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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.
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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
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
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
Large Extra Dimension Phenomenology • Tower of graviton excitations, referred as Kaluza-Klein (KK) modes • Small energy spacing between KK modes: ~1 meV to 100 MeVnon-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.
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
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
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)%
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
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
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
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
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
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
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
Limits for ADD • 95% CL cross section limits: 4.5 fb 95% CL cross section limit: 4.5 fb
High Mass Events M=704 GeV M=637 GeV M=647 GeV
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…
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
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
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
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.