Tau Jet Identification in Charged Higgs Search

Monoranjan Guchait TIFR, Mumbai

India-CMS collaboration meeting 27-28th March,2009 University of Delhi

M.Guchait, R.Kinnunen, M.Kortelainen, Sami Lehti A. Nikitenko, L. Wendland

CMS AN 09/036

Motivation

MSSM: 5 Higgs h, H, A , H+, H-

Standard model: one Higgs, mass is not predictable

Predictable in terms of Parameters

Two parameters: MA and tanβ

Signature of Charged Higgs carry unambiguous Signal of NEW Physics

Charged Higgs Production

RLc

RbLt

Wmscm

btmbtmH

M

gL

tancot

tancot

2

Coupling

High tanβ

Charged Higgs Decay

H → t b is dominant for Higher higgs, but huge contamination

H→ tau + nu is Sub-dominant, useful to find the Higgs signal

Tau decay and Helicity Correlations

~ 2/3

Tau polarization

Angular distributions ~

cos1 P

Helicity Correlations

Fast simulations

Guchait,Kinunnen,Lehti,CMS IN 2008/008

1 prong

3 prong

Event SamplesCMSSW 1_6_12 + TAUOLA for tau decays

Signal for MH=200,300,400,tanβ=30 250 K events

QCD(PYTHIA)Pt_hat=80-230 GeV3.4 M events

tt + 0/1 jets(ALPGEN)1.8 M events

W+3/4 jetsPeak sample:MW<150 GeV, 1.3 M eventsTail sample: MW>150 GeV, BW, 76 K events

Signal

QCD

ttbar

W+3/4 jets

Jet and Track Reconstruction

Calorimeter tau jets(Calotau)are usedMC based jet energy corrections are used CMS IN 2007/029

Iterative tracking used for tracksTracks down to pt>0.3 GeV are used CMS IN 2007/035

Jet energy resolution for MC matched calorimeter tau jets (CaloTau) for mH+=300 GeV/c2

Why to Optimize against QCD BG• [P-TDR II]: The transverse mass

(mT) of the H+ is reconstructed from the tagged tau and the MET

– H+ events acquire mT valuesmainly up to mH+

– W events acquire mT values mainly up to mW

– QCD multi-jet events may faketau jet and MET;

o can contaminate the signal region

o very large cross-section– also off-shell W events can

contaminate the mT signal regio

–but relatively low cross-section

Optimize against QCD multi-jet background anduse helicity correlations to suppress W decays

Selection Strategy for 1 prong

• Jet ET > 119 GeV, jet eta: ||<1.7

• Leading track pT>20 GeV/c

–through R cut, pT>95 GeV/c

• 1 isolated charged track–isolation cone R=0.50; min. track pT>1.0 GeV/c

• Standard track quality cuts–Nhits>=8, normalized track 2<10, IPT<300 m, |IPz|<1 mm

Selection Strategy for 1 prong

Isolated electromagnetical energy deposition–isolation annulus R=0.10-0.50, allowed energy ET

isol<1.8 GeV

• Matching of track momentum to hadronic energy deposition–to reject electrons; ET

HCAL / pTtrack - 1 > -0.90

• Helicity correlations, R=ptrack/Evis. jet > 0.8

–to suppress taus from W decays–suppresses further also hadronic jets with neutral particles

Jet Et threshold• Jet Et threshold of 119 GeV was found to be optimal

against QCD multi-jet events in the 1-prong final state

The high jet ET threshold

viable also for signal with

mH+~mt

Efficiency of the jet ET threshold for MC matched

H+ decays

PAS Figure 2

after allother cuts

Electromagnetic Isolation

• Due to the boost effect, the 0’s are contained within a narrow cone in tau decays; the ECAL energy deposition is calculated in an isolation annulus around this signal cone

[CMS Note 2006/028]

Optimum cut for 1-prong: ET

isol.<1.8 GeV in an annulus of R=0.10-0.5

Electron rejection • Main sources of electrons are

– Wee and Wee

decays• These electrons can be effectively

suppressed by matching the HCAL energy deposition to the momentum carried by the track,

• i.e. ETHCAL/pT

track-1 = Re

– the HCAL energy is summed in a coneof R=0.50 around the leading trackaxis

• Optimum cut was found to be givenby Re> -0.90

Tracker Isolation• Low charged track multiplicity and

isolated track signature in tau jet

• Required 1 charged track in isolation cone of 0.50

• Counted tracks with pT > pTmin to

filter out very soft tracks

• Only tracks from interaction vertexwere considered

– |IPz|<1 mm

• Rejected tracks, which consist of hitsbelonging to different tracks

– IPT<300 m[CMS Note 2006/028]

• Optimum choice for 1 prongs:

– pTmin =1.0 GeV/c (same as at trigger

level)– could use smaller value (e.g. 0.7

GeV/c), if necessary

Tau Helicity CorrelationDifferent polarization effects in tau decay from H and W decay is exploited

R distribution including all 1-prong tau decay modes after all other

cuts

PAS Figure 7

after allother cuts

Signal eff ~ 0.5 Bg ~ 0.2 or less

Tracker

Calorimeter

Selection strategy for 3 prongs• Choose a1

+++- decays (2/3 of 3-prongs)

• Jet ET > 100 GeV, jet eta: ||<1.8

• Leading track pT>20 GeV/c (to mimic single tau trigger)

• 3 isolated charged tracks– isolation annulus R=0.04-0.50; min. track pT>0.8 GeV/c

• Standard track quality cuts– Nhits>=8, norm. track 2<10, Qtrack = ±1, IPT<300 m, |IPz|<1 mm

• Isolated electromagnetical energy deposition– isolation annulus R=0.15-0.50, allowed energy ET

isol<1.8 GeV

• Matching of energy carried by the tracks to calorimeter energy E=Etracks/Ejet-1 > -0.2; to reject neutral hadrons

• Flight path of the tau lepton and tau invariant mass

• Helicity correlations, R=pldg.track/Evis. jet > 0.55

– to suppress taus from W decays– suppresses further also hadronic jets with neutral particles

Tau invariant mass

• tau invariant mass calculated from the tracks (no 0’s)

–robust method–signal distribution is

a distinct peak smeared a little due to the tau neutrino

• Optimum value of m<1.5 GeV/c2 chosen

Rejecting Neutral hadrons

• Energy carried by the tracks is matched to the jet energy to reject jets with considerable neutral particle content–select the a13+decay for the signal (~2/3 of 3-prongs)

• Optimum value of E=Etracks/Ejet-1 > -0.2 chosen

Helicity Correlations

Can be used R variable

More useful is

Optimum cut value >0.5 Rejects good fraction fromW

Summary of Results: 1prong

Signal

QCD

ttbar

W+3/4 jets

Summary of Results: 3 prong

Signal

QCD

ttbar

W+3/4jets

Summary of Results:Signal

H+200

H+300

H+400

1-prong 13.4 2.71 1.73

error ±0.4 ±0.09 ±0.04

Efficiency 1.7 % 3.2 % 4.6 %

purity 99.5 % 98.8 % 99.6 %

3-prong 2.9 0.82 0.37

error ±0.2 ±0.04 ±0.02

Efficiency 0.37 % 0.70 % 0.98 %

purity 99.0 % 99.7 % 99.8 %

Summary of Results:QCD

QCD80-120

QCD 120-170 QCD170-230

<2400 4800 1400±1400 ±400

<7.9e-7 9.7e-6 1.4e-5

<2400 <400 220±150

<7.9e-7 <8.0e-7 2.2e-6

1 prong

Error

Eff.

3 prong

Error

Eff.

Summary of Results:ttbar, W+3/4 jets

ttbar ttbar+1 jet

62 27±5 ±4

1.0e-4 1.5e-4

38 13.8±4 ±2.5

6.1e-5 7.8e-5

1 prongError

Eff.

3 prongError

Eff.

W+3jpeak

W+4jpeak

W+3jtail

W+4jtail

1.6 0.76 0.40 0.07±1.2 ±0.4 ±0.11 ±0.02

2.8e-6 6.2e-6 3.7e-4 3.6e-4

1.6 0.76 0.20 0.022±1.2 ±0.44 ±0.08 ±0.010

2.8e-6 6.2e-6 1.9e-4 1.1e-5

Conclusions• Robust tau jet idenfication presented for the H+ channel

– The tau jet ID part without helicity correlations is basically a standard tau ID with a high pT cut

• Tau-identification successful for 1-prong final states– Signal efficiency 1.7-4.6 % with high signal purity– QCD multi-jet background can be reduced by a factor of ~105 or

better– Also the ttbar and W+jets backgrounds are suppressed strongly,

due to hadronic jets suppression and tau polarization effects on W decay

• 3-prong final states can be used– 21-30 % increase in signal– 10-15 % increase in QCD multi-jet events, but ttbar background

increases with ~3-4 times and W+jets with ~4-6 times as much as the signal

– precise estimation of background events would require factorization (or huge MC production)