Beam Dump Experiments at JLab and SLAC

Transcription

1 Beam Dump Experiments at JLab and SLAC Brief History (E137 at SLAC) BDX at Jefferson Lab Detector and signal Backgrounds Expected Sensitivity Elton S. Smith, Jefferson Lab On behalf of the BDX Collaboration Light Dark Matter at Accelerators May 24-28, 2017 Elton S. Smith LDMA 2017 May 24-28,

2 SLAC E137 Beam Dump Search for neutral metastable penetrating particles Axions Photinos EM calorimeter and multi-wire proportional chambers Masses < 100 MeV, small production σ, long lifetime PEP Ring E137 Beam Dump End Station A Bjorken PRD 38 (1988)

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

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

5 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 5

6 Kinematics Main features follow from thin-target kinematics and e - energy loss and secondary emission in dump A emitted with forward kinematics, E A ~ E beam High-energy χ beam strongly focused along primary beam direction e- in dump: lower electrons in shower contributes broadening of χ kinematics χ-e - elastic scattering detected in detector with E shower > 0.5 GeV 6

7 Jefferson Lab site 99.7% Complete Elton S. Smith LDMA 2017 May 24-28,

8 Jefferson Lab site Hall A Beam Dump 99.7% Complete Elton S. Smith LDMA 2017 May 24-28,

9 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 Elton S. Smith LDMA 2017 May 24-28,

10 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 0 Elton S. Smith 500 LDMA May 24-28, Z (cm) 10

11 Detector Signal requirements Sensitivity to GeV EM showers Low thresholds Compact footprint and good segmentation Background rejection High efficiency, fast timing Active veto Passive veto Crystal based detector Plastic scintillator Lead Plastic scintillator BUT multiple detectors can be stacked behind each other! Add complementarity with DRIFT Completely different technology and sensitivities Directionality See this session: Dan Snowden-Ifft 11

12 BDX inner detector A. Celentano 12

13 BDX active veto 13

14 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 ) ) dnsig [ GeV -1 EOT -1 ] dee Ee [GeV] 0 10 Eshower (GeV) Signal Efficiency ~ 20% for E thresh > 0.3 GeV Parameters: M χ =10 MeV, m A =100 MeV 14

15 Cosmic-ray Backgrounds 15

16 Cosmic-ray Backgrounds Cosmogenic Background Eliminated with E thresh > 0.3 GeV 16

17 Detector simulations (GEANT4 and FLUKA) Muons Neutrons Exit of beam dump E (GeV) E (GeV) 14 m from beam dump Photons Electrons E (GeV) E (GeV) 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 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. 19

20 Test plan to measure muon flux We have a test plan to measure the muon flux behind the existing Hall A beam dump. The measurements will validate MC and help understand backgrounds Location B Y (cm) 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 Dump to detector = 2064 cm grade level 500 Muon flux Rate ~ 1kHz/µA 0 beam line 500 Fe Det A B C Z (cm) 20

21 Background summary Cosmic-ray Backgrounds Beam-related Backgrounds Measured (beam-off) and subtracted Several meters of overburden Time uncorrelated (CW beam prevents fast time coincidence) Solution: Measurements with BDX prototype and expected overburden, extrapolation to 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 For E thresh >0.3 GeV ν are ultimate background 21

22 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 m(mev) χ [MeV] m A (MeV) 22

23 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. 23

24 Backup Slides 24

25 Visible vs Invisible: Complementarity Viable region of g-2 band (prior to NA64) 25

26 Invisible decay sensitivity 26

27 Inelastic DM scenario 27

28 Signal detection 28

29 29

30 C1 elevation for BDX Y (cm) Dirt density = 1.7 g/cm2 Concrete density = 2.7 g/cm2 3 BDX dimensions = x 70.0 x cm 3 Shaft = x x cm 3 Building = x x cm grade level X (cm) 30

31 X (cm) Dirt density = 1.7 g/cm2 C1 plan for BDX Concrete density = 2.7 g/cm2 3 BDX dimensions = x 70.0 x cm 3 Shaft = x x cm Z (cm) 31