1. Mani Tripathi, UCLA, Feb23, 2006. A Search for Neutralino Dark Matter usingGamma-rays Paulo Afonso Maxwell Chertok Carly Kopecki Juan Lizarazo Peter Marleau John Stilley Melinda Sweany Mani Tripathi Senior Engineer: Britt Holbrook Junior Specialist: Tiffany Landry. Technical Assistants: John Linn, Joe Trad.

2. Mani Tripathi, ICHEP, Moscow, July 27, 2006. Outline Draco as a source for Gamma-rays from Neutralino annihilations. CACTUS Experiment: Technique and Resolutions. Calibrations with the Crab. Draco Observations: Flux Limits Status and Future http://ucdcms.ucdavis.edu/solar2/

3. Mani Tripathi, ICHEP, Moscow, July 27, 2006. Draco and Dark Matter Dwarf Spheroidal galaxy ~ 82kpc away Odenkirchen et al 2001 Total Luminosity ~2 x 105 L solar Rave et al 2003 M/L ~ 92 +- 28 Solar Units Angular size ~ 0.5 o Optically faint (mag ~11) => an ideal candidate for observations using Air Cherenkov Telescopes. Grillmair et al 1997

4. Mani Tripathi, ICHEP, Moscow, July 27, 2006. Neutralinos: Previous attempts at understanding Draco. Neutralino annihilations will result in hadronic jets that will contain gammas from neutral pion decays. The rate will depend on  2, where  ~ r -  is the density profile of the neutralinos. Tyler (2002) obtained exclusion contours using EGRET data in the region of Draco. A survey by Whipple(2004) did not yield any excess for energies above ~300 GeV. Neutralino Mass 

5. Mani Tripathi, ICHEP, Moscow, July 27, 2006. CACTUS: Using the Solar 2 Heliostat Array Located 15 miles outside Barstow, CA Over 1,900 42m 2 heliostats. The largest array in the world. We have ~160 heliostats in the FOV of our camera. Total mirror area ~6,700 m 2. Collection (ground) area ~ 40,000 m 2 Effective (100% eff) area for E>200 GeV ~ 61,000 m 2 - 83,000 m 2.

6. Mani Tripathi, ICHEP, Moscow, July 27, 2006. Part of the field being used. 160 heliostats* available. 116-144 used in this campaign. *limited by aperture CACTUS is capable of collecting nearly the entire Cherenkov light pool 80 channel PMT camera and 160 Heliostat Field

7. Mani Tripathi, ICHEP, Moscow, July 27, 2006. Data Acquisition Using Multi-hit TDCs  rise = 3.2 ns  fall = 1.7 ns 200 showers Time of Arrival (ns) Mapping of multiple heliostats on one PMT allows for ~250 effective pixels. time-of-arrival resolution ~0.5 ns. Excellent S/N ratio for Cherenkov wavefront detection. Pulse heights are measured with a time-over- threshold technique.

8. Mani Tripathi, ICHEP, Moscow, July 27, 2006. Typical events with a fitted paraboloid wavefront overlaid on the hits. Partial rejection of cosmic rays is inherent. Event Shape Analysis

9. Mani Tripathi, ICHEP, Moscow, July 27, 2006. Reconstruction of Shower Centroid on the Ground Simulations: Reconstructed vs Generated Radial Position of Shower Centroid Data: Reconstructed Positions of Shower Centroid on the ground for Energy ~100-200 GeV.

10. Mani Tripathi, ICHEP, Moscow, July 27, 2006. Energy Resolution Optimized via the paraboloid fit Pulse height is corrected for accepted fraction of the shower after fitting the shower centroid on the ground. Some showers suffer from wrong centroid determination. 50 GeV

11. Mani Tripathi, ICHEP, Moscow, July 27, 2006. Fractional Resolution Energy Resolution A resolution in the 20-30% range is achieved at low energies. Saturation effects begin to show up at energies above 500 GeV.

12. Mani Tripathi, ICHEP, Moscow, July 27, 2006. Standard Candle for High Energy gamma- rays. We rely on our own measurements to validate the simulations. The Crab spectrum has not been very well established in the 10-100 GeV region. Cross-check at high energies with recent new results. Calibrations using the Crab Nebula

13. Mani Tripathi, ICHEP, Moscow, July 27, 2006. We require >7 channels in a 13 ns window for the event to be triggered. This 28 min sample from the Crab represents an excess rate of 42/min and a significance of 13  CRAB: The observed CACTUS Excess in Total Pulse-Height. Data are recorded in pairs of 28 min ON-source (heliostats track the Crab) and OFF-source (heliostats revert and track a point 30 mins away from the Crab). Energy 70 500 2000 Number of Events

14. Mani Tripathi, ICHEP, Moscow, July 27, 2006. CRAB: Efficiency and Effective Area Events were generated spread uniformly over a radius of 180m with an input spectrum of k*E -2.4 Simulations indicate an effective area >50,000 m 2 for energy > ~200 GeV. Area eff = 61,000 - 1.1 x 10 6 E -0.73 m 2

15. Mani Tripathi, ICHEP, Moscow, July 27, 2006. CACTUS Measurement of the Crab Differential Flux CACTUS Fit dF/dE ~ 3.39x 10 -3 E –2.29 (GeV -1 m -2 s -1 ) Errors: Systematic error in energy not shown ~10% in Flux from effective area Flux (GeV -1 m -2 s -1 ) Energy (GeV) CELESTE: Piron et al 2002 Preliminary 70 500 2000

16. Mani Tripathi, ICHEP, Moscow, July 27, 2006. Angular Resolution for the Crab A planar fit to the shower wave-front yields the incidence angle. The Crab is a point source and the excess is peaked at zero cone-angle. Simulations reproduce the resolution in   (~ 0.15 o ) measured in the data. ON-Crab ON-OFF Simulation  OFF-Crab

17. Mani Tripathi, ICHEP, Moscow, July 27, 2006. CACTUS Observations of Draco Variable degrees in RA ~1 deg in Dec 0.5 deg in Dec 1 deg in RA 12 nights observation period in July 2005. 12 ON/OFF pairs (5 analyzed) Drift scans: +-1, +- 2 and +-3 in physical degrees. The raw rates recorded by CACTUS displayed variability with RA. We have now completed a first pass analysis of all the data using the spherical wave-front fitting technique and improved stabilization of trigger against fluctuations in night sky background..

18. Mani Tripathi, ICHEP, Moscow, July 27, 2006. Calculation of Trigger Probability Per Event Number of Channels in Coincidence Single Event One 4 o Scan For each event, the noise conditions preceeding the trigger is sampled for 1 us. A trigger turn-on probability distribution for each event is calculated. For example, the distribution shown indicates that this event would have triggered if there were 6 signal hits. This is the effective threshold for this event. A curve is fit to the turn-on probability. Demand that each event have > 50% probability of triggering. An overlap of such curves is shown for one scan. Probability of Triggering

19. Mani Tripathi, ICHEP, Moscow, July 27, 2006. Effective Thresholds The data are cleaned up by remving rate “spikes” after cuts based on background noise. The cut is 1 sigma from the mean of each data set.

20. Mani Tripathi, ICHEP, Moscow, July 27, 2006. Noise balancing technique applied to a typical Crab data set. Before After The trigger rate is stabilized for the 28 min observing period. Noise Immunity for Crab

21. Mani Tripathi, ICHEP, Moscow, July 27, 2006. Sum of 65 scans. Stabilized rate from Draco scans.

22. Mani Tripathi, ICHEP, Moscow, July 27, 2006. 2.7 Hz Draco Scans after a > 100 GeV cut Preliminary The total live-time (On Draco) for this data set, after correcting for trigger suppression etc is ~5 hours. The background rate from cosmic rays is 2.7 Hz per 0.2 bin in R.A.

23. Mani Tripathi, ICHEP, Moscow, July 27, 2006. Draco: Analysis of 5 ON/OFF pairs The significance of (ON-OFF) rates normalized to the square-root. Total live Time for the sum of 5 runs is ~95 mins. The lack of excess is converted into upper limit on Flux. Preliminary

24. Mani Tripathi, ICHEP, Moscow, July 27, 2006. Setting Flux Limits: Effective Area. Simulated effective area for Draco observing angles is higher than for Crab due to higher number of heliostats used in the July run. Areaeff = 83,000 – 2.3 x 10 6 E - 0.79 m 2

25. Mani Tripathi, ICHEP, Moscow, July 27, 2006. CACTUS Limits Density Profiles Space Probed by CACTUS -Blue curve : modified SIS -Red curve: SIS with a 1 au core -Pink curve: NFW profile CACTUS Preliminary Preliminary Upper Limits on Draco Flux obtained from 5 ON/OFF pairs.

26. Mani Tripathi, ICHEP, Moscow, July 27, 2006. Summary FUTURE Hardware Upgrades: Improve electronics for low energy response. Lower threshold to ~30 GeV. Outrigger mini-cameras for improved cosmic ray rejection. Future dSph Observations: Draco, Leo II and Sextans. 1.We have measured the Crab spectrum in the region above EGRET and below ACTs. 2.We have observed no excess from the direction of Draco above ~ 70 GeV. 3.The upper limit on the Flux is ~400 milli-Crab for energies in the range 70-1000 GeV. CACTUS Preliminary