Daniele Benedetti CMS and University of Perugia Chicago 07/02/2004 High Level Trigger for the ttH channel in fully hadronic decay at LHC with the CMS detector

Daniele Benedetti CMS and University of Perugia Chicago 07/02/2004

High Level Trigger for the ttH channel in fully

hadronic decay at LHC with the CMS detector

Daniele Benedetti

On behalf of CMS Collaboration


OutlookReason for studying ttH channel

Study of the data acquisition

• Current Higgs mass limits

• The role of the LHC collider

• CMS data acquisition system

• The Level 1 Trigger

• The High Level Trigger (HLT) ttH in fully

hadronic decay


Large Hadron Collider (LHC)

Circumference: 27 KmEnergy CM (p-p)=14 TeV

Hadronic Calorimeter

Electromagnetic Calorimeter

Tracker

Chambers


Higgs mass previsionFrom Lep measures Higgs mass > 114.1 GeV at 95% C.L.

With the new world average for:

MH<251 GeV (2 ) 95% C.L.

Mtop = (178.0 ± 4.3) GeV

And the best estimate for Higgs mass is:

MH=117 GeV


Interactions at LHC

s [TeV]

H(mH=500 GeV)10-7

10-5

10-3

10-1

101

103

105

107

109

10-6

10-4

10-2

100

102

104

106

108

1010

tot

b

jet(ETjet>s/20)

W

Z

jet(ETjet>100 GeV)

t

jet(ETjet>s/4)

H(mH=120 GeV)

TeVatron LHC

[n

b]

R@

L=10

34 c

m-2s-1

[H

z]

.1 1 10

Production of quarks b

Production of quarks top

Production ofHiggs


Higgs observabilityFor MH (120-130) GeV

Cross Section

BranchingRatio

ExpectedBackgroun

d

Observability

ggHbb P1+D1

No

ggH P1+D2

Yes

ggttHttbb P2+D1

?

P1

D2

D1

P2


The Channel ttH Fully hadronic final state

8 (or more) jets in the final state and 4 from quark b

quarkHadronization

jets

MH=120 GeV

Branching Ratio

W qq 67.6%H (120 GeV) bb 71.3%Total hadronic 32.6% (pb)

ttH (LO) 0.5773ttH(NLO) 0.7015ttH hadronic (LO) 0.1881ttH hadronic (NLO) 0.2286


Background considered

Cross Section (mb)Exepected rate at lowLuminosity (2x1033 cm-

2s-1)

QCD(30<pT<50 GeV)

0.195770 ~4x105

QCD(50<pT<80 GeV)

0.025870 ~ 5x104

QCD(80<pT<120 GeV)

0.003629 ~ 7.3x103

QCD(120<pT<170 GeV)

0.000619 ~ 1.2x103

For the trigger study we used non resonant background. The QCD samples are datasets of the official CMS Production 2002


CMS Trigger

105 events/s (Hz)

Use of chamber and calorimeters

100 Hz

Also using tracker

Interaction p-p: 40 MHz

Total reduction factor >105

L1

HLT


Eff ttH Rate QCD4 ET > 40 GeV

80 % 1 KHz

4 ET > 50 GeV

65 % ~200 Hz

Rate(s-1)=eff x (mb) x 1027x L(cm-2 s-1)Luminosity=2x1033 cm-2 s-

1

p pT ET

Trigger L1 ttH hadronic


Fast b-tagging for HLT

jetvs

vpd0

d0

• Regional Tracking

•Conditional Tracking

Only tracks within a jet cone R=0.4

R2= (jettracks)2+(jettracks)2

(jet, jet) from L1 jet reconstruction

Limited number of hits

Pt tracks in pixel line > 2 Gev/c

do resolution

pt resolution

do = impact parameter


High Level Trigger We use the Tracker information to recognise the jets from quark b

Partial reconstruction 5 hits track reco 0.4 cone 2 GeV pxl line Pt cut

Requiring SIP 2D > 2 We reject more QCDthan signal

SIP2D = Significance of impact parameter in 2D

Sip2D

track

s

Black = ttH hadronic Red = QCD

Sip2D= d0

d0


High Level Trigger

The b-tagging is a track counting algorithm:2 tracks at different SIP2D

For 1 b-tagging jet0.5 < Sip2D < 5For 2,3,4 b-tagging jet0.5 < Sip2D <2.5

2 tracks with Sip2D>2.0:

85% sig eff25% QCD eff

Preselection ET>10 GeV


2 tracks with Sip2D>2.0:

30 Hz QCD Rate with 60 % Eff

High Level Trigger (100 Hz)

• 4 jets with ET>50 GeV• 1,2,3,4 b-tagged jet

Requiring:

Energy Trigger + b-tagging


Conclusions• With the L1 Trigger (4 jets with ET>50 GeV) we obtain65% signal efficiency at ~200 Hz of QCD rate.

• With the High Level Trigger we can decrease the QCD rate to 30 Hz still selecting 60% of signal events.

…next steps

Study the offline reconstruction and estimate the signal significance with respect to the resonant backgrounds.

Documents

Daniele Benedetti CMS and University of Perugia Chicago 07/02/2004 High Level Trigger for the ttH channel in fully hadronic decay at LHC with the CMS detector