Search for Higgs bosons decaying to tautau pairs in ppbar collisions at sqrt(s) = 1.96 TeV

Abstract

We present a search for the production of neutral Higgs bosons decaying into
tautau pairs in ppbar collisions at a center-of-mass energy of 1.96 TeV. The
data, corresponding to an integrated luminosity of 5.4 fb-1, were collected by
the D0 experiment at the Fermilab Tevatron Collider. We set upper limits at the
95% C.L. on the product of production cross section and branching ratio for a
scalar resonance decaying into tautau pairs, and we then interpret these limits
as limits on the production of Higgs bosons in the minimal supersymmetric
standard model (MSSM) and as constraints in the MSSM parameter space.

Full text

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arXiv:1106.4555v1 [hep-ex] 22 Jun 2011
Fermilab-Pub-11-288-E
Search for Higgs bosons decaying to τ+τ−pairs in pp collisions at√s = 1.96 TeV
V.M. Abazov,35B. Abbott,73B.S. Acharya,29M. Adams,49T. Adams,47G.D. Alexeev,35G. Alkhazov,39
A. Altona,61G. Alverson,60G.A. Alves,2M. Aoki,48M. Arov,58A. Askew,47B.˚ Asman,41O. Atramentov,65
C. Avila,8J. BackusMayes,80F. Badaud,13L. Bagby,48B. Baldin,48D.V. Bandurin,47S. Banerjee,29E. Barberis,60
P. Baringer,56J. Barreto,3J.F. Bartlett,48U. Bassler,18V. Bazterra,49S. Beale,6A. Bean,56M. Begalli,3
M. Begel,71C. Belanger-Champagne,41L. Bellantoni,48S.B. Beri,27G. Bernardi,17R. Bernhard,22
I. Bertram,42M. Besan¸ con,18R. Beuselinck,43V.A. Bezzubov,38P.C. Bhat,48V. Bhatnagar,27G. Blazey,50
S. Blessing,47K. Bloom,64A. Boehnlein,48D. Boline,70E.E. Boos,37G. Borissov,42T. Bose,59A. Brandt,76
O. Brandt,23R. Brock,62G. Brooijmans,68A. Bross,48D. Brown,17J. Brown,17X.B. Bu,48M. Buehler,79
V. Buescher,24V. Bunichev,37S. Burdinb,42T.H. Burnett,80C.P. Buszello,41B. Calpas,15E. Camacho-P´ erez,32
M.A. Carrasco-Lizarraga,56B.C.K. Casey,48H. Castilla-Valdez,32S. Chakrabarti,70D. Chakraborty,50
K.M. Chan,54A. Chandra,78G. Chen,56S. Chevalier-Th´ ery,18D.K. Cho,75S.W. Cho,31S. Choi,31B. Choudhary,28
S. Cihangir,48D. Claes,64J. Clutter,56M. Cooke,48W.E. Cooper,48M. Corcoran,78F. Couderc,18
M.-C. Cousinou,15A. Croc,18D. Cutts,75A. Das,45G. Davies,43K. De,76S.J. de Jong,34E. De La Cruz-Burelo,32
F. D´ eliot,18M. Demarteau,48R. Demina,69D. Denisov,48S.P. Denisov,38S. Desai,48C. Deterre,18K. DeVaughan,64
H.T. Diehl,48M. Diesburg,48P.F. Ding,44A. Dominguez,64T. Dorland,80A. Dubey,28L.V. Dudko,37D. Duggan,65
A. Duperrin,15S. Dutt,27A. Dyshkant,50M. Eads,64D. Edmunds,62J. Ellison,46V.D. Elvira,48Y. Enari,17
H. Evans,52A. Evdokimov,71V.N. Evdokimov,38G. Facini,60T. Ferbel,69F. Fiedler,24F. Filthaut,34W. Fisher,62
H.E. Fisk,48M. Fortner,50H. Fox,42S. Fuess,48A. Garcia-Bellido,69V. Gavrilov,36P. Gay,13W. Geng,15,62
D. Gerbaudo,66C.E. Gerber,49Y. Gershtein,65G. Ginther,48,69G. Golovanov,35A. Goussiou,80P.D. Grannis,70
S. Greder,19H. Greenlee,48Z.D. Greenwood,58E.M. Gregores,4G. Grenier,20Ph. Gris,13J.-F. Grivaz,16
A. Grohsjean,18S. Gr¨ unendahl,48M.W. Gr¨ unewald,30T. Guillemin,16F. Guo,70G. Gutierrez,48P. Gutierrez,73
A. Haasc,68S. Hagopian,47J. Haley,60L. Han,7K. Harder,44A. Harel,69J.M. Hauptman,55J. Hays,43T. Head,44
T. Hebbeker,21D. Hedin,50H. Hegab,74A.P. Heinson,46U. Heintz,75C. Hensel,23I. Heredia-De La Cruz,32
K. Herner,61G. Heskethd,44M.D. Hildreth,54R. Hirosky,79T. Hoang,47J.D. Hobbs,70B. Hoeneisen,12
M. Hohlfeld,24Z. Hubacek,10,18N. Huske,17V. Hynek,10I. Iashvili,67Y. Ilchenko,77R. Illingworth,48A.S. Ito,48
S. Jabeen,75M. Jaffr´ e,16D. Jamin,15A. Jayasinghe,73R. Jesik,43K. Johns,45M. Johnson,48D. Johnston,64
A. Jonckheere,48P. Jonsson,43J. Joshi,27A.W. Jung,48A. Juste,40K. Kaadze,57E. Kajfasz,15D. Karmanov,37
P.A. Kasper,48I. Katsanos,64R. Kehoe,77S. Kermiche,15N. Khalatyan,48A. Khanov,74A. Kharchilava,67
Y.N. Kharzheev,35M.H. Kirby,51J.M. Kohli,27A.V. Kozelov,38J. Kraus,62S. Kulikov,38A. Kumar,67A. Kupco,11
T. Kurˇ ca,20V.A. Kuzmin,37J. Kvita,9S. Lammers,52G. Landsberg,75P. Lebrun,20H.S. Lee,31S.W. Lee,55
W.M. Lee,48J. Lellouch,17L. Li,46Q.Z. Li,48S.M. Lietti,5J.K. Lim,31D. Lincoln,48J. Linnemann,62
V.V. Lipaev,38R. Lipton,48Y. Liu,7Z. Liu,6A. Lobodenko,39M. Lokajicek,11R. Lopes de Sa,70H.J. Lubatti,80
R. Luna-Garciae,32A.L. Lyon,48A.K.A. Maciel,2D. Mackin,78R. Madar,18R. Maga˜ na-Villalba,32S. Malik,64
V.L. Malyshev,35Y. Maravin,57J. Mart´ ınez-Ortega,32R. McCarthy,70C.L. McGivern,56M.M. Meijer,34
A. Melnitchouk,63D. Menezes,50P.G. Mercadante,4M. Merkin,37A. Meyer,21J. Meyer,23F. Miconi,19
N.K. Mondal,29G.S. Muanza,15M. Mulhearn,79E. Nagy,15M. Naimuddin,28M. Narain,75R. Nayyar,28
H.A. Neal,61J.P. Negret,8P. Neustroev,39S.F. Novaes,5T. Nunnemann,25G. Obrant‡,39J. Orduna,78N. Osman,15
J. Osta,54G.J. Otero y Garz´ on,1M. Padilla,46A. Pal,76N. Parashar,53V. Parihar,75S.K. Park,31J. Parsons,68
R. Partridgec,75N. Parua,52A. Patwa,71B. Penning,48M. Perfilov,37K. Peters,44Y. Peters,44K. Petridis,44
G. Petrillo,69P. P´ etroff,16R. Piegaia,1M.-A. Pleier,71P.L.M. Podesta-Lermaf,32V.M. Podstavkov,48P. Polozov,36
A.V. Popov,38M. Prewitt,78D. Price,52N. Prokopenko,38S. Protopopescu,71J. Qian,61A. Quadt,23B. Quinn,63
M.S. Rangel,2K. Ranjan,28P.N. Ratoff,42I. Razumov,38P. Renkel,77M. Rijssenbeek,70I. Ripp-Baudot,19
F. Rizatdinova,74M. Rominsky,48A. Ross,42C. Royon,18P. Rubinov,48R. Ruchti,54G. Safronov,36G. Sajot,14
P. Salcido,50A. S´ anchez-Hern´ andez,32M.P. Sanders,25B. Sanghi,48A.S. Santos,5G. Savage,48L. Sawyer,58
T. Scanlon,43R.D. Schamberger,70Y. Scheglov,39H. Schellman,51T. Schliephake,26S. Schlobohm,80
C. Schwanenberger,44R. Schwienhorst,62J. Sekaric,56H. Severini,73E. Shabalina,23V. Shary,18A.A. Shchukin,38
R.K. Shivpuri,28V. Simak,10V. Sirotenko,48P. Skubic,73P. Slattery,69D. Smirnov,54K.J. Smith,67G.R. Snow,64

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J. Snow,72S. Snyder,71S. S¨ oldner-Rembold,44L. Sonnenschein,21K. Soustruznik,9J. Stark,14V. Stolin,36
D.A. Stoyanova,38M. Strauss,73D. Strom,49L. Stutte,48L. Suter,44P. Svoisky,73M. Takahashi,44A. Tanasijczuk,1
W. Taylor,6M. Titov,18V.V. Tokmenin,35Y.-T. Tsai,69D. Tsybychev,70B. Tuchming,18C. Tully,66L. Uvarov,39
S. Uvarov,39S. Uzunyan,50R. Van Kooten,52W.M. van Leeuwen,33N. Varelas,49E.W. Varnes,45I.A. Vasilyev,38
P. Verdier,20L.S. Vertogradov,35M. Verzocchi,48M. Vesterinen,44D. Vilanova,18P. Vokac,10H.D. Wahl,47
M.H.L.S. Wang,48J. Warchol,54G. Watts,80M. Wayne,54M. Weberg,48L. Welty-Rieger,51A. White,76D. Wicke,26
M.R.J. Williams,42G.W. Wilson,56M. Wobisch,58D.R. Wood,60T.R. Wyatt,44Y. Xie,48C. Xu,61S. Yacoob,51
R. Yamada,48W.-C. Yang,44T. Yasuda,48Y.A. Yatsunenko,35Z. Ye,48H. Yin,48K. Yip,71S.W. Youn,48
J. Yu,76S. Zelitch,79T. Zhao,80B. Zhou,61J. Zhu,61M. Zielinski,69D. Zieminska,52and L. Zivkovic75
(The D0 Collaboration∗)
1Universidad de Buenos Aires, Buenos Aires, Argentina
2LAFEX, Centro Brasileiro de Pesquisas F´ ısicas, Rio de Janeiro, Brazil
3Universidade do Estado do Rio de Janeiro, Rio de Janeiro, Brazil
4Universidade Federal do ABC, Santo Andr´ e, Brazil
5Instituto de F´ ısica Te´ orica, Universidade Estadual Paulista, S˜ ao Paulo, Brazil
6Simon Fraser University, Vancouver, British Columbia, and York University, Toronto, Ontario, Canada
7University of Science and Technology of China, Hefei, People’s Republic of China
8Universidad de los Andes, Bogot´ a, Colombia
9Charles University, Faculty of Mathematics and Physics,
Center for Particle Physics, Prague, Czech Republic
10Czech Technical University in Prague, Prague, Czech Republic
11Center for Particle Physics, Institute of Physics,
Academy of Sciences of the Czech Republic, Prague, Czech Republic
12Universidad San Francisco de Quito, Quito, Ecuador
13LPC, Universit´ e Blaise Pascal, CNRS/IN2P3, Clermont, France
14LPSC, Universit´ e Joseph Fourier Grenoble 1, CNRS/IN2P3,
Institut National Polytechnique de Grenoble, Grenoble, France
15CPPM, Aix-Marseille Universit´ e, CNRS/IN2P3, Marseille, France
16LAL, Universit´ e Paris-Sud, CNRS/IN2P3, Orsay, France
17LPNHE, Universit´ es Paris VI and VII, CNRS/IN2P3, Paris, France
18CEA, Irfu, SPP, Saclay, France
19IPHC, Universit´ e de Strasbourg, CNRS/IN2P3, Strasbourg, France
20IPNL, Universit´ e Lyon 1, CNRS/IN2P3, Villeurbanne, France and Universit´ e de Lyon, Lyon, France
21III. Physikalisches Institut A, RWTH Aachen University, Aachen, Germany
22Physikalisches Institut, Universit¨ at Freiburg, Freiburg, Germany
23II. Physikalisches Institut, Georg-August-Universit¨ at G¨ ottingen, G¨ ottingen, Germany
24Institut f¨ ur Physik, Universit¨ at Mainz, Mainz, Germany
25Ludwig-Maximilians-Universit¨ at M¨ unchen, M¨ unchen, Germany
26Fachbereich Physik, Bergische Universit¨ at Wuppertal, Wuppertal, Germany
27Panjab University, Chandigarh, India
28Delhi University, Delhi, India
29Tata Institute of Fundamental Research, Mumbai, India
30University College Dublin, Dublin, Ireland
31Korea Detector Laboratory, Korea University, Seoul, Korea
32CINVESTAV, Mexico City, Mexico
33Nikhef, Science Park, Amsterdam, the Netherlands
34Radboud University Nijmegen, Nijmegen, the Netherlands and Nikhef, Science Park, Amsterdam, the Netherlands
35Joint Institute for Nuclear Research, Dubna, Russia
36Institute for Theoretical and Experimental Physics, Moscow, Russia
37Moscow State University, Moscow, Russia
38Institute for High Energy Physics, Protvino, Russia
39Petersburg Nuclear Physics Institute, St. Petersburg, Russia
40Instituci´ o Catalana de Recerca i Estudis Avan¸ cats (ICREA) and Institut de F´ ısica d’Altes Energies (IFAE), Barcelona, Spain
41Stockholm University, Stockholm and Uppsala University, Uppsala, Sweden
42Lancaster University, Lancaster LA1 4YB, United Kingdom
43Imperial College London, London SW7 2AZ, United Kingdom
44The University of Manchester, Manchester M13 9PL, United Kingdom
45University of Arizona, Tucson, Arizona 85721, USA
46University of California Riverside, Riverside, California 92521, USA
47Florida State University, Tallahassee, Florida 32306, USA
48Fermi National Accelerator Laboratory, Batavia, Illinois 60510, USA

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49University of Illinois at Chicago, Chicago, Illinois 60607, USA
50Northern Illinois University, DeKalb, Illinois 60115, USA
51Northwestern University, Evanston, Illinois 60208, USA
52Indiana University, Bloomington, Indiana 47405, USA
53Purdue University Calumet, Hammond, Indiana 46323, USA
54University of Notre Dame, Notre Dame, Indiana 46556, USA
55Iowa State University, Ames, Iowa 50011, USA
56University of Kansas, Lawrence, Kansas 66045, USA
57Kansas State University, Manhattan, Kansas 66506, USA
58Louisiana Tech University, Ruston, Louisiana 71272, USA
59Boston University, Boston, Massachusetts 02215, USA
60Northeastern University, Boston, Massachusetts 02115, USA
61University of Michigan, Ann Arbor, Michigan 48109, USA
62Michigan State University, East Lansing, Michigan 48824, USA
63University of Mississippi, University, Mississippi 38677, USA
64University of Nebraska, Lincoln, Nebraska 68588, USA
65Rutgers University, Piscataway, New Jersey 08855, USA
66Princeton University, Princeton, New Jersey 08544, USA
67State University of New York, Buffalo, New York 14260, USA
68Columbia University, New York, New York 10027, USA
69University of Rochester, Rochester, New York 14627, USA
70State University of New York, Stony Brook, New York 11794, USA
71Brookhaven National Laboratory, Upton, New York 11973, USA
72Langston University, Langston, Oklahoma 73050, USA
73University of Oklahoma, Norman, Oklahoma 73019, USA
74Oklahoma State University, Stillwater, Oklahoma 74078, USA
75Brown University, Providence, Rhode Island 02912, USA
76University of Texas, Arlington, Texas 76019, USA
77Southern Methodist University, Dallas, Texas 75275, USA
78Rice University, Houston, Texas 77005, USA
79University of Virginia, Charlottesville, Virginia 22901, USA
80University of Washington, Seattle, Washington 98195, USA
(Dated: June 24, 2011)
We present a search for the production of neutral Higgs bosons decaying into τ+τ−pairs in p¯ p
collisions at a center-of-mass energy of 1.96 TeV. The data, corresponding to an integrated luminosity
of 5.4 fb−1, were collected by the D0 experiment at the Fermilab Tevatron Collider. We set upper
limits at the 95% C.L. on the production cross section multiplied by the branching ratio for a scalar
resonance decaying into τ+τ−pairs, and we then interpret these limits as limits on the production
of Higgs bosons in the minimal supersymmetric standard model (MSSM) and as constraints in the
MSSM parameter space.
PACS numbers: 14.80.Ec,14.80.Da,13.85.Rm
Supersymmetry (SUSY) [1] is one of the extensions of
the standard model (SM) proposed to address its short-
comings, such as the hierarchy problem caused by the
divergent radiative corrections to the Higgs boson mass.
In the minimal supersymmetric standard model (MSSM),
two complex Higgs boson doublets lead to five physical
Higgs bosons: two neutral CP-even (h, H), one neutral
CP-odd (A), and two charged Higgs bosons (H±). The
three neutral Higgs bosons (h,H,A) are collectively de-
∗with visitors fromaAugustana College, Sioux Falls, SD, USA,
bThe University of Liverpool, Liverpool, UK,cSLAC, Menlo Park,
CA, USA,
dUniversity College London, London, UK,
de Investigacion en Computacion - IPN, Mexico City, Mexico,
fECFM, Universidad Autonoma de Sinaloa, Culiac´ an, Mexico, and
gUniversit¨ at Bern, Bern, Switzerland.‡Deceased.
eCentro
noted as φ. At tree level, the Higgs sector of the MSSM is
fully described by two parameters, which are commonly
chosen to be the mass of the CP-odd Higgs boson, MA,
and the ratio of the vacuum expectation values of the
two Higgs doublets, tanβ. Radiative corrections intro-
duce dependencies on additional MSSM parameters. The
neutral MSSM Higgs bosons decay into τ+τ−and bb pairs
with branching fractions of ≈ 10% and ≈ 90%, respec-
tively. Their production cross section is enhanced by a
factor that depends on tanβ with respect to the cross
section for the SM Higgs boson at the same Higgs boson
mass. Moreover, for large tanβ, the Higgs bosons A and
either h or H are nearly degenerate in mass which leads
to an approximate doubling of σφ(Mφ).
Searches for the production of neutral MSSM Higgs
bosons have been performed at the CERN e+e−Col-
lider (LEP), excluding Mh,A< 93 GeV for all tanβ [2].

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4
The CDF and D0 Collaborations at the Fermilab Teva-
tron Collider and the CMS Collaboration at the CERN
Large Hadron Collider have extended the exclusion to
higher MA of up to 300 GeV in a restricted region of
tanβ ≈ 30−100, by searching for the exclusive processes
(b)bφ → (b)bb¯b [3] and bφ → bτ+τ−[4], and for the in-
clusive process φ → τ+τ−[5–8].
This Letter presents a search for the inclusive process
gg,bb → φ → τ+τ−, where the tau lepton pairs are recon-
structed through their decay into eµ or µτhfinal states,
and τh represents the hadronic decay modes of the tau
lepton. The search for τ+τ−final states is performed in
a model-independent way before the MSSM is chosen as
one of the models to interpret the results. The data were
recorded with the D0 detector [9] at a p¯ p center-of-mass
energy of√s = 1.96 TeV and correspond to an integrated
luminosity of 5.4 fb−1. This represents a significant in-
crease compared to the results previously published by
the CDF and D0 Collaborations, which are based on in-
tegrated luminosities of 1.8 fb−1[7] and 1.0 fb−1[8], re-
spectively.
Signal samples are generated using the pythia [10]
Monte Carlo (MC) event generator with the CTEQ6L1
parton distribution functions (PDF) [11].
background processes comprise Z+jets, W+jets, and
multijet production. Background from multijet events
arises when jets are misidentified as leptons. Additional
backgrounds include t¯t and SM diboson production. The
backgrounds from Z+jets, W+jets, and t¯t production
are modeled using alpgen [12], with parton showering
and hadronization provided by pythia. Diboson pro-
cesses (WW, WZ, ZZ) are simulated using pythia. In
all cases tauola [13] is used to model the tau lepton de-
cays. Simulated events are then processed by a geant-
based [14] simulation of the D0 detector, and data events
from random beam crossings are overlaid to model de-
tector noise and multiple pp interactions. Higher order
quantum chromodynamics (QCD) calculations of cross
sections are used to normalize the simulated background
samples, except for the background from multijet pro-
duction, for which the normalization and differential dis-
tributions are derived from data.
Events are selected by requiring at least one single
muon trigger for the µτhchannel, while for the eµ chan-
nel, they need to fulfill either inclusive electron or muon
trigger conditions. Electrons are reconstructed using
their characteristic energy deposits, including the trans-
verse and longitudinal shower profiles in the electromag-
netic (EM) calorimeter. Muons are identified by combin-
ing tracks in the central tracking detector with patterns
of hits in the muon spectrometer. Electrons and muons
are required to be isolated in the calorimeter and in the
tracking detectors.
Tau lepton decays into hadrons are characterized as
narrow, isolated jets with lower track multiplicity than
quark or gluon jets. Three types of tau lepton decays
Dominant
are distinguished by their detector signature. One-prong
tau decays consisting of energy deposited in the hadronic
calorimeter associated with a single track (π±ν-like) are
denoted as τ-type 1; τ-type 2 corresponds to one-prong
tau decays with energy deposited in both the hadronic
and EM calorimeters, associated with a single track (ρ±ν-
like); and τ-type 3 are multi-prong decays with energy in
the calorimeter and two or more associated tracks with
invariant mass below 1.7 GeV. A calibration for the en-
ergy of τhcandidates measured in the calorimeter is de-
rived from data. It is based on the ratio of the calorimeter
energy and the transverse momentum, pT, measured in
the tracking detector for the τhcandidates. The ratio is
adjusted in the simulation to match the data as a func-
tion of the fraction of the τhenergy deposited in the EM
calorimeter.
A set of neural networks, one for each τ-type, is ap-
plied to discriminate hadronic tau decays from jets [15].
The input variables are related to isolation and shower
shapes, and exploit correlations between calorimeter en-
ergy deposits and tracks.
network discriminants (NNτ) to be NNτ > 0.9 for τ-
types 1, 2 and NNτ > 0.95 for τ-type 3, approximately
67% of Z/γ∗→ τ+τ−events are retained, while 98% of
the multijet background events are rejected.
When requiring the neural
A series of selections is used to reduce the background
from Z+jets, W+jets, and multijet production.
Z/γ∗→ τ−τ+process differs from a Higgs boson signal
only through the mass and spin of the produced reso-
nance and cannot be further reduced. One isolated muon
with pµ
T> 15 GeV and an isolated hadronic tau lepton
with transverse energy Eτ
T> 12.5 GeV (τ-types 1,2) or
Eτ
T> 15 GeV (τ-type 3) are required in the µτhchannel.
The muon and the τhmust be oppositely charged, where
the charge of the τhcandidate is determined by the cur-
vature of the associated track, which in case of τ-type 3
is taken to be the highest pT track. The pseudorapidity
η [16] is required to be |ηµ| < 1.6 for muons and |ητ| < 2.5
for tau leptons. The transverse momentum sums of all
tracks associated with the τhcandidate, pτ
to be greater than 7, 5, 10 GeV for τ-types 1, 2, and 3,
respectively. At least one hit in the active layers of the
D0 silicon vertex detector is required for the tracks asso-
ciated with the τh. The τhand the muon are required to
originate from the same pp vertex and must be separated
from each other by ∆R =?(∆η)2+ (∆ϕ)2> 0.5, where
∆ϕ is the difference in azimuthal angle. This require-
ment suppresses the Z/γ∗→ µ+µ−background. The
transverse W boson mass in W → ℓν events is given
by Mℓν
T
=
2pℓ
The components ?Exand ?Eyof the missing transverse en-
ergy, ?ET, are computed from calorimeter cells and the
momenta of muons, and corrected for the energy re-
sponse of electrons, tau leptons, and jets. We require
Mµν
T
< 50 GeV to reject W(→ µν)+jets events where
The
T, are required
?
T?ET[1 − cos(∆ϕ(ℓ,?ET)] with ℓ = e,µ.

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5
jets are misidentified as τhcandidates.
In the eµ channel, events with at least one muon with
pµ
T> 10 GeV and |ηµ| < 1.6, and an oppositely charged
electron with pe
T> 12 GeV and |ηe| < 2 are selected.
The eµ pair formed by the leptons with the highest pT
are selected as a candidate; they must be separated by
∆R > 0.4.
candidate is rejected if it shares the same track with a
muon. Multijet background and W boson production
are suppressed by requiring the mass of the eµ pair to be
larger than 20 GeV and ?ET+ pµ
ground from W+jets production is reduced by requiring
min{Meν
imuthal angle, ∆ϕ(ℓ,?ET), has to be < 0.3 where ℓ = e,µ
is the lepton with the smaller pT. This requirement re-
jects background from WW, t¯t, and W+jets production.
Requiring the scalar sum of the transverse momenta of all
jets to be < 70 GeV rejects a large fraction of t¯t events.
To determine the expected background contribution
from multijet production in the µτh channel, two NNτ
regions are selected in addition to the high NNτ “sig-
nal” region defined previously: the “medium” region in
the range 0.25 ≤ NNτ≤ 0.75 and the “low” region with
NNτ ≤ 0.1. The samples are further divided depending
on whether the muon and the τhcandidate have the same
or opposite charge. Background from W+jets production
in these samples is reduced by requiring Mµν
The transverse mass is calculated from the missing trans-
verse energy in the calorimeter, ?ET, and from the az-
imuthal angle ∆ϕ(µ,?ET) between the direction of the
muon transverse momentum pµ
mated contribution from MC-simulated background pro-
cesses is then subtracted from the resulting distributions,
and the shape of the multijet background is derived from
the distributions of same-sign µτhpairs with NNτ> 0.9.
Multijet events mainly populate the low NNτregion, and
the ratio of opposite to same-sign µτhpair events in this
region yields the normalization of multijet events in the
signal sample. This estimate of the multijet background
contribution is verified by an independent method which
uses the medium NNτ region. The difference between
the estimates obtained by the two methods is used as
systematic uncertainty on the multijet background.
Multijet background in the eµ channel is determined
by applying the same selection criteria as for signal apart
from the electron likelihood and muon isolation criteria,
which are inverted. The normalization is then taken from
the ratio of the numbers of events in the opposite and
same-sign samples.
Since there are multiple neutrinos in the µτhand eµ fi-
nal states, the τ+τ−mass cannot be fully reconstructed.
Therefore, we search for an enhancement above the ex-
pected background in the distribution of the visible mass
Mvis =
?(Pτ1+ Pτ2+ ?PT)2, which is calculated us-
ing the four-vectors of the measured tau lepton decay
products, Pτ1,2, and the missing transverse momentum,
To reject Z → µµγ events, an electron
T+ pe
T> 65 GeV. Back-
T,Mµν
T} < 10 GeV. The difference in the az-
T
< 50 GeV.
Tand the ?ET. The esti-
Visible Mass (GeV)
00 5050100100 150150 200 200250 250300 300350350400400
Events / 10 GeV
-1-1
1010
11
10 10
22
10 10
33
1010
Data
→
Z
Other EW + tt
(120)
φ
W + jets
Multijet
τ τ
= 50 pb
σ
,
τ τ
→
)
h
τ
(
-1
, 5.4 fb DO
μ
(a)
Visible Mass (GeV)Visible Mass (GeV)
00 5050 100100 150 150200200 250250
Events
11
1010
22
10 10
Data
→
Z
Multijet
W + jets
Other EW + tt
(120)
φ
ττ
= 50 pb
σ
,
ττ→
Events / 10 GeV
) (
-1
, 5.4 fbDO
eμ
(b)
FIG. 1: Distributions of Mvis in the (a) µτhand (b) eµ chan-
nels after all selections. The data, shown with statistical un-
certainties, are compared to the sum of the predicted back-
grounds for an integrated luminosity of 5.4 fb−1. The Higgs
boson signal for Mφ= 120 GeV is normalized to a production
cross section of σφ = 50 pb. All entries exceeding the range
of a histogram are added to the last bin.
?PT = (?ET,?Ex,?Ey,0).
vectors Pτ1,2are calculated using the reconstructed elec-
tron and muon, respectively. After imposing all selection
requirements, the Mvisdistributions for the µτhand eµ
final states are shown in Fig. 1. Table I gives the yields
of the predicted background and of data, summed over
the Mvisdistributions shown in Fig. 1.
In the eµ final state, the four-
Several sources of systematic uncertainty affect both
the signal efficiency and background estimation. Both
uncertainties that modify only the normalization and un-
certainties that change the shape of the Mvisdistribution
are taken into account. Those that affect the normaliza-
tion include the integrated luminosity (6.1%), muon iden-
tification efficiency (2.9%), τhidentification (12%, 4.2%,
7% per τ-type), efficiency to reconstruct the τh track