daniele benedetti cms and university of perugia chicago 07/02/2004 high level trigger for the tth...
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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
Daniele Benedetti CMS and University of Perugia Chicago 07/02/2004
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
Daniele Benedetti CMS and University of Perugia Chicago 07/02/2004
Large Hadron Collider (LHC)
Circumference: 27 KmEnergy CM (p-p)=14 TeV
Hadronic Calorimeter
Electromagnetic Calorimeter
Tracker
Chambers
Daniele Benedetti CMS and University of Perugia Chicago 07/02/2004
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
Daniele Benedetti CMS and University of Perugia Chicago 07/02/2004
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
Daniele Benedetti CMS and University of Perugia Chicago 07/02/2004
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
Daniele Benedetti CMS and University of Perugia Chicago 07/02/2004
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
Daniele Benedetti CMS and University of Perugia Chicago 07/02/2004
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
Daniele Benedetti CMS and University of Perugia Chicago 07/02/2004
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
Daniele Benedetti CMS and University of Perugia Chicago 07/02/2004
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
Daniele Benedetti CMS and University of Perugia Chicago 07/02/2004
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
Daniele Benedetti CMS and University of Perugia Chicago 07/02/2004
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
Daniele Benedetti CMS and University of Perugia Chicago 07/02/2004
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
Daniele Benedetti CMS and University of Perugia Chicago 07/02/2004
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
Daniele Benedetti CMS and University of Perugia Chicago 07/02/2004
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.