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

15

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~ +