A h tt and h tn in cms
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Physics at LHC Prague July 6 - 12, 2003. A/H -> tt and H + -> tn in CMS. R. Kinnunen. Helsinki Institute of Physics Helsinki, Finland. Contents. H/A -> tt. Cross sections and branching fractions Hadronic t trigger t -jet identification and hadronic jet suppression

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A h tt and h tn in cms

Physics at LHC

Prague July 6 - 12, 2003

A/H -> tt and H+ -> tn in CMS

R. Kinnunen

Helsinki Institute of Physics

Helsinki, Finland

R. Kinnunen

Helsinki Institute of Physics


A h tt and h tn in cms

Contents

H/A -> tt

Cross sections and branching fractions

Hadronic t trigger

t-jet identification and hadronic jet suppression

t tagging with impact parameter measurement

b-jet tagging in bbH/A

Signal to background ratios and expected discovery reaches,

tanb mesurement from event rates

H+ -> tn

Cross sections and branching fractions

Trigger for H+ -> tn in fully hadronic events

t polarization in H+ -> tn and W+ -> tn

Signal to background ratios and expected discovery reaches,

tanb mesurement from event rates

R. Kinnunen

Helsinki Institute of Physics


A h tt and h tn in cms

How to search for heavy neutral MSSM Higgs bosons

Relative to SM, H/A -> ZZ, WW are strongly suppressed but

Hbb, Htt, Hmm couplings are enhanced at high tanb

use bbH for production with H/A -> tt, mm decay channels

- Efficient background reduction with b tagging in bbH/A

- 3 final states for H/A -> tt (jet+jet, lepton+jet, lepton+lepton)

- Higgs boson mass reconstruction for H,A -> tt, mm

- H/A -> bb may be also viable (under study)

R. Kinnunen

Helsinki Institute of Physics


A h tt and h tn in cms

Production and decay of H, A

Production through gg -> H/A and gg -> bbH/A

g

H

g

gg->bbH/A dominates the production at large tanb:

~90% of the total production cros section

b

g

H

g

b

HIGLU,HQQ from of M. Spira et al.

BR(H -> tt) ~ 10% for tanb > 10

Pole mass for Yukawa coupling

H -> tt

For large mA, enhancement of BR(H->tt) for larger

|m| parameter due suppression of H,A -> cc decays

R. Kinnunen

Helsinki Institute of Physics


A h tt and h tn in cms

Final states investigated for H, A ->tt

H -> tt -> 2 t jets BR ~ 42.0%

Backgrounds from QCD multijet events, Z,g* ->tt, tt, Wt, W+jets

H, A -> tt -> lepton + t jet BR ~ 45.6%

H, A -> tt ->2 leptons BR ~ 12.4%

Backgrounds from Z,g* ->tt, tt, bb, Wt, WW, W+jets

Simulation tools

PYTHIA for event generation

HDECAY for normalization of cross sections and branching fractions

for two-t jet and two-lepton channels

Full simulation for trigger, t selection, b tagging, mass reconstruction

Fast simulation for signal to background ratios

R. Kinnunen

Helsinki Institute of Physics


A h tt and h tn in cms

Hadronic Tau trigger

Trigger requirements:

Level-1 output rate of 1-Tau and 2-Tau triggers: 3 kHz at low luminosity

6 kHz at high luminosity

HLT output rate on tape for t’s: 4 (10) Hz at low (high) luminosity

Level-1 1-Tau and 2-Tau triggers

The required Level-1 rate can be achieved with the thresholds of

93 (112) GeV for 1-Tau for low (high) luminosity

66 (76) GeV for 2-Tau for low (high) luminosity

on the calorimeter jet reconstructed in 12x12 trigger towers with maximum Et

in the central 4x4 towers and no significant activity in the neighbouring towers (trigger tower = HCAL cell + 5x5 ECAL cells, DhxDf = 0.087x0.087 in the barrel)

Efficiency:

78 (54)% for H->tt, mH = 200 GeV, 1 or 2 Tau

81 (72)% for H+->tn, mH+ = 200 GeV, 1 Tau

R. Kinnunen

Helsinki Institute of Physics


A h tt and h tn in cms

Level-2 Tau trigger

Reconstruction of a jet centered at the hardest Level-1 t jet

Isolation in the EM calorimeter:

- sum of the Et deposits in ECAL within 0.13 < DR(jet direction, cell) < 0.4

Efficiency (QCD vs H->tt-> 1/3 prong jets)

as a function of Etcut-off

t jet definition: SEtem < Etcut-off

Suppression of 3 for QCD background with SEtem < 5.6 GeV

Signal efficiency ~ 85%

same for mH = 200 and 500 GeV

R. Kinnunen

Helsinki Institute of Physics


A h tt and h tn in cms

Level-3 Pixel Tau trigger

using track counting in the Pixel (vertexing) detector:

- good efficiency required, high pt accuracy not needed

1. Reconstruction of tracks around the Level-1 jet direction

2. Small signal cone (DRS = 0.07) around the hardest track

3. Larger isolation cone around jet direction

Efficiency (QCD vs H->tt-> 1/3 prong jets)

as a function of the isolation cone size

Accept tracks only in the signal cone

HLT efficiency for 1 or 3 tracks in the

signal cone and for DR = 0.35:

QCD suppression ~ 103

signal efficiency ~ 40%

R. Kinnunen

Helsinki Institute of Physics


A h tt and h tn in cms

Off-line t jet identification

Exploits further the narrowness and the isolation of the t jet in the full tracker

1. Leading track cut:

Find the leading track in the L1 t jet, set a cut pt > 40 GeV

Define a narrow signal cone Dr = 0.03 (0.07 for HLT)

around the leading track direction

2. t jet isolation:

No track, pt > 1 GeV, allowed within 0.03 < DR < 0.4

3. Number of tracks in the signal cone:

1 or 3 tracks in the signal cone (ptleading > 40 GeV)

4. Further reduction of hard QCD jets:

Very hard QCD jets can be further suppressed with a cut in ptleading / Etjet

R. Kinnunen

Helsinki Institute of Physics


A h tt and h tn in cms

Simulation of the QCD di-jet background

using (for the moment) a rejection factor as a function of Etjet

(initial QCD di-jet rate ~1012 events for 60 fb-1)

t selection efficiency for hadronic QCD jets

from fast simulation

Suppression of ~ 1000 per jet

can be obtained

Signal efficiency (per event)

including Level-1 and HLT trigger from full simulation:

mH = 200 GeV 0.8%

mH = 500 GeV 8.9%

efficiency verified with full simulation and complet reconstruction for ptgen < 170 GeV

R. Kinnunen

Helsinki Institute of Physics


A h tt and h tn in cms

t impact parameter tagging in H -> tt

The t lifetime is small, ct ~ 90 mm, but can be still used to further supress the

fake t’sfrom Z -> lland from QCD multi-jet events using impact parameter measurement (1 or 3 prong t’s) and vertex reconstruction (3 prong t’s)

Best separation combining the measurements

in the two t jets into one variable

CMS full simulation and reconstruction

sqrt(sip(t1)2 + sip(t2)2)

where sip(t1) and sip(t2) are significansies

of the impact parameter measurements

of the leading tracks in jets 1 and 2

S. Lehti

Signal efficisiency ~ 60%

QCD suppression factor of ~ 9

R. Kinnunen

Helsinki Institute of Physics


A h tt and h tn in cms

B jet tagging in gg -> bbH/A

Tagging of the associated b jets is the most efficient way to reduce

the Z,g* -> tt (bbZ ~ 1-2 %)and to further reduce the QCD multijet events

Associated b jets in gg -> bbH/A are soft and uniformly distributed over |h| < 2.5:

Efficiencies (Et threshold + tagging propability) relatively low

Significance of the signed transverse impact parameter

CMS full simulation and complete reconstruction

Tagging algorithm:

at least 2 tracks, pt > 1 GeV, sip > 2,

inside the jet cone

non-t jets in

gg -> bbH/A

Efficiency per jet:

32% non-t jets in bbH

~ 2 % light quark and gluon jets

jets in QCD

di-jet events

R. Kinnunen

Helsinki Institute of Physics


A h tt and h tn in cms

Higgs boson mass reconstruction in H -> tt

The neutrinos from H -> tt (t -> hadrons+n, t -> l+nn) are emitted close

to the directions of the visible t’s (jets or leptons):

Etmiss

neutrino reconstruction possible using the Etmiss measurement in events with Df(t1,t2) < 180o, efficiency ~ 50 % (for En1 En2 >0)

t jet, e, m

t jet, e, m

qjj

mH = sqrt(2 En1 En2 (1-cosqjj))

jet

Higgs boson mass from full simulation for

H -> tt -> two jets, mH = 500 GeV, tanb = 20,

with Df(t jet1,t jet2) < 175o

Efficiency (Df cut, En1 En2>0)36%

sfit 14.9%

Efficiency and resolution sensitive to the Etmiss measurement and to the Df(t1,t2) cut

R. Kinnunen

Helsinki Institute of Physics


A h tt and h tn in cms

Event selection for A,H->tt -> 2 t jets

  • Basic event selection:

  • - 2 t jets passing the Level-1 and HLT triggers

  • and the off-line t selection (1 or 3 hard tracks, isolation)

  • - t tagging with impact parameters

  • Higgs boson mass reconstruction (Df(t1,t2) cut, En1, En2 > 0)

Two alternatives for further reduction:

i) Further selection with Etmiss:

- Etmiss > 40 GeV

-central jet veto beyond 30 GeV

ii) Further selection with b-jet tagging:

- one b-tagged jet, Et > 20 GeV

- central jet veto beyond 30 GeV

Total background

Total background

Total background

larger staistics but poor S/B

much improved S/B but lower statistics

R. Kinnunen

Helsinki Institute of Physics


A h tt and h tn in cms

Leptonic final states, H/A -> tt -> em, ll

Event selection:

- 2 isolated leptons, pt > 20 GeV

- one tagged b jet, veto on second central jet beyond 30 GeV

- impact parameter t tagging

lepton+lepton final states can be used to double the statistics

- Higgs boson mass reconstruction

H/A -> tt -> em

mA = 200 GeV

tanb = 20

H/A -> tt -> ll

lepton + t jet final states, H/A -> tt ->l + t jet

Event selection:

- one isolated lepton (pt > 20 GeV), one t jet (Et > 40 GeV)

- one tagged b jet, second jet veto

- Higgs boson mass reconstruction

Reach not yet optimized for large mA (> 200 GeV) in CMS

R. Kinnunen

Helsinki Institute of Physics


A h tt and h tn in cms

Expected 5s-discovery reach for H/A -> tt

Results for H/A -> mm

from full simulation and

complete reconstruction

Higgs boson mass resolution ~ 2%

Variation of BR(H -> tt) due to H -> cicj

decay modes ~ 40% at mH=500 GeV, tanb=20,

for -200 GeV < m < 500 GeV

R. Kinnunen

Helsinki Institute of Physics


A h tt and h tn in cms

Measurement of tanb in H -> tt from event rates

using the tanb dependence s*BR ~ tan2b * x

Dtanb/tanb = ½ * sqrt((NS+NB) / NS2 + (DL/L)2 + (Dx/x)2)

- Luminosity uncertainty DL/L ~ 5%

- Theoretical uncertainty on the cross section for gg -> bbH: dx/x ~ 30%

- The gg -> bbH component is selected by b jet tagging: 1b or 2b tagging,

less theoretical uncertainty and higher experimental purity with 2b tagging

Dtanb/tanb

1b tagging 2b tagging

H/A -> tt -> 2 t jets, mA= 500 GeV, tanb = 40, 60 fb-116% 19%

dominated by

rate uncertainty

up to tanb ~ 30

H/A -> tt -> lepton + t jets, mA= 200 GeV, tanb = 20, 30 fb-116%

H/A -> tt -> em, mA= 140 GeV, tanb = 14, 30 fb-1 18%

Precision of Higgs boson mass measurement in H/A -> tt -> 2 t jets

mA= 500 GeV, tanb = 40 , 60 fb-1DmH/mH = 1.5%

mA= 200 GeV, tanb = 40 , 60 fb-1DmH/mH = 1. 2%

R. Kinnunen

Helsinki Institute of Physics


A h tt and h tn in cms

How to search for charged Higgs bosons at LHC

If mH+ < mtop:

Production through tt events, t -> bH+

- accessible through the H+ -> tn, t2-> lepton+qqfinal state

If mH+ > mtop:

Production through gg -> tbH+, gb -> tH+, qq’ -> H+,

gg -> H+H-, gg -> W+H-

- gg -> H+H-, gg -> W+H- have small production cross sections

  • Event rate sufficient for qq’ -> H+-> tn but suppression of

  • the qq’ -> W-> tn background is difficult

t

g

H+

g

b

  • gg -> tbH+, gb -> tH+ most promising processes,

  • cross sections large enough andtheassociated top

  • and b jets can be used for background reduction

g

t

H+

b

R. Kinnunen

Helsinki Institute of Physics


A h tt and h tn in cms

One tagged b jet enough to suppress the backgrounds, use

gb -> tH+

Event generation with PYTHIA

Normalization of the production cross sections to

T. Plehn, MADPH-02-1275

Normalization of branching fractions to HDECAY

H+ -> tn

T. Plehn

HDECAY

tanb = 30

R. Kinnunen

Helsinki Institute of Physics


A h tt and h tn in cms

Trigger for H+ -> tn, t -> jet + n

Level-1: single Tau trigger (Et > 93 GeV, low luminosity)

High Level Trigger:

cut on Etmiss in the calorimetry (possible due to off-line Etmiss > 100 GeV)

QCD rejection ~ 100 for Etmiss > 65 GeV

Level-3 Single Tau:

Efficiency (QCD vs H->tt-> 1/3 prong jets)

as a function of pt cut for the leading track

  • Cut on the leading track

  • and isolation needed

- Reconstruction of tracks in the

full tracker within the L1 t jet

Efficiency for ptleadingtrack > 20 GeV and isolation in 0.065 < DR < 0.4:

QCD rejection ~ 30

Signal efficiency ~ 58%

R. Kinnunen

Helsinki Institute of Physics


A h tt and h tn in cms

t polarization in H+ -> tn and W+ -> tn

n

t+

n

t+

W+

H+

n

p+

p+

t+

n

t+

H+ -> t+n leads to harder pions from t -> p+n and from the longidutinal

components of r and a1 than the corresponding decays in W+ -> t+n

TAUOLA interfaced to PYTHIA

Large suppression of W -> tn

in tt, Wt, W+jet using the cut:

pleadingtrack / Etjet > 0.8:

tt background

t jet = calorimeter jet

from t -> hadrons + n

t -> p+n

rT ,a1T

rL

Signal, mH+= 400 GeV 46%

Signal, mH+= 200 GeV 22%

tt background 1.8%

rL ,a1L

Signal

R. Kinnunen

Helsinki Institute of Physics


A h tt and h tn in cms

Event selection for gb -> tH±, H± ->tn

- Ettjet > 80 – 100 GeV, containing a hard track with pttrack/Ettjet > 0.8

- Etmiss > 100 GeV

mT(t jet, Etmiss)

- Reconstruction of associated hadronic top

from two jetand one b-tagged jet

- Veto on 5th jet, veto on second top quark

30 fb-1

background

Quasi two-body decay between the t jet and

Etmiss in fully hadronic events -> almost

background-free situation in mT(t-jet,Etmiss)

Signal

Df(t jet, Etmiss) > 20o

Df(t jet, Etmiss)

Cut on Df(t jet, Etmiss) ->

low mass background can

be suppressed

30 fb-1

background

tt background

Signal

Signal

R. Kinnunen

Helsinki Institute of Physics


A h tt and h tn in cms

Expected 5s-discovery reach for charged Higgs boson

H+ -> tb and

qq’ -> H+ -> tn

are also promising

Excess of t’s can

be measured in

tt, t -> bH+,

H+ -> tn

for mH+ < mtop

good background

knowledge needed

No sensitivity for intermediate tanb with gb -> tH+ (with SM decay channels):

H+ -> Wh, h -> bb accessible (in MSSM) only at small tanb

tanb measurement from event rates using s ~ tan2b at high tanb

Expected uncertainty for tanb >30 with 20% theoretical uncertainty :

Dtanb/tanb < 14% for mH+ = 200 GeV

Dtanb/tanb < 20% for mH+ = 400 GeV

R. Kinnunen

Helsinki Institute of Physics


A h tt and h tn in cms

Conclusions

Search for H/A and H+ can start early, with < 10 fb-1

With ~ 60 fb-1 masses in the 500 – 800 GeV range accessible

more specifically:

H/A ->tt accessible for 30 fb-1 with

em and ll final states for tanb > 14 at mA = 140 GeV

jet+ lepton final states for tanb > 10 at mA = 200 GeV

and for 60 fb-1 with

2 t jet final states for tanb > 18 at mA = 200 GeV

tanb > 25 at mA = 500 GeV

H+ -> tn accessible in gb -> tH+ in fully hadronic final states with 30 fb-1 for

tanb > 20 at mA = 200 GeV

tanb > 32 at mA = 400 GeV

DmH/mHin H/A -> tt -> 2 t jets, tanb = 40, 60 fb-1 : 1.2% for mA = 200 GeV

1.5% for mA = 500 GeV

  • tanb determination with event rates:

  • Dtanb/tanb = 16% for H/A ->tt -> 2 jets, mA = 500 GeV, tanb = 40

  • 16% for H/A ->tt -> lepton+jet, mA = 200 GeV, tanb = 20

  • 18% for H/A ->tt -> em, mA = 140 GeV, tanb = 14

  • 14% for gb -> tH+ ,H+ -> tn , mA = 200 GeV, tanb = 30

R. Kinnunen

Helsinki Institute of Physics


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