Search for Extra Dimensions in the Diphoton Final State

1. J.P. Chou, J. Hardenbrook, C. Henderson, G. Landsberg, Y. Ma, D. Nguyen, T. Orimoto, S. Simon 15 July 2011 Search for Extra Dimensions in the Diphoton Final State EXO – 11 - 038 Approval

2. Motivation • The existence of extra dimensions could solve the hierarchy problem • Randall-Sundrum (RS) and the large extra dimension (ADD) models propose that the fundamental Planck scale is ~TeV • In the simplest RS model • We have a single, compactified warped extra-dimension • 3D Weak brane where SM particles are confined and 3D Planck brane where gravitons are mostly localized, separated by a 4D warped bulk • The curvature causes distances and masses to rescale exponentially; gravity as a consequence appears weak near our brane • In the ADD model • SM is constrained to 3+1 dimensions • Gravity propagates through entire multidimensional space and its strength is diluted Yousi Ma

3. RS Phenomenology ~ • k = 1 • k = 0.5 • k = 0.1 • k = 0.05 • k = 0.01 ~ ~ ~ ~ H. Davoudiasl, J.L. Hewett, T.G. Rizzo Phys.Rev.D63:075004,2001 • Gravitons appear as a tower of KK excitations with separation wide enough such that they appear as resonance states • Masses and widths are determined by parameters: • M1 (lowest excitation mass) • = k/MPl (dimensionless coupling parameter) • 0.1 > k > ~0.01 B. C. Allanach et al JHEP 0212 (2002) 039 • Diphoton channel has higher BR than di-electron channel; Gravitons are spin-2, so the decay to into di-leptons is suppressed For Approval

4. Tower of graviton excitations, referred as Kaluza-Klein (KK) modes Small energy spacing between KK modes: ~1 meV to 100 MeVnon-resonance excess above the SM spectrum Large Extra Dimension Phenomenology • Drell-Yan like virtual graviton production decaying to diphotons or difermions. • Diphoton is the dominant channel • Cross section • ED effects are parameterized by • MS is an ultraviolet (UV) cutoff to avoid UV divergence of KK modes.

5. EXO-11-038 Yousi Ma

6. Data and Selection • 1091 pb-1 of data • /Photon/Run2011A-May10ReReco-v1/AOD: 204 (pb-1) • /Photon/Run2011A-PromptReco-v4/AOD: 887 (pb-1) • Selection • Uses EB-EB diphotons only, based on signal optimization Yousi Ma

7. Perform pseudo-experiments on the SM background and ADD signal Maximize the z-score of the Pes for Mgg cut (EB-EB) Optimize cut at 800 GeV (for 1/fb scenario) Invariant Mass Optimization for LED Eta optimization from expected limit suggests EB-EB is optimal For Approval For Approval

8. nVtx <= 2 nVtx > 2 MC Photon Efficiency (I) For Approval For Approval • Combined efficiency estimated in MC: 90.0 ± 2.5 (syst)% • Pixel seed veto efficiency 96.6±0.5 (syst)% • Adding 4% systematic uncertainty to cover pile-up effect

9. MC Photon Efficiency (II) For Approval For Approval

10. Data/MC Scale Factor (I) R. Yohay eff = 0.857 ± 0.014 eff = 0.876 ± 0.033 Data MC • Z Tag and Probe to measure photon efficiency in data-driven way • Data/MC scale factor: 1.02 ± 0.04 • Total photon efficiency: (88.7 ± 4.2)% • Diphoton efficiency: (78.7 +- 7.5)%

11. Data/MC Scale Factor (II)

12. Jets may fragment into a leading π0, resulting in a mis-reconstructed photon Estimate by measuring photon/EM-object ratio in photon triggered sample; subtract out direct photon contamination in numerator by using sigma_etaeta templates EM-object is similar to photon, but with an inverted isolation or shape requirement One may estimate the dijet and photon+jet contamination of a sample of two tight reconstructed photons according to the formula: where T=tight photon, L=loose photon, and x (y) refers to the pT of the first (second) object, respectively fx is the fake rate for a photon with pT=x dijet contribution --> first term in parentheses gamma+jet contribution --> second term in parentheses Photon Fake Rate (I)

13. Photon Fake Rate (II) Numerator Denominator 13

14. EB Purity Fits Jet PD 14

15. Photon Fake Rate (III) 2011 Barrel • For Single Photon, first two points are from Photon30, the latter two from Photon75 • Dashed red line corresponds to ±20%; Fit is only to Photon points ET (GeV) • Fake rate is a non-issue in the signal region as the dominant background is SM diphoton production; principle value is to validate control region

16. Background k-factor • Background k-factor (EB-EB only) • Invariant mass dependence • Calculated by DIPHOX. • Box process is included in the LO and its corresponding higher order is estimated by gamma2MC ADD Mγγ For Approval

17. Diphoton Invariant Mass For Approval For Approval Yousi Ma

18. Expected Background and Yield For Approval

19. k-factors are from M.C. Kumar, P. Mathews, V. Ravindran, and A. Tripathi Note: K-factors are higher than what we have used in 2010 (1.3) For the RS: The mass depend k-factors are used For the ADD: central value of k-factor is used, and variation is treated as systematic Signal k-factor ADD For Approval

20. Systematic Uncertainties • Signal efficiency (data/MC, PU, and ET/eta): 12.2% relative • Background efficiency (data/MC, PU): 11.1% relative • Background K-factor: 7% relative • Signal K-factor (ADD): 6.3% relative • Luminosity: 6% relative • Fake Rate: 20%

21. RS analysis: 95% Cross Section Limits For Approval For Approval For Approval • The 1 and 2 s bands merge with the expected limits as the background rate goes to 0 • The lower side of the bands also disappear since it is not possible to fluctuate to negative values of event yields. 21

22. RS analysis: Limits on Model Parameters For Approval • The upper limit on cross section are translated into lower limits on the graviton mass For Approval

23. RS: Limits by coupling parameter For Approval We easily surpass all existing limits.. by A LOT. 23

24. Limits for ADD For Approval For Approval • 95% CL cross section limits: 4.5 fb Update these limits 95% CL cross section limit (Mgg>800 and |eta|<1.44): 4.5 fb For Approval

25. Limits for ADD For Approval For Approval ADD ADD 95% CL cross section limit (Mgg>800 and |eta|<1.44): 4.62 fb For Approval 25

26. 813GeV Event For Approval

27. Searches for extra dimensions in the diphoton channel are updated to 2011 data With 1091 pb-1 data, the 95% CL limits are RS: cross section limits from 3.1 to 7.8 fb, graviton mass limit from 782 GeV to 1.81 TeV LED: cross section limit is 4.62 fb (M>800 GeV and |eta| < 1.4442), Ms limits from 2.43 to 3.63 TeV Start to see TeV events Conclusions

28. BONUS MATERIAL Yousi Ma

29. High Mass Events M=704 GeV M=637 GeV M=647 GeV

30. 1.4 TeV Event M=1.4 TeV! The photons appear to be real; well isolated, not spikes, etc P-value in 1/fb ~0.1 Spotted in the Exotica hotline.. But e/gamma triggers were affected in the signal region

31. Table of Yields (RS) Yousi Ma

32. RS Diphoton Selection x Efficiency Mγγ (GeV)

33. Signal Parametrization • The signal shape is not well parametrized by a single Gaussian, so we compute a measure of signal width, σeffective the half-width of the narrowest mass interval containing 68% of the signal • Our signal window is defined as ± 5s; our signal mass window efficiency is > 96% 33

34. Correlation of seff with intrinsic width Intrinsic width is proportional to M1 and k2 Yousi Ma

35. PU effect on efficiency 30 GeV < pT < 60 GeV 60 GeV < pT < 1000 GeV Yousi Ma

36. PU effect on efficiency EXO-11-038 selection is looser than e.g. Hgg selection Effect of PU in high ET bins is within 5% of central value Yousi Ma

37. H/E(PU) Yousi Ma

38. EcalISO (PU) Yousi Ma

39. HcalISO (PU) Yousi Ma

40. TrkISO(PU) Yousi Ma

41. AllISO(PU) Yousi Ma

42. shh(PU) Yousi Ma