Abstract: It is well-known that at tree-level the d = 5 Weinberg operator can be generated in exactly three different ways, the famous seesaw models. In this paper we study the related question of how many phenomenologically consistent 1-loop models one can construct at d=5. First, we discuss that there are two possible classes of 1-loop neutrino mass models, that allow avoiding stable charged relics: (i) models with dark matter candidates and (ii) models with “exits”. Here, we define “exits” as particles that can decay into standard model fields. Considering 1-loop models with new scalars and fermions, we find in the dark matter class a total of (115+203) models, while in the exit class we find (38+368) models. Here, 115 is the number of DM models, which require a stabilizing symmetry, while 203 is the number of models which contain a dark matter candidate, which maybe accidentally stable. In the exit class the 38 refers to models, for which one (or two) of the internal particles in the loop is a SM field, while the 368 models contain only fields beyond the SM (BSM) in the neutrino mass diagram. We then study the RGE evolution of the gauge couplings in all our 1-loop models. Many of the models in our list lead to Landau poles in some gauge coupling at rather low energies and there is exactly one model which unifies the gauge couplings at energies above 10(15) GeV in a numerically acceptable way.

Abstract: Jet energy scale and resolution measurements with their associated uncertainties are reported for jets using 36-81 fb-1 of proton-proton collision data with a centre-of-mass energy of root s=13 TeV collected by the ATLAS detector at the LHC. Jets are reconstructed using two different input types: topo-clusters formed from energy deposits in calorimeter cells, as well as an algorithmic combination of charged-particle tracks with those topo-clusters, referred to as the ATLAS particle-flow reconstruction method. The anti-kt jet algorithm with radius parameter R=0.4 is the primary jet definition used for both jet types. This result presents new jet energy scale and resolution measurements in the high pile-up conditions of late LHC Run 2 as well as a full calibration of particle-flow jets in ATLAS. Jets are initially calibrated using a sequence of simulation-based corrections. Next, several in situ techniques are employed to correct for differences between data and simulation and to measure the resolution of jets. The systematic uncertainties in the jet energy scale for central jets (|eta|<1.2) vary from 1% for a wide range of high-pT jets (250<pT<2000 GeV), to 5% at very low pT (20 GeV) and 3.5% at very high pT (>2.5 TeV). The relative jet energy resolution is measured and ranges from (24 +/- 1.5)% at 20 GeV to (6 +/- 0.5)% at 300 GeV.

Abstract: Jet quenching is the process of color-charged partons losing energy via interactions with quark-gluon plasma droplets created in heavy-ion collisions. The collective expansion of such droplets is well described by viscous hydrodynamics. Similar evidence of collectivity is consistently observed in smaller collision systems, including pp and p+ Pb collisions. In contrast, while jet quenching is observed in Pb + Pb collisions, no evidence has been found in these small systems to date, raising fundamental questions about the nature of the system created in these collisions. The ATLAS experiment at the Large Hadron Collider has measured the yield of charged hadrons correlated with reconstructed jets in 0.36 nb-1 of p+ Pb and 3.6 pb-1 of pp collisions at 5.02 TeV. The yields of charged hadrons with p(T)(ch) > 0.5 GeV near and opposite in azimuth to jets with p(t)(je) T > 30 or 60 GeV, and the ratios of these yields between p+ Pb and pp collisions, IpPb, are reported. The collision centrality of p+ Pb events is categorized by the energy deposited by forward neutrons from the struck nucleus. The IpPb values are consistent with unity within a few percent for hadrons with p(T )(ch)> 4 GeV at all centralities. These data provide new, strong constraints that preclude almost any parton energy loss in central p+ Pb collisions.

Abstract: Jet substructure has provided new opportunities for searches and measurements at the LHC, and has seen continuous development since the optimization of the large-radius jet definition used by ATLAS was performed during Run 1. A range of new inputs to jet reconstruction, pile-up mitigation techniques and jet grooming algorithms motivate an optimisation of large-radius jet reconstruction for ATLAS. In this paper, this optimisation procedure is presented, and the performance of a wide range of large-radius jet definitions is compared. The relative performance of these jet definitions is assessed using metrics such as their pileup stability, ability to identify hadronically decaying W bosons and top quarks with large transverse momenta. A new type of jet input object, called a 'unified flow object' is introduced which combines calorimeter- and inner-detector-based signals in order to achieve optimal performance across a wide kinematic range. Large-radius jet definitions are identified which significantly improve on the current ATLAS baseline definition, and their modelling is studied using pp collisions recorded by the ATLAS detector at TeV during 2017.

Abstract: Jets created in association with a photon can be used as a calibrated probe to study energy loss in the medium created in nuclear collisions. Measurements of the transverse momentum balance between isolated photons and inclusive jets are presented using integrated luminosities of 0.49 nb(-1) of Pb + Pb collision data at root(NN)-N-s = 5.02 TeV and 25 pb(-1) of pp collision data at. root s= 5.02 TeV recorded with the ATLAS detector at the LHC. Photons with transverse momentum 63.1 < p(T)(gamma) < 200 GeV and vertical bar eta(gamma vertical bar) < 2.37 are paired with all jets in the event that have p(T)(jet) > 31.6 GeV and pseudorapidity vertical bar eta(Jet)vertical bar < 2.8. The transverse momentum balance given by the jet-to-photon p(T) ratio, x(j gamma), is measured for pairs with azimuthal opening angle Delta phi > 7 pi/8. Distributions of the per-photon jet yield as a function of x(j gamma), (1/N-gamma)(dN/dx(j gamma)), are corrected for detector effects via a two-dimensional unfolding procedure and reported at the particle level. In pp collisions, the distributions are well described by Monte Carlo event generators. In Pb + Pb collisions, the x(j gamma) distribution is modified from that observed in pp collisions with increasing centrality, consistent with the picture of parton energy loss in the hot nuclear medium. The data are compared with a suite of energy-loss models and calculations.