1. A new dark photon search P-Division Seminar Los Alamos National Laboratory Roy J. Holt Physics Division Argonne National Lab 26 February 2015

2. What’s the matter? Argonne National Laboratory 2 Dark matter is: a most profound mystery of modern physics a central element of cosmology and astronomy most of the mass of the Universe

3. Argonne National Laboratory 3 Intensity Frontier Workshop, Dec 2011, www.intensityfrontier.org Convenors for nuclear physics: Haxton, Lu, Ramsey-Musolf Priorities according to Nima Arkani-Hamed, Institute for Advanced Study (Princeton)

4. Dark Matters  Dark matter exists and interacts by gravity –Rotation curves of galaxies, gravitational lensing –Cluster galaxies –…  Is there a Standard Model connection to the dark sector? –Does dark matter interact in any other way than by gravity?  Dark photons might provide a “portal” to the dark sector  U(1) extensions of the Standard Model are natural –Pseudoscalar U(1)  axions (strong CP problem) –Vector U(1)  dark photons Argonne National Laboratory 4

5. Rotation curves of galaxies Argonne National Laboratory 5 F. Zwicky, ApJ 86 (1937) 217, V. Rubin et al, ApJ 238 (1980) 471 Figure credit: H. Merkel

6. Dark photons explain mass extinctions? Argonne National Laboratory 6 FIG. 2: Our Solar System orbits around the Milky Way’s center, completing a revolution every 250 million years. Along this path, it oscillates up and down, crossing the galactic plane about every 32 million years. If a dark matter disk were concentrated along the galactic plane, as shown here, it might tidally disrupt the motion of comets in the Oort cloud at the outer edge of our Solar System. This could explain possible periodic fluctuations in the rate of impacts on Earth. (APS/Alan Stonebraker) L. Randall and M. Reece, PRL 112 (2014) 161301; J. I. Read et al, Mon. Not. Roy. Astro. Soc 389 (2008) 1041

7. Very active field with many new results Argonne National Laboratory 7

8. Positron observations from satellite data Argonne National Laboratory 8 M. Aguilar et al., PRL 113 (2014) 121101

9. Positron excess from AMS-02 Argonne National Laboratory 9 typical theory Expectation Pulsars? M. Aguilar et al., PRL 113 (2014) 121101

10. Positron excess decreases at high energy Argonne National Laboratory 10 Consistent with ~ 1 TeV dark matter particles annihilating? S. Ting, CERN press release for AMS collaboration, Sept. 18, 2014

11. No anti-proton excess Argonne National Laboratory 11 O. Adriani et al., Nature 458 (2009) 607

12. Gamma-ray excess from the Galactic Center Argonne National Laboratory 12 P. Agrawal et al., arXiv: 1404.1373 T. Daylan et al, arXiv: 1402.6703 Hooper and Linden, PRD, arXiv:1110.0006 B. D. Fields, S. L. Shapiro, J. Shelton, PRL 113 (2014) 151302 The Economist, April 12, 2014 Not yet explained by known astrophysical sources Can be explained by dark matter annihilation What about a black hole spike? Sagittarius A* Supermassive black hole at GC

13. Dark matter search strategies Argonne National Laboratory 13 SM   Direct production: LHC Direct search: CDMS, DAMA, XENON, CREST, LUX COUPP, PICO, MiniCLEAN, … Indirect search: PAMELA, Fermi, HESS, ATIC, AMS-02, WMAP

14. New Force ? Argonne National Laboratory 14 Standard Model Quarks, leptons g W Z  Standard Model Quarks, leptons g W Z  Hidden Sector dark matter A’ Hidden Sector dark matter A’ Known forces Dark force? SU(3) C x SU(2) W x U(1) Y U(1)’ Strong weak EM

15. Dark photons might provide a portal to dark matter Argonne National Laboratory 15 Standard Model Quarks, leptons g W Z  Standard Model Quarks, leptons g W Z  Hidden Sector dark matter A’ Hidden Sector dark matter A’ B. Holdom, PLB 166 (1986) 196 J. D. Bjorken et al, PRD 80 (2009) 075018  ~ 1E-2 to 1E-8 from loops of heavy particles Discovery of dark photons would be revolutionary Dark photons could explain: positron excess in high energy Cosmic rays Gamma ray excess near Galactic Center (g-2) of the muon anomaly …

16. Muon (g-2) Argonne National Laboratory 16 H. Davoudias et al, PRD 89 (2014) 095006

17. 17 Dark Photons at RHIC ? Muon g-2 experiment (E821) has 3.6  result beyond the Standard Model PHENIX has excellent dark photon search capabilities No dark photon signal seen PHENIX upper limit, plus others rules out dark photons with no hidden sector decays as g-2 explanation A. Adare et al, arXiv:1409.0851

18. The search is on … Argonne National Laboratory 18

19. Argonne National Laboratory 19 Courtesy: R. Milner at the Fundamental Interactions Town Meeting, Chicago, Sept. 28-29, 2014 XA’ (also ALICE)

20. Possible production mechanisms for dark photons  Bremsstrahlung   0, , … decay  Drell-Yan (J.-C. Peng, S. Prasad) Argonne National Laboratory 20 A’ p p l+l+ l-l-

21. Dark forces: decay Argonne National Laboratory 21 Courtesy: N. Toro

22.   ~ 1E-2 to 1E-8 from loops of heavy particles  Most of the relevant parameter space is not shown Argonne National Laboratory 22 Plot: W. Marciano

23. Non-Standard Model Higgs decays at the LHC Argonne National Laboratory 23 arXiv: 1409.0746 Hidden Lightest Stable Particle Hidden fermion Hidden scalar BR(H -> 2  d ) = 5 -40% ??

24. Main injector at FNAL - 120 GeV protons Argonne National Laboratory 24

25. 25 Fermilab E906/SeaQuest Collaboration Abilene Christian University Ryan Castillo, Michael Daugherity, Donald Isenhower, Noah Kitts, Lacey Medlock, Noah Shutty, Rusty Towell, Shon Watson, Ziao Jai Xi Academia Sinica Wen-Chen Chang, Ting-Hua Chang, Shiu Shiuan-Hao Argonne National Laboratory John Arrington, Don Geesaman*, Kawtar Hafidi, Roy Holt, Harold Jackson, David Potterveld, Paul E. Reimer*, Brian Tice University of Colorado Ed Kinney, Joseph Katich, Po-Ju Lin Fermi National Accelerator Laboratory Chuck Brown, Dave Christian, Su-Yin Wang, Jin-Yuan Wu University of Illinois Bryan Dannowitz, Markus Diefenthaler, Bryan Kerns, Hao Li, Naomi C.R Makins, Dhyaanesh Mullagur R. Evan McClellan, Jen-Chieh Peng, Shivangi Prasad, Mae Hwee Teo, Mariusz Witek, Yangqiu Yin KEK Shin'ya Sawada Los Alamos National Laboratory Gerry Garvey, Xiaodong Jiang, Andreas Klein, David Kleinjan, Mike Leitch, Kun Liu, Ming Liu, Pat McGaughey Mississippi State University Lamiaa El Fassi University of Maryland Betsy Beise, Yen-Chu Chen, Kazutaka Nakahara University of Michigan Christine Aidala, McKenzie Barber, Catherine Culkin, Vera Loggins, Wolfgang Lorenzon, Bryan Ramson, Richard Raymond, Josh Rubin, Matt Wood National Kaohsiung Normal University Rurngsheng Guo, Su-Yin Wang RIKEN Yoshinori Fukao, Yuji Goto, Atsushi Taketani, Manabu Togawa Rutgers, The State University of New Jersey Ron Gilman, Ron Ransome, Arun Tadepalli Tokyo Tech Shou Miyaska, Kei Nagai, Kenichi Nakano, Shigeki Obata, Florian Sanftl, Toshi-Aki Shibata Yamagata University Yuya Kudo, Yoshiyuki Miyachi, Shumpei Nara * Co-Spokespersons 5 national labs, 11 universities!

26. Drell-Yan measurements on the proton and deuteron Argonne National Laboratory 26 ubar > dbar J.-C. Peng et al, PLB 736 (2014) 411 Revealing the “Peng effect”

27. Ideal beam stop experiment Argonne National Laboratory 27  Detector is well-shielded from Standard Model background  Vertex for pair production is downstream from the target  m A’ = invariant mass of     Resonance production     target shield pair spectrometer High energy Proton beam    A’ l+l+ l-l-

28. SeaQuest Experiment Argonne National Laboratory 28 L int (Fe) = 0.17 m = target length Shield (Fe) = 4.8 m – Fiducial region = L Fe + 0.95 m Figure credit: Kenichi Nakano, Shou Miyasaka Solid Fe magnet – thanks to DOE for funding and for lack of funding 1-m Fe

29. Branching ratios for A’ decay assuming no hidden sector decays Argonne National Laboratory 29 D. Curtin, et al, arXiv 1312.4992v2 R. Essig, priv. comm. (2014)

30. SeaQuest Experimental Setup Argonne National Laboratory 30 Spectrometer commissioned in March 2014 Experiment will run for at least another year followed by LANL’s E1039 experiment Nearly ideal for a dark photon search LANL LDRD -> more ideal Thanks to R. Evan McClellan Preliminary

31. Decay length vs. mass, energy,  Argonne National Laboratory 31 J. D. Bjorken et al, PRD 80 (2009) 075018

32. Charged particle production at 120 GeV Argonne National Laboratory 32 S. Mahajan, R. Raja, arXiv:1311.2258; FNAL E907, MIPP  = 2.2 b for all charged particle production Assume that  ’s represent 90% of charged particles, and  production is 1/10 of this value. Resonance production    

33. Proton bremsstrahlung Argonne National Laboratory 33 p p’ l+l+ l-l-  + p ->  ’  + p’ Generalized Fermi-Williams-Weizsacker approximation J. Blumlein, J.Brunner, PLB 731 (2014) 320 z = (E p – E p ’)/E p ; s = 2ME p ; s’ = 2M(E p – E A’ )

34. Proton bremsstralung flux Argonne National Laboratory 34  = 1

35. Worldwide search for dark photons (exclusion plot) Argonne National Laboratory 35 JLab projections FNAL E906 SeaQuest projections preliminary Plot credit: A. Tadepalli 2E12 ppp 100% efficiency 200 days 10 event contours

36. How would 50 events with S/B = 1:1 appear? Argonne National Laboratory 36

37. SeaQuest Projections preliminary With e + e - detection

38. Dark Matter can come in different shades of gray? Argonne National Laboratory 38 Slide credit: S. Gardner The visible and hidden sectors can mix in different ways… [Note Batell, Pospelov, and Ritz, PRD 80 (2009) 095024 for a review re fixed target expts.] Here we consider a non-Abelian (gluon) portal [Baumgart et al., JHEP 0904, 014 (2009); Gardner and He, PRD 87 (2013) 116012] The “shining through walls” design – unique to Seaquest – makes this possible, to yield, e.g., via a “minimal” decay….

39. With     detection SeaQuest Projections preliminary Production [

40. First look at background events Argonne National Laboratory 40 Monte Carlo: p - inelastic scattering Actual data - 8 hours Fiducial region Fiducial region Thanks to Kun Liu 09 May 2014 Tracker is not yet optimized for dark photons Trigger 57, not optimal for dark photons

41. Second look for possible events Argonne National Laboratory 41 Runs 8919-9117 ~90 hours, Very preliminary Thanks to R. Evan McClellan 20 October 2014 Same tracker as before Trigger 59 Distance (cm)

42. Summary  Existence of dark matter is a reason to investigate new forces  New initiative for SeaQuest - search for dark photons  Leverage the newly commissioned spectrometer and 120 GeV proton beam at FNAL  Ultimate goal is to discover dark photons and provide a window into dark matter in a laboratory setting  Detecting e + e - and     in SeaQuest would greatly extend the reach, possibly including some non-Abelian dark forces  Next few years: a discovery or a large excluded region of parameter space  Don’t be afraid of the dark! Argonne National Laboratory 42

43. Extra slides Argonne National Laboratory 43

44. Confidence levels  CLs or Becker method  P(n,x) is the Poisson probability to observe n events for a mean value of x  N = number of event observed, b = background events, s = signal  N=1, b=0.7, 95% CL exclude signal of 4.5 events, proton bremsstrahlung J. Blumlein, J.Brunner, PLB 731 (2014) 320  N=5, b=3.5, 95% CL exclude a signal of 7.3 events,  0 decay J. Blumlein, J.Brunner, PLB 701 (2011) 155 Argonne National Laboratory 44

45. Mass distribution for events 3-5 m downstream Argonne National Laboratory 45 Thanks to R. Evan McClellan Mass (GeV) Events Very preliminary

46. More assumptions  Beam intensity – 6 x 10 12 protons per minute  Beam protons rejected - 40%  Dark photon acceptance – 50%  Dead time - 15%  Target thickness – 1 interaction length of Fe  Dimuon tracking efficiency – 50%  Time – nominal year - 200 days  Minimum number of dark photon events – 10  Signal to background – 1:1  Confidence level - 95% Argonne National Laboratory 46

47. Drell-Yan is the best way to measure sea-quark distributions Argonne National Laboratory 47 What is the A dependence of antiquarks? Longer term: Polarized FNAL/target, J-PARC Commissioning completed March 2014