Beam Dump Experiments with Photon and Electron Beams

Transcription

1 Beam Dump Experiments with Photon and Electron Beams 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 Elton S. Smith APS April Meeting April 16,

2 Beam Dump Experiments Parasitic to experimental program. Use electrons that are otherwise thrown away Produce invisible decays of heavy photon (Beam Dump) Izaguirre PRD 88 (2013) A 0! εe Detect dark matter particle interaction (Experiment Detector) Signature is EM shower E > 0.5 GeV y = 2 D (m /m A 0) 4 Yield y 2 1 D (m A > 2 mχ) ma 0 m 4 α D εe 2

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 tot 100 tot 1 3

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

5 Jefferson Lab site Hall A Beam Dump Elton S. Smith APS April Meeting April 16,

6 Location of BDX at JLab Highest beam current ~ 65 µa Integrated charge ~ 1022 EOT (41 weeks) Ebeam up to 11 GeV New underground facility ~$1.5M Hall A Beam Dump / C1 Y (cm) 1500 Hall A Beam Dump 1000 Vertical overburden = 10.0 mwe 3 Dirt density = 1.7 g/cm 3 Concrete density = 2.7 g/cm 3 BDX dimensions = 70 x 165 x 250 cm Iron = 700 cm, Weight=404 t Grade level = 762 cm above beamline grade level Dump to detector = 2064 cm 500 Shielding Concrete+Iron 0 beam line 500 BDX detector Elton S. Smith APS April Meeting April 16, Z (cm) 6

7 Detection of Dark Matter χ 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 7

8 Background Summary (crystal detector) Cosmic-ray Backgrounds Beam-related 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 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 E thresh >0.3 GeV ν are ultimate background 8

9 BDX Reach Leptophilic Inelastic DM, m χ = 10 MeV, Δ = 50 MeV, α D = 0.1 BDX can be conclusive for some Light Dark Matter scenarios The BDX sensitivity has been evaluated assuming EOT ε 2 ϵ 2 =(gv /e) (g- 2) μ > 5σ (g- 2) μ ± 2σ Borexino (νe νe) E137 BaBar Leptophilic inelastic y = ϵ 2 αd (m χ/ma') Thermal Relic DM, Most Conservative α D = 0.5, m A' = 3 m χ BaBar Thermal Relic E137 LSND E787 E949 Relic Density Scalar BDX@JLab EOT 3, 10, 20 events Relic Density Fermion mm χ (MeV) χ (MeV) y = ϵ 2 αd (m χ/ma') BDX@JLab EOT, 3,10 & 20 Events Leptophilic DM, Most Conservative: m A ' [MeV] α D = 0.5, m A' = 3 m χ BaBar Borexino Leptophilic E137 Relic Density Scalar Relic Density Fermion BDX@JLab EOT 3, 10, 20 events m χ (MeV) m χ [MeV] m A (MeV) 9

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 10

11 Muon flux measurement 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/µA 11

12 Hall T ent 12

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

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 ~10 22 electrons on target. 14

15 Backup Slides 15

16 Signal: χ interaction in detector CsI Detector Electron Recoils, m A ' = 100 MeV, m χ = 10 MeV, ϵ = 10-3, α D = 0.1 Log( Rate (GeV -1 ) ) [ GeV -1 EOT -1 ] dnsig dee E e [GeV] 0 10 Eshower (GeV) Signal Efficiency ~ 20% for E thresh > 0.3 GeV Parameters: M χ =10 MeV, m A =100 MeV 16

17 Estimated neutrino fluxes at the detector Decays at rest Decays in flight Expect < 10 ν e background interactions for EOT There are 10 times more ν µ interactions, but they are identifiable and can be used to normalize the ν rate. 17

18 Beam Backgrounds ν µ Neutrinos survive to detector FLUKA ν e Muons range out in Fe GEANT4 Photon and neutron cascades absorbed in shielding Detector 18

19 SLAC E137 LDMA limits No events seen EOT ~ GeV Battel PRL 113 (2014)

20 BDX-Hodo prototype 20

21 BDX Collaboration 21

22 BDX inner detector A. Celentano 22

23 BDX active veto 23