status of invisible higgs study

INDIA-CMS meeting, BARC 20-21 July,2007

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Status of Invisible Higgs Study

Sunil Bansal, Prof. Kajari Mazumdar, Prof. Jasbir Singh

Overview:

1. Introduction

2. First look using CMSSW

3. Estimation of ttbar background.

4. HLT Exercise : Signal Efficiency for Jet + MET trigger

5. Background Generation

6. Conclusions and Plans.


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Introduction• Invisible decays of the Higgs Boson do not play any role in the Standard

Model.• Discovering them would be clear indication of physics beyond the Standard

Model.• Many models with invisible decays: 4th Generation Neutrino Extra Dimensions SUSY Littlest Higgs Model … . .• Different models give very different branching ratio to invisible decay

mode vs. Higgs-mass not a problem: reconstruction of the Higgs mass as a resonance

structure is anyway not possible in this mode. • Only event excess can be seen. Crucial aspect of analysis is precise estimation of backgrounds.• Hence challenging and interesting !


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Phenomenological Considerations

• Invisible decay of Higgs event should be identified using other particles produced along with Higgs.

• Hence ggH production channel is not suitable though rate is highest. In LO there is no other particle in final state.

• Best process, Weak Boson Fusion (qq qqH) has distinctive event topology tagging jets in forward-backward direction.

• Associated production processes (W/Z H, ttH ) are more difficult due to many backgrounds and lower rates.


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More on Weak/Vector Boson Fusion (VBF) Process

• Final state: qq qqH Missing energy (MET) + VBF jets

• Absence of color connection between incoming partons leads to jets which are mostly in forward-backward direction large rapidity gap between jets.

• Jets carry lot of energy, not much in transverse direction.

Final state jets, satisfying these condition tagging jet

• Due to absence of color exchange among involved particles there is hardly any hadronic activity in the central region of detector.

• Jets get balanced by Higgs so azimuthal angle between jets is relatively small.


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First Look Using CMSSW• Till one year back all related studies done with CMSJET, OSCAR+ORCA

CMS note (2002), Internal note (2005) etc.

• During CSA06 exercise, analysis tools in CMSSW were handled, but signal

samples were not available.

• Data sample available during Spring07 production (May)

• (Generation + Simulation CMSSW_1_2_0, Digi + Reco with CMSSW_1_3_1).

• 20k event for Higgs mass ( GeV) 100, 120, 140, 160, 200.

• Signal selection criteria used has been taken from previous study, to be tuned

with latest reconstruction codes and analysis, after comparing with various

backgrounds.

• Presented results of on-going studies regularly in Higgs meeting during May/June.

(quoted by Y. Sirois during his talk in June CMS Week at CERN)

• Being considered as a priority analysis topic in CMS .


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• Sample : /qqHinv200/CMSSW_1_3_1-Spring07-1130/GEN-SIM-DIGI- RECO

• Jet Algorithm iterativeCone5

• Jet matching (reco. Vs. MC) for jets with pT > 20 GeV

• Each reconstructed jet is looped over generated jets, jets with ΔR < 0.1 are accepted ( matching efficiency 97 %).

• Most of the events have only one jet above 40 GeV (Forward- backward jets, so pT is not high).

• We need 2 jets above 40 GeV low acceptance of signal events

Event kinematics for Invisible Higgs


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Reconstructed jet have lower pT compared to

generated jet as these are uncalibrated

Signal event properties:

∆η for leading jets ( pT( j1 , j2) > 40 GeV)

MET after VBF (∆η > 4.4)


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cuts No. of Events

Efficiency ( % )

VBF 2103 10.56

+ MET 1435 7.18

+ Mjj 1121 5.60

+ ∆Φjj 427 2.14

Selection efficiency is 2.48 in CMS IN 2004/028 ( K. Mazumdar & A. Nikitenko

Cont….

Mjj after MET (> 100 GeV)

∆φjj after Mjj

(1.2 TeV)


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Estimation of ttbar background

• ttbar background not checked so far, so given priority. • ttbar sample: 2.5M events at CERN /ttbar_inclusive_TopRex/CMSSW_1_3_1-Spring07-1122/GEN-SIM-DIGI-RECO

Additional Conditions: i) Only hadronics events Lepton veto: no electron with pT > 10 GeV, |η| < 2.5 and no muon with pT > 5 GeV, |

η| < 2.5

ii) Central jet veto : For Signal there is low jet activity in central region. If 3rd jet exist it is due to ISR or FSR. No track information is involved. Zeppenfeld variable Z i = ηi - (η1 + η2) / 2

For signal this variable is large.


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Comparsion of ttbar events with Signal

Δη between leading jets after lepton veto.

Missing transverse energy after cut | ∆η |>4.4


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Mjj after lepton veto, VBF and MET > 100 GeV

ΔΦjj between leading jets after Lepton veto, VBF, MET > 100 GeV and Mjj > 1.2 TeV

Comparison cont…

ttbar

Higgs120


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Zeppenfeld variable

Zi = ηi –(η1 + η2)/2

| Zi | > 2 for signal events.

Jet veto no jet with pT > 20 GeV and | Zi | < 2

ΔΦjj after jet veto

Comparison cont…


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selection MH=120 MH = 140 MH = 160 MH = 200 ttbar_incl.

Lepton veto 78.99 79.15 80.16 81.12 28.58

+ VBF 40.04 39.34 42.82 46.42 0.76

+ MET 8.96 9.48 11.10 13.39 0.03

+ Mjj 2.43 2.67 3.35 4.02 3 × 10 -3

+ jet veto 2.41 2.66 3.33 4.00 10 -3

+ΔΦjj 0.96 1.05 1.32 1.52 1.6 × 10 -4

X-section(SM NLO) pb

4.47 3.83 3.32 2.57 830

Expected No. of events for 1fb-1

43 40 44 39 1.3

Selection efficiency for Signal and ttbar background


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HLT Exercise• All triggers ( L1 and High Level ) thresholds being optimized for LHC

startup Luminosity 10 32 cm -2 s -1.• pp interaction event rate is ~ 105 Hz

• L1-trigger accept rate is 17 kHz and that for HLT is 150 Hz.

Sequence in CMSSW: MC-generated events are simulated, digitised. L1 Emulator duplicate the behavior of the L1-trigger hardware at bit lavel Subsequently L1 seeds are used for HLT information. A trigger table (variables with optimised kinematic thresholds) is used

for trigger studies to check event rates. eg., di electron, isolated: Pt >10 GeV event rate = 0.2 Hz di electron, non isolated: Pt >12 GeV event rate = 0.8 Hz

A report is submitted to LHCC in June by CMS collaboration.CMS Note 80 authors (including S. Bansal, K.Mazumdar)


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Trigger Study for Invisible Higgs Signal

• Final state is forward-backward jets satisfying VBF conditions and large MET.

• L1-trigger : L1 MET is calculated using x and y components of energy deposited in each trigger region.

• HLT : Jets are reconstructed using IC5 algorithm, inputs are calorimeter towers ( pT > 0.5 GeV) . A correction for the calorimeter response is applied for jets ( Full simulated QCD dijet sample used for correction).

• MET is also calculated with same algorithm as used in offline. MET is not corrected.


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• L1 Trigger used MET > 30 GeV • VBF filter is used which select events with η1 * η2 < 0 , Δη > 4.2 and Jet pT > 40 GeV. HLT condition is MET > 60 GeV + VBF Total rate (due to QCD) for these thresholds is 0.2 Hz

Higgs Signal samples are stored only at Wisconsin, to be accessed via CRAB. But required software (CMSSW 1_3_1_HLTX) was not installed there, so Grid job

submission was not possible. Samples for Mh = 200 and 160 GeV copied to cern castor, but failed for other samples.

• L1 : MET > 30 GeV eff. = 79.07% for mH = 200 GeV eff. = 77.80% for mH = 160 GeV• HLT: MET > 60 GeV + VBF eff. = 8.53% for mH = 200 GeV eff. = 7.02% for mH = 160 GeV

Trigger Details


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Backgrounds Generation

• Z/W + Jets are potential background for Invisible Higgs:

Z νν and jets satisfying VBF and

W l ν where lepton pass undetected .

• Z (νν ) /W ( l ν ) + Jets ( EWK & QCD) being generated using Alpgen and Madgraph.

• Generating events for few fb -1 Luminosity.

Alpgen Generation :

• To achieve good event statistics “soft VBF” preselections have been used at generator level

Soft VBF | Δη | > 2 && Mjj > 300 GeV in usercut.f

Alpgen Generation is almost done and will be sent for production

MadGraph Generation :

• Using Same “soft VBF” condition for generation and generation has to done


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•To stabilize the post-warm up technique is used.• Grid is created using small run and run the iteration over the previous grid till it become stable ( in term of cross-section fluctutation)

• This grid is used for final events generation.• To submit parallel batch jobs, a pearl script is used. This script submit the desired number of parallel jobs by changing the input seed for each job and also unweight the events.

• These events hadronised using Alpgen Interface provided in CMSSW

• input file to this interface are .unw and .par.


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Conclusion and Plans

• The signal selection efficiency in CMSSW, in good agreement with previous study using OSCAR+ORCA.

• ttbar background has been studied for the first time for this analysis found to be reducible to very good extent.

• L1 + HLT efficiency is calculated for Signal. contribution to HLT note.

• Estimation for QCD background is going on.• Background Generation using Alpgen and Madgraph ( Z/W +

NJets) is going on, file be will be sent for Summer production.• W/Z + Jets backgrounds to be studied during CSA07.• Double parton-parton and proton- proton scattering

contributation has to estimated.


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Back - up


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Back-up

• Starting from the same grid produces identical events• Change seed1 and seed2 in the input to create parallel jobs from a single grid2

• Alpgen Interface Provided in CMSSW_1_4_X used for hadronisation

In 1_4_0 there were two problems

i) Input file needed to be in same directory

ii) When changed the increased input events there was core dump.

In 1_4_5 these problems has been fixed

Files to be provided as input : file.unw & file_unw.par

Alpgen.cfg : source = Alpgensource {

untracked vstring fileNames = “ file: /tmp/sunil/alpgen”

untracked int32 maxEvents = 1000

Pset PythiaParameters = {

vstring parameterSets = { "pythia" }

vstring pythia = { "MSEL=0 !(D=1) ",

"MSTJ(11)=3 !Choice of the fragmentation function",

"MSTP(143)=1 !Call the matching routine in ALPGEN" }

}


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PSet GeneratorParameters = { vstring parameterSets = { "generator" } vstring generator = { "IXpar(2) = 1 ! inclus./exclus. sample: 0/1", #Inputs for clustering: minET(CLUS), deltaR(CLUS) "RXpar(1) = 20. ! ETCLUS : minET(CLUS)", "RXpar(2) = 0.7 ! RCLUS : deltaR(CLUS)" } }

100 parallel batch submitted for Z ( νν) + 2Jets using soft VBF conditions and post warup technique. Rest are in progress.


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Search Strategy

• So generation is always done in Pythia using SM process H ZZ 4 nu.

• No dedicated generator for invisible decay of Higgs available.

• Production cross-section ( qq qqH) and decay branching for

• (H invisible) are both model dependent. • In experimental searches, model independent

limits are given, since• the product of two determines the number of

events.

Simulation studies needed to optimise potential of the experiment

status of invisible higgs study

Documents

higgs meeting

backward jets

higgs boson

generated jets

indiacms meeting

final state jets

higgs mass gev

cms week