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Jin Huang Brookhaven National Lab For the PHENIX Collaboration A MERICAN P HYSICAL S OCIETY A PRIL M EETING, A PRIL 13, 2015, B ALTIMORE, M ARYLAND Outline: Motivation Detector Setup Analysis Results Future

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APS April Meeting 2015 Jin Huang 2 Cosmic Positron fraction VS energy Among many experimental hints for dark matter, muon (g-2) anomaly and cosmic ray positron excess strongly motivates models of a U(1) dark photon, that weekly coupled to EM photon Experimentally, this dark photon can be searched through peak finding over a large flux of virtual photons, including Dalitz decay of 0 / A + (e + e - ) PHENIX@RHIC accumulated large statistics of Dalitz decay data for a dark photon search A similar approach was/is being also used by COSY-WASA, HADES, NA48/2 ? ? Muon (g-2) Theory VS exp. A * *

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The most versatile hadron collider in the world, and worlds first and only spin-polarized proton collider Two major experiments as of today Pioneering High Energy Nuclear Interaction eXperiment (PHENIX) Solenoidal Tracker At RHIC (STAR) APS April Meeting 2015 Jin Huang 3

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APS April Meeting 2015 Jin Huang 4 :Used in this search

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2006 Run: p + p 2008: d + Au 2009 Run: p + p w/ hadron blind detector (X 0 ~2.4%) APS April Meeting 2015 Jin Huang 5 Detection of e + e - pairs in PHENIX Central arms spectrometers (-0.35< 1000) + electromagnetic calorimeter (hadron rejection ~ 10) e+e+ e-e- s NN = 200 GeV

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In the search region (30 < m ee < 90 MeV/c 2 ), observed e + e - pairs contain Dalitz decay of 0 / and background contributions Category of background: Combinatorial of e + e - that are born through uncorrelated process e + e - possibly correlated through non- Dalitz origin of the same pion, or through jet productions Background estimates: 2009: same-sign pairs of e e combinatorial + correlated background 2006/08: mix event + simulation Selection region where background < 10% of pair yield for this search APS April Meeting 2015 Jin Huang 6

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APS April Meeting 2015 Jin Huang 7 Search window No peak observed

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Under assumption of a narrow dark photon mass width, the expected peak width is detector resolution dominated Width quantified through simulation We estimated possible events with dark photon candidates under 90% confidence limit using CLs approach No dark photon signal was observed Upper limit of event count is given APS April Meeting 2015 Jin Huang 8 Simulated dark photon mass peak and width Color coding in p T Color coding in m ee

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Upper limit of of dark photon-QED photon coupling is given in mass range of 30-90 GeV Preliminary release Oct. 2013, final result published in PRC rapid communication (2015) Together with published data, almost rule out muon g-2 preferred band Exciting to see new search coming to this region too: NA48/2 (as in Cencis talk, arXiv:1504.00607) BELL (II) (as in Jaegles talk) ALICE, APEX, HPS, DarkLight, MESA, VEPP3, Mu3e,... APS April Meeting 2015 Jin Huang 9 PHENIX Collaboration, arXiv:1409.0851, PRC 91, 031901 (2015)

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The PHENIX collaboration carried out a search for dark photon through Dalitz decay of 0 / No dark photon signal was observed in 2006-2009 data Upper limit of dark photon coupling to QED photon over the mass range 30 < m ee < 90 MeV/c 2 With published world data, dark photon as explanation for observed (g-2) anomaly almost ruled out APS April Meeting 2015 Jin Huang 10 Future directions @ PHENIX : use of recent high luminosity data and silicon detector to perform displaced vertex search. PHENIX Collaboration, arXiv:1409.0851, PRC 91, 031901 (2015)

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APS April Meeting 2015 Jin Huang 11 ~200020172020~2025Time Current PHENIX sPHENIX (+fsPHENIX) An EIC detector 14y+ operation 100+M$ investment Broad spectrum of physics (QGP, Hadron Physics, DM) 147 published papers to date Last run in this form 2016 Comprehensive central upgrade based on BaBar magnet Rich jet and beauty quarkonia physics program nature of QGP fsPHENIX : forward tracking, Hcal and muon ID Spin, CNM PHENIX upgrade path leads to a capable EIC detector Large coverage of tracking, calorimetry, and PID Welcome new collaborators and new ideas Welcome new collaborators and new ideas! Documented: http://www.phenix.bnl.gov/plans.html RHIC: A+A, spin-polarized p+p, spin-polarized p+A EIC: e+p, e+A

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APS April Meeting 2015 Jin Huang 17 JHEP 1502 (2015) 157

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1312.4992 C. Hearty Taku Gunji talk @ BNL workshop APS April Meeting 2015 Jin Huang 18 Excising and future data courtesy: Bertrand Echenard

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PHENIX: Pioneering High Energy Nuclear Interaction eXperiment One of the largest experiment @ RHIC 14y+ operation 100+M$ investment Broad spectrum of physics QGP, Spin puzzle, New Physics 147 published papers to date APS April Meeting 2015 Jin Huang 19 18.5 m