update on h zz 2l2n analysisindiacms/indiacms-meetings/august-2012/arun-kumar... · 2 arun kumar,...

Update on HZZ2l2n Analysis

Arun Kumar, Kirti Ranjan, Ashok Kumar University of Delhi

India-CMS Meeting, 3-4 August,2012 BARC (Mumbai)

04/08/2012 Arun Kumar, University of Delhi 1

Introduction

ICHEP Update

Further improvements in Analysis

Summary and Outlook

Outline


Motivation and Introduction

Motivation:

SM Higgs is already excluded in mass region (127.5 – 600 GeV) but we still need to

understand processes involving scattering of vector bosons.

The most sensitive analysis at high mass region, also in region which has not been

excluded (>600 GeV).

It has 6 times higher branching ratio than HZZ4l channel.

Signatures: Signature is given by two high PT leptons of same flavor with di-lepton mass close to Z

peak and large MET.

Both Glu-Glu and VBF production modes considered

Full reconstruction of Higgs mass not possible.

Backgrounds: Z+Jets (Most Dominant, difficult to model in MC) TTJets (2nd Dominant) ZZ,WZ,WW (Irreducible ZZ) Single T & W+Jets (Minimal Contribution) QCD


Previous Results and Improvements

2011 Analysis:

Results: exclusion in range 310 – 465 GeV using cut & count and 270 – 440 GeV

using mass shape analysis

Published in JHEP 1203 (2012) 040

New Features of Analysis:

Analysis of 2012 dataset

Reanalyzing 2011 datasets

Updated physics objects

VBF selection

Jet binning

Extension of the analysis to region 200-250GeV ( good sensitivity from VBF category)


ICHEP Update Analysis Strategy:

Analysis is optimized separately for Gluon-Gluon and VBF categories.

Selection can be divided into two parts : Preselection + Final Selection

Pre-selection:

Events are selected with 2 same flavored, well identified and isolated leptons with di-

Lepton mass |Mll - MZ | < 15 GeV

Third Lepton Veto: to suppress WZ background.

Min D(jet,PFMET) < 0.5 reduce the instrumental background from jet mis-measurements.

PT (Z) > 55 GeV For background control sample

Anti b-Tagging

Soft Muon Veto

Final Selection:

PFMET with Type1 corrections is used. Mass dependent cut for non-VBF category.

Mass dependent two sided Transverse Mass of Higgs cut is applied for non-VBF categories.

PAS: HIG-12-023 AN: AN-12-138

To suppress TTbar, Single T

We categorize all events based on the number of jets (PT >30 GeV) in event.


VBF Category

An Event is VBF Tagged if it has:

2 non-b-tagged jets with PT > 30 GeV

|Dh| > 4.0 between jets

di-jet mass Mjj > 500 GeV

di-lepton between jets

Central Jet Veto

Including VBF improves sensitivity greatly at low mass

Overall increase in sensitivity 2% – 50 %

Final Selection: PFMET > 70 GeV


Background Estimation

Z+Jets (instrumental background with fake missing energy) is estimated from

data using g+jets events.

Non Resonant backgrounds (Top/WW/W+Jets, have real MET) are estimated

from data using em events.

Irreducible electroweak ZZ background and fully leptonic WZ decays are

estimated from Monte Carlo.


Z+Jets Background Estimation

7TeV

Non-VBF

Non-VBF

8TeV

g+jets events are used to model Z+Jets from data.

g+jets has similar kinmeatic distributions as

Z+Jets

Larger Statistics

Photons are selected using V + g photon selection

Procedure PT distribution of g’s reweighted to match

to Z’s Number of primary vertex distribution in

g’s is reweighted to match to Z’s Each photon is assigned a mass by

sampling Z line shape from data done separately for each event category

Final estimate is taken as half of the prediction from photon events with 100% systematic error on prediction


Non-Resonant Background Estimation

Estimation of non-resonant backgrounds is performed with standard technique, using em events passing analysis selection (Nem

SIG )

Using sidebands (55 < mll < 70 and 110 < mll < 200 GeV) of the Z peak a scale factor a is determined from ratio of ee/mm and em events passing MET > 70 GeV and requiring at least one b-tagged jet.

Predicted number of background events is given then as

This method treats contribution from HWW*2l2n as background and properly accounts on it.

7TeV+8TeV


Results: Combined Categories Exclusion Limit, R

Expected Exclusion: 299 – 505 GeV

Observed Exclusion: 258 – 589 GeV


Trigger Efficiencies Studies

June 4, 2012 Arun Kumar, University of Delhi 11

Sample Used:

Double Electron dataset 2012A and 2012B

Single Muon dataset 2012A and 2012B

Lumi ~ 2.0 fb-1

Introduction and Data Samples

Trigger Studied

HLT path :

HLT_Ele17_CaloIdT_CaloIsoVL_TrkIdVL_TrkIsoVL_Ele8_CaloIdT_CaloIsoVL_TrkIdVL_TrkIsoVL_v*

HLT_Mu17_Mu8_v* and HLT_IsoMu24

Tag&Probe method used.

HLT path has two legs so efficiency is calculated per leg

June 4, 2012 Arun Kumar, University of Delhi 12

Selection and Definition Tag Selection

Tag must pass the Medium WP of the Electron ID and Tight ID for Muons •(Tables are in back-up) Effective Area-Based PF Isolation < 0.15(0.2) for Electrons (Muons) Tag must pass through the first leg of the HLT path:

HLT_Ele23_CaloIdT_CaloIsoVL_TrkIdVL_TrkIsoVL_HFT30_v* (for Electrons) HLT_IsoMu24_eta2p1_v* (for Muons) Tag PT > 30 GeV |h| < 2.5(2.4), for Electrons(Muons)Transition region excluded DR matching of 0.2 has been used.

Probe Selection

All cuts are same as Tag except the requirement of passing the Trigger and PT requirement. PT > 20 GeV

Tag&Probe pairs are then selected using Z mass window of 15 GeV from the nominal Z mass, 76.2 GeV < M

ee < 106.2 GeV

Definition

Probe Passed

Probe Passed + Probe Falied Trigger Efficiency =

Efficiencies for di-electron Trigger in PT and Eta Bins

HLT_Ele17* HLT_Ele8*


Fig. 43 in AN-12-138 Fig. 43 in AN-12-138

Fig. 43 in AN-12-138 Fig. 43 in AN-12-138


Efficiencies for di-muon Trigger in PT and Eta Bins

HLT_Mu17 HLT_Mu8

IsoMu_24

Fig. 44 in AN-12-138 Fig. 44 in AN-12-138

Fig. 44 in AN-12-138


TMVA BDT Analysis for HZZ2l2n

Arun Kumar, Delhi University 16

TMVA based BDT studies for HZZ2l2n

TMVA Based BDT is chosen with Random Forest Technique. Various BDT configurations

trained and tested.

Training/Testing is done separately for each Higgs Mass point from 200 GeV, to 600 GeV

Analysis is done in inclusive jet bins with VBF.

We allow more phase space in BDT than C&C by either not imposing cut on variables

like MT (Higgs), di-Lepton PT, Min(d (Jet,MET)) OR relaxing the cuts on variables like

M(ll) and PFMET.

Di-Lepton Invariant Mass cut : 60GeV < Mll < 120 GeV

PFMET > 60 GeV

Input variables chosen for training, testing:

di-Lepton invariant Mass

di-Lepton PT

di-Lepton Eta

di-Lepton Phi

PFMET

Min(d (Jet,MET))

Transverse Mass of Higgs

Only 7TeV for the moment

PU Reweighing is applied


Data/MC Comparison Plots for HZZ 2m2n

< 5% differences in data/MC distributions.

04/08/2012 Arun Kumar, Delhi University 18

Input Variables for HZZ2m2n at m(H) = 200 GeV

M(ll) Di-Lepton PT

Di-Lepton Eta

Di-Lepton Phi

PFMET MT Higgs

dPhi (Jet,MET)

N_Jets 1. MT Higgs 2. dPhi(Jet,MET) 3. PFMET 4. Di-Lepton PT 5. N_Jets 6. di-Lepton Mass 7. Di-Lepton Eta 8. Di-Lepton Phi

Ranking of Variables:

9 July 2012 Arun Kumar, Delhi University 19

TMVA BDT Response and ROC Curves for HZZ2m2n

200 GeV

400 GeV

600 GeV


Mass (GeV) Cut&Count* BDT Improvement

200 10.38 2.67 ~74%

250 1.84 0.89 ~51%

300 1.10 0.60 ~45%

350 0.72 0.45 ~37%

400 0.86 0.48 ~44%

450 1.05 0.68 ~35%

500 1.52 0.97 ~36%

550 2.27 1.41 ~38%

600 2.85 1.63 ~42%

• Limits are calculated using Higgs combination package after optimizing the mva cut value using LandS package. • Figure of merit for optimizing the MVA output cut is Expected Limit on sSM

Table for Mean Expected Limits at 5fb-1 7TeV Analysis


Summary and Outlook

Presented the ICHEP Update of the HZZ2l2n Analysis

Our contribution was mainly in Trigger Efficiencies, Data/MC Comparison.

We are introducing TMVA BDT analysis for further improvements. First Results

looks promising.

I took 22 Trigger Online Shifts in my last CERN Visit ( 27/03/2012 to 27/06/2012)

and 1 week of ECAL PFG Expert Shift.

Involved in ECAL Reconstruction Software development service tasks.

Perform the TMVA BDT Analysis for both 7TeV and 8TeV. Carry out the analysis

for full 2012 dataset.

Try more signal samples with the same final state.

I will take 2 more weeks of ECAL PFG Expert shifts this year.

Planning for Tracker Alignment Service Task this year.

Poster has been approved for PIC 2012 for HZZ->2l2nu Analysis.


Back Up

EE Plots(1/2)


EE Plots(2/2)


MUMU Plots(1/2)


MUMU Plots(2/2)


7TeV 8TeV

7TeV+8TeV


Results: Combined Categories Exclusion Limit, R


Trigger Efficiency Numbers

Di-Electron 2012A+2012B

HLT Leg (-2.5,-1.5) (-1.5,0) (0,1.5) (1.5,2.5)

First leg 97.9+-0.23 98.3+-0.03 98.2+-0.03 97.9+-0.23

Second leg 96.5+-0.29 97.6+-0.03 97.5+-0.03 96.1+-0.31

HLT Leg 20-30 GeV 30-40GeV 40-50GeV 50-100GeV

First leg 96.3+-0.08 98.2+-0.03 98.7+-0.03 98.7+-0.05

Second leg 96.1+-0.09 97.4+-0.04 97.8+-0.03 97.8+-0.06


Di-Muon (2012A)

HLT Leg (-2.1,-1.5) (-1.5,0) (0,1.5) (1.5,2.1)

Mu17 93.8+-1.05 95.7+-0.47 95.2+-0.49 93.2+-1.11

Mu8 95.6+-0.90 96.1+-0.45 95.9+-0.46 93.9+-1.06

Di-Muon (2012B)

HLT Leg (-2.4,-1.5) (-1.5,0) (0,1.5) (1.5,2.4)

Mu17 90.7+-0.73 95.2+-0.32 95.3+-0.33 93.1+-0.65

Second leg 93.9+-0.61 95.8+-0.31 95.9+-0.31 95.0+-0.56


Systematics


Combined Limits for 7TeV+8TeV 10fb-1


Event categories: Improved Sensitivity 7TeV 5fb-1


Lepton Selection


Events Cut Flow

Arun Kumar, Delhi University 39

Introduction and Motivation

We aim to investigate the scope of improvement in the analysis with the application

of MVA BDT.

MVA utilizes the whole information of a discriminating variable so better chances of

rejecting background and also it takes care of the correlations between the variables.

Many major analyses like HWW*2l2n and Hgg are getting benefitted so it can

be tried in this analysis.

Fall 11 MC samples and whole 2011 DoubleElectron based HZZ skim datasets are used.

Apply the same ID and Isolation to Leptons as C&C

3rd Lepton Veto and Anti b-Tagging is used.

Di-Lepton Invariant Mass cut relaxed. 60GeV < Mll < 120 GeV

MET > 60 GeV is required to suppress the Drell-Yan background

Main idea is to loosen the cuts used in C&C and open more phase space to do the analysis

Samples and Event Selection:

Only 7TeV for the moment

PU Reweighing is applied


Data/MC Comparison Plots for HZZ 2e2n (1/2)


Data/MC Comparison Plots for HZZ 2e2n (2/2)


Input Variables for HZZ2e2n at m(H) = 200 GeV

M(ll)

Di-Lepton PT

Di-Lepton Eta

Di-Lepton Phi

PFMET MT Higgs

dPhi (Jet,MET) N_Jets

Ranking of Variables:

1. MT Higgs 2. Di-Lepton PT 3. PFMET 4. N_Jets 5. dPhi(Jet,MET) 6. Di-Lepton Eta 7. di-Lepton Mass 8. Di-Lepton Phi


TMVA BDT Response and ROC Curves for HZZ2e2n

200 GeV

400 GeV

600 GeV

√s=8 TeV: 25-30% higher s than √s=7 TeV at low mH

All production modes to be exploited

gg VBF VH ttH

Latter 3 have smaller cross sections but better S/B in many cases

Higgs Production at the LHC

5 decay modes exploited

High mass: WW, ZZ

Low mass: bb, ττ, WW, ZZ, gg

Low mass region is very rich but

also very challenging:

main decay modes (bb, ττ) are hard

to identify in the huge background

Very good mass resolution (1%):

H gg and HZZ4l

Higgs Decay Modes The lifetime of Higgs itself is very short (10-22 second). It is only by measuring the characteristics of its decay via various final states (decay channels) into other subatomic particles according to the SM that the Higgs boson will be identified.

Decay products: e, m, t, g, g,qjets, n->missing energy

Higgs Decay Modes

update on h zz 2l2n analysisindiacms/indiacms-meetings/august-2012/arun-kumar... · 2 arun kumar,...

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