INDIA – CMS, PU, 5-6 April 2007 Ashok Kumar PU & GNDU Search for the Standard Model Higgs Boson Decaying to Muons via Weak Gauge Boson Fusion Ashok Kumar Ashok Kumar and and Suman Beri Suman Beri Panjab University – Chandigarh Panjab University – Chandigarh Ritva Kinnunen Ritva Kinnunen Helsinki Institute of Physics Helsinki Institute of Physics INDIA – CMS, 5-6 April 2007 INDIA – CMS, 5-6 April 2007
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Search for the Standard Model Higgs Boson Decaying to Muons via Weak Gauge Boson Fusion
INDIA – CMS, 5-6 April 2007. Search for the Standard Model Higgs Boson Decaying to Muons via Weak Gauge Boson Fusion. Ashok Kumar and Suman Beri Panjab University – Chandigarh Ritva Kinnunen Helsinki Institute of Physics. Cross-sections and Branching Fractions. - PowerPoint PPT Presentation
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INDIA – CMS, PU, 5-6 April 2007Ashok KumarPU & GNDU
Search for the Standard Model Higgs Boson Decaying to Muons via Weak Gauge Boson Fusion
Ashok Kumar Ashok Kumar andand Suman BeriSuman BeriPanjab University – ChandigarhPanjab University – Chandigarh
Ritva KinnunenRitva Kinnunen Helsinki Institute of Physics Helsinki Institute of Physics
INDIA – CMS, 5-6 April 2007INDIA – CMS, 5-6 April 2007
INDIA – CMS, PU, 5-6 April 2007Ashok KumarPU & GNDU
Though the H → branching fraction is tiny and the backgrounds from Z→- and ttbar production are large, but it is an interesting channel because it provides information on the H coupling
Cross-sections and Branching FractionsCross-sections and Branching Fractions
Two search methods possible: - - Inclusive search profiting from the larger cross section, fast simulation study in CMS IN 2005/013 - Search in the weak gauge boson fusion, exploits an efficient background reduction with forward jet tagging
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INDIA – CMS, PU, 5-6 April 2007Ashok KumarPU & GNDU
Event Generation and ReconstructionEvent Generation and Reconstruction
generator reconstructed
events used x BR x BR x
preselection
Signal, mH = 120 GeV PYTHIA 8000 1.1 fb 1.1 fb
Z+jet, 10 < pT < 100 GeV1) PYTHIA 288413 5.1 nb 5.1 nb
Standard ORCA packages for reconstruction: - Muons: GlobalMuonReconstructor- Hadronic jets: TransientJetAlgorithm with Jet reconstruction cone = 0.5, Corrections: MCJet with SplittedEcalPlusHcalTowerInput, Et
tower > 0.5 GeV, Etower > 0.8 GeV and with ET(raw jet) > 20 GeV- MET from EcalPlusHcalTowers with Type1 jet corrections
INDIA – CMS, PU, 5-6 April 2007Ashok KumarPU & GNDU
Higgs boson mass reconstructionHiggs boson mass reconstruction
Select events with exactly two isolated muons with pT> 20 GeV, passing
the L1 andHLT di-muon or single muon triggers Muon isolation: no tracks with pT>1 GeV in a cone of R = 0.4 around the muon
MC muons
Results from a gaussian fit: = 1.42 GeV (1.18%), <m> = 120.1 GeV
Event Selection
Reconstructed muons
New values due to the potential bb+jets background, pT>15 GeV
and R = 0.3 were used in the first version
INDIA – CMS, PU, 5-6 April 2007Ashok KumarPU & GNDU
Central variables for event selectionCentral variables for event selection
1. No neutrinos in the signal event: an upper bound on ETmiss can be used to
suppress the ttbar background2. Expect more boosted di-muon system in the signal than in the Z+jet background: cut in pT
Rejection of tt ~4 for ETmiss < 50 GeV Rejection of Z+jets ~12 for pT
>60 GeV
INDIA – CMS, PU, 5-6 April 2007Ashok KumarPU & GNDU
Signal qqZ Z+jets ttbar
Events for 60 fb-1 66 5160 3.05 x 108 1.25 x 106
L1 61.8 (93.5%) 5142 (99.7%) 1.18 x 108 (38.7%) 1.25 x 106(100%)
HLT 57.5 (93.0%) 4930 (95.9%) 4.84 x 107 (41.0%) 1.00 x 106(80.2%)
PV 56.6 (98.5%) 4863 (98.6%) 4.74 x 107 (97.8%) 9.97 x 105(99.4%)
2 ,pT>20 GeV 41.9 (74.4%) 3668 (75.4%) 2.09 x 107 (44.1%) 3.79 x 105(38.0%)
muon isolation 28.8 (68.9%) 2546 (69.4%) 1.44 x 107 (68.9%) 1.60 x 105(42.2%)
MET < 50 GeV 25.7 (89.2%) 2179 (85.6%) 1.37 x 107 (95.1%) 4.26 x 104(26.6%)
pT > 60 GeV 16.6 (64.4%) 1396 (64.1%) 1.10 x 106 (8.0%) 2.27 x 104(53.3%)
Number of signal and background events and cut Number of signal and background events and cut efficienciesefficiencies
after central event cuts and mass windowafter central event cuts and mass window
No signal visibility possible even with large integrated luminosity, assume that Higgs boson mass is known from other processes to select the mass window
INDIA – CMS, PU, 5-6 April 2007Ashok KumarPU & GNDU
Forward jet tagging Forward jet tagging in the mass windowin the mass window1)1)
Selection of forward jets: two hardest jets anywhere in rapidity with j1*j2 < 0
Signal vs qqZ differences due to generator level cuts on qqZDifferences may arise also due to the possibility of the Z originating from a final state quark
Select lowest possible value, ET > 20 GeV,due to PYTHIA generation of Z+jetbackgroundNo optimization of this variable
1) Due to the small mass window, statistics low for Z+jets: - need to open the mass window and - assume decoupling of pT
and tagging cuts
INDIA – CMS, PU, 5-6 April 2007Ashok KumarPU & GNDU
Expect large rapidity gap for the q jets in qq -> qqH
|q1 –q2| > 4.2 at the generator levelfor qqZ
|j1 - j2| > 4.5
Rapidity gap between the tagging jets
INDIA – CMS, PU, 5-6 April 2007Ashok KumarPU & GNDU
Di-jet invariant mass
Optimal cut value: Mtagging jets > 1 TeV
With all (previous) event selection cuts, including |j1 - j2| > 4.5
INDIA – CMS, PU, 5-6 April 2007Ashok KumarPU & GNDU
Selection of central jets:
- All corrected jets between the two tagging jets within min + 0.5 < jet < max – 0.5 and with ET > 20 GeV
Central jet veto
Statistics too low for Z+jet to obtain the efficiency curve
ETjet = 20 GeV taken as the
threshold
INDIA – CMS, PU, 5-6 April 2007Ashok KumarPU & GNDU
Number of signal and background events and cut Number of signal and background events and cut efficienciesefficiencies
for forward jet tagging and central jet veto cutsfor forward jet tagging and central jet veto cuts
INDIA – CMS, PU, 5-6 April 2007Ashok KumarPU & GNDU
Comparison of PYTHIA and ALPGEN generation for the Z+jets background
Data samples: - existing ALPGEN production samples for exclusive 2-5 jet final states, generated with Z-> ee, ,, mll > 40 GeV
- generation of PYTHIA events with the data cards used for the ORCAproduction samples but with mll > 40 GeV
Comparison method:Jet reconstruction within | | < 5 with the PYTHIA jet reconstruction package in CMKINMain event selection cuts: - two leptons (electrons or muons) with pT > 15 GeV/c - cut in the di-lepton pT, pT
ll > 60 GeV/c - two tagging jets with the method used for the ORCA analysis - central jet veto - No MET cut, no mass window cut
INDIA – CMS, PU, 5-6 April 2007Ashok KumarPU & GNDU
- Assume that for the remaining selection the efficiency is similar to that of Z+jets-Result: ~ 4x10-3 events in the mass window
Estimate of bb+jets background
INDIA – CMS, PU, 5-6 April 2007Ashok KumarPU & GNDU
Signal superimposed on the total background
With all selection cuts, for 60 fb-1
INDIA – CMS, PU, 5-6 April 2007Ashok KumarPU & GNDU
JES uncertainty in the background determinationJES uncertainty in the background determination
Signal visibility not obtained with 60 fb-1 , background could be estimatedaround the already known Higgs mass (from H->Main uncertainty expected from JES uncertainty
Uncertainty on the backgrounds from JES uncertainty, 10% MET uncertainty included
tt most sensitive to theincrease of JES uncertaintydue to large jet multiplicity
30% uncertainty in this estimate due to MC statistics
INDIA – CMS, PU, 5-6 April 2007Ashok KumarPU & GNDU
Estimate of statistical significance
Total background in the mass bin 3.74 events
Systematic uncertainties: JES uncertainty dominates for this channel tt 20% Z+jets 16% qqZ 8% Assume 5% uncertainty for all production cross sections
Total background with systematics 3.74 ± 0.73 events
Significance (Poisson stat., ScPf program): 0.75 with systematic uncertainty 0.80 without systematic uncertainty
INDIA – CMS, PU, 5-6 April 2007Ashok KumarPU & GNDU
ConclusionsFull simulation study on qq → qqH, H → with forward jet tagging and central jet veto yields S/B ~ 0.5 in a mass window assuming mH to be known from H → for 60 fb-1
Statistical significance = 0.75 and upper bound for xBR = 12.7 fb at 95% CL, including systematic uncertainty
Main backgrounds from Z+jets, ttbar and qqZ were simulated
For better optimization of jet tagging and veto cuts, generation of the Z+jets background with a NLO generator needed
For high luminosity, Lt > 100 fb-1, inclusive H-> channel more profitable:background can be extracted with high precision around the known mass value(0.5% from fast simulation for 60 fb-1)
INDIA – CMS, PU, 5-6 April 2007Ashok KumarPU & GNDU
AN2006/105 Search for the Standard Model Higgs Boson Decaying into Muons
- Comments from room: approach of the analysis is not the right one.presently this is approached like a discovery analysis, while there is nochance in this analysis. Instead one should take into account thealready measured mass of the Higgs, select on a mass windowin the di-muon system and then optimize the cuts against background.In any case it will remain a difficult channel for the LHC.
- Z+jets ALPGEN files are now available so these files can be used tomake the background analysis of that channel, or at least cross checkexplicitely against PYTHIA
- Concerns from the referees are to be taken to be taken into account
STATUS: Not approved. Sent back to the Higgs group to re-discuss the analysis strategy
The analysis note was presented in the Physics meeting on December 8, 2006 by Suman Beri