the drift experiment: recent results from the drift-iid detector james battat wellesley college [for...
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The DRIFT experiment: Recent results from the DRIFT-IId detector
James BattatWellesley College
[for the DRIFT collaboration]
CYGNUS 2015 @ Oxy2015 June 2nd
James Battat, Wellesley College, CYGNUS2015
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Overview of talk
• CS2 as negative ion driftMartoff et al. NIMA, 400 (2000); Snowden-Ifft, Martoff, Burwell, PRD 61 10 (2000).
• DRIFT’s successful quest to reduce backgroundsCurrently operating background-freeSnowden-Ifft, Rev. Sci. Instrum. 85 013303 (2014)[DRIFT collab.] Battat et al., JINST, 9 P11004 (2014)[DRIFT collab.] Battat et al., NIMA 794 (2015)
• 2014 SD-proton limit: 1 pb at 100 GeV/c2.[DRIFT Collab.], Battat et al., arXiv:1410.7821, submitted to Phys. of Dark UniverseSteve Sadler, PhD Thesis Sheffield University, 2014
• Additional improvements give preliminary result of σSD-p~0.3 pb
6/2/2015
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Occidental College
Dan Snowden-Ifft - PI
Jean-Luc GauvreauChuck OravecAlex LumnahNick Waldram
Colorado State University
John Harton – PIJeff Brack
Dave WarnerAlexei Dorofeev
Fred Shuckman II
Sheffield University
Neil Spooner – PIEd Daw – PI
Matt RobinsonDan WalkerSteve Sadler
Andrew ScarffAnthony EzeribeFrederic MoutonTrevor Gamble
Directional Recoil Identification From Tracks
6/2/2015
University of New Mexico
Dinesh Loomba - PIMichael Gold – PI
John Matthews - PIEric Lee
Eric MillerNguyen PhanRandy LaflerJoshua Martin
The University of Edinburgh
Alex Murphy – PI
Wellesley CollegeJames Battat – PI
University of Hawaii
Sven Vahsen – PITom ThorpeJosh Murillo
Boulby Laboratory
Sean Paling – PIEmma MeehanLouise Yeoman
Chris Toth
James Battat, Wellesley College, CYGNUS2015
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DRIFT in Boulby: 2805 m.w.e.
Mei & Hime [astro-ph/0512125]
For scope of work at Boulby, see talk by Chris Toth, Thursday 14:30.6/2/2015
Operated by the UK’s Science & Technology Facilities Council (STFC) in partnership with the mine operators ICL
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Negative ion formationN
ucl
ear
Rec
oil
WIM
PW
IMP
e-e-
e-e-
e-
e-
e-
E-field
Drift direction
Mean electron capture distance is a few hundred microns
Martoff et al., NIMA, 440 (2000)Snowden-Ifft, et al., PRD, 61, 101301 (2000)Snowden-Ifft & Gauvreau, Rev. Sci. Instrum., 84, 053304 (2013)6/2/2015
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Transport of CS2 negative ions
• Diffusion is ~ thermal (both transverse and longitudinal)
low diffusion increases active volume per readout area
• Drift speeds are ~5 cm/ms or ~20 us/mm
Snowden-Ifft & Gauvreau, Rev. Sci. Instrum., 84, 053304 (2013) [arXiv:1301.7145v2]6/2/2015
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Negative ion gas mixtures
• Ar:CH4:CS2, Xe:CS2, CF4:CS2 , CF4:O2:CS2…Martoff et al., NIMA 440 (2000)Lightfoot et al., Astropart. Phys. 27 (2007)
• CS2 is not the only negative ion gasNitromethane (CH3NO2) [Martoff et al., NIMA 598 (2009)]SF6 [see Nguyen Phan’s talk Thr., 13:30]
6/2/2015
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Some DRIFT detector nomenclature
DRIFT-IId 0.8 m3 Demonstrated 2 pb sensitivity in 2012Has since been upgraded and is currently running background-free (texturized thin-film cathode, and 3D fiducialization)
DRIFT-IIe 0.8 m3 engineering prototype for DRIFT-IIICurrently at Occidental College.
DRIFT-III 24 m3 (Proposed)
D-HDDRIFT-HD 0.25 m3 high spatial-resolution (Proposed)
6/2/2015
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DRIFT-IId geometry
6/2/2015James Battat, Wellesley College,
CYGNUS2015
Dimensions in mmFiducial volume is 0.8 m3
900
Image from Burgos et al., NIMA 584 (2008)
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Grid wires-2.8kV100 um diam.
DRIFT-IId geometry
6/2/2015James Battat, Wellesley College,
CYGNUS2015
Left MWPC Right MWPC
Anode wiresGrounded20 um diameter
MWPC: 3 wire planes1 cm gaps552 wires448 fid.2mm pitch
Cathode-32kV
z=0 z=50 cm z=0
900
James Battat, Wellesley College, CYGNUS2015
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Image from M. Pipe PhD Thesis, U. Sheffield, 2011
… 448 anode wires …
Heavy grouping, low channel count100% spatial ambiguity (8-wire = 16 mm periodicity)
DRIFT readout
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The War on Backgrounds
• 2005: 500 evt/day• 2012: 130 evt/day (material
selection)• 2014: 1 evt/day (0.9 um thin-
film cathode)• 2014: 0 evt/day (z-
fiducialization)
6/2/2015
See talk by Eric Miller, Wed., 13:30
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z-fiducialization: differential drift speeds
6/2/2015
Drift direction Proportionality
constant can be measured for various gas mixtures, or calibrated in-situ.
MWPC
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z-fiducialization: limitations
6/2/2015
Po-210
Snowden-Ifft, Rev. Sci. Instrum. 85 013303 (2014).
Data from an R&D vessel, not DRIFT-IId
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DRIFT-IId: some numbers• CS2:CF4:O2 30:10:1 Torr
• Mass of F: 40 g/0.8m3
C: 18 g/0.8m3
S: 96 g/0.8m3
• 30 keVr F recoil = 1 mm range
• CS2- drift speed ~5 cm/ms. (10 ms for full 50 cm drift, 20us/mm)
• Gas gain ~1000
• Source-free running for 46.3 live daysFe-55 calibrations every 6 hoursCf-252 neutron calibration 5 runs, 3.2 live days
6/2/2015
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Events in DRIFT
6/2/2015
RG = Right grid (1 – 8 and sum)
RVG = Right veto (grid)RVA = Right veto (anode)
RA = Right anode (1 – 8 and sum)
• Any anode channel > 30 mV triggers readout of all channels.
• Raw trigger rate ~ 1 Hz• Adverse effect on Ethresh
50% efficiency at ~50 keVr F• Improved trigger
implemented50% eff. at ~20 keVr F
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Events in DRIFT
6/2/2015
RG = Right gridRVG = Right veto (grid)RVA = Right veto (anode)RA = Right anode
Right MWPC, Anode #7 Line
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Data processing
6/2/2015
Stage I cuts
E recon
Bkg rejection
z recon
Signalconditioning
Raw triggers
Noise filtering, undershoot removal, saturation cut
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Data processing
6/2/2015
• xy-fiducialization (veto above threshold)• Temporal ROI cut (+/- 700 us)• Cathode-crossing events (hits in both
TPCs)• Multiples (non-contiguous hits)• Maximum range (all 8 anode channels Ry
>16 mm)• Impulse charge deposition (risetime < 3us)
Stage I cuts
E recon
Bkg rejection
z recon
Raw triggers
Signalconditioning
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Data processing
6/2/2015
• Ratio of ionization in Min. Car. region to total ROI
• Require comparable ionization on anodes and grid
E recon
Bkg rejection
z recon
Raw triggers
Signalconditioning
Stage I cuts
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Data processing
6/2/2015
E recon
Bkg rejection
z recon
Raw triggers
Signalconditioning
Stage I cuts
• Compute event energy in mV*usSum up waveform integrals for all anode channels above an analysis threshold (9 mV).
• Convert to keVee (equivalently NIPs)mV*us to keVee via 55Fe calibration (every 6h, stable to 4%)keVee to NIPs via W=25.2 eV *
• Convert to keVr
Use [Hitachi 2008] prediction.For CS2:CF4 quenching measurements, see talks by Eric Miller (Wed., 13:30) and Alex Lumnah (Thr., 14:00)
* W not yet measured for CS2:CF4:O2 mixture, but expect ~1% change from CS2:CF4, which has been measured [P&S 2009].
[Hitachi 2008] Hitachi, Radiat. Phys. Chem. 77 (10–12) (2008)[P&S 2009] Pushkin & Snowden-Ifft, NIMA 606 (2009)
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Data processing
6/2/2015
Require 3 peaks, evenly spaced
E recon
Bkg rejection
z recon
Raw triggers
Signalconditioning
Stage I cuts
dt ~ 150 us (S to I)Z ~ (0.24 cm/us)*dt ~ 36 cm
I peak width is ~ 50 us, so z-recon gets hard below z ~10 cm.
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Cathode RPR/LEAs
6/2/2015
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Detection efficiency post-Stage I
6/2/2015
50% at ~50 keV50% at ~20 keV
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Nuclear Recoil Detection Efficiency Map
6/2/2015
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DRIFT’s 2015 SD-proton limit
6/2/2015
NEWAGE (2015)
PICO (2015)
DRIFT (2012)DRIFT (2015)
DMTPC (2011)
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Room for improvement
• Improved trigger to capture lower energy eventsFactor of ~2 in threshold
• Improve efficiency at high-zz-reconstruction does not rely on S-peak
• Gas circulation to maintain O2 partial pressureMinority peak ionization is strongly O2 dependent.
• Can we do better at low z (z<10cm)?• Will new backgrounds appear?6/2/2015
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Efficiency Map (prelim.)
6/2/2015
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Preliminary analysis shows 0.3 pb
6/2/2015
DRIFT (2015b, preliminary)
Prelimin
ary
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Events passing cuts
6/2/2015
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Summary
• A 1 pb limit is on the arXiv:1410.7821
• Since then, upgrades to the detector and analysis have improved the reach by another factor of ~3 to give σSD-p~ 0.3 pb
• Have ~65 live-days in-hand (and counting).
6/2/2015
END
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Quenching
6/2/2015
James Battat, Wellesley College, CYGNUS2015
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DAQ has a high-pass filter• To get rid of 50 Hz mains noise.
(1/50Hz = 20ms = 20000us)• For C=2200 pF, R=50 Ohm, tau=RC= 0.1us • (see M. Pipe’s thesis, page 61).
6/2/2015
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Waveform conditioning
• Frequency filtering – 55 kHz noise notch filter (HV supply)– 50 Hz line noise (subtract sine fit)
• Undershoot correction– Shaping electronics (4 us shaping time)
cause undershoot
• Analysis threshold is 9 mV (trigger threshold was 30 mV). What is waveform baseline RMS?
6/2/2015
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DRIFT readout
6/2/2015
Anode wires1 9 17 25 …
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Grid512 wires100 um diameter
Anode512 wires20 um diameter
MWPC3 planes1 cm gaps
6/2/2015
James Battat, Wellesley College, CYGNUS2015
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Passes cuts on:• xy
fiducialization• Risetime• Multiples
Fails cut because:• Cathode-
crossing• Range too long
(all anode lines hit)
• ROI cut
• RATE OF ALPHAS???
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Background rejection
Spark cutRatio of ionization in minority carriers region to total ROI ionization
“Ringer” cutRequire comparable ionization on anodes and grid
6/2/2015
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Stage I cuts
• xy-fiducialization (veto above threshold)• Temporal ROI cut (+/- 700 us)• Cathode-crossing events (hits in both
TPCs)• Multiples (non-contiguous hits)• Maximum range (all 8 anode channels Ry
>16 mm)• Impulse charge deposition (risetime <
3us)
6/2/2015
James Battat, Wellesley College, CYGNUS2015
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Energy reconstruction
• Compute event energy in mV*usSum up waveform integrals for all anode channels above an analysis threshold (9 mV).
• Convert to NIPs (equivalently keVee)Calibration constant derived from frequent 55Fe calibrations studies – stable to ~4% over experiment. Also: W=25.2 eV *
• Convert to keVr
Use [Hitachi 2008] prediction.For CS2:CF4 quenching measurements, see talks by Dinesh Loomba (DAY, TIME) and Alex Lumnah (DAY, TIME)
* W not yet measured for CS2:CF4:O2 mixture, but expect ~1% change from CS2:CF4, which has been measured [P&S 2009].
[P&S 2009] Pushkin & Snowden-Ifft, NIMA 606, 2009[Hitch 2008] Hitachi, Radiat. Phys. Chem. 77 (10–12) (2008)
6/2/2015
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Transport of CS2 negative ions
• Diffusion is ~ thermal (both transverse and longitudinal)
• Drift speeds are ~5 cm/ms aka ~20 us/mm“low-field” approximation hold even at 580 V/cm
Snowden-Ifft & Gauvreau, Rev. Sci. Instrum., 84, 053304 (2013) [arXiv:1301.7145v2]6/2/2015
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Grid552 wires, 448 fid.2 mm pitch100 um diameter
Anode552 wires, 448 fid.2 mm pitch20 um diameter
MWPC3 planes1 cm gaps
z=0 z=50 cm z=0
DRIFT-IId geometry
6/2/2015
900
TO DO• Dates for new limit run (July to October 2014)• Verify gas gain = 1000• Why is 55-day efficiency so high at z~50cm? (used to be 10-30%, is now 25-90%)?• Capacitance of ONE anode wire? Cap. when grouping 56 of them into one preamp?
• Rates of events that get cut???• What is alpha rate? ~1/4 Hz.
• Why are so many anode wires needed for the veto? (43 on each side, plus 9 guard wires on each side).
• What is new triggering scheme (integral?)18 us boxcar averaging for trigger. New threshold is 15 mV. 50% at 500 NIPs
• Validation that waveform filtering (notch filter, 50 Hz, undershoot removal) preserve event quantities like energy, head tail, etc.?
• Why integrate waveforms (vs. take amplitude) for NIPs? Isn’t it already integrated by electronics?
• Check collaboration slide• Fix “Boulby Mine” slide.• Fe55 252 e-
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Events passing cuts
6/2/2015