HPS Heavy Photon Search A Proposal to Search for Massive Photons - - PowerPoint PPT Presentation

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

January 11, 2011 Heavy Photon Search 2

HPS Collaboration

16 Institutions, 58 and counting Physicists and Engineers

January 11, 2011 3

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 εe to electric charge.

• mA’ is expected to be MeV–GeV if U(1)’ symmetry breaks via Higgs

mechanism.

Heavy Photon Search

mA’ ∼ (εgDgγ/g2

2)1/2 mW ∼ MeV - GeV

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)

January 11, 2011 4

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.

• Dark matter coupling to the A’ could explain DM annihilation into e+e –

Inelastic scattering via A’ could account for the DAMA results.

theory

PAMELA e+/e- FERMI/HESS e Flux

Heavy Photon Search

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Heavy Photon Signatures

• A heavy photon appears as a narrow e+e- resonance on a copious

background of QED tridents.

• The A’ lifetime depends on mass and ε

γcτ ~ 0.8 cm (E0/10 GeV) (10-4/ε)2 (100 MeV/mA’)2 Displaced A’ decay vertices can be identified over much of the m-ε parameter space, distinguishing them from QED tridents.

Trident Background A’ Signal Heavy Photon Search

Decay Length cτ Bump Hunt A’ Signal Trident Background γ* γ

Present Limits and Region of Interest

J.D. Bjorken, R. Essig, P.Schuster, and N. Toro, Phys. Rev. D80, 2009,075018 (BEST) January 11, 2011 Heavy Photon Search 6

α’/α ≡ ε2

Both “naturalness” arguments and fits to astrophysical data suggest α’/α ≡ ε2 ~ 10-4 – 10-10 mA’ ~ MeV - GeV Both resonance-bump and separated decay vertex signatures are needed to explore this region

HPS Design evolved from BEST Concept

January 11, 2011 Heavy Photon Search 7

• A’ kinematics ⇒ forward coverage required:

EA’ ≈ Ebeam θA’ ≈ 0 θdecay = mA’/EA’ Want ∆m/m ~ 1% for bump hunt Want ∆z ~ 1mm

• Vertexing A’ decays requires detectors close to the target. Bump hunting

needs good momentum/mass resolution. Both need tracking and a magnet.

• Trigger with high rate Electromagnetic Calorimeter

downstream of the magnet to distinguish e+ and e-.

• 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” e+ and e- entering ECal

HPS Design

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• 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.

CEBAF Beam and HPS Beamline

9

• CEBAF meets HPS Beam Requirements

E 2.2, 6.6 GeV I 100-450nA σx,y < 30 µm ∆x,y < 30 µm halo < 10-5

• 12 GeV will have small spots

12 GeV 3-pass beam emittance and the addition of new quads will give 10 µm spots.

• Beam Stability < 30 µm

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 µm, 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.

New optics/quads gives10 µm spots

quads chicane dump

Halo measured <10-5 at 6 GeV

HPS sits behind CLAS in Hall B

.

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.

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Si Tracker/Vertexer

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• 6 Layers of Si detectors mounted
• n 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 cm2 Hamamatsu sensors.

60 µm sense pitch; CMS APV25 provides 40 MHz analogue readout.

• Entire assembly in vacuum to

minimize backgrounds. Rolls in/out for installation and servicing. Layer 6 S and V

Heavy Photon Search

B

EM Calorimeter and Muon System

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• 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%

Heavy Photon Search

Pb Glass Modules

High Rate DAQ

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• 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

Heavy Photon Search

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.

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MC Tracker Studies

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Radiation Damage in Layer 1 Charged Particle Occupancy ( e± hits/cm2/month ) in Layer 1 Si µstrip detector

Large but manageable dose on innermost strips. No degradation in performance up to 5 x 1015/cm2 (6 mn); useable up to 9 mn. Occupancies are high, but manageable. Occupancy ≤ 1% beyond “dead zone” at Y = 1.5 mm (above electron beam). Dead Zone

Heavy Photon Search 400 nA on .25% X0 target

Sensitive Area ≥ 1.5 mm 1 % Occupancy

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

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Occupancy ~10-4 Photons not a problem

GEANT4 Photon Flux < 100MeV EGS5 Calculation of Photon Occupancy in Si Dead Zone

MC Tracker Performance

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• 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.

Before quality cuts After quality cuts Tracks with miss-hits make tails Vertex Resolution along the beam direction, Zv

MC Trigger Performance

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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 < E1,2< 5.0 GeV E1 + E2 < Ebeam ∆E < 4.0 GeV Co-planar

Heavy Photon Search

HPS Stage I: Test Run

• 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.
• Cost ~$500k for HPS Stage I.

The right first step for a challenging experiment.

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G4 and EGS5 Occupancies

Magnet and Tracker ECal Beamline

HPS Run Plan

• Stage I Test Run (6 GeV Era)

2 weeks installation 1 week commission 1 week data run

2.2 GeV 1-100 nA 0.125% X0 0.6 x 106 s

• Stage II Data Runs (12 GeV Era)

1 month installation ½ month commission 2 x 3* month data runs

2.2 GeV 200 nA 0.125% X0 9 x 106 s *assumes 100% efficiency

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6.6 GeV 450 nA 0.25% X0 9 x 106 s

HPS Reach*

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6.6 and 2.2 GeV Reach

2σ 5σ

Combined 2σ Reach

* Small changes since proposal: muons added at high masses, improving reach; low mass cut-off was about 18, now 25 MeV.

January 11, 2011 22

Other Physics with ~109 Tridents

thanks to Stan Brodsky

• Discover and measure “true muonium” (µ+ µ- atom).

True muonium will decay to e+e- with m=2mµ, a decay length of γcτ=17mm (at 6.6 GeV), and kinematics just like those of the A’. For data run at Ebeam=6.6 GeV:

95 n=1 triplet states escape target ~10 events detected beyond 1.5 cm

• Detect π0 → e+e- and measure its branching ratio?

Study is needed.

• High statistics studies of trident production

Study is needed.

Heavy Photon Search

• HPS searches for heavy photons in a unique region of parameter

space with unparalleled sensitivity by exploiting both separated vertex and invariant mass signatures, and capitalizing on CEBAF’s excellent beam properties,100% duty cycle, and recent very high rate readout technologies.

• HPS provides JLab with an exciting and topical research program

which has the potential for truly fundamental discoveries.

• HPS must be pursued aggressively if this potential is to be realized.

Illuminating Dark Matter

HPS Backup Slides

January 11, 2011 Heavy Photon Search 24

Bump Hunt Reach

• Significance depends on A’ signal and trident background
• Trident background is calculated with MadGraph and MadEvent for

nominal run conditions (2.2 and 6.6 GeV; 9 x 106 sec each energy)

• Bump hunt reach is given by the 2σ contour in the mA’, α’/α plane.

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Typical trident statistics: few x107 – 108 in each 2.5σ mass bin

Heavy Photon Search

Vertex Search

Trident rejection is all in the tails!

• Trident vertices originate in the target, Zv = 0.
• A’ decays can extend to large Zv.
• Count vertices beyond Zcut to minimize trident background.

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Ebeam = 5.5 GeV α’/α = 10-8.5 α’/α = 10-9.5 Vertex Distribution for mA’ = 200 MeV ± 1.25σ

Heavy Photon Search

Reach

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5σ Reach 1 month 3 months Combined 3 Month Runs

5σ 2σ

Reach: Muons

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Muons 2σ 6.6 GeV 2σ 2.2 GeV 2σ

Reach: Other Experiments

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HPS Costs

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• Considerable savings from “donations”

Fermilab ~150 Hamamatsu Si microstrip detectors SLAC 18D36 H Magnet JLab PbWO4 crystals, magnets, power supplies, FADCs, DAQ infrastructure, Data Storage Collaborators Engineering and design for Ecal and Muon Systems

• Cost Summary (including lab indirects and contingency)

Test Run $523k

Beamline and target $ 20k Test Run Tracker $148k Test SVT readout $184k Test Run Ecal $138k Ecal Trigger and DAQ $ 32k

HPS Proper $1880k

Beamline $587k Tracker/Vertexer $628k EM Calorimeter $ 89k Muon System $178k SVT DAQ $342k Ecal Trigger/DAQ $ 55k

January 11, 2011 31

Other Physics with ~109 Tridents

thanks to Stan Brodsky

• Discover and measure “true muonium” (µ+ µ- atom).

True muonium will decay to e+e- with m=2mµ, a decay length of γcτ=17mm (at 6.6 GeV), and kinematics just like those of the A’. For data run at Ebeam=6.6 GeV:

95 n=1 triplet states escape target ~10 events detected beyond 1.5 cm

• Detect π0 → e+e- and measure its branching ratio?

Study is needed.

• High statistics studies of trident production

Study is needed.

Heavy Photon Search

Other Physics with HPS

January 11, 2011 Heavy Photon Search 32

Other Physics with HPS

January 11, 2011 Heavy Photon Search 33

Test Run

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Test Run Tracker/Magnet

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Cut-away View of Hall B Analyzing Magnet

Test Run Ecal

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Acceptance 2.2 GeV

Layer 4 Layer 3 75 MeV A’ ECal Si Sensor PbWO4 Crystals

Test Run Tracker Acceptance

Beam energy: 2.2 GeV Analyzing magnet: 0.5 Tesla Layer #4: (1) (2) (3) (4)