High Energy Physics Experiment

We apply an Adversarially Learned Anomaly Detection (ALAD) algorithm to the problem of detecting new physics processes in proton-proton collisions at the Large Hadron Collider. Anomaly detection based on ALAD matches performances reached by Variational Autoencoders, with a substantial improvement in some cases. Training the ALAD algorithm on 4.4 fb-1 of 8 TeV CMS Open Data, we show how a data-driven anomaly detection and characterization would work in real life, re-discovering the top quark by identifying the main features of the t-tbar experimental signature at the LHC.

The performance of the ATLAS Inner Detector alignment has been studied usingppcollision data ats√=13TeV collected by the ATLAS experiment during Run 2 (2015 to 2018) of the Large Hadron Collider (LHC). The goal of the detector alignment is to determine the detector geometry as accurately as possible and correct for time-dependent movements. The Inner Detector alignment is based on the minimization of track-hit residuals in a sequence of hierarchical levels, from global mechanical assembly structures to local sensors. Subsequent levels have increasing numbers of degrees of freedom; in total there are almost 750000. The alignment determines detector geometry on both short and long timescales, where short timescales describe movements within an LHC fill. The performance and possible track parameter biases originating from systematic detector deformations are evaluated. Momentum biases are studied using resonances decaying to muons or to electrons. The residual sagitta bias and momentum scale bias after alignment are reduced to less than∼0.1 TeV−1and 0.9×10−3, respectively. Impact parameter biases are also evaluated using tracks within jets.

In this note,ZHHproduction in the all-hadronic final state is studied ine+e−collisions at the Compact Linear Collider at the 3 TeV stage. At this stage this Higgs boson pair production mode is sub-leading to theW+W−fusion production cross-section ofe+e−→HHνν. The events are characterised by a topology of six jets, where the masses of the three pair-wise combinations of two jets are compatible with originating from twoHand oneZbosons. The event selection concentrates on the dominantHboson decays into two b-quarks by requiring a presence of multiple b-jets. The study is based on full simulation using the CLICdet model, including beam-induced backgrounds fromγγ→hadrons. Results on the measurement of the totalZHHcross section are given.

Using 6.32 fb??ofe+e??collision data collected by the BESIII detector at the center-of-mass energies between 4.178 and 4.226 GeV,~an amplitude analysis of theD+s??K0SK???+?+decays is performed for the first time to determine the intermediate-resonant contributions. The dominant component is theD+s??K??(892)+K¯¯¯¯¯??(892)0decay with a fraction of(40.6±2.9stat±4.9sys)%. Our results of the amplitude analysis are used to obtain a more precise measurement of the branching fraction of theD+s??K0SK???+?+decay, which is determined to be(1.46±0.05stat±0.05sys)%.

Results are reported from an amplitude analysis of theB+→D+D−K+decay. The analysis is carried out using LHCb proton-proton collision data taken ats√=7,8,and13TeV, corresponding to a total integrated luminosity of 9 fb−1. In order to obtain a good description of the data, it is found to be necessary to include new spin-0 and spin-1 resonances in theD−K+channel with masses around 2.9 GeV/c2, and a new spin-0 charmonium resonance in proximity to the spin-2χc2(3930)state. The masses and widths of these resonances are determined, as are the relative contributions of all components in the amplitude model, which additionally include the vector charmoniaψ(3770),ψ(4040),ψ(4160)andψ(4415)states and a nonresonant component.

The results of a 3+1 sterile neutrino search using eight years of data from the IceCube Neutrino Observatory are presented. A total of 305,735 muon neutrino events are analyzed in reconstructed energy-zenith space to test for signatures of a matter-enhanced oscillation that would occur given a sterile neutrino state with a mass-squared differences between 0.01\,eV2and 100\,eV2. The best-fit point is found to be atsin2(2θ24)=0.10andΔm241=4.5eV2, which is consistent with the no sterile neutrino hypothesis with a p-value of 8.0\%.

The NA62 experiment reports an investigation of theK+→π+νν¯mode from a sample ofK+decays collected in 2017 at the CERN SPS. The experiment has achieved a single event sensitivity of(0.389±0.024)×10−10, corresponding to 2.2 events assuming the Standard Model branching ratio of(8.4±1.0)×10−11. Two signal candidates are observed with an expected background of 1.5 events. Combined with the result of a similar analysis conducted by NA62 on a smaller data set recorded in 2016, the collaboration now reports an upper limit of1.78×10−10for theK+→π+νν¯branching ratio at 90\%\,CL. This, together with the corresponding 68\%\,CL measurement of(0.48+0.72−0.48)×10−10, are currently the most precise results worldwide, and are able to constrain some New Physics models that predict large enhancements still allowed by previous measurements.

We report on the data set, data handling, and detailed analysis techniques of the first neutrino-mass measurement by the Karlsruhe Tritium Neutrino (KATRIN) experiment, which probes the absolute neutrino-mass scale via theβ-decay kinematics of molecular tritium. The source is highly pure, cryogenic T2gas. Theβelectrons are guided along magnetic field lines toward a high-resolution, integrating spectrometer for energy analysis. A silicon detector countsβelectrons above the energy threshold of the spectrometer, so that a scan of the thresholds produces a precise measurement of the high-energy spectral tail. After detailed theoretical studies, simulations, and commissioning measurements, extending from the molecular final-state distribution to inelastic scattering in the source to subtleties of the electromagnetic fields, our independent, blind analyses allow us to set an upper limit of 1.1 eV on the neutrino-mass scale at a 90\% confidence level. This first result, based on a few weeks of running at a reduced source intensity and dominated by statistical uncertainty, improves on prior limits by nearly a factor of two. This result establishes an analysis framework for future KATRIN measurements, and provides important input to both particle theory and cosmology.

We present a reanalysis of the experimental data of electron capture in7Be embedded in Ta which have been published by other authors. Our goal is to set upper limits on a mixture of electron neutrino with a possible right-handed heavy neutrino in the 150--800 keV mass range. In the published experiment a7Li recoil energy spectrum in the 20--200 eV range was measured. In case of electron capture with emission of a heavy neutrino, the recoil spectrum should be shifted to the lower energies. We search for an additional Gauss-shaped structure with the same energy width as the main K-shell transition peak. For this we digitize the published spectrum curve, find the energy resolution, calculate the moving sum of the events along the spectrum in the energy interval of about 3 sigma of energy resolution. Then we use the statistical error of this sum to exclude at some level the appearance of an additional peak. Finally, we present the upper limits at a 95\% confidence level on electron neutrino -- heavy neutrino mixing element,U2, in the mass matrix. New upper limits are at least one order of magnitude lower than the existing data in 300--800 keV mass range.

Using a data sample of2.93 fb−1ofe+e−collisions collected ats√=3.773GeVin the BESIII experiment, we perform an analysis of the decayD0→K0SK+K−. The Dalitz plot is analyzed using1856±45flavor-tagged signal decays. We find that the Dalitz plot is well described by a set of six resonances:a0(980)0,a0(980)+,ϕ(1020),a2(1320)+,a2(1320)−anda0(1450)−. Their magnitudes, phases and fit fractions are determined as well as the coupling ofa0(980)toKK¯,gKK¯=3.77±0.24(stat.)±0.35(sys.)GeV.The branching fraction of the decayD0→K0SK+K−is measured using11660±118untagged signal decays to be(4.51±0.05(stat.)±0.16(sys.))10−3. Both measurements are limited by their systematic uncertainties.