warp - international center for relativistic astrophysics · 2009. 8. 7. · fast component for...

WArP

The WArP Experiment

Claudio Montanari

I.N.F.N. - Pavia - Italy

WArP Collaboration

P. Benetti, E.Calligarich, M.Cambiaghi, C.!Montanari, A.Menegolli, G.L.Raselli,

M.Roncadelli, M.Rossella, C.Vignoli"

INFN and Department of Physics at University of Pavia (Italy)

F.Carbonara, A.G.Cocco, G.Fiorillo, G.Mangano"

INFN and Department of Physics at University of Napoli (Italy)

R. Acciarri, M. Antonello, N. Canci, F.Cavanna, F. Di Pompeo, L. Grandi,

O.Palamara, L. Pandola, C. Rubbia*, A. Szelc, E. Segreto"

Laboratori Nazionali del Gran Sasso, INFN and L’Aquila University (Italy)

F. Calaprice, C. Cao, A. Chavarria, C.Galbiati, B. Loer, R. Saldanha"

Princeton University (USA)

B.Baibussinov, S. Centro, M.B. Ceolin, G. Meng, F. Pietropaolo, S. Ventura"

INFN and Department of Physics at University of Padova (Italy)

Claudio Montanari - The WArP Experiment – MG12 Conference –Paris, July 17, 2009! 2!

The WArP Programme

•! The WARP experiment is intended to search for WIMP recoils in LAr with 140 kg fiducial volume and a detection threshold of < 20 KeVion.

•! A unique feature of this experiment is that the active volume is tightly surrounded by a ! 8 ton, 4 " active anticoincidence, also of LAr, in order to veto not only ! and ", but especially, entering and exiting neutrons with a recoil detection threshold as low as ! 20 keV.

•! The WArP technology has been established during several years of R&D, started in 1992 in CERN and prosecuted during the last decade in few INFN Labs (LNGS, Pavia and Padova).

•! The 100 liters detector is coming to operation. Filling with ultra-purified liquid argon was completed at the beginning of May, 2009. Calibration procedures are ongoing. Data taking will be started soon.

•! The 100 liters is the largest detector for direct dark matter searches presently in operation.

3!Claudio Montanari - The WArP Experiment – MG12 Conference –Paris, July 17, 2009!

WIMP Detection in WArP •! Three simultaneous criteria to discriminate

potential WIMP recoils from backgrounds:

1! Simultaneous detection of prompt scintillation and drift time-delayed ionisation in Liquid

Argon:

!!pulse height ratio strongly dependent from columnar recombination of ionizing tracks.

!!3D reconstruction of event position.

2! Pulse shape discrimination of primary scintillation:

!!wide separation in rise times between fast (! 10 ns) and slow (! 1.6 "s) components of the

emitted UV light.

3! Precise 3D reconstruction of event position:

!!Precise definition of fiducial volume; additional rejection of multiple neutron recoils and gamma background

4!

PMTs

Primary scintillation

Secondary scintillation

Interaction

E-F

ield Ionization

electrons

Liq

uid

Gas

Double Phase Argon Chamber!

Only detector with triple discrimination technology. !

Largest discrimination of "/!-induced backgrounds. !

Claudio Montanari - The WArP Experiment – MG12 Conference –Paris, July 17, 2009!

Discrimination Technique

5!

!!S1 = primary (prompt) scintillation signal!

!!S2 = secondary (delayed) scintillation signal (proportional to ionization)!

"!Minimum ionising particles: high S2/S1 ratio (~100) + slow S1 signal.!

"! # particles and nuclear recoils (R-like events): low (<30) S2/S1 + fast S1.!

Argon recoil!Electron!(A)! (B)!S2!

S1!

S2!

S1!

S1! S1!

Drift time!


R&D Activities •! Several years of demanding R&D have been carried on in the Collaboration

Labs (and are still in progress) in order to develop the WArP technology:

–! In CERN: first developments of the technology in Xenon; detailed studies

of wavelength shifter performance; detailed studies of PMTs performances

(Quantum Efficiency and Collection Efficiency); dedicated tests and measurements of light yield in liquid Argon.

–! In Pavia: first developments of the double phase technology in Argon;

PMTs studies; early studies of wavelength shifter performances; development and first measurements with the 2.3 liters prototype;

procurement and study of depleted Argon (! 6 kg) from centrifugation.

–! At LNGS: extensive tests and measurements with the 2.3 liters prototype;

measurements of the effects of liquid Argon contamination from Nitrogen and Oxygen; tests of light yield in liquid and gas Argon.

–! In Naples: extensive tests of PMTs behavior in liquid argon.

–! At Princeton: R&D on high light yield detectors (! 5 phel / keV); search,

extraction and purification of depleted Argon from underground sources (two sources identified and qualified; 5 kg of depleted argon produced and

under measurement).


7!

The 100 liters detector

"! Sensitive volume = 100 liters (140 kg).

!! 3-D event localization by means of:

#! Drift time recording (vertical axis);

#! Centroid of PM’s secondary signal amplitudes (horizontal plane).

"! 4$ active VETO system:

!! tags and measures the neutron-induced background with an ID-factor ! 99.99 %;

"!Construction accomplished between mid 2004 and November 2008.

"!Detector commissioning: December 2008

to May 2009 (vacuum, cooling and filling with ultra-purified Lar)

"!Data taking starting.

"!Designed also to host a 1 ton detector. Passive neutron and gamma shield

Active Veto

(6000 liters Lar)

100 liters

Chamber


8!

Clean Room Construction (Sept. 2007 - March 2008)

Dressing room

•! Equivalent to 100000 class

clean room

•! De-humidified: humidity kept to less than 50% to

preserve the waveshifting

layer


9!

Pre-assembly Operations

(Mar-May, 2008)

$!Detector components have been pre-assembled in a clean area of the external facilities of LNGS

$!The wavelength shifter was then evaporated on the plastic reflective layer

$!Quality of the evaporation has been routinely controlled with a dedicated chamber operating with argon gas

$!Components have then been transported underground for the final assembly

Active Veto components

3” PMT

Final divider

(Kapton substrate)


10!

Photomultipliers

"! Use photomultipliers developed in co-operation with Electron Tubes EMI

to work at LAr temperature with high photocathode efficiency. "! 7% coverage in the Active VETO (300 3” PMTs)

"! 10% coverage in the Inner Detector "! High level of quality testing implemented both from manufacturer and on

WArP Collaboration side (Labs of Naples, Italy).


11!

Inner Detector Assembly (Jun, 2008)

Race Tracks

Reflector

Grids

Phototubes


12!

Active Shield Assembly (Oct, 2009)


13!

Active Shield

Assembly

(Nov., 2008)

13


14!14

Installation in the main cryostat (December 17th 2008)


15!

R/O Electronics

Front-end custom made from

CAEN. DAQ and logic based on

commercial components.


SAN

FE PC1

EB PC1

SAN

FC switch

EB PC N EB PC2

PM

cPCI

PM

EBM

GTP

80 MB/s @ 300 Hz 1/10 zero skipping

~80 MB/s

100 MB/s

~400 MB/s

10x20 GE switch

~400M B/s Tot. Thrgh

ac240 ac240 ac240 ac240

PM PM PM PM PM PM

FE PC5

cPCI ac240

PM PM

ac240

PM PM

Based on high level commercial solution

from Aquiris. Online data reduction and pre-processing

with high speed FPGA Easily scalable

INNER DETECTOR! ACTIVE SHIELD!

100 liters Vacuum

Vacuum was measured!

by three gauges,!

two cold cathode !

(identical model) and !

a mass spectrometer.!

The gauges are located !

on the top of the !

cryostat.!

Final vacuum (before

cooling):!

2 ÷ 6 x 10-6 mbar!

Lowest value was given by

the mass spectrometer.!

Phase 1:

Vacuum pumping (Dec. 23rd, 2008 % May 5th, 2009)


17!

•! On May 5th (the day after LNGS restart, after the earthquake),

WArP-100 commissioning (cooling+filling) was started.

•! Initial Vacuum level (by pumping): 2÷6 x 10-6 mbar

•! Cooling: by “low quality” LAr circulation detector cooling down to

~ 200 K has been achieved in ~ 2 days.

•! Final Vacuum level (by cryo-pumping): 1÷ 2 x 10-6 mbar

•! Filling:

- “good quality” LAr (equiv. 5.5 GAr grade) further purified

by in line H2O and O2 double stage filter.

- internal material cooling down to ~ 100 K (~ 3 day)

- GAr recirculation/reliquifaction ON

- LAr level rise up to nominal: ~ 3 days

On May 13th, WArP-100 detector technical

commissioning

was successfully completed


18!

During the last weeks all detector components are slowly moving

into operation:

•! PMT bias voltage rise (and PMT test): 335/337 OK % see first

recorded events

•! noise reduction - completed

•! LAr purity measurement - rather good % see plot

•! inner detector HV - problem under investigation

•! DAQ & trigger - debugging phase

•! off-line - under tuning/development


19!

“SLOW” Event

(Beta from 39Ar)


20!

Average waveform

(June 1st data)

waveform fit

(two exp. components).

&long % indication of LAr

purity:

&long(fit) ! 1 #s

(nominal 1.2 "s)

'

satisfactory LAr purity

(after filling)

Long decay

Fast decay


21!

WArP Discovery Potentials

WArP Report – Consiglio di Sezione di Pavia – 23 maggio

2008

(3)-WArP 100

liters 3 months

no background

(2009÷2010)

(4)-WArP 1 ton

3 months no

background

(2011÷2012)

(2)-WArP 2.3 liters

“clean” liquid, no

background

(5)-SuperWArP

(10 ton)

3 months no

background Claudio Montanari - The WArP Experiment – MG12 Conference –Paris, July 17, 2009!

22!

Conclusions

•! Since May 13, 2009 WArP is an active experiment.

•! The 100 liters detector, with a 4# active shield of about 8 tons is the largest experiment for direct Dark Matter searches presently in operation.

•! The detector can be upgraded to 1 ton sensitive mass as part of the approved program.

•! Calibration and debugging procedures are in progress.

•! Data taking for WIMP search to be started soon.


WArP Main Extrapolation Data Electrons total light yield @ no field 1.7(pessimistic) phe / keVe

Electrons (20-60 keV) reduction @ 1 kV / cm 0.67

Electrons total light yield @ 1 kV / cm 1.14 phe / keVe

Electron energy 30 40 50 60 keV

Fast component fraction (electrons) 0.35 0.32 0.30 0.29

Fast component for electrons @ 1 kV / cm 0.40 0.37 0.35 0.34 phe/keVe

Slow component for electrons @ 1 kV / cm 0.74 0.77 0.79 0.80 phe/keVe

Lindhard factor @ no field 0.25 0.25 0.25 0.25

Recoils total yield (any field) 0.425 0.425 0.425 0.425 phe/keVi

Fast component for recoils 0.32 0.32 0.32 0.32 phe/keVi

Slow component for recoils 0.11 0.11 0.11 0.11 phe/keVi

Energy scan

Recoil energy 30 40 50 60 keV

Fast component for recoils 9.6 12.7 15.9 19.1 phe

Fast component for electrons (identical) 9.6 12.7 15.9 19.1 phe

Slow component for recoils 3.2 4.25 5.3 6.4 phe

Slow component for electrons 17.8 26.9 36.4 45.8 phe

Electrons energy 28.5 38.0 47-5 57.0 keV

Rate above threshold @ ((p) = 10^-42 cm^2 0.058 0.042 0.031 0.021 ev/kg/day

Rate for 100 kg WArP @((p) = 10^-44 cm^2 21.2 15.4 11.3 7.5 ev/year

Rate of 39Ar in 100 kg WArP @ 20keVe < E < 40keVe 1.1 E 08 ev/year

Rate for 1 ton WArP @((p) = 10^-45 cm^2 21.2 15.4 11.3 7.5 ev/year

Rate of 39Ar in 1 ton WArP @ 20keVe < E < 40keVe 1.1 E 09 ev/year

Rate for 10 ton WArP @((p) = 10^-44 cm^2 21.2 15.4 11.3 7.5 ev/year

Rate of 39Ar in 10 ton WArP @ 20keVe < E < 40keVe 1.1 E 10 ev/year

25!

Inner Detector (100 liters) External Heigth! 89 cm!

External

Diameter!68 cm!

Internal Heigth! 60 cm!

Max Int. Diam.! 50 cm!

Min. Int. Diam.! 46 cm!

LAr Volume! 100 liters!

LAr Mass! 140 kg!

PMTs!31 x 3” ∅ 6 x 2” ∅ !

Coverage! 10 %!

Walls

Reflectivity!94%!

Trigger

Threshold!≲ 5 keV!

Drift Field! 1 kV/cm!

Max Drift Field! 1.5 kV/cm!


26!

Active Shield

External Heigth! 260 cm!

External Diameter! 220 cm!

Internal Heigth! 220 cm!

Internal Diameter! 180 cm!

Minimum LAr

Thickness!60 cm!

LAr Volume! 5600 liters!

LAr Mass! 7850 kg!

PMTs!264 x 3” ∅ 36 x 2” ∅

Coverage! 7 %!

Walls Reflectivity! 94 %!

Threshold! 8 keV!


warp - international center for relativistic astrophysics · 2009. 8. 7. · fast component for...

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