Version 1:
Title: Forward physics at STAR using the Event Plane Detector

The first phase of Beam Energy Scan (BES) program of the Relativistic Heavy Ion Collider (RHIC) was an exploration of the QCD phase diagram. The second phase is a search for the signals of  criticality and phase transition. For the Solenoidal Tracker at RHIC (STAR) a quantitative understanding of these signals requires an increase in statistics in 7.7, 11.5, 14.5 and 19.6 GeV AuAu collisions as well as dedicated hardware upgrades. The Event Plane Detector (EPD) is a $2.1<|\eta|<5.1$ hit detector which should improve the trigger and first order event plane determination. Additionally the large segmentation and low occupancy allows for higher order TPC independent event plane determination, TPC independent centrality determination, and charge hit based physics.

An eighth of the detector was put in place in STAR for commissioning during the 2017 run, which included a few weeks of AuAu 54GeV beamtime. The shape of the partial detector isn’t ideal for event plane determination, but perfectly reasonable for other physics. Charged particle occupancy can be statistically determined in the detector which opens up analyses of $dN_{ch}/d\eta$ and charged particle flow measurements as compared to a TPC determined event plane.

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QM2015 abstracts below
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Version I
The first phase of Beam Energy Scan (BES) program of the Relativistic Heavy Ion Collider (RHIC) was an exploration of the QCD phase diagram. The second phase is an exploration for criticality and phase transition signals. For the Solenoidal Tracker at RHIC (STAR) a quantitative understanding of these signals requires an increase in statistics in for 7, 11, 14, and 19GeV AuAu collisions as well as dedicated hardware upgrades to remove trivial correlations, improve triggering, and better determine event plane positions. The Event Plane Detector (EPD) is a proposed high $\eta$ hit detector that would replace the STAR Beam Beam Counter (BBC – a 32 channel hit detector 3.3 $< |\eta| <$ 5.0 used for BES triggering and first order event plane reconstruction) for BES II, which is scheduled to begin in 2019. The EPD would provide improved triggering, increased detector coverage in jet-like $\eta$-$\phi$ correlation measurements, improved resolution for event plane determination independent of the STAR Time Projection Chamber (TPC – a charged particle tracker $| \eta | < 1$), and provide a TPC independent centrality definition. Divorcing the determination of the event plane positions as well as collision centrality from the TPC via a forward detector is crucial for correlation measurements performed at mid-rapidity.
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The EPD design consists of two scintillator discs at $\pm$ 3.75m, each is separated into ~500 tiles. A tile has embedded wavelength shifting fiber coupled to clear fiber outside of the tile which is, in turn, coupled to a silicon photomultiplier (SiPM) – an inexpensive and magnetic field insensitive replacement for traditional phototubes. A pre-prototype of the detector, featuring scintillator with embedded fiber coupled to SiPMs was integrated into STAR during the 2015 run. Currently tile designs varying geometry and detector specifications are being fabricated and tested along with latest generation SiPMs. Additionally simulations have been performed to optimize tile $\eta$/$\phi$ segmentation, size, and shape. A newly machined prototype featuring the anticipated geometry of the EPD will be put in place during the 2016 STAR run.

VERSION II
The first phase of Beam Energy Scan (BES) program of the Relativistic Heavy Ion Collider (RHIC) was an exploration of the QCD phase diagram. The second phase is an exploration for criticality and phase transition signals. For the Solenoidal Tracker at RHIC (STAR) a quantitative understanding of these signals requires an increase in statistics in for 7, 11, 14, and 19GeV AuAu collisions as well as dedicated hardware upgrades. The Event Plane Detector (EPD) is a proposed high $\eta$ hit detector that would replace the STAR Beam Beam Counter (BBC – a 32 channel hit detector 3.3 $< |\eta| <$ 5.0 used for BES triggering and first order event plane reconstruction) for BES II, which is scheduled to begin in 2019. The EPD would provide improved triggering, increased detector coverage in jet-like $\eta$-$\phi$ correlation measurements, improved resolution for event plane determination independent of the TPC ($|\eta| < 1$), and provide a TPC independent centrality definition. Divorcing event plane and centrality determination from the TPC via a forward detector is crucial for correlation measurements performed at mid-rapidity.
\\
\\
The EPD design consists of two scintillator discs at $\pm$ 3.75m, each is separated into ~500 tiles. A tile has embedded wavelength shifting fiber coupled to clear fiber outside of the tile which is, in turn, coupled to a silicon photomultiplier (SiPM) – an inexpensive and magnetic field insensitive replacement for traditional phototubes. A pre-prototype of the detector, featuring scintillator with embedded fiber coupled to SiPMs was integrated into STAR during the 2015 run. Currently tile designs varying geometry and detector specifications are being fabricated and tested along with latest generation SiPMs. Additionally simulations have been performed to optimize tile $\eta$/$\phi$ segmentation, size, and shape. A newly machined prototype featuring the anticipated geometry of the EPD will be put in place during the 2016 STAR run.

Version III

The first phase of Beam Energy Scan (BES) program of the Relativistic Heavy Ion Collider (RHIC) was an exploration of the QCD phase diagram. The second phase is an exploration for criticality and phase transition signals. For the Solenoidal Tracker at RHIC (STAR) a quantitative understanding of these signals requires an increase in statistics in 7.7, 11.5, 14.5 and 19.6 GeV AuAu collisions as well as dedicated hardware upgrades. The Event Plane Detector (EPD) is a proposed high $\eta$ hit detector that would replace the STAR Beam Beam Counter (BBC – a 32 channel hit detector 3.3 $< |\eta| <$ 5.0 used for BES triggering and first order event plane reconstruction) for BES II, which is scheduled to begin in 2019. The EPD would provide improved triggering, increased detector coverage in jet-like $\eta$-$\phi$ correlation measurements, improved resolution for event plane determination independent of the TPC ($|\eta| < 1$), and provide a TPC independent centrality definition. Divorcing event plane and centrality determination from the TPC via a forward detector is crucial for correlation measurements performed at mid-rapidity.
\\
\\
The EPD design consists of two scintillator discs at $\pm$ 3.75m, each is separated into ~500 tiles. A tile has embedded wavelength shifting fiber coupled to clear fiber outside of the tile which is, in turn, coupled to a silicon photomultiplier (SiPM) – an inexpensive and magnetic field insensitive replacement for traditional phototubes. A pre-prototype of the detector, featuring scintillator with embedded fiber coupled to SiPMs was integrated into STAR during the 2015 run. Currently tile designs varying geometry and detector specifications are being fabricated and tested along with latest generation SiPMs. Additionally simulations have been performed to optimize tile $\eta$/$\phi$ segmentation, size, and shape. A newly machined prototype featuring the anticipated geometry of the EPD will be put in place during RHIC run 2016.