HPS Heavy Photon Search A Proposal to Search for Massive Photons in Hall B at Jefferson Laboratory John Jaros for the Heavy Photon Search Collaboration Jefferson Laboratory PAC37 January 11, 2011
HPS Collaboration 16 Institutions, 58 and counting Physicists and Engineers January 11, 2011 Heavy Photon Search 2
Why Consider Heavy Photons? B. Holdom, Phys. Lett. B166 (1986) 196 • Are there additional U(1)’s in Nature, additional “photons”? They are expected in many BSM theories. Holdom noted that they would kinetically mix with the SM photon, which would induce their coupling ε e to electric charge . Loops of heavy particles, which couple to both γ and A’, give a coupling ε which is independent of the heavy particle mass. ε ∼ 10 -2 – 10 -4 ε ∼ 10 -3 – 10 -5 (if SM unifies in a GUT) • m A’ is expected to be MeV–GeV if U(1)’ symmetry breaks via Higgs mechanism. m A’ ∼ ( ε g D g γ /g 2 2 ) 1/2 m W ∼ MeV - GeV January 11, 2011 Heavy Photon Search 3
Does Dark Matter Couple to Heavy Photons? N. Arkani-Hamed, D.P. Finkbeiner, T.R.Slayter, and N. Weiner, Phys. Rev. D79, 015014 (2009) M. Pospelov and A. Ritz, Phys. Lett. B671 , 391 (2009) Observation of unexpected fluxes of e ± in the cosmic rays prompted • explanations involving DM annihilation. theory FERMI/HESS e Flux PAMELA e + /e - • Dark matter coupling to the A’ could explain DM annihilation into e + e – Inelastic scattering via A’ could account for the DAMA results. January 11, 2011 Heavy Photon Search 4
Heavy Photon Signatures A heavy photon appears as a narrow e + e - resonance on a copious • background of QED tridents. Bump Hunt Trident Background A’ Signal Trident Background A’ Signal γ * γ Decay Length c τ The A’ lifetime depends on mass and ε • γ c τ ~ 0.8 cm (E 0 /10 GeV) (10 -4 / ε ) 2 (100 MeV/m A’ ) 2 Displaced A’ decay vertices can be identified over much of the m- ε parameter space, distinguishing them from QED tridents. January 11, 2011 Heavy Photon Search 5
Present Limits and Region of Interest J.D. B jorken, R. E ssig, P. S chuster, and N. T oro, Phys. Rev. D80 , 2009,075018 ( BEST ) Both “naturalness” arguments and fits to astrophysical data suggest α ’/ α ≡ ε 2 ~ 10 -4 – 10 -10 α ’/ α ≡ ε 2 m A’ ~ MeV - GeV Both resonance-bump and separated decay vertex signatures are needed to explore this region January 11, 2011 Heavy Photon Search 6
HPS Design evolved from BEST Concept • A’ kinematics ⇒ forward coverage required: E A’ ≈ E beam θ A’ ≈ 0 θ decay = m A’ /E A’ • Vertexing A’ decays requires detectors close to the target. Bump hunting needs good momentum/mass resolution. Both need tracking and a magnet. Want ∆ m/m ~ 1% for bump hunt e + and e - Want ∆ z ~ 1mm • Trigger with high rate Electromagnetic Calorimeter downstream of the magnet to distinguish e + and e - . entering ECal • Survive beam backgrounds by spreading them out maximally in time and avoiding multiple scattered and degraded electrons Need CEBAF 100% duty cycle Need very high rate DAQ Avoid “Wall of flame” January 11, 2011 Heavy Photon Search 7
HPS Design • Thin target positioned 10 cm before tracker • Compact Si microstrip tracker/vertexer in 1T analyzing magnet • Fast, segmented Ecal for triggering, e ID • Muon detector for alternate trigger, muon ID • All detectors are split vertically to avoid “wall of flame” occupied by primary beam, degraded electrons, bremsstrahlung photons, etc. January 11, 2011 Heavy Photon Search 8
CEBAF Beam and HPS Beamline HPS sits behind CLAS in Hall B • CEBAF meets HPS Beam Requirements E 2.2, 6.6 GeV I 100-450nA σ x,y < 30 µm ∆ x,y < 30 µm halo < 10 -5 • 12 GeV will have small spots quads chicane dump 12 GeV 3-pass beam emittance and the addition of new quads will give 10 µ m spots. New optics/quads Halo measured <10 -5 . • Beam Stability < 30 µm gives10 µm spots at 6 GeV HPS will use new corrector magnets and BPMs in Fast Feedback to keep beam stable. Quads and correctors will be mounted on the CLAS forward carriage. Vibrations are measured < ± 2 µ m, so won’t spoil stability. • 12 GeV halo expected < 10 -5 Halo should be better than current machine, since there are fewer passes, less beam gas scattering. 9
HPS Target • Small beam spots are needed to constrain A’ trajectory and reduce vertex tails • Small, stable beam spots and high beam currents cause significant target heating. Solution is to rotate the target. January 11, 2011 Heavy Photon Search 10
Si Tracker/Vertexer • 6 Layers of Si detectors mounted on CF modules supports, split into upper and lower planes: XY, XY, XY,XX’,XX’,XX’, where X measures momentum, X’ provides small angle stereo. • 4 x 10 cm 2 Hamamatsu sensors. 60 µ m sense pitch; CMS APV25 B provides 40 MHz analogue readout. • Entire assembly in vacuum to minimize backgrounds. Rolls in/out for installation and servicing. Layer 6 S and V January 11, 2011 Heavy Photon Search 11
EM Calorimeter and Muon System Pb Glass Modules • EM Calorimeter triggers HPS * Uses CLAS IC PbWO4 crystals/APDs * Outer layers use Pb Glass modules/PMTs * Beam passes between upper and lower segments in vacuum chamber • Muon System provides µ ID and trigger * 4 layers of 5 cm wide scintillator strips. * Record pulse height and time with MAPTs * Pion punch-through ~ 1% January 11, 2011 Heavy Photon Search 12
High Rate DAQ • Ecal and Muon use CLAS 250 MHz FADCs * FADC Crate Trigger Processors generate trigger inputs every 8ns * Subsystem Processor generates system trigger • Tracker uses SLAC ATCA crates *APV25 signals go to Readout Boards every 25 ns *Trigger Interface board accepts and distributes Jlab trigger *Cluster Interconnect Module connects to Jlab DAQ Level 1 Trigger <50 kHz Data Rate <100 Mbyte/s January 11, 2011 Heavy Photon Search 13
Staging a challenging experiment Key environmental questions: • Can Si microstrip detectors be operated downstream of a target in close proximity to an intense electron beam with manageable occupancies and without radiation damage? • Can the EM calorimeter trigger the experiment at an acceptable trigger rate (<50kHz)? • Is detector performance in the presence of realistic backgrounds good enough to do the physics? Two ways to answer these questions. We’ve done one. We need both! Extensive full GEANT4 and EGS5 Monte Carlo studies of trigger rates, tracker occupancies, tracker pattern recognition efficiencies and purities, and tracker and vertexing performance in the presence of backgrounds. Stage I Test Run (proposed for Spring 2012) to check MC calculations, measure occupancies and trigger rates, and exercise detector. January 11, 2011 Heavy Photon Search 14
MC Tracker Studies Radiation Damage in Layer 1 Charged Particle Occupancy ( e ± hits/cm 2 /month ) in Layer 1 Si µ strip detector 400 nA on .25% X 0 target Sensitive Area ≥ 1.5 mm Dead Zone 1 % Occupancy Occupancies are high, but manageable. Large but manageable dose on Occupancy ≤ 1% beyond “dead zone” at innermost strips. No degradation Y = 1.5 mm (above electron beam). in performance up to 5 x 10 15 /cm 2 (6 mn); useable up to 9 mn. January 11, 2011 Heavy Photon Search 15
MC Tracker Studies • EGS5 and GEANT4 simulate EM interactions to < 10 keV, including low energy bremsstrahlung and fluorescent x-ray production in the target. • Photon fluxes ~ charged particle fluxes, but interaction probability is much lower, and energy deposition is often below Si threshold. • Detected photon backgrounds << charged particle backgrounds GEANT4 Photon Flux < 100MeV EGS5 Calculation of Photon Occupancy in Si Dead Occupancy ~10 -4 Zone Photons not a problem January 11, 2011 Heavy Photon Search 16
MC Tracker Performance • Stand-alone pattern recognition is 98% efficient in presence of realistic backgrounds. Only ~1% of tracks have ≥ 1 miss-hits. • Momentum resolution ∆ p/p = 1.5 % gives mass resolution ∆ m/m = 1 %. • Track, vertex quality, and trajectory cuts nearly eliminate vertex tails. Vertex Resolution along the beam direction, Z v Before quality cuts After quality cuts Tracks with miss-hits make tails January 11, 2011 Heavy Photon Search 17
MC Trigger Performance Full GEANT4 simulations are used to study trigger occupancies and rates. • Occupancies OK for 8ns window and 100 MeV threshold • Cluster, Energy, and Geometry cuts yield a trigger rate < 30 kHz Trigger (6.6. GeV) ≥ 2 clusters 0.5 < E 1,2 < 5.0 GeV E1 + E2 < E beam ∆ E < 4.0 GeV Co-planar January 11, 2011 Heavy Photon Search 18
HPS Stage I: Test Run G4 and EGS5 Occupancies • Multiple Motives * Measure and check occupancy and trigger rates. Resolve discrepant EGS5 and GEANT4 results. * Test prototype si modules, PbWO4, and readout * Integrate Jlab and SLAC DAQ systems * Get running experience: beam properties, alignment, data taking, and data analysis. • Simplified apparatus uses existing Hall B magnets and beamline. Magnet and Tracker ECal Beamline • Cost ~$500k for HPS Stage I. The right first step for a challenging experiment. 19 January 11, 2011 Heavy Photon Search
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