Search for Extra Dimensions in the Diphoton Channel

1. Search for Extra Dimensions in the Diphoton Channel RS: Josh Hardenbrook (Caltech) Conor Henderson (U. Alabama) Yousi Ma (Caltech) Toyoko Orimoto (CERN) Sean Simon (UCSD) ADD: John Paul Chou, Greg Landsberg, Duong Nguyen (Brown) Exotica Preapproval Meeting June 28, 2011

2. Introductions • The existence of extra dimensions solve the hierarchy problem • Randall-Sundrum and large extra dimensions (ADD) model propose the fundamental Planck scale at TeV scale. • 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 in 3+1 dimensions • Gravity propagates through entire multidimensional space and its strength is diluted -> fundamental Planck at TeV scale is observed

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, while 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

4. Large Extra Dimension Phenomenology • 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 • 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. RS and ADD Documents

6. Data and Selections • 881 pb-1 of data • /Photon/Run2011A-May10ReReco-v1/AOD: 203.7 (pb-1) • /Photon/Run2011A-PromptReco-v4/AOD: 677.6 (pb-1) • Selection • RS analysis uses EB-EB and EB-EE diphotons • ADD analysis use EB-EB diphoton only

7. MC Photon Efficiency nVtx <= 2 nVtx > 2 • 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

8. RS Monte Carlo Signal Efficiency EB-EE

9. Data/MC Scale Factor eff = 0.857 ± 0.014 eff = 0.876 ± 0.033 • 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)%

10. Photon Fake Rate • MC • 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

11. Background k-factor • Background k-factor • Invariant mass dependence • Calculated by DIPHOX. • Box process is included in the LO and its corresponding higher order is estimated by gamma2MC

12. Diphoton Invariant Mass

13. Expected Background and Yeild

14. Invariant Mass Optimization for LED • Perform pseudo-experiments on the SM background and ADD signal • Maximize the z-score of the experiment • Optimize cut at 800 GeV

15. Signal k-factor • 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 background K-factor doesn’t directly effect the result. However, the signal K-factors have a large impact on the model limits

16. RS analysis: 95% Cross Section Limits k/MPl=0.01 k/MPl=0.05 0.0041pb 0.0036pb • The 1 and 2 s bands merge with the expected limits when 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. k/MPl=0.1 0.0035pb 16

17. RS analysis: Limits on Model Parameters • The upper limit on cross section are translated into lower limits on the graviton mass 877 GeV for k/MPl=0.01 1456 GeV for k/MPl=0.05 1780 GeV for k/MPl=0.1

18. RS analysis: Limits for Categories It’s clear that most of the sensitivity comes from EB-EB We easily surpass all existing limits.. by A LOT. 18

19. Limits for ADD • 95% CL cross section limits: 4.5 fb 95% CL cross section limit: 4.5 fb

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

21. 1.4 TeV Events M=1.4 TeV! The photons appear to be real; well isolated, not spikes, etc Spotted in the Exotica hotline.. But it turns out HE+ was BAD for this run…

22. Conclusions • Searches for extra dimensions in the diphoton channel are updated to 2011 data • With 881 pb-1 data, the 95% CL limits are • RS: cross section limits from 3.5 to 4.1 fb, graviton mass limit from 887 GeV to 1.78 TeV • LED: cross section limit is 4.5 fb, Ms limits from 2.42 to 3.62 TeV • Start to see TeV events

23. 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% Toyoko Orimoto (CERN) 23

24. Background Parametrization • Background estimation is done with a fit to the data distribution • Sum of three exponential function from 200 to 2000 GeV • Shaped is fixed using the expected background distribution from MC (diphoton) and data-driven fake rate (gJet and dijet) • Then overall normalization to fitted from data in control region 200-500 GeV • Function is then extrapolated into signal region to compute # bkg Data EB-EB Data EB-EE

25. Expected Signal & Background, Yields

26. Limit setting • Perform limit setting for a counting experiment with > 500 GeV • Apply Bayesian procedure • Use Poisson likelihood for model • Lognormal prior for nuisance parameter • Flat prior for cross section • 95% upper bound • Upper bound on the <0.11 pb at 95% C.L.