1. Gamma-Hadron Separation Aous Abdo & James Linnemann Michigan State University Milagro Collaboration Meeting, UMD January 21-22, 2005

2. Distributions ➢ We studied different 2D distributions of the following parameters: ➢ nOut, nTop, nBot, nFit, nb2, nb4, nb8, mxPE, cxPE. ➢ Distributions were generated for Gamma and Proton MC. ➢ We concentrated on distributions that showed significance differences between these distributions.

3. 1) ((nOut*nTop*nFit)/cxPE) vs (nb2/cxPE)

4. Q-Factor Distribution Events maybe on or off the pond Two dimensional Q-Factor for on and off the pond events Top view of the Q-Factor The peak is bounded by: (nOut*nFit*nTop)/cxPE > 10^4 and 3 < (nb2/cxPE) < 6

5. Q-Factor for on the pond events The Q-Factor peak is closer to the origin, so we expect to keep more gammas if we make a cut on that peak.

6. 2) (nOut + nTop)*nFit/cxPE vs (nb2/cxPE)

7. Q-Factor Distribution Events maybe on or off the pond The peak is bounded by: 3500 < (nOut+nTop)*nFit/cxPE < 5500 and (nb2/cxPE) < 6

8. Q-Factor for on the pond events Again we see that the Q-Factor peak is closer to the origin, so we expect to keep more gammas if we make a cut on that peak. The peak is bounded by (nOut+nTop)*nFit/cxPE < 2000 and (nb2/cxPE) < 4

9. 2) (nTop*nFit)/cxPE vs nb2 The offset of the two peaks is clear here. Gamma peak is bounded by: (nTop*nFit)/cxPE < 2000 and 10 < nb2 < 50 Protons peak is bounded by: (nTop*nFit)/cxPE < 800 and 20 < nb2 < 90

10. Q-Factor Distribution Events maybe on or off the pond The peak is not wide and smooth enough to be trusted, it could be due to fluctuations in the MC

11. Q-Factor with peak excluded We still see a smooth peak for which the Q-Factor is ~ 3.

12. Q-Factor for on the pond events We see a wider peak for which the Q-Factor ~ 1.8 The peak is bounded by 30 < nb2 < 160 and 800 < (nTop*nFit/cxPE) < 2000

13. Cuts For each distribution we did the following: ➢ Study the Q-Factor distributions and look for the cut that will optimize the Q-Factor. ➢ Energy dependence of the cut selected. ➢ The gamma and proton efficiencies for the cut. ➢ Looked at the Crab for each cut and compared it to the standard cut, i.e. nFit > 20 and X 2 > 2.5

14. Crab with the standard cut

15. 1) Cuts for ((nOut*nTop*nFit)/cxPE) vs (nb2/cxPE) If we apply the following cuts: dAngle 80 & (nb2/cxPE) > 4.28 & (nOut*nTop*nFit)/cxPE > 10^5 We get a Q-Factor of 2.7 while keeping 15% of the gamma and 0.3% of the protons. The cut is high energy biased. ➢ Crab Significance increases to 5.05 ➢ Crab excess decreases to 382

16. 2) On-pond events cuts for ((nOut*nTop*nFit)/cxPE) vs (nb2/cxPE) If we apply the following cuts: dAngle 80 & (nb2/cxPE) > 2.1 & (nOut*nTop*nFit)/cxPE > 3200 We get a Q-Factor of 1.4 while keeping 60% of the gamma and 18% of the protons. By comparing this cut to the previous one we expect a significance of 2.6, this agrees very well with what we got, namely 2.55

17. 3) Cuts for ((nOut+nTop)*nFit/cxPE) vs (nb2/cxPE) If we apply the following cuts: dAngle 80 & (nb2/cxPE) > 4.0 & (nOut*nTop*nFit)/cxPE > 3800 We get a Q-Factor of 2.7 while keeping 15% of the gamma and 0.3% of the protons. Again the cut is high energy biased. By comparing this cut to the first one we expect a significance of 5.05, we got 3.94. Crab excess decreased to 227.

18. 4) On-pond events cuts for ((nOut+nTop)*nFit/cxPE) vs (nb2/cxPE) If we apply the following cuts: dAngle 80 & (nOut+nTop)*nFit/cxPE > 800 We get a Q-Factor of 1.4 while keeping 72% of the gamma and 26% of the protons. By comparing this cut to the previous one we expect a significance of 2.0 which is in exact agreement with what we got.

19. 5) Cuts for (nTop*nFit/cxPE) vs nb2 If we apply the following cuts: dAngle 80 & (nTop*nFit)/cxPE > 4000 We get a Q-Factor of 2.66 while keeping 10% of the gamma and 0.1% of the protons. Again the cut is high energy biased. By comparing this cut to the first one we expect a significance of 4.9, which is in exact agreement with what we got. However the Crab excess decreases by almost one half.

20. 6) On-pond events cuts for (nTop*nFit/cxPE) vs nb2 For this distribution we applied two sets of cuts: dAngle 80 & nb2 > 60 & nTop*nFit/cxPE > 1000 We get a Q-Factor of 1.57 while keeping 47% of the gamma and 8% of the protons. By comparing this cut to the previous one we expect a significance of 2.9, we got 2.34

21. Second set of cuts for on-pond events for (nTop*nFit/cxPE) vs nb2 If we apply: dAngle 80 & nb2 > 100 & nTop*nFit/cxPE > 1400 We get a Q-Factor of 1.68 while keeping 26% of the gamma and 2% of the protons. By comparing this cut to the cut for all events, cut #5, we expect a significance of 3.0, which is in good agreement with what we got, namely 2.8