlung, or Drell-Yan processes.
The 

%To investigate the sea-quark asymmetry of the proton the SeaQuest experiment at Fermilab uses proton beam of 120 GeV/c interacting with liquid Hydrogen or Deuterium. Alongside of that the SeaQuest also probes the quark energy loss and EMC effect using targets of Iron, Carbon and Tungsten. Data taking ended in July of 2017, having recorded dimuon events from 1.4*10^18 protons interacting with various targets. A preliminary result of extracting sea-quark asymmetry based on about 50% of data collected will be given in this presentation. Progress in understanding quark energy loss and the nuclear EMC effect will also be presented.
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