A search for the narrow structure, X (5568), reported by the D0 Collaboration in the decay sequence X → B$0\atop{s}$π ± , B$0\atop{s}$ → J/ψΦ, is presented. The analysis is based on a data sample ...recorded with the ATLAS detector at the LHC corresponding to 4.9 fb-1 of pp collisions at 7 TeV and 19.5 fb-1 at 8 TeV. No significant signal was found. Upper limits on the number of signal events, with properties corresponding to those reported by D0, and on the X production rate relative to B$0\atop{s}$ mesons, ρX, were determined at 95% confidence level. The results are N (X) < 382 and ρX < 0.015 for B$0\atop{s}$ mesons with transverse momenta above 10 GeV, and N (X) < 356 and ρX < 0.016 for transverse momenta above 15 GeV. Finally, limits are also set for potential B$0\atop{s}$π ± resonances in the mass range 5550 to 5700 MeV.
Dark matter particles, if sufficiently light, may be produced in decays of the Higgs boson. This Letter presents a statistical combination of searches for H→invisible decays where H is produced ...according to the standard model via vector boson fusion, Z(ℓℓ)H, and W/Z(had)H, all performed with the ATLAS detector using 36.1 $fb^{-1}$ of pp collisions at a center-of-mass energy of $\sqrt{s}$ =13 TeV at the LHC. In combination with the results at $\sqrt{s}$ =7 and 8 TeV, an exclusion limit on the H→invisible branching ratio of 0.26($0.17_{-0.05}^{+0.07}$) at 95% confidence level is observed (expected).
The inclusive production of four isolated charged leptons in pp collisions is analysed for the presence of hard double-parton scattering, using 20.2 fb–1 of data recorded in the ATLAS detector at the ...LHC at centre-of-mass energy √s = 8 TeV. In the four-lepton invariant-mass range of 80 < m4l < 1000 GeV, an artificial neural network is used to enhance the separation between single- and double-parton scattering based on the kinematics of the four leptons in the final state. As a result, an upper limit on the fraction of events originating from double-parton scattering is determined at 95% confidence level to be fDPS = 0.042, which results in an estimated lower limit on the effective cross section at 95% confidence level of 1.0 mb.
Measurements of the per-event charged-particle yield as a function of the charged-particle transverse momentum and rapidity are performed using p+Pb collision data collected by the ATLAS experiment ...at the LHC at a centre-of-mass energy of sNN=5.02TeV. Charged particles are reconstructed over pseudorapidity |η|&lt;2.3 and transverse momentum between 0.1 GeV and 22 GeV in a dataset corresponding to an integrated luminosity of 1 μb−1. The results are presented in the form of charged-particle nuclear modification factors, where the p+Pb charged-particle multiplicities are compared between central and peripheral p+Pb collisions as well as to charged-particle cross sections measured in pp collisions. The p+Pb collision centrality is characterized by the total transverse energy measured in −4.9&lt;η&lt;−3.1, which is in the direction of the outgoing lead beam. Three different estimations of the number of nucleons participating in the p+Pb collision are carried out using the Glauber model and two Glauber–Gribov colour-fluctuation extensions to the Glauber model. The values of the nuclear modification factors are found to vary significantly as a function of rapidity and transverse momentum. A broad peak is observed for all centralities and rapidities in the nuclear modification factors for charged-particle transverse momentum values around 3 GeV. The magnitude of the peak increases for more central collisions as well as rapidity ranges closer to the direction of the outgoing lead nucleus.
Higgs boson production cross-sections in proton–proton collisions are measured in the H → WW∗→ eνμν decay channel. The proton–proton collision data were produced at the Large Hadron Collider at a ...centre-of-mass energy of 13 TeV and recorded by the ATLAS detector in 2015 and 2016, corresponding to an integrated luminosity of 36.1fb-1. The product of the H→WW∗ branching fraction times the gluon–gluon fusion and vector-boson fusion cross-sections are measured to be 11.4$_{-1.1}^{+1.2}$(stat.)$_{-1.7}^{+1.8}$(syst.) pb and 0.50$_{-0.22}^{+0.24}$(stat.)±0.17(syst.) pb, respectively, in agreement with Standard Model predictions.
A
bstract
Charged-particle spectra obtained in Pb+Pb interactions at
s
N
N
=
2.76
TeV and
pp
interactions at
s
N
N
=
2.76
TeV with the ATLAS detector at the LHC are presented, using data with ...integrated luminosities of 0.15 nb
−1
and 4.2 pb
−1
, respectively, in a wide transverse momentum (0
.
5
< p
T
<
150 GeV) and pseudorapidity (|
η
|
<
2) range. For Pb+Pb collisions, the spectra are presented as a function of collision centrality, which is determined by the response of the forward calorimeters located on both sides of the interaction point. The nuclear modification factors
R
AA
and
R
CP
are presented in detail as a function of centrality,
p
T
and
η
. They show a distinct
p
T
-dependence with a pronounced minimum at about 7 GeV. Above 60 GeV,
R
AA
is consistent with a plateau at a centrality-dependent value, within the uncertainties. The value is 0
.
55 ± 0
.
01(stat
.
) ± 0
.
04(syst
.
) in the most central collisions. The
R
AA
distribution is consistent with flat |
η
| dependence over the whole transverse momentum range in all centrality classes.
Narrow resonances decaying into WW, W Z or Z Z boson pairs are searched for in 139 fb-1 of proton–proton collision data at a centre-of-mass energy of √s = 13 TeV recorded with the ATLAS detector at ...the Large Hadron Collider from 2015 to 2018. The diboson system is reconstructed using pairs of high transverse momentum, large-radius jets. These jets are built from a combination of calorimeter- and tracker-inputs compatible with the hadronic decay of a boosted W or Z boson, using jet mass and substructure properties. The search is performed for diboson resonances with masses greater than 1.3 TeV. No significant deviations from the background expectations are observed. Exclusion limits at the 95% confidence level are set on the production cross-section times branching ratio into dibosons for resonances in a range of theories beyond the Standard Model, with the highest excluded mass of a new gauge boson at 3.8 TeV in the context of mass-degenerate resonances that couple predominantly to gauge bosons.
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