ATLAS and CMS diphoton resonance searches at TeV Marco Delmastro CNRS/INP LAPP Annecy January th, 6 Marco Delmastro ATLAS and CMS high-mass diphoton resonance searches at TeV
Overview ü https://cds.cern.ch/record/ 485 ü https://cds.cern.ch/record/ 488 ü. fb ü Optimized for scalars ü.6 fb ü Optimized for spin- Marco Delmastro ATLAS and CMS high-mass diphoton resonance searches at TeV
What are we talking about? Events / 4 GeV 4 ATLAS Preliminary Data Background-only fit s = TeV,. fb Events / ( GeV ) CMS Preliminary Data Fit model ± σ ± σ.6 fb ( TeV) EBEB category Data - fitted background 4 6 8 4 6 5 [GeV] 5 5 5 4 6 8 4 6 [GeV] m γγ m γγ (data-fit)/σ stat 4 - -4 4 5 m γ γ (GeV) Marco Delmastro ATLAS and CMS high-mass diphoton resonance searches at TeV
Selections ü Trigger E T γ > 5 GeV, E T γ > 5 GeV Loose quality Fully efficient for E t γ > 4 GeV ü Offline η <.7,.7.5 excluded E T γ > 4 GeV, E T γ > GeV E T γ >.4 m γγ, E T γ >. m γγ Effectively deplete EndCaps Tight quality (cuts) + isolation Select m γγ > 5 GeV Search m γγ > GeV ü Trigger E T γ > 6 GeV, E T γ > 6 GeV H/E <.5 Fully efficiency for m G > 6 GeV ü Offline η <.5,.44.57 excluded At least one γ with η <.44 No E-E combination E T γ > 75 GeV, E T γ > 75 GeV Tight quality (cuts) + H/E <.5 + isolation Select m γγ > GeV ( if EC γ) Search m γγ > 5 GeV ü Efficiency (ggf Scalar) m X ~ GeV à ~ 5% m X > 6 TeV à > 4 % Efficiency (RS Gravitons) m G ~ 6 GeV à ~ % m G ~ TeV à ~ 45% Marco Delmastro ATLAS and CMS high-mass diphoton resonance searches at TeV 4
Signal modeling ü Signal properties Higgs-like scalar m X = [ GeV - TeV] Different production modes ggf (Powheg-box), VBF (Powheg-box+ Pythia), VH, tth (Pythia) systematic uncertainties to avoid model dependence Narrow Width Approximation (NWA) Full Simulation ü Signal properties RS Graviton m X = [5 GeV 4.5 TeV] Theoretical line shape convoluted to detector response Width ~ 4 MeV for all m X Large Width Approximation (LWA) Width %-% m X Theoretical line shape convoluted to detector response Powheg implementation of a large-width scalar resonance when assuming SM-like couplings (BW distribution with a mass-dependent width + dependence of propagator on the gg parton lumi) ü Implementation Double-Sided Crystal Ball parameterization Simultaneous fit of parameter parameterization ü Implementation Moment morphing Marco Delmastro ATLAS and CMS high-mass diphoton resonance searches at TeV 5
Background modeling ü Data driven γγ purity (wrt γγ, γj) ~ 9% ü Functional form ü Data driven γγ purity (wrt γγ, γj) ~ 9% ~ 8% (BB, BE) ü Functional form ü Bias evaluated on MC Spurious signal S+B fits to high-statistics of background MC Fitted S component must be smaller then % of expected background uncertainty at given mass ü F-test on data to evaluate need for higher order in background function ü Bias evaluated on MC Additional uncertainty assigned to background parameterization From fit MC pseudoexperiment (toys) Assigned if median of pull distributions from toy fits toys is larger than.5 Marco Delmastro ATLAS and CMS high-mass diphoton resonance searches at TeV 6
Systematic uncertainties (not given by CMS) (crucial to decode NWA ATLAS result!) ü Bias term on parametric background model (no size given) ü Luminosity : 4.6% ü Trigger and photon ID : % ü Signal PDF : 6% ü Photon energy scale : % (not in ATLAS, several production processes) (negligible in ATLAS) Marco Delmastro ATLAS and CMS high-mass diphoton resonance searches at TeV 7
Statistical treatment ü Profile likelihood ratio ü Profile likelihood ratio ü Look Elsewhere Effect D à several mass hypothesis in NWA scan D à several mass and width hypothesis ü Look Elsewhere Effecct D à several mass and Marco Delmastro ATLAS and CMS high-mass diphoton resonance searches at TeV 8
Spectrum Events / 4 GeV Data - fitted background 4 5 4 6 8 4 6 [GeV] 5 5 5 ATLAS Preliminary Data Background-only fit s = TeV,. fb 4 6 8 4 6 [GeV] m γγ m γγ 4 5 6 m γ γ (GeV) Marco Delmastro ATLAS and CMS high-mass diphoton resonance searches at TeV 9 Events / ( GeV ) (data-fit)/σ stat Events / ( GeV ) (data-fit)/σ stat 4 - -4 4 - -4 CMS CMS Data Fit model ± σ ± σ Preliminary Data Fit model ± σ ± σ 4 Preliminary 5.6 fb ( TeV) EBEB category m γ γ (GeV).6 fb ( TeV) EBEE category (CMS plots have different m scale!)
Significance Local p-value ü NWA 4 5 σ σ σ σ 4σ Pull on resolution NP ATLAS Preliminary s = TeV,. fb Observed 4 6 8 4 6 8 [GeV] ü Local p ~.6 σ at ~75 GeV ü Global p ~. σ m X ü =. p - - 5 FWHM(5 GeV) BB = 4 GeV (~%) CMS Preliminary.6 fb ( TeV) κ =. Observed p m G (GeV) ü Local p ~.6 σ at ~76 GeV ü Global p ~. σ σ σ σ Marco Delmastro ATLAS and CMS high-mass diphoton resonance searches at TeV
Significance ü LWA Minimum p for width ~ 6% ü =. FWHM(5 GeV) BB = 6 GeV (~7%) 76 GeV ~6% (EOYE seminar) p CMS Preliminary.6 fb ( TeV) κ =. Observed p σ σ - - 5 m G (GeV) σ ü Local p ~.9 σ ü Global p ~. σ ü Local p ~.6 σ Marco Delmastro ATLAS and CMS high-mass diphoton resonance searches at TeV
Limits ü Fiducial limit! Isolation in fiducial volume definition ü NWA BR [fb] 95% CL Upper Limit on σ fid ATLAS Preliminary s = TeV,. fb 4 6 8 4 6 8 ü Validity for LWA Bias smaller than % (%) for width.4% (.4%) m X Observed Expected ± σ ± σ m X [GeV] ü RS Graviton Marco Delmastro ATLAS and CMS high-mass diphoton resonance searches at TeV
Conclusions (and perspectives?) and CMS reported mild excess in TeV diphoton spectrum ü Around 75 (76) GeV ü Largest local significance ~.9 σ ATLAS for width ~6% ü Global significance is really small! No reason to get (too) excited! :. σ, CMS:. σ significance largest for smaller width Analyses targeting different signal ü ATLAS à scalar ; CMS à graviton ü Both analyses have (sub-optimal) sensitivity to other signal What can we expect before 6 data taking? ü ATLAS has graviton-like analysis still to be made public ü Scalar analysis from CMS? ü Better calibration in both experiments energy scale (mass and significance), resolution (significance) ü Extended compatibly/combination with 8 TeV results? Otherwise, more data needed to establish excess origin Marco Delmastro ATLAS and CMS high-mass diphoton resonance searches at TeV
Compatibility/combination with 8 TeV results ratios of LHC parton luminosities: TeV / 8 TeV WJS luminosity ratio gg_ Σqq qg M X (GeV) MSTW8NLO e.g. s-channel gluon-initiated process à parton-luminosity ratio = 4.7 Marco Delmastro ATLAS and CMS high-mass diphoton resonance searches at TeV 4
8 TeV results for compatibility/combination ü arxiv:47.658 ] [GeV γ dn / dm γ ü Scalar NWA ü m X = [65-6] GeV ü Preliminary extension of analysis to estimate compatibility ATLAS 8 6 4 8 6 Data Continuum+H fit (m X = 5 GeV) Continuum component of the fit 5 5 5 ü CMS-PAS-EXO-45 Events / GeV ü Graviton ü m G = GeV,.5 TeV ü Change in statistical treatment to enable combination CMS 4 Data Preliminary 9.5 fb SM Diphoton Photon+Jet Jet+Jet DY, Wγ, Zγ (8 TeV) s = 8 TeV, Ldt =. fb Data Continuum+H fit (m X = 5 GeV) Continuum+H fit (m X = 5 GeV) Continuum+H fit (m X = 5 GeV) 4 5 6 7 m γ γ [GeV] - 4 6 8 4 6 8 M γ γ (GeV) Marco Delmastro ATLAS and CMS high-mass diphoton resonance searches at TeV 5
Compatibility/combination with 8 TeV results ü 8 TeV analysis à scalar ü Compatibility NWA à. LWA (6%) à.4 σ ü 8 TeV analysis à graviton ü Combination 8 TeV + TeV Local p ~ σ Global p <.7 σ - log L 8 6 CMS Preliminary Combined TeV 8 TeV m G = 75 GeV κ =..6 fb ( TeV) + 9.7 fb (8 TeV) p CMS Preliminary.6 fb ( TeV) + 9.7 fb (8 TeV) σ σ 4 5 5 σ RS ( TeV) BR γ γ (fb) 5 8 m G (GeV) Marco Delmastro ATLAS and CMS high-mass diphoton resonance searches at TeV 6 - - 6 κ =. Combined TeV 8TeV 7 σ