Searches for New Physics in Photonic Final States at the LHC with CMS APS April Meeting Denver CO, May 03, 2009 Andy Yen California Inst. of Technology CMS Collaboration 1
The CMS Detector CMS is general purpose detector with good sensitivity towards Higgs and other New Physics signatures. High precision crystal ECAL is the source of much of its discovery potential. 2
Barrel: 61,200 crystals in 170 φ- rings of 360 ( η < 1.48) Capable of energy resolution of < 0.5% for ~100 GeV photons (testbeams). Goal is to achieve and maintain this resolution in situ at the LHC. The CMS ECAL (76k PbWO 4 crystals, 90 tons) Two Endcaps: 7,324 crystals each (1.48< η < 3) Barrel Crystals EndCap(s) 3
Searching for Higgs at CMS H γγ is the most promising decay channel at CMS. Direct Signal Relatively low SM background. BR ~ 2 x 10-3 115 140 GeV Combined LEP, CDF and D, Mar 09 M H < 160 GeV (95% CL) 4
H Signal and Backgrounds SIGNAL (NLO) 2 Isolated, High ET Photons Gluon Fusion Vector Boson Fusion Associated Production with Z, W, tt BACKGROUND Irreducible backgrounds (two real photons) qq γγ (born diagram) gg γγ (box diagram) Reducible backgrounds (at least one fake photon pp g +jets or isolated π 0 pp jets (2 fake g) pp ee (Drell Yan), e s mis-ided as photons g g box q born q brem q g q 5
CMS: Optimized H Analysis Higgs Signal and Backgrounds Integrated luminosity for 5s discovery (CMS NOTE-2006/112) m H (GeV) L fb -1 115 8.5 120 7.7 130 11 140 16 150 ~30 We see that photon energy resolution is very important in this analysis. Photon ID is also key. Diphoton QCD background will need to be measured when first data become available. 6
Search for RS Gravitons G /e + e - Gravity scale = M Pl exp(-kr c ) ~TeV; for kr c ~11-12, no hierarchy problem Graviton resonances m n = x n k exp(-kr c ), J 1 (x n )=0 Two parameters control graviton couplings and widths: mass m G and constant c=k/m Pl Signals: Narrow, high-mass resonance states in di-lepton and di-photon systems 7
RS Gravitons G Fully Simulated with Backgrounds; ECAL Saturation Corrected (for E > 2 TeV) CMS NOTE-2006/051 Bkgds: QCD Jets, Direct Photons, Drell- Yan Can Directly Measure the Width Discovery Reach 10 fb -1 : M G > 3.14 TeV for c=0.1; M G > 1.32 TeV for c=0.01 30 fb -1 : M G > 3.54 TeV for c=0.1; M G > 1.59 TeV for c=0.01 8
ADD Graviton Emission in γ+met Channel Signature: A single high-p T photon in the central η region. High missing p T back-to-back with the photon in the azimuthal plane The γ+(z νν) CMS NOTE-2006/129 background can be estimated by studying the γ+(z μμ) process L=60 fb -1 M D = 1 1.5 TeV for 1 fb -1 2-2.5 TeV for 10 fb -1 9
For early CMS runs, using π⁰ mass peaks is optimal. L=2x10 33 gives average π 0 γγ rate of 1.5 khz or 2,100 π 0 /crystal/day ECAL Calibration 10
Barrel Pi0 Callibration (Work in Progress) Data after L1 Trigger Online Farm p 0 Calibration >10 khz ~1 khz Good results after correcting for ECAL cracks and pileup π⁰ s Calibration algorithm converges rapidly. Can calibrate most of ECAL to 0.5% in under 100 hours. 11
Effect of ECAL Calibration Crystals Pulse Amplitudes in a clustering algorithm Calibration Particle Energy Achieving a precise in situ crystal-by-crystal calibration of the CMS ECAL will be crucial for the H γγ search (CMS NOTE-2006/021) Calibration Target January 09, 2008 12
Conclusion Only a small sampling of CMS physics with photonic final states presented. Many early discovery opportunities. Detector performance, especially achieving ECAL calibration will be crucial to success of CMS physics program. Jet fake rates and Photon ID are also very important due to the large SM backgrounds. Photonic events also serve as a useful test of SM QCD predictions. The most exciting times are just beginning! andyyen@hep.caltech.edu 13
Extra Slides Follow
G Discovery Potential CMS NOTE-2006/051 15
Excited Leptons (Preliminary Results) e* and μ* can be produced copiously at the LHC (via contact interactions), and then decay via contact and electroweak interactions into ordinary photons and leptons Analysis benefits from good resolution of ECAL qq ee* ee qq μμ* μμ Discovery Potential (1 fb -1 ): Me* to ~2 TeV, Λ up to ~10 TeV 16