Physics Letters B 763 (2016) 251–268
Contents lists available at ScienceDirect
Physics Letters B
www.elsevier.com/locate/physletb
Search for dark matter produced in association with a hadronically
decaying vector boson in pp collisions at
√
s =13 TeV with the ATLAS
detector
.The ATLAS Collaboration
a r t i c l e i n f o a b s t r a c t
Article history:
Received
9 August 2016
Received
in revised form 9 October 2016
Accepted
17 October 2016
Available
online 20 October 2016
Editor:
W.-D. Schlatter
A search is presented for dark matter produced in association with a hadronically decaying W or Z
boson
using 3.2 fb
−1
of pp collisions at
√
s = 13 TeV recorded by the ATLAS detector at the Large
Hadron Collider. Events with a hadronic jet compatible with a W or Z boson and with large missing
transverse momentum are analysed. The data are consistent with the Standard Model predictions and
are interpreted in terms of both an effective field theory and a simplified model containing dark matter.
© 2016 The Author. Published by Elsevier B.V. This is an open access article under the CC BY license
(http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP
3
.
Dark matter is the dominant component of matter in the uni-
verse,
but its particle nature remains a mystery. Searches for a
weakly interacting massive particle (WIMP), denoted by χ , and for
interactions between χ and Standard Model (SM) particles are a
central component of the current set of dark-matter experiments.
At
particle colliders, dark-matter particles may be produced
in pairs via some unknown intermediate state. While in many
models direct detection experiments have the greatest sensitivity
for dark-matter masses m
χ
between 10 and 100 GeV, searches
for dark matter at particle colliders are most powerful for lower
masses [1–3]. The final-state WIMPs are not directly detectable,
but their presence can be inferred from the recoil against a visible
particle [1]. Two example processes are shown in Fig. 1.
The
Tevatron and LHC collaborations have reported limits on
the cross section of p
¯
p → χ
¯
χ + X and pp → χ
¯
χ + X, respec-
tively,
where X is a hadronic jet [1–3], aphoton (γ ) [4,5], a W /Z
boson [6,7],
or a Higgs boson [8,9]. In many cases, results are re-
ported
in terms of limits on the parameters of an effective field
theory (EFT) formulated as a four-point contact interaction [10–18]
between
quarks and WIMPs. For such models, the strongest lim-
its
come from data in which the recoiling object is a jet. In other
models, however, the interaction is between dark matter and vec-
tor
bosons [19], such that the primary discovery mode would be in
final states such as those analysed here, where the recoiling object
is a W or Z boson.
E-mail address: atlas.publications@cern.ch.
In this Letter, asearch is reported for the production of a W
or
Z boson decaying hadronically (to q
¯
q
or q
¯
q, respectively) and
reconstructed as a single massive jet in association with large
missing transverse momentum from the undetected χ
¯
χ parti-
cles
in data collected by the ATLAS detector from pp collisions
with centre-of-mass energy
√
s = 13 TeV. This search is sensitive
to WIMP pair production, as well as to other dark-matter-related
models which predict invisible Higgs boson decays (WH or ZH
production
with H → χ
¯
χ ).
The ATLAS detector [20] at the LHC covers the pseudorapidity
1
range |η| < 4.9 and the full azimuthal angle φ. It consists of an
inner tracking detector surrounded by a superconducting solenoid,
electromagnetic and hadronic calorimeters, and an external muon
spectrometer incorporating large superconducting toroidal mag-
nets.
Atwo-level trigger system is used to select interesting events
to be recorded for subsequent offline analysis. Only data for which
beams were stable and all subsystems described above were oper-
ational
are used. Applying these requirements to pp collision data,
recorded during the 2015 LHC run, results in a data sample with a
time-integrated luminosity of 3.2fb
−1
. The systematic uncertainty
1
ATLAS uses a right-handed coordinate system with its origin at the nominal in-
teraction
point (IP) in the centre of the detector and the z-axis along the beam pipe.
The x-axis points from the IP to the centre of the LHC ring, and the y-axis points
upward. Polar coordinates (r, φ) are used in the transverse (x, y) plane, φ being the
azimuthal angle around the beam pipe. The pseudorapidity is defined in terms of
the polar angle θ as η =− lntan(θ/2).
http://dx.doi.org/10.1016/j.physletb.2016.10.042
0370-2693/
© 2016 The Author. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Funded by
SCOAP
3
.
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