1. Milagro at Tibet Gus Sinnis LANL/P-23

2. Challenge and Opportunity Milagro will run for ~2 more years (or less) No viable candidate to replace Milagro on horizon –ARGO marginal sensitivity gain (and technical problems) –HD Tibet marginal sensitivity gains NSF has little money (2% cut this FY) International Research and Education Grants –5 years up to $2.5M What can be done with this budget? Move Milagro to high altitude

3. Outline Detector design and constraints –We now have a chance to do it right (based on what we have learned) Detector sensitivity calculations –Is it worth it? Rate expectations –Can we keep existing daq and electronics? Open challenge(s) Verification testing at Milagro Path forward - discussion

4. Detector Design Constraints –no new pmts –Keep as much electronics as possible –Funding < $2M Lessons learned –Bottom layer important (want bigger) –Top layer PMTs not deep enough –Pond not big enough –Outriggers are a pain in the neck –Cross-talk is bad, very bad

5. Detector Design (II) 2 layers (equal size) Grid of 21 x 21 uses up all PMTs (with ~30 spares) Top depth of 2 meters Detector spacing of 4 meters –Total area of ~7700 m 2 Black curtains extending from top of water to 3 meter depth (5% reflectivity in MC)

6. Detector Schematic 6 m 88 meters 2 m 4m

7. GEANT3.2 Simulation Modified survey file Added curtains to ugeom.F Changed altitude in CORSIKA to 4300m Ran ~4M gamma and 4M proton showers –50 GeV – 100 TeV –Gammas E -2.4, protons E -2.7 –0-45 degrees zenith angles –Flat in core distance to 1000m Tony’s reconstruction used (modified Milinda code checked into CVS). –Gaussian core fitter –2-layer angle fitter –Combined curvature and sampling from Tony Trigger & fit criteria –Tibet nTop>40 PMTs (Milagro nTop>50) –nFit>20 and for gammas dAngle<1.2 degrees

8. Basic Simulation Results  -ray effective area Tibet Milagro

9. Basic Results II proton effective area!! Tibet Milagro

10. Core Distance of Triggers Tibet Milagro NTop>40NTop>50

11. Background Rejection Use nTop/cxPE as found for HAWC –cxPE is PEs in hottest bottom layer PMT (excluding region <10m of fit core from search) Gammas Protons

12. Background Rejection II Q-factor ~1.8 possible while retaining ~80% of gamma rays (Require nTop/cxPE > 4) Gammas Protons

13. Crab Sensitivity Use Sensi() routine from Andy Scale from Milagro Events/day given below (triggered and fit)  uncut p uncut  cut p cut Tibet2206717311 Milagro * 378517.88.5 * 50 PMT trigger, nFit>20, dAngle 2.5 ~8x more sensitive than Milagro ~32  on Crab in year

14. Expected Trigger Rate From previous slide –Proton rate on Crab of 67 events/day (triggered) –Milagro MC gives 85 events/day (triggered) With Milagro trigger of 1800 Hz Tibet trigger rate will be <1500 Hz Current DAQ can be used Singles rates will be lower –TOT will work better (fewer late hits) No new electronics needed

15. Gamma-Ray Bursts Under construction (issue of real z in Primack code). But, to get estimate of improvement over Milagro – look at ratio from Sensi() for a “source-day” for Dec=36. Second number is N  /sqrt(p) (arb units in p-flux) ZMilagroTibet rawTibet cut 0.215.6 /160.8/6.841.8/9.7 0.410.6 /0.7239.8/4.427/6.2 0.66.8/0.4722.3/2.514.7/3.4 0.84.3/0.308.0/0.95.2/1.2 p’s2088018.6

16. Remaining Challenge Calibration of PMTs (timing and pulse height) With curtains PMTs can not see neighbors –Or common light source at top of pond HAWC-like calibration system would require complete re-design of electronics Ideas? –Laser balls at bottom of pond (no baffles)? –Bright light on inflated cover? –Muons for pulse heights?

17. Proposal Issues IHEP is on board –But have no source of internal funding (ARGO issues) –US will have to provide entire cost Site prep, etc. –IHEP could provide some manpower to help with overseeing of contracts for pond construction –Skip Neal contacted working on cover quote Water system – cheaper to ship or purchase in China? Investigate ITAR issues Proposal due March 10 Realistic cost estimates Needs equipment funding from MPS

18. Testing at Milagro Install curtains on 4x4 patch of PMTs –Investigate singles rate –Investigate timing distributions Should become narrower, but we may be dominated by our angular resolution Build small water tank to determine altitude effect on singles rates (Dylan S.) –Take to Colorado

19. Conclusions With slight design modifications moving Milagro to high altitude can have a significant impact on our sensitivity. With curtains all electronics will continue to function. Expect 8x improvement in Crab sensitivity –Crab at 5 sigma in 10 days (1.6  /sqrt(days)) –GRBs @z~0.8 similar sensitivity to z=0.2 in Milagro Compare to straight move of Milagro at 4300m –Gary’s talk Complete sensitivity calculations (GRBs and AGN) Trigger rate estimate needs scaler simulation Excellent prototype for HAWC