Transcript MajidPosterHCP09

(*)
H→WW
Higgs search in
channel with the CMS detector
Majid Hashemi, University of Antwerp, Belgium,
On behalf of CMS collaboration
The H→WW decay is one of the main discovery channels of the Higgs boson in CMS,
The signal events are produced via gluon fusion or vector boson fusion,
The main production process is however through the gluon fusion.
Cross sections:
Selection of events:
σxBR(H→WW→lνl’ν’)=2.34 pb
2340 events at 1fb-1
Main Backgrounds: WW (12pb), tt(836pb) , W+jets(58nb) , …
WW background is irreducible background,
tt background is suppressed well by central jet veto,
W+jets is suppressed by isolation requirements against fake leptons.
Online selection (trigger):

Events with one muon or one electron in the event passing L1+HLT requirements,
Preselection:
 Lepton pair selection:
Two leptons with transverse momentum above 10,20 GeV, |h|<2.5
 Kinematic preselection:
Missing transverse energy > 30 GeV, Invariant mass of lepton pair > 12 GeV
Final event selection:
Example kinematic distributions:
em final state, Δφ and Invariant mass of the lepton pair
Mass dependent cuts on Met,Δφ(2 leptons), lepton pair invariant mass,pTmax ,pTmin
The last two variables belong to the hardest and softest lepton in the event
Number of events (at 1fb-1 ) after preselection and final selection for each final
state search for signal with m(H)=160GeV and background samples
HWW
WW
WZ
ZZ
tW
tt
W+jets
DY
Ee preselection
81
258
277
122
215
2472
150
15340
Final selection
20.1
13.7
1.7
0.0
0.0
4.3
2.0
1.0
Mumu preselection
143
459
226
184
461
5128
177
39814
Final selection
21.0
10.0
0.1
0.0
0.3
6.0
0.1
0.6
Emu preselection
195
632
42
4
604
6008
453
471
Final selection
31.5
16.0
0.3
0.0
1.4
7.0
6.3
0.0
Number of signal events (at 1fb-1 ) for different Higgs boson masses
M(H) [GeV]
130
150
160
170
200
ee preselection
24
58.7
81
82.7
58
Final selection
6.6
12.5
20.1
21.2
11.0
Mumu preselection
49
108
143
144
97
Final selection
8.7
9
21.0
17
5.6
Emu preselection
61
150
195
202
139
11.0
20.6
31.5
33.1
12.2
Final selection
Number of events from Multivariate analysis (neural net) at 1 fb-1
Control of background from data
M(H)
Signal
Background
120
7.5
87.3
130
17.3
89.4
140
31.4
121.4
150
24.4
42.5
160
67.5
37.4
170
66.8
40.0
180
50.9
67.3
190
31.2
73.3
200
29.6
115.8
Comparison for
m(H)=160GeV:
Cut based: S/B~70/70
MVA NN: S/B~67/37
WW (control region approach):
tt (control region approach):
A control region is defined for tt events,
This region is defined by a set of cuts which are close
to signal selection cuts,
WW background is also estimated from data using control region approach,
Central jet veto (applied for signal selection) is
replaced by requiring two jets in the event,
Central jet veto cut is kept contrary to the case of tt control region,
Selection cuts are optimized to have a WW dominant sample,
The total uncertainty of this sample in the signal region is estimated to be 22%,
Extrapolation from a tt dominant sample (control
sample) to signal region is done using the formula :
N
S
bckg



S
bckg
C
bckg
N
C
bckg
W+jets (fake rate approach),
S(C) denotes signal (control) region, and Nbckg. is the
number of background events under study. The final
uncertainty is calculated using the formula:
C
C
S
tt  background
background
tt
S
C
C
tt
tt
tt
N
R N


N
R
N
R=eff(CJV)/eff(2jets),
ΔR/R is obtained from jet energy variation,

N
N
Statistical uncertainty of
the observed events in the
control region
Fake muon estimate: define probability of a loosely isolated track to pass muon ID cuts,
Fake electron estimate: define probability of a jet to pass electron ID,
 18%
Run on QCD (plenty of events, benefit from large statistics) and obtain fake rate,
Re-weight signal search which is looking for loosely isolated tracks and jets,
Fluctuation of the background in
the control region
Results in terms of signal significance and exclusion limits
Input is the jet energy scale uncertainty
Systematic uncertainties
Source
Signal (%)
Background(%)
Luminosity
5
5
Lepton & trigger effi.
4
4
Muon miscalibration and
misalignment
2
2
Electron miscalibration and
misalignment
4
4
Met modeling
1
2
Jet reconstruction
3
8
PDF uncertainties
5
5
tt cross section
-
18
WW cross section
-
22
WZ/ZZ/tW cross sections
-
10
DY cross section
-
5
W+jets cross section
-
100
MC statistics
5
10
Conclusion:
With a collected data corresponding to an integrated luminosity of 1fb-1 at LHC running
on 14 TeV center of mass energy, the SM Higgs boson can be excluded in the mass range
140 GeV < m(H) < 200 GeV only with H->WW search,
The 5s signal is observable for m(H) ~ 160 GeV, for other masses more data is needed.