DRIFT I experiment forDark Matter Search
Dark Matter Review
Setupand Installation
Results.
R&D for DRIFT II .
Conclusion.
Rachid Ayad , Temple University, for:
R. Ayad, C. J. Martoff, M. Schachter Temple University, PA, USA
J. Kikpatrick, D. P. Snowden Occidental College, CA, USA
T. B. Lawson, P. K. Lightfoot, B. Morgon, M.
Robinson, N. J. C. Spooner .
University Of Sheffield, UK
Evidence Of Dark Matter
Zwicky (1930): From speed and mass of galaxies, galaxies cannot hold together
Later on, same problem with galaxies: stars orbit too fast to be bound by visible light.
WMAP(Wilkinson Microwave Anisotropy Probe)
CMB photons (Cosmic Microwave Background) decoupled during the Big Bang at a temperature of ~ 3K: For a flat universe the size of cluster is ~ 1 Deg., so ~1
With the help of other peaks, WMAP was able to give:
tot = 1.02 +/- 0.02
dark-energy = 0.73 +/- 0.04
CDM = 0.27 +/- 0.04
baryonic = 0.044 +/- 0.004
A. Kosowsky et al Phys. Rev. D, 66, 63007, 2002.astro-ph/0302218, and astro-ph/0302207
AnodeWires
Anode Wires
Bottom MWPC (512 Chans)
Top MWPC (512 Chans)
DAQ RACKSlow Control RACK
VME ADC BAORD
Ribbon Connector32 wires TPC Input
Gain: -Full range: 2.4 pC -1pC/V,~4000 e-/adc count
Shaper:-24 Sec FWHM
Digitizer:-Resolution: 12bits-Sampling Rate: 1MS/sec-Buffer Memory Depth: 16K Samples/Channel-Relative Accuarcy: +/- 1 LSB
Electronic Calibration
Trigger System
(modified comedi driver)
Gas Gain Calibration Using Fe55 Source
Escape Peak
Gain= (2998*158)/300 ~ 1579
Neutron CalibrationSend Neutrons from
252Cf source: dN/dE = sqrt(E)exp(-E/T) T = 1.3 MeV
Use Geant3 to generate nuclear recoil and dE/dX
Garfield drifts Primary Negative Ions to the anode wires .
Simulated Neutron Event
Erecoil = W*NIPS W = 45 eV +/- 5 eV
...we need neutron shielding to achieve proposal goals.
Unshielded vessel With .5m (8 tons) CH2 shielding
(installed March 23, 2004)
Daya Analysis
Analysis based on 400 GB recorded data .
~ 70,000 triggers
trigger rate (veto rejection) below .05 Hz
More EventsClean neutron recoil Range-Energy from 252-Cf source
green; unshielded n 90% limit
red: shielded n 90% limit
(shielded, no software veto)
Analysis Procedures
DST produced; then 14 simple, fully automated cuts applied
Bottom Line
Two independent analyses (Temple, Oxy-Sheffield) consistent on this effect.
Unshielded: 2.4 +/- 0.52 events per day
Shielded: 1.1 +/- 0.33 events per day
Rates:
Shielding Effect: 1.3 +/- 0.62
Accepted Background: still zerostill zero
Focus on WIMP region
Events below the 90% neutron line are WIMP candidates or background neutrons.
One event in 9 days unshielded data looks like a room neutron
5 more below 1000 NIPS are probably neutrons .
Nuclear RecoilZone
R&D for DRIFT II and Helium Mixtures
NI drift and gain works fine with GEMs (physics-0310124 Miyamoto et al [experiments run at Temple Univ.]
allow pixelization to few 100 um with row-and-column readout
Helium mixtures with CS2 also studied in TPC prototype at Temple Univ., physics-0406114.
Helium buffer gas allows NI drift and gain at total pressure 1 bar
NO vacuum vessel- great cost and BG savings
Conclusion DRIFT I showed that negative ion gases can be
used in TPCs for Dark Matter Search: No need to magnetic field.
Promising low background capability. Upgrade to DRIFT II is at the development
phase: - - Use GEM or TPCs at 1 bar, with light buffer gas, which will reduce the cost of a vacuum vessel and its maintenance. - Use large mass of ionizing medium for WIMP limit study and directionality study/rejection.
WIMP Direct Experiments
DAMA (Dark Matter Search): In Gran Sasso, with 100 kg target NaI scintillator crystal,, where nuclear recoil/ electron-gamma Ionization rejection is achieved by Pulse Shape discrimination. 1400 m deeper
CDMS “Cryogenic Dark Matter Search”: 0.52 Kg of Ge/Si, where Nuclear recoil/electron-gamma Ionization rejection by comparing phonon surface heat to Ge/Si ionization. 10 m deeper (Now In Soudan)
EDELWEISS “Experience pour DEtecter Les Wimps En Site Souterrain” In Modane Site”: 0.32 Kg of Ge/Si, where Nuclear recoil/electron-gamma Ionization rejection by comparing phonon surface heat to Ge/Si ionization. 1700 m deeper
ZEPLIN “Zoned Proportional scintillation in Liquid Noble gases” In Boulby Mine: 3kg of Pure Xenon, where Excited Xenon* gives two Gamma Rays that can be discriminated for Nuclear recoil/electron-gamma ionization by pulse height. 1100 m deeper.
Nuclear-Electron Recoil Rejection in Ge/Si detector
DM experiments Upper limits
CS2-He(Ar) GEM test at Temple Univ.