1. University of Sheffield Dan Tovey 1 ZEPLIN-MAX Design Options General considerations ZEPLIN-I design ZEPLIN-II design ZEPLIN-III design Charge read-out

2. University of Sheffield Dan Tovey 2 Introduction Small study group formed to study options for a ZEPLIN- MAX module with view to input to new Proposal. No design concept considered out-of-bounds. Studying: ZEPLIN-I scale-up with improved light collection ZEPLIN-II scale-up with improved light collection ZEPLIN-III scale-up with reduced cost/kg. Charge read-out concepts. Charged with identifying issues requiring further study. Also common problems/solutions associated with different designs. Must identify and solve any potential 'stoppers' !

3. University of Sheffield Dan Tovey 3 We need to be sensitive to majority of SUSY parameter space. Will allow us to discover/rule-out SUSY models (e.g. mSUGRA). General Considerations Complementary to LHC Most favourable case (tan(  ) = 55)

4. University of Sheffield Dan Tovey 4 General Considerations Minimum requirement is sensitivity to  p ~10 -10 pb in the crucial 100 - 300 GeV mass region. Family of sensitivity curves generated using WINDLAS for different thresholds and 1  upper limit on nuclear recoil rate. Gaussian statistics assumed: Conservative Less accurate for high discrimination & low exposure Given detector discrimination, threshold & background rate can use to find required target exposure. Looking at modules in the 100 kg range. Will need neutron shielding, muon veto, multiple neutron rejection (a la CDMS?)

5. University of Sheffield Dan Tovey 5 General Considerations PMTs expensive and also …. … high levels of U/Th/K in graded seal. Gives e-recoil background (but can discriminate). Also gives nuclear recoil events via neutrons (  -n processes) contained within detector (TJS): Neutron veto less efficient (although multi-scatter tag?) Single scatter + absorption is irreducible Could limit  p > 10 -8 pb?  potential 'stopper'! PFS investigating rate  can active neutron veto help? Alternatives include: low background sapphire ET 9226B (~£5000/2"  expensive!) Electrical read-out (see later). APDs

6. University of Sheffield Dan Tovey 6 Gas Phase Detector Proposed by James White et al. (DM2002) 1 tonne Xe gas in 6m x 2m  cylinder (10 bar?) Internal PMTs Central electroluminescence grid. Primary/Secondary discrimination. Needs: No dump No cooling. PMTs

7. University of Sheffield Dan Tovey 7 ZEPLIN-I Consider scaled-up ZEPLIN-I style detector. Increased target mass with PMTs in liquid (factor 2 improvement: NJTS) Similar to fully filled ZEPLIN-II Questions include: What is maximum depth of xenon? What effect does faster PMTs/APDs have on discrim? How can improve light-yield further: integrating sphere? How is Compton veto efficiency effected by increased depth? Take low 85 Kr Xe into account. rig diagram

8. University of Sheffield Dan Tovey 8 ZEPLIN-II Simple scale-up of ZEPLIN-II. BUT can threshold be maintained /reduced? Questions include: What limits the depth: drift field or purity? Does Xe absorbed in PTFE limit disrim (Also an issue for ZII)? If yes can veto fringe events a la ZIII? What do Xe-PTFE events look like (primary/secondary)? Can improve discrim with PMTs in liquid/two layers of PMTs? PMTs in turrets with S 3 type cut to reject background? Efficiency of cut?

9. University of Sheffield Dan Tovey 9 ZEPLIN-III More expensive to get 1 tonne. Not necessary (threshold)? Possible scenario (TJS): Double depth Increase active diameter to 1250 mm Gives 20 X Fid. Vol. (100 kg) Needs 300-400 PMTs. Must minimise LXe reverse field region. Block light from fringe events (DRT)? Reduces PMT granularity (fiducialisation) Try cylinder of ET low background glass? Opaque to 175 nm Primary PS measurement required.

10. University of Sheffield Dan Tovey 10 Charge Read-Out Avoids PMT problems Various options (using CsI): GEMs PPAC (a la ZIII) Micromegas All will need Xe + CH4 2% CH4 saturates in liquid Light propagation in liquid OK? Tests needed: GEM system (condensation?) - see later PPAC - is gain high enough? Micromegas - condensation (uniform field)? Potentially more flexible read-out. Liquid Xe Xe Gas He Cooling Xe Fill GEMs CsI PTFE Reflector CsI Field Shaping Rings e-e- e-e- e-e-   Anode

11. University of Sheffield Dan Tovey 11 Other Ideas Also avoid PMT problems with other schemes: APDs Charge collection in liquid with Si device (needs internal gain) Large area gas-filled photon detectors (e.g. GEMs/Micromegas + CsI, requires window and different gas mixture)  work by Peskov et al. (physics/0106070). Demonstrates an interest from Torino and Aprile groups. Much further study needed.

12. University of Sheffield Dan Tovey 12 Conclusions Long term goal of UKDMC must be to gain sensitivity to complete region of parameter space predicted by at least minimal Supergravity SUSY models. This requires sensitivity to  p ~ 10 -10 pb. Implies tonne-scale Xe detectors. Many ideas for how to achieve this. More ideas welcome. Must firm up designs / identify / answer key remaining questions by end of August  Baseline Design(s) for Proposal.

13. University of Sheffield Dan Tovey 13 Electrical Read-Out of Double-Phase Xenon Detectors Concept Read-out strategies What have we learned so far? Other options

14. University of Sheffield Dan Tovey 14 Concept Need to avoid use of PMTs in ZEPLIN-MAX Expensive Radioactive (gammas)  needs veto! Radioactive (neutrons) Relatively difficult to instrument large area Reduced effective QE through internal reflection at window Direct read-out of charge a favourable option (if it works!) Internal reflective CsI photocathode to detect photons (QE ~ 31% at 175 nm with high E-field) No windows Little radioactivity Simple read-out

15. University of Sheffield Dan Tovey 15 Read-Out Strategies GEMs Believed to work in pure noble gases Cheap (~1$/cm 2 ) Low activity (kapton used extensively in CAST etc.) PPAC Simple (similar to ZIII mirror) Uniform field (see later) Robust Micromegas Hybrid of GEM and PPAC Cheap Robust Uniform field Kapton Cu

16. University of Sheffield Dan Tovey 16 What Have We Learned ? GEMs may work in pure Xe but fragile HV trip does not prevent spark damage Saturated vapour too dense for appreciable gain GEMs do work in Xe + CH 4 at stp (nothing new) Quenches UV photons in gas  increases gain Tischauser et al (1992)  2% CH 4 absorbed in liquid but scintillation in liquid unaffected. GEMs work (for a while) in Xe + CH 4 at 160K Proportional pulses  saturated pulses  no pulses (20 mins)! Gain returns when raise voltage Xenon condensation in non-uniform field (Vadim)? Primary pulses from CsI observed? Need photopeak to confirm. Next try PPAC (HV high enough?), Micromegas Field more uniform in avalanche region.

17. University of Sheffield Dan Tovey 17 Other Options If are unable to obtain stable charge gain in Xe, what other options are there for low background read-out? Opto-electrical read-out using electroluminescence + large area gas avalanche photon detection. Studied by Peskov et al. (physics/0106070) Use gas avalanche PMT Divide chamber in two Quartz window divider above (or below) Xe volume Fill second volume with e.g. Ne. Seal. Electroluminescence in Xe chamber (a la ZII/ZIII) Transmissive CsI coating on window in second volume GEM stack / Micromegas +anode for avalanche multiplication. Guaranteed to work, but complicated. Ne Xe