Search for the SM Higgs Boson in the H γγ Decay Channel and Calibration of the CMS Electromagnetic Calorimeter with π 0 γγ Decays Marat Gataullin,
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Presentation on theme: "Search for the SM Higgs Boson in the H γγ Decay Channel and Calibration of the CMS Electromagnetic Calorimeter with π 0 γγ Decays Marat Gataullin,"— Presentation transcript:
Search for the SM Higgs Boson in the H γγ Decay Channel and Calibration of the CMS Electromagnetic Calorimeter with π 0 γγ Decays Marat Gataullin, Vladimir Litvine, Yong Yang Marat Gataullin, Vladimir Litvine, Yong Yang DoE Review, July 25, 2007
Integrated luminosity for 5 discovery Keys: Clean Photon ID, 0.7% Mass Resolution, Precise Calibration Next Steps: NLO Monte Carlo Generator for Higgs & Backgrounds; Optimize S/B Separation; Study ECAL Calibration Effects Higgs Signal and Backgrounds Caltech + UCSD Optimized H Analysis Fitting NN and Mass for Higgs and QCD
Higgs : Vector Boson Fusion forward jets Photons from Higgs decay qqH → qq γγ M H = 120 GeV Jets from qq are at high rapidity and large Δη. Jet- tagging gives a background reduction of 95% M H M H After photon selection After photon selection After Jet Tagging 120 GeV 37.1%16% Selection Efficiency:
Higgs : Vector Boson Fusion CMS Note 2006/097: Two scenarios considered (Caltech) CompHEP includes the complete set of tree level (leading order) diagrams for the partonic subprocess ug→ gu
5 Modifications to the Properties of the Higgs Boson Manohar and Wise, Phys. Lett. B636 (2006) 107-113 Motivation “Minimal” solution to the Hierarchy Puzzle, through new physics at ~ 1 TeV LHC: Promising Scenario gg →h already at one loop: a higher order process in perturbation theory WW → h, ZZ → h etc. affected less New Top-like mesons also could appear A New Effective Theory New “dimension 6” operators that couple the gluon & higgs fields 0.01 < C G < 0.1 from Tevatron data and neutron dipole moment Higgs gg fusion rate could be several times, or much less than in the SM … T T T
Effects on H Discovery SURF’06 (Yike Lu) Higgs can be discovered much faster or slower ! We plan expansion to other decay channels Can be inverted to measure the Higgs couplings Working on combining with with H ZZ* 4μ channel (also for the SM search)
Precise ECAL Calibration with π 0 Data after L1 TriggerOnline Farm 0 Calibration >10 kHz ~1 kHz Level 1 trigger rate dominated by QCD: several π 0 ‘s/event Useful π 0 γγ decays selected online from such events. Main advantage: high π 0 rate (nominal L1 rate is 100kHz !) No track reconstruction (no alignment) required. “Design” calibration precision better than 0.5% Achieving this would be crucial for a fast H γγ detection. Studies: Selected 0.3M π 0 from 5M fully simulated QCD events Scenario L =2x10 33 cm -2 s -1 and L1 rate of 17 kHz (end of 2008). Also works at lower instantaneous luminosities, at the startup ! Alternative strategies ( W e ν) require 5-10 fb: months/years.
π 0 γγ Selection Selection based on local, crystal-level variables — suitable for online Kinematics: P T ( γ ) >1 GeV, P T (pair) > 3.5 GeV and η < 1.48 (barrel) Simple cuts on photon shower shape and isolation to remove converted γ ’s Trigger Tower (5x5 crystals)
Selection Results rate of 1.5 kHzor 2,100 π 0 /crystal/day with S/B ≈ 2.0 π 0 γγ rate of 1.5 kHz or 2,100 π 0 /crystal/day with S/B ≈ 2.0 High-rapidity regions suffer both in rate and S/B (3 1) Cracks between supermodules give a -1.5% shift and selective readout: a -0.4% shift with a period of 5 crystals. Dedicated procedure corrects to a 0.1% level. CMS-IN 2007/002
Calibration Performance Precision is then fitted to N is the number a=27±1% and b=0.20±0.25% of π 0 /crystal Calibration performed using an iterative algorithm developed for the RFQ calibration at L3, where we achieved a 0.5% calibration precision
π 0 γγ in the Endcaps (preliminary) π 0 γγ rate comparable to that in the barrel (selection cuts applied) The same event selection approach, with slightly relaxed P T cuts First results are promising: calibration will take only ~5 times longer than in the barrel. Working on the ECAL+Preshower analysis. Currently this is the only viable calibration technique for the endcaps. 2x10 33 cm -2 s -1 10 32 cm -2 s -1
Calibration Studies in Test Beams π 0 decays produced through: π - +Al π 0 +X (11/2006) Three different π - beam energies: 9, 20, and 50 GeV Consider only 9x8 crystal matrix: about 140 π 0 decays/crystal Caltech group co-lead this effort (with the University of Minnesota)
First Resonance Observed by CMS Improvement over the uncalibrated peak (L3 algorithm): 7% 5.5% Currently working on π 0 test beams for the endcaps (October/2007): redesigning the target and improving the trigger setup. π 0 γγ produced in upstream scintillators
Calibration Precision with 50 GeV Electrons For each crystal, electron energy spectra fitted to a Gaussian. Distributions of the obtained peak positions for 9x8 crystal matrix: Precision: 1.0±0.1% with 0.9±0.1% expected. Calibration with ~5 GeV photons works well for higher-energy showers! CMS-DN 2007/007
15 μ + μ - γ μ + μ - γ production through final-state radiation provides a valuable tool to calibrate and study the response of the CMS ECAL. 30,000 events with P T (γ) >10 GeV produced after 1 fb -1, allowing us to perform ring-by-ring ECAL calibration to 0.5% precision; faster and independent of tracker systematic effects, which will affect the Z ee calibration. Complementary to the ongoing of L1/HLT trigger efficiency study using Z+ γ events. μ + μ - γ Final State Topology Ashok Kumar, Jan Veverka
Conclusions and Outlook with full detector simulation: Proof-of-principle achieved with full detector simulation: crystal-by-crystal calibration to 0.5% after 20-80 hours crystal-by-crystal calibration to 0.5% after 20-80 hours at L=2x10 33 cm -2 s -1 (50-200 hrs. at L=10 32 cm -2 s -1 : startup). at L=2x10 33 cm -2 s -1 (50-200 hrs. at L=10 32 cm -2 s -1 : startup). Other methods are much slower and tracker dependent. Other methods are much slower and tracker dependent. Many months of work on understanding the ECAL performance. Very useful for our physics analyses ( performance. Very useful for our physics analyses ( H Test beams demonstrated a 1% calibration precision with ~5 GeV photons: successful reconstruction of with ~5 GeV photons: successful reconstruction of 50 GeV electrons. No noticeable systematics (~0.3% from test beam). 50 GeV electrons. No noticeable systematics (~0.3% from test beam). Caltech is playing a leading role in this multi-national effort: Detector Performance Group task led by Gataullin/Litvine.
CompHEP EW background: ud→ du This background topology is very similar to Higgs signal CompHEP EW 2 +2jets background has smaller cross section compare to QCD 2 +2jets background (300 fb vs 50 pb), but has long hard tails in p T distributions and many photons at small from ladder diagrams like 3,4. These tails are much harder than for the CompHEP QCD 2 +2jets background sample
Correcting for Cracks and SRO Cracks between baskets/supermodules give a -1.5% shift. Selective readout: a -0.4% shift with a period of 5 crystals. Dedicated procedure developed to correct to 0.1-0.2% level.
Calibration Algorithm Iterative algorithm (successful L3/RFQ Calibration) (w i fraction of shower energy deposited in this crystal) Both photon energy and direction reconstructed using crystal level information (same as during selection). After each iteration pairs are re-selected with new constants (typically 10-15 iterations to converge). Miscalibration is done before selecting events (4%). Calibration precision defined as R.M.S. of the product of the final and initial miscalibration constant. Use only pairs from ±2σ window around fitted π 0 mass
Effects of Corrections Correcting for cracks and selective readout gives an improvement of 0.9% (in quadrature), and removing pileup eliminates an additional constant term of 0.6%.
Calibration Performance Precision is then fitted to a=27% and b=0.2%