The DRIFT experiment: Recent results from the DRIFT-IId detector James Battat Wellesley College [for...

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


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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]

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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)

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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


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


116/2/2015

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

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Drift direction Proportionality

constant can be measured for various gas mixtures, or calibrated in-situ.

MWPC


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z-fiducialization: limitations

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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

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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

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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

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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.)

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Preliminary analysis shows 0.3 pb

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DRIFT (2015b, preliminary)

Prelimin

ary


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Events passing cuts

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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).

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Quenching

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346/2/2015


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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).

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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?

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DRIFT readout

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Anode wires1 9 17 25 …


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Grid512 wires100 um diameter

Anode512 wires20 um diameter

MWPC3 planes1 cm gaps

6/2/2015


396/2/2015

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

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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


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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-


CYGNUS201545


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Events passing cuts

6/2/2015

The DRIFT experiment: Recent results from the DRIFT-IId detector James Battat Wellesley College [for...

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