Search for the SM Higgs Boson in the Hγγ Decay Channel and Calibration of the CMS Electromagnetic
Calorimeter with π0γγ Decays
Marat Gataullin, Vladimir Litvine, Yong YangMarat Gataullin, Vladimir Litvine, Yong Yang DoE Review, July 25, 2007 DoE Review, July 25, 2007
Integrated luminosity for Integrated luminosity for 55 discovery discovery
mH GeV L fb-1 115 8.5 120 8 130 11 140 16 150 ~30
Keys: Keys: Clean Photon ID, 0.7% Mass Resolution, Clean Photon ID, 0.7% Mass Resolution, Precise CalibrationPrecise Calibration Next Steps:Next Steps: NLO Monte Carlo Generator NLO Monte Carlo Generator for Higgs & Backgrounds; for Higgs & Backgrounds;
Optimize S/B Separation; Study ECAL Calibration Effects Optimize S/B Separation; Study ECAL Calibration Effects
Higgs Signal and Backgrounds
Caltech+ UCSD
Optimized Optimized HH AnalysisAnalysisFitting NN and Mass for Higgs and QCDFitting NN and Mass for Higgs and QCD
HiggsHiggs: Vector Boson Fusion: Vector Boson Fusion
forward jets
Photons from Higgs decay
qqH → qqγγ MH = 120 GeV
Jets from qq are at high rapidity and large Δη. Jet-tagging gives a background reduction of 95%
MMHH After photon selectionAfter photon selection After Jet TaggingAfter Jet Tagging
120 GeV120 GeV 37.1%37.1% 16%16%
Selection Efficiency:Selection Efficiency:
HiggsHiggs: Vector Boson Fusion: Vector Boson Fusion
CMS Note 2006/097: Two scenarios considered CMS Note 2006/097: Two scenarios considered (Caltech)(Caltech)
CompHEP includes the complete set of tree level (leading CompHEP includes the complete set of tree level (leading order) diagrams for the partonic subprocess ugorder) diagrams for the partonic subprocess ug→→gugu
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 mesonsalso could appear
A New Effective Theory
New “dimension 6” operators that couple the gluon & higgs fields
0.01 < CG < 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 π0
Data after L1 Trigger Online Farm 0 Calibration
>10 kHz~1 kHz
Level 1 trigger rate dominated by QCD: several π0‘s/event Useful π0γγ decays selected online from such events. Main advantage: high π0 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 Hγγ detection. Studies: Selected 0.3M π0 from 5M fully simulated QCD events Scenario L=2x1033cm-2s-1 and L1 rate of 17 kHz (end of 2008). Also works at lower instantaneous luminosities, at the startup ! Alternative strategies (Weν) require 5-10 fb: months/years.
π0γγ Selection
Selection based on local, crystal-level variables — suitable for online Kinematics: PT (γ) >1 GeV, PT (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 Trigger Tower (5x5 crystals)crystals)
Selection Results
π0γγ rate of 1.5 kHzrate of 1.5 kHz or 2,100 or 2,100 ππ00/crystal/day with S/B /crystal/day with S/B ≈≈ 2.0 2.0 High-rapidity regions suffer both in rate and S/B (31)
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 2007/002CMS-IN 2007/002
Calibration Performance
Precision is then fitted to N is the number a=27±1% and b=0.20±0.25% of π0/crystal
22
bNa
CC +=
Calibration performed using an iterative algorithm developed for the RFQ calibration at L3, where we achieved a 0.5% calibration precision
π0γγ in the Endcaps (preliminary)
π0γγ rate comparable to that in the barrel (selection cuts applied) The same event selection approach, with slightly relaxed PT 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.
2x1033cm-2s-
1
1032cm-2s-1
Calibration Studies in Test Beams
π0 decays produced through: π-+Al π0+X (11/2006)
Three different π- beam energies: 9, 20, and 50 GeV
Consider only 9x8 crystal matrix: about 140 π0 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 π0 test beams for the endcaps (October/2007):
redesigning the target and improving the trigger setup.
π0γγ 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 2007/007CMS-DN 2007/007
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μμ++μμ--γγ production through final-state radiation provides a valuable tool to calibrate and study the response of the CMS ECAL.
30,000 events with PT (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 Zee 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
Proof-of-principle achieved with full detector simulation: with full detector simulation: crystal-by-crystal calibration to crystal-by-crystal calibration to 0.5% after 20-80 hours 0.5% after 20-80 hours at L=2x10at L=2x1033 33 cmcm-2-2ss-1 -1 (50-200 hrs. at L=10 (50-200 hrs. at L=103232 cm cm-2-2ss-1-1: startup).: 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 Many months of work on understanding the ECAL performance. performance. Very useful for our physics analyses (Very useful for our physics analyses (H
Test beams demonstrated a 1% calibration precision Test beams demonstrated a 1% calibration precision with ~5 GeV photons: successful reconstruction of with ~5 GeV photons: successful reconstruction of 50 GeV electrons. 50 GeV electrons. No noticeable systematics No noticeable systematics
(~0.3% from test beam). (~0.3% from test beam). Caltech is playing a leading role in this multi-national effort: Detector Performance Group task led by Gataullin/Litvine.
Extra Slides Follow
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 pT 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)Iterative algorithm (successful L3/RFQ Calibration)
(wi 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 π0 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%
22
bNa
CC +=
SBa /1~ +