1. Beam Dump Experiments with Photon and Electron Beams
BDX at Jefferson Lab
Signal and backgrounds
Muon flux measurements
Status
Elton S. Smith, Jefferson Lab
On behalf of the BDX Collaboration
APS April Meeting – Focus Session on sub-GeV Dark Matter
April 16, 2018

2. Beam Dump Experiments ee √aD ee
Izaguirre PRD 88 (2013)
Parasitic to experimental program. Use electrons that are otherwise thrown away
Produce “invisible decays” of heavy photon (Beam Dump) ee
Detect dark matter particle interaction (Experiment Detector)
Signature is EM shower E > 0.5 GeV
√aD ee
(mA’ > 2 mc)

3. Electron and Photon Beams
Neutrinos are an Irreducible Background
to Beam dump experiments
Neutrinos come from pion and muon decays
Electron and photon beams dump their energy by radiating
Hadronic beams dump their energy by producing pions
electrons
protons

4. Proposal: Dark Sector Search Facility at SLAC
LDMX
J. Mans S09.07
Dump 400 C/year
At 4 GeV
1.1 ms bunch
separation
ESB
Beam Dump

5. Jefferson Lab site
Hall A
Beam Dump

6. Location of BDX at JLab Highest beam current ~ 65 mA
Integrated charge ~ 1022 EOT (41 weeks)
Ebeam up to 11 GeV
New underground facility ~$1.5M
Hall A
Beam Dump
BDX detector
Shielding
Concrete+Iron

7. Detection of Dark Matter c
Crystal Detector
Signals are EM showers, E > 0.3 GeV
High efficiency active and passive veto
Compact footprint and good segmentation
Complementary Gaseous Detector (DRIFT)
Negative ion Time Projection Chamber
Measures elastic nuclear recoils
Sensitive to the incident particle direction

8. Background Summary (crystal detector)
Cosmic-ray Backgrounds
Measured (beam-off) and subtracted
Several meters of overburden
Time uncorrelated (CW beam prevents fast time coincidence)
Solution: Characterized with BDX prototype at Catania and Jlab. Measured during experiment and beam-off
Beam-related Backgrounds
Detection thresholds define the background level
Charged particles easy to shield, neutrals more difficult
Low-energy particles are below threshold
Solution: Heavy Shielding
Simulations for irreducible backgrounds
Normalize MC to muon flux measurements
For Ethresh>0.3 GeV n are ultimate background

9. BDX Reach BDX can be conclusive for some Light Dark Matter scenarios
The BDX sensitivity has been evaluated assuming 1022 EOT e2
Leptophilic
inelastic
mA’ (MeV)
Thermal Relic
Leptophilic
mc (MeV)
mc (MeV)

10. Status of BDX experiment
Received C2 Conditional Approval by PAC 44 (June 2016)
PAC 45 (June 2017) affirmed our plan to address the concerns raised by PAC 44
Expand simulation tools based on GEANT to include FLUKA with a tuned set of biasing weights. Work completed in collaboration with experts from Jlab Radiation Control.
Measure muon flux from Hall A beam dump during accelerator operations.
PAC 46 (June 2018): Request full approval

11. Muon flux measurement Well 1 Well 2
We are measuring the muon flux behind the existing Hall A beam dump.
The measurements is validating MC and helping to understand backgrounds
Well 1
Well 2
Location ‘B’
Muon flux
Rate ~ 1kHz/mA

12. Hall “T”ent

13. Measure muon flux behind Hall A
Data taking is ongoing / preliminary online analysis 10
Crystal Rate (kHz)
Normalized Flux (cm) 20
Hall A Beam Current (uA)
Vertical Position (cm)
Measured flux profile
agrees with MC
Rate agreement ~ 30%
Muon flux proportional
to beam current

14. Summary and Status
Beam-dump experiments are sensitive to invisible decays of dark photons, which probe regions of the parameter space that are not covered by visible decays.
Beam-dump experiments at electron facilities have significantly reduced neutrino backgrounds compared to hadron beams.
The BDX experiment is conditionally approved to run parasitically at Jefferson Lab for 41 weeks at ~11 GeV, which will allow it to collect ~1022 electrons on target.

15. BDX Collaboration

16. BDX inner detector
A. Celentano

17. BDX active veto