taup conference - darkma’er%search%results%from% … · 2015. 9. 7. · 4 (2012) wimp mass...

Dark Ma'er Search Results from PICO-‐60 and PICO-‐2L

Russell Neilson, Drexel University TAUP 2015, Torino, September 7-‐11 2015

•  COUPP-‐4: superheated fluid 4 kg of CF3I

•  Observe bubbles with two cameras and piezo-‐acoustic sensors.

PICO bubble chambers

TAUP, September 7, 2015 2 Russell Neilson

Bubble chambers as nuclear recoil detectors

•  Thermodynamic parameters are chosen for sensitivity to nuclear recoils but not electron recoils.

•  Better than 10-‐10 rejection of electron recoils (betas, gammas).

•  Alphas are (were) a concern because bubble chambers are threshold detectors.


Gamma background rejection


Bubble nucleation probability from gamma interactions in C3F8 and CF3I

0 2 4 6 8 10 1210−12

10−11

10−10

10−9

10−8

10−7

10−6

10−5

10−4

10−3

10−2Gamma Rejection

Threshold (keV)

Prob

abilit

y

CF3I (various)CF3I fitC3F8 variousC3F8 fit

Preliminary

•  Discovery of acoustic discrimination against alphas (Aubin et al., New J. Phys.10:103017, 2008)

–  Alphas deposit their energy over tens of microns.

–  Nuclear recoils deposit theirs over tens of nanometers.

•  In PICO bubble chambers alphas are several times louder.

Daughter heavy nucleus (~100 keV)

Helium nucleus (~5 MeV)

~40 μm

~50 nm

Observable bubble ~mm

Acoustic discrimination


Three new results

•  PICO-‐60 (experiment formerly known as COUPP-‐60) –  preliminary DM results.

•  PICO-‐2L Run-‐1 –  2015 DM result.

•  PICO-‐2L Run-‐2 –  Status report from an ongoing run.

TAUP, September 7, 2015 Russell Neilson 6

PICO-‐60


Filled with 36.8 kg of CF3I. PICO-‐60 Run-‐1: June 2013 to May 2014. Run-‐2 with C3F8 target in 2016.

8

PICO-‐60 at SNOLAB

TAUP, September 7, 2015 Russell Neilson

PICO-‐60 results

−1 −0.5 0 0.5 1 1.5 2 2.50

50

100

150

200

250

300

350

400

450

500

ln(APhigh)

Cou

nts

AmBe source dataWIMP search data

Alphas

Unknownbackground


WIMP search data show ~2000 background events of unknown origin, with mean Acoustic Parameter (AP) slightly above nuclear recoil peak.

The unknown background

0 100 200 300 400 500

101

102

Expansion time [s]

Rat

e [c

ount

s/da

y]

Unknown backgroundAlphas


Unknown background Alphas

The unknown background distributions are markedly different from alphas (and Dark Matter).

Combined PICO-‐60 cuts

0 10 20 30 40 500

10

20

30

40

50

Expansion time bin (equal exposure)

AP b

in (e

qual

exp

osur

e)

0

5

10

15

20

25

30

35

40


0 50 100 150−150

−100

−50

0

50

100

150

200

R2/Rjar

[mm]Z

[m

m]

48.2% combined efficiency, and no surviving background events

PICO-‐60 preliminary limits

101 102 103

10−45

10−44

10−43

10−42

PICO−60 (prelim.)

XENON100

CDMS−II

DarkSide−50

LUX

COUPP−4 (2012)

WIMP mass [GeV/c2]

SI W

IMP−

nucl

eon

cros

s se

ctio

n [c

m2 ]


cMSSM

SIMPLE

COUPP−4 (2012)

(χχ→

W+ W

)

(χχ→

bb)

IceCu

beSK (hard)SK (soft)

CMS

ATLAS

PICASSO (2012)

PICO−2L

XENON100

PICO−60 (prelim

.)

WIMP mass [GeV/c2]

SD W

IMP−

prot

on c

ross

sec

tion

[cm

2 ]101 102 103 10410−40

10−39

10−38

10−37

10−36

Statistical penalty for setting cuts on data is calculated with Monte Carlo (similar to Optimum Interval method: S. Yellin, Phys.Rev. D66 (2002) 032005) We’re currently upgrading PICO-‐60 for a new run with C3F8 target.

PICO-‐2L

Silica jar is an exact replica of COUPP-‐4 jar.


Two liter active mass of C3F8. •  Same size as COUPP-‐4. •  Re-‐uses COUPP-‐4 location/water shield at SNOLAB. Better fluorine sensitivity than CF3I: • Twice the F density. • Lower threshold. • Improved efficiency. • More stable chemistry.

Water (buffer)

C3F8 (target)

To Hydraulic Cart Mineral Oil

(hydraulic fluid)

Bellows

Acoustic Sensors

Fused Silica Jar

Pressure Vessel Cameras

PICO-‐2L at SNOLAB


Filled with 2.9 kg C3F8. Run 1 Oct 2013 to May 2014. Run 2 started Feb 2015.

PICO-‐2L Run-‐1 results

15 TAUP, September 7, 2015 Russell Neilson

No expected neutron background (<1 event at 3.2keV), and no multiple bubble events observed, so these are not neutron events. There are timing correlations of events at 3.2keV with previous events, therefore not DM or neutrons. We set limits by applying a timing cut with MC-‐derived statistical penalty, similar to PICO-‐60.

PICO-‐2L limits


C. Amole et al., Phys. Rev. LeV. 114, 231302 (2015)

3 4 5 6 7 8 9 10 15 20 2510−43

10−42

10−41

10−40 DAMA

CDMS−Si

CoGent

XENON10/100

SuperCDMS

CDMS−lite

LUX

PICASSO 2012

CRESST−II

PICO−2L

WIMP mass [GeV/c2]

SI W

IMP−

nucl

eon

cros

s se

ctio

n [c

m2 ]

cMSSM

SIMPLE

COUPP−4 (2012)

(χχ→

W+ W

)

(χχ→

bb)

IceCu


CMS

ATLAS

PICASSO (2012)

PICO−2L

XENON100

PICO−60 (prelim

.)

WIMP mass [GeV/c2]

SD W

IMP−

prot

on c

ross

sec

tion

[cm

2 ]101 102 103 10410−40

10−39

10−38

10−37

10−36

Background hypothesis


Neutron events ParWally contained alpha decays

Droplet detector: S. Archambault et al.; New J. Phys. 13(2011)043006

Partially contained alpha decays are slightly louder than nuclear recoil events in droplet detectors. Similar effect expected in a monolithic bubble chamber for alpha decays originating in suspended particulate. Program to test this hypothesis by assaying the DM chambers and reproducing the effect in small test chambers.

Background studies

•  To look for particulate impurities, fluids in PICO-‐60 and PICO-‐2L were filtered as they were emptied.


Filter sample from PICO-‐2L buffer fluid. Silica and steel particles found

19

Background studies Filter sample from PICO-‐60 buffer fluid


Quartz particle

PICO-‐2L Run-‐2 •  First bubble February 27, 2015.

•  Physics run started June 12, 2015.

•  Natural quartz inner vessel flange replaced with low-‐radioactivity fused silica.

•  Assembled and filled with particular focus on minimizing particulate contamination.

•  Technical improvements to cooling and piezo-‐acoustic sensors (0% sensor failure in Run-‐2).

•  Bulk event rate consistent with expected neutron background.


flange

active camera cooling

0 20 40 60 80−80

−60

−40

−20

0

20

40

60

80

100

120

R (mm)

Z (m

m)

edge eventshigh APlow AP

0 20 40 60 80−60

−40

−20

0

20

40

60

80

100

120

R (mm)

Z (m

m)

edge eventshigh APlow AP

PICO-‐2L Run-‐1 vs Run-‐2

Run-‐1 3.2keV data •  32 live days •  Est. neutron bkgd 0.9+0.2-‐0.7 events

Run-‐2 3.2keV prelim. data •  ~51 live days and counWng •  Est. neutron bkgd 1.5+0.3-‐1.1 events


Next steps

cMSSM

SIMPLE

COUPP−4 (2012)

(χχ→

W+ W

)

(χχ→

bb)

IceCu


CMS

ATLAS

PICASSO (2012)

PICO−2L

XENON100

PICO−60 (prelim

.)

PICO−60 C3F8 (proj.)

WIMP mass [GeV/c2]

SD W

IMP−

prot

on c

ross

sec

tion

[cm

2 ]

101 102 103 10410−41

10−40

10−39

10−38

10−37

10−36


PICO-‐60 with C3F8 •  C3F8 target fluid •  New vessel with fused

silica flange •  Coated bellows to

eliminated steel particulate

•  Active fluid recirculation with filtering

“Right-‐side-‐up” bubble chamber with no buffer fluid •  Stable against convection

currents •  Simplified fluid handling/

recirculation. •  Wider range of possible

target fluids

Summary •  PICO-‐2L and PICO-‐60 have produced world-‐leading limits on Spin-‐Dependent

WIMP-‐proton interactions with different target fluids.

•  PICO-‐2L also has excellent Spin-‐Independent limits on low-‐mass (few GeV) WIMPs.

•  Both experiments observed a population of background events we believe is due to particulate contamination of the target fluids.

•  After efforts to reduce the background, Run-‐2 of PICO-‐2L now shows an event rate consistent with neutron background.

•  PICO-‐60 is being prepared for a second run with similar improvements and C3F8 target fluid.


C. Amole, M. Besnier, G. Caria, G. Giroux, A. Kamaha, A. Noble

M. Ardid, M. Bou-Cabo, I. Felis

D.M. Asner, J. Hall

D. Baxter, C.E. Dahl, M. Jin, J. Zhang

E. Behnke, H. Borsodi, O. Harris, A. LeClair, I. Levine, E. Mann,

J. Wells

P. Bhattacharjee. M. Das, S. Seth

S.J. Brice, D. Broemmelsiek, P.S. Cooper, M. Crisler,

W.H. Lippincott, E. Ramberg, M.K. Ruschman, A. Sonnenschein

J.I. Collar, A.E. Robinson

F. Debris, M. Fines-Neuschild, C.M. Jackson, M. Lafrenière, M. Laurin, J.-P. Martin, A. Plante, N. Starinski, V. Zacek

R. Filgas, I. Stekl

S. Fallows, C. Krauss, P. Mitra

I. Lawson

D. Maurya, S. Priya

K. Clark R. Neilson

E. Vázquez-Jáuregui

J. Farine, F. Girard, A. Le Blanc, R. Podviyanuk,

O. Scallon, U. Wichoski

Extra slides


26

Particle detection with bubble chambers

•  A bubble chamber is filled a superheated fluid in meta-‐stable state. •  Energy deposition greater than Eth in radius less than rc from particle

interaction will result in expanding bubble (Seitz “Hot-‐Spike” Model). •  A smaller or more diffuse energy deposit will create a bubble that

immediately collapses. •  Classical Thermodynamics says-‐

Surface energy Latent heat

University of Maryland, November 5th, 2014

Russell Neilson

pl

pv

σ

Alpha acoustic calorimetry

10 20 30 40 50 60 70 80 90 100 110

101

kHz

AP

1st in chain2nd in chain3rd in chain


222Rn 4 d

218Po 3 m

210Pb 22 y

214Bi 20 m

214Pb 26 m

214Po 164µs

α (5.6MeV)

α (6.1MeV)

α (7.9MeV)

β β

28 0 5 10 15 20

0

0.01

0.02

0.03

0.04

Seitz Threshold (keV)

Bubb

le R

ate

(nor

mal

ized

)

6.9

F−recoilThreshold 15.2 30.9 61.0

Max Fluorine Recoil: 11.6 keV

C3F8 with waterC3F8 with LABG4 sim with SRIM

Mono-‐energetic neutron beam


Bubble chamber operation

•  Expand the chamber to the superheated state (10sec).

• Cameras see the bubble • Trigger • Stereoscopic position information

• Recompress the chamber (100msec) and wait 30sec after every bubble.

Buffer fluid (water)

Hydraulic fluid

Target fluid (CF3I/C3F8)

to hydraulic controller

Synthetic silica jar


PICO-‐250L

30

•  Proposed 250-‐liter active volume bubble chamber. •  Designed for CF3I or C3F8 target.


taup conference - darkma’er%search%results%from% … · 2015. 9. 7. · 4 (2012) wimp mass...

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