Slide N 1

University of Iowa

qqHqq ZZ qq e+e-ee

Alexi Mestvirishvili

2005 Fall HCAL Meeting

Slide N 2

Event generation and reconstruction

PYTHIA 6.2, CMSIM , ORCA version 7.6.0, Pileup

No tracker was simulated, e+ e- were selected from

generator particle information

Signal events - qqH 300,350 and 500 GeV mass Higgs weregenerated. Higgs and Z decay (forced) modesH Z Z e+e-

ee

N. Of Ev. CS(fb)

68874 1.98

63384 1.56

70164 0.66Background considered in this analysis

7.3x10344257t tCS(fb)N. Of Events

All cross sections listed hereare basically BR decay chain

Analysis note submitted CMS AN 2005/014 – In stage of reviewPresented on HIGGS working group meeting -- good response.Closely working with referees.

Slide N 3

Pre selection cuts

1) At least two “tracks” with opposite charge,

which then can be Identified as electron/positron

2) Soft cut on Pt of “tracks” > 10 GeV

1) Iterative cone algorithm Cone radius – 0.52) At the preselection stage as jet was Accepted any object found by the jet

finder with Et > 20 GeV

3) Jets are well within CMS detector acceptance || 54) No calibration

Slide N 4

Some assumptions

Main assumption in thisanalysis is made on theElectron identificationand its efficiency.

IT IS ASSUMED THAT ELECTRON IDENTIFICATION EFFICIENCY WILLBE AT THE LEVEL OF 94 – 95 %

a) Well isolated two opposite charge tracksb) Cut on Et of the tracks etc.

Assumption is based on Many different sources.One of them DC04 data with full track simulationMY STUDY

VERY PRELIMINARY

In a region between arrowsFalls more than 90% of Electrons, provided selectionCuts are applied on tracks

Slide N 5

Cuts for leptons and missing ET

Leptons (e+ e- ) were selected from generator particles data. Lepton cuts: ||<2.4, ET > 20GeV, |M(e+ e-)-M(Z)|<15GeV, Leptons are between tag jets

a) b)

c) d)

Missing Et distribution for signalAnd background eventsa) H(M=300GeV)b) H(M=350GeV)c) H(M=500GeV)d) t t

Cut for reconstructedmissing ET > 50GeV

Slide N 6

FORVARD JET TAGGING

Jets selection

Jets ET 30GeV – reduces Pileup contamination

Forward jets were searched using rapidity gap methodOver all pseudo rapidity range.

Jet isolation criteria – nothing around the jet in cone 0.5Jets must be in opposite hemisphere 1 . 2 < 0Difference between jets Pseudorapidity more than 4.0If more than one combination of such jets found, jets with largest rapidity difference were accepted as a tagged jets

If no such combination was Found, event was dropped

Jet pairs per event

H(M=300GeV) H(M=350GeV)

H(M=500GeV) t t

Majority of signal events hasAt lest one pair of tagged jets

Slide N 7

FORVARD JET TAGGING Jets Et and di jet mass

H(M=300Gev) H(M=300Gev)

H(M=300Gev) t t

H M=300 – Green points,

H M=350 – Red points

H M=500 – Blue points,

– Black points

t t

Di Jet mass distribution forSignal and background events

Cut is applied at 500 GeV

E t of tagged jets

Slide N 8

Central Jet veto

MH=300GeV MH=350GeV MH=500GeV

13.9% 16.8% 19.0% 0.05%

9.3% 11.0% 13.3% 0.016%

Pseudo rapidity range -2.0 << 2.0

Events with central jets were vetoed before forward jet tagging

No need to use b tagging at all

First veto events with central jets, than search for tag jest

tt

Standard approach: first to find tag jets, then to veto events with

additional central jets.

Slide N 9

Signal Significance

.

range

MH=300GeV MH=350GeV MH=500GeV

||<2.4 1.16 1.16 0.58

||<2.0 1.3 1.3 0.6

||<1.5 1.1 1.1 0.55

Signal Significance for different range

Even the background eventsAre suppressed substantially,Small cross section for signalEvents and huge cross sectionFor background is main reasonFor such low significance.

BUT SIGNAL SIGNIFICANCEIS STILL WELL BELLOW THE ACCEPTABLE 5 LEVEL

Significance is calculatedFor 60 fb–1 LHC integratedluminosity

Slide N 10

Significance extrapolation

Results presented on previous slides are for the one particulardecay channel H ZZe+e-ee. H and Z’s were forced to decayThrough this channels. Taking into account Z boson other decay modes one can extrapolate obtained significance

Significance is calculatedFor 60 fb–1 LHC integratedluminosity

Decays considered ---One Z decay to electronsSecond Z to any kind of neutrino

BUT…Anyway below the 5 levelFor 60 fb–1 LHC integrated

luminosity

Slide N 11

Significance extrapolation

Extrapolation gives 6 timesMore events for signal, whilebackground goes up by factor 2.Increase factor for significanceis app. 4.26

Taking into account Z decay to muons electrons And neutrinos -- Very similar Analysis. High efficiency For muon identification (97%) according DAQ TDR

Significance is calculatedFor 60 fb–1 LHC integratedluminosity

Could be considered as An upper limit – muon Efficiency is not included

Slide N 12

SUMMARY

1. 300,350 and 500GeV mass Higgs production via VBF with subsequent decay to ZZ when one Z decays to electron - positron pair and another to neutrinos, and the tt major background for this channel were studied.2. No b - tagging is necessary, if central jet veto is used before forward jets are searched and tagged.3. Significance for this particular decay channel assuming 60 fb-1 LHC integrated luminosity is well below acceptable 5 level.4. However, taking into account Z decay modes it could be possible to have significance around 5 sigma Higgs produced via WBF and decayed through Z Z for 60 fb-1 at low luminosity condition.