Search for non-SM Light Higgs Boson in the h -> to gamma gamma Channel at D0 in Run II

0.09 MB·English

by  Alex Melnitchouk

February 6, 2008 17:2 WSPC/INSTRUCTION FILE ws-ijmpa
International JournalofModernPhysicsA
(cid:13)c WorldScientificPublishingCompany
5
0 Search for non-SM Light Higgs Boson in the h → γγ Channel at DØ in
0
2 Run II

n
a
J ALEXMELNITCHOUK∗

7 Department of Physics and Astronomy,
2 The Universityof Mississippi,
108 LewisHall, P.O. Box 1848
1 University,MS 38677-1848
v
7
6 Received(31October2004)
0 Revised(31October 2004)
1
0
Asearchfornon-SMlightHiggsbosonwithanenhancedbranchingfractionintophotons
5
inpp¯collisionsattheFermilabTevatronispresentedusingRunIIDØdatatakenbetween
0
April2002andSeptember2003.Weset95%CLlimitsonthediphotonbranchingfraction
/
x asafunctionofHiggsmassforFermiophobicandTopcolorHiggsscenarios.
e
- Keywords:Higgs;fermiophobic;photon.
p
e
h 1. Motivation
:
v γγ is a very clean signature which makes it promising and important especially
i
X for the hadron collider environment. There are many extensions of the SM that
r allow enhanced γγ decay rate of the Higgs largely due to suppressed couplings
a 1
withfermions .WeconsiderFermiophobicHiggs(noHiggs-fermioncouplings)and
Topcolor Higgs (coupling with the top quark is allowed)
2. Dataset
We used the data collected by the DØ detector between April 2002 and September
−1
2003.Theintegratedluminosityofthissampleis191.0±12.4pb Triggerselection
a
wasdonewithhighpT di-EM trigger.Offlinewe requiretworeconstructedphoton
objectsinthe goodη fiducialregion(|η|<1.05,1.5<|η|<2.4)withpT >25GeV.
2
We require that the pT of the diphoton system is above 35 GeV .
3. Backgrounds
∗
Major sources of background to h →γγ are Z/γ →ee, direct diphotons, γ+jet,
and multijet QCD processes.
∗Fermilab,MS#352,Batavia, IL,60510, USA.
aEMstandsfor“electromagnetic object”, i.e.electronorphoton
1
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2 Alex Melnitchouk
4. Results
The γγ invariant mass distributions for the data and predicted background, as
well as the event yields are shown in Fig. 1. Figure 2 shows 95% CL limits on the
B(h →γγ ) as a function of Higgs mass. Comparison is made with DØ Run I and
5
LEP results as well as Run II Monte Carlo studies for Tevatron .
5. Conclusions
A search for non-SM light Higgs boson with an enhanced branching fraction into
−1
photons was performed using 191pb of data collected by the DØ experiment in
Run II of the Fermilab Tevatron.We set 95% CL limits onthe diphoton branching
fractionasafunctionofHiggsmassforFermiophobicandTopcolorHiggsscenarios.
Our current sensitivity is comparable with Run I.
Fig. 1. γγ invariant mass distributions and event counts for different event topologies with
new photon ID after analysis optimization cut (pγγ >35GeV) is applied. Points – γγ spectrum
T
observedindata,redrectangles–totalSMbackgroundwitherrors,greenline–QCDbackground,
brownline–Drell-Yanbackground, blackline–directdiphotonbackground.
Acknowledgments
We thank the staffs at Fermilab and collaborating institutions, and acknowledge
support from the Department of Energy and National Science Foundation (USA),
Commissariat `a L’Energie Atomique and CNRS/Institut National de Physique
Nucl´eaire et de Physique des Particules (France), Ministry for Science and Tech-
nology and Ministry for Atomic Energy (Russia), CAPES, CNPq and FAPERJ
(Brazil), Departments of Atomic Energy and Science and Education (India), Col-
ciencias(Colombia),CONACyT(Mexico),MinistryofEducationandKOSEF(Ko-
rea), CONICET and UBACyT (Argentina), The Foundation for Fundamental Re-
search on Matter (The Netherlands), PPARC (United Kingdom), Ministry of Ed-
ucation (Czech Republic), A.P. Sloan Foundation, Civilian Research and Develop-
ment Foundation, Research Corporation, Texas Advanced Research Program, and
the Alexander von Humboldt Foundation.
February 6, 2008 17:2 WSPC/INSTRUCTION FILE ws-ijmpa
Search for non-SM Light HiggsBoson in theh→γγ Channel at DØ inRun II 3
DØ Run II Preliminary
)) 11
gg Run II 191 pb-1
gg
fifihh
B(B( Run I 100 pb-1 100 pb-1
MC predictions
--11
1100
2 fb-1
benchmark
LEP
model
6600 8800 110000 112200 114400
((ffeerrmmiioopphhoobbiicc)) MM ((GGeeVV))
hh
DØ Run II Preliminary
) 1
g
g
fih
(
B
-1
10
60 80 100 120 140
(topcolor) M (GeV)
h
Fig.2. 95%CLlimitsontheHiggsdecaybranchingfractionintophotonsasafunctionofmass
(blackcurve).Topplot–fermiophobicHiggsscenario,bottom plot–topcolorHiggsscenario.On
the top plot exclusion contours from DØ Run I 3 (red) and LEP 4 (blue) are overlaid. Magenta
linesshow100pb−1and2fb−1MonteCarlopredictionsforTevatronRunII5basedonRunIDØ
andCDFefficienciesandmisIDrates.Greenpoints–theoreticalcurveforbenchmarkfermiophobic
Higgsmodel4.
References
1. S.Mrenna, J. Wells, Phys. Rev. D63, 015006 (2001).
2. Alex Melnitchouk,Ph.D Thesis, Brown University (2003) (Unpublished).
3. B.Abbotetal.(DØCollaboration),PhysRev.Lett.82,2244(1999);BrianLauer,Ph.D
Thesis, Iowa State University(Unpublished)(1997).
4. A.Rosca, hep-ex/0212038 (2002).
5. G. Landsberg, K. Matchev, Phys.Rev. D62, 035004 (2000).