r&d for future zeplin

R&D for Future ZEPLINM.J. Carson, H. Chagani, E. Daw, V.A. Kudryavtsev,

P. Lightfoot, P. Majewski, M. Robinson, N.J.C. Spooner

University of Sheffield

Pawel Majewski, Univ. of Sheffield Cryogenic Liquid Detectors for Future Particle Physics; LNGS, 13-14 III 2006

D.B. Cline, W.C. Ooi, F. Sergiampietri(a), H. Wang, P. Smith(b), X. Yang

Physics and Astronomy, UCLA , (a) Pisa, (b) RAL&UCLA J.T. White, J. Gao, J. Maxin, G. Salinas, R. Bissit, J. Miller, J. Seifert

Department of Physics, Texas A&M University T. Ferbel, U. Schroeder (Chemistry), F. Wolfs, W. Skulski,

J. TokeDepartment of physics and Astronomy, Rochester University

Y. GaoSouthern Methodist University, Texas

Presentation outline

• Introduction• Detector geometry • Principles of operation - characteristics of an event• Light collection• Signal readout - charge gain in liquid xenon• Dark Matter limit• Program for R&D


IntroductionOur goals:• Large mass of sensitive LXe in a scale of Tonnes• Simple detector geometry • Very low background radiation• Sensitivity to very low energy events - possibility of few photons detection - large surface photocathode - possibility of few electrons detection -> Both requires high gain in liquid

Large mass with maximum surface acting as a photocathode : SPHERICAL GEOMETRY


LXe physical properties• Energy/scintillation photon W_ph =21.6 eV • Scintillation Absorption length > 100 cm• Energy/el-ion pair: W=15.6 eV• Saturation velocity of electrons from E=3 kV/cm: v=2.6 mm/s• Threshold electric field for proportional

scintillation: E=400-700 kV/cm• Threshold electric field for electron multiplication: E~1 MV/cm• Maximum charge gain measured 200-400


(table from T.Doke NIM 196 (1982) 87)

Spherical TPC filled with LXe

Outer sphere

Photocathode coated with CsI

Central ball with charge readout Field shaping rings


Detector structure

Central ball 4 covered with charge collecting and amplifying micro-structure

•Sensitivity to single electron•High readout segmentation for position information

Requirements:


Electric field distributionCan detector operate with a non uniform

field ?

Electron drift velocity = f (E)

3 kV/cm

(L.S.Miller at al. Phys. Rev. Vol. 166, 1967)


Charge and light yield = f (E)

Measured charge and light yield for E<5 kV/cm

Extrapolation to E<75 kV/cm(Thomas-Imel model Phys.Rev A 38 (1998)

5793) (T.Doke et al. Jpn.J.Appl.Phys. 41 (2002) 1538)


(E.Aprile et al. astr-ph/0601552)E= 3 kV/cm

5e/keVr@ 2KV/cm

Charge and light readout

• Scintillation light photons converted into photoelectrons from the CsI photocathode

- CsI QE ~ 30 % @ E>3 kV/cm (E.Aprile et al. NIM A 343, 1994) - 4 coverage except shadowing

• Ionisation electrons and photoelectrons readout with segmented charge amplifying device delivering energy and position information

- low primary charge sensitivity with charge gain


Charge amplification in LXE

Conditions for electron multiplication and secondary scintillation in liquid xenon :

Electric field threshold for avalanche development : ~ 1MV/cm

Electric field threshold for proportional light: 100-150 kV/cm (B.A. Dolgoshein et al. JETP Lett. Vol. 6, 1967)

400-700 kV/cm (K.Masuda et al. NIM 160, 1979)


H.Wang 1991, gain : 40

Event generation (1)



Interaction in the sensitive volume



Simultaneous creation of scintillation UV light and …



… creation of ionisation charge



Scintillation UV photons converted into photoelectrons



First pulse generated



Proportional scintillation UV photons converted into photoelectrons



Second pulse generated



First after–pulse generated



Second after–pulse generated and pulses generation continues …


Light collection MC calculations

•Energy to produce UV photon: W= 21.6 eV

•Light attenuation length: 100 cm

•CsI QE : 20, 30 %

•Electron lifetime: 0.5, 1 and 5 ms

Shadowing

3D example:


MC calculations: results

At R=50 cm, light collection = 4-7.5 phe/keV


Charge amplification - wires

S.E Derenzo et al. Phys. Rev. A Vol 9,1974 maximum gain : 400

M.Miyajima et al. NIM Vol 134 ,1976 maximum gain : 100


Readout wires

Problems with gain in liquid

• Slow motion of avalanche ions building space charge

• Local imperfections of the readout structure

• Purity of LXe

• Large amount of created UV photons causing after-pulses leading to discharge

• Bubble formation on the sharp edges of the readout electrode hence conducting path creation(J.G. Kim et al. NIM A 535 2004)


Charge readout - microstructures

Micropattern detectors :• micromegas• micro-dot• MSGC (already used in LXe with gain =10) (A.P.L. Policarpo et al. NIM A 365 1995)

Already used in LAr (no gain due to discharges)

Cold field emission device:

High electric field ~ 1MV/cm with small differential voltage

(J.G. Kim et al. NIM A 535 2004)


Charge readout – simulation (1)

Tools: Garfield (Analytic) by R.Veenhof (CERN) Maxwell (FEM) by Ansoft

Electric field near wire surface

Recalculated LXe gain in single wire chamber

Townsend coefficient from S. Derenzo et al. Phys. Rev. A Vol 9,1979 (large errors)


Charge readout - simulation (2)

Microstructure modelling

What is needed :

• Local high electric field for high gain

• 100 % 4 charge collection

• Electric field < 400 kV/cm when V_cath=0 and E_drift = 75 kV/cm

Drift field

75 kV/cm

5 kV/cm


Charge readout – simulation (3)

Simulated multiplication Electric field strengthon the axis of the cell

75 kV/cm

0 V at the cathode


How to avoid feedback pulses ?

Using HV switch : When V_cath = 0 E_max < 400 kV/cm

Field on the cell axis:

Field at the cell entrance:


Dark Matter Limit

Assumptions:• LXe mass: 1 Tonne• Run period: 1 year• Energy range: 4-50 keVnr

O events detected

1O events detected


Backgrund sources in 1 Tonne LXe detector:(M.Carson et. al. NIM A 548 (2005) 418)

A)222 Rn events/year: 1.46*10^6B) PMTs (Hamamatsu R8778) events/year: 3.65*10^5C) 85 Kr events/year: 9.1*10^5

R&D program (goals to achieve)

• Study of the scintillation properties of LXe at high electric field (scintillation light and

charge yield)

• Study of the electric field threshold for proportional light creation

• Explore possibility of the high gain in LXe using micro-structure devices

(study of the limitations: maximum gain, stability in time, energy resolution)

• Work on the feedback pulses suppression


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