A summary of the constraints from the ATLAS experiment on R-parity-conserving supersymmetry is presented. Results from 22 separate ATLAS searches are considered, each based on analysis of up to 20.3 fb−1 of proton-proton collision data at centre-of-mass energies of s√=7 and 8 TeV at the Large Hadron Collider. The results are interpreted in the context of the 19-parameter phenomenological minimal supersymmetric standard model, in which the lightest supersymmetric particle is a neutralino, taking into account constraints from previous precision electroweak and flavour measurements as well as from dark matter related measurements. The results are presented in terms of constraints on supersymmetric particle masses and are compared to limits from simplified models. The impact of ATLAS searches on parameters such as the dark matter relic density, the couplings of the observed Higgs boson, and the degree of electroweak fine-tuning is also shown. Spectra for surviving supersymmetry model points with low fine-tunings are presented.
COBISS.SI-ID: 29040423
We report a measurement of the branching fraction of B+→τ+ντ decays using a data sample of 772×10^6 BB¯ pairs, collected at the ϒ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e− collider. We reconstruct the accompanying B meson in a semileptonic decay and detect the recoiling B candidate in the decay channel B+→τ+ντ. We obtain a branching fraction of ℬ(B+→τ+ντ)=[1.25±0.28(stat.)±0.27(syst.)]×10−4. This result is in good agreement with previous measurements and the expectation from the calculation based on the Standard Model.
COBISS.SI-ID: 29268263
The dark photon A′ and the dark Higgs boson h′ are hypothetical constituents featured in a number of recently proposed dark sector models. Assuming prompt decays of both dark particles, we search for their production in the so-called Higgstrahlung channel e+e−→A′h′, with h′→A′A′. We investigate ten exclusive final states with A′→e+e−, μ+μ−, or π+π− in the mass ranges 0.1 GeV/c2 (mA′(3.5 GeV/c2 and 0.2 GeV/c2 (mh′(10.5 GeV/c2. We also investigate three inclusive final states 2(e+e−)X, 2(μ+μ−)X, and (e+e−)(μ+μ−)X, where X denotes a dark photon candidate detected via missing mass, in the mass ranges 1.1 GeV/c2 (mA′(3.5 GeV/c2 and 2.2 GeV/c2 (mh′(10.5 GeV/c2. Using the entire 977 fb−1 data set collected by Belle, we observe no significant signal. We obtain individual and combined 90% credibility level upper limits on the branching fraction times the Born cross section, ℬ×σBorn, on the Born cross section σBorn, and on the dark photon coupling to the dark Higgs boson times the kinetic mixing between the standard model photon and the dark photon, αD×ε2. These limits improve upon and cover wider mass ranges than previous experiments. The limits from the final states 3(π+π−) and 2(e+e−)X are the first placed by any experiment. For αD equal to 1/137, mh′( 8 GeV/c2, and mA′(1 GeV/c2, we exclude values of the mixing parameter ε above ∼8×10−4.
COBISS.SI-ID: 29255975
This Letter describes a model-agnostic search for pairs of jets (dijets) produced by resonant and non-resonant phenomena beyond the Standard Model in 3.6 fb−1 of proton–proton collisions with a centre-of-mass energy of View the sqrt(s)=13 TeV recorded by the ATLAS detector at the Large Hadron Collider. The distribution of the invariant mass of the two leading jets is examined for local excesses above a data-derived estimate of the smoothly falling prediction of the Standard Model. The data are also compared to a Monte Carlo simulation of Standard Model angular distributions derived from the rapidity of the two jets. No evidence of anomalous phenomena is observed in the data, which are used to exclude, at 95% CL, quantum black holes with threshold masses below 8.3 TeV, 8.1 TeV or 5.1 TeV in three different benchmark scenarios; resonance masses below 5.2 TeV for excited quarks, 2.6 TeV in a W′ model, a range of masses starting from mZ′=1.5 TeV and couplings from gq=0.2 in a Z′ model; and contact interactions with a compositeness scale below 12.0 TeV and 17.5 TeV respectively for destructive and constructive interference between the new interaction and QCD processes. These results significantly extend the ATLAS limits obtained from 8 TeV data. Gaussian-shaped contributions to the mass distribution are also excluded if the effective cross-section exceeds values ranging from approximately 50–300 fb for masses below 2 TeV to 2–20 fb for masses above 4 TeV.
COBISS.SI-ID: 29362983
We report the first observation of the radiative charm decay D0→ρ0γ and the first search for CP violation in decays D0→ρ0γ, ϕγ, and K*0(892)γ, using a data sample of 943 fb−1 collected with the Belle detector at the KEKB asymmetric-energy e+e− collider. The branching fraction is measured to be B(D0→ρ0γ)=(1.77±0.30±0.07)×10−5, where the first uncertainty is statistical and the second is systematic. The obtained CP asymmetries ACP(D0→ρ0γ)=+0.056±0.152±0.006, ACP(D0→ϕγ)=−0.094±0.066±0.001, and ACP(D0→¯K*0γ)=−0.003±0.020±0.000 are consistent with no CP violation. We also present an improved measurement of the branching fractions B(D0→ϕγ)=(2.76±0.19±0.10)×10−5 and B(D0→¯K*0γ)=(4.66±0.21±0.21)×10−4. The letter is based on the doctoral thesis of Tara Nanut.
COBISS.SI-ID: 30335271