119261475
Composite Dirac neutrinos
We present a mechanism that naturally produces light Dirac neutrinos. The basic idea is that the right-handed neutrinos are composite. Any realistic composite model must involve ‘hidden flavor’ chiral symmetries. In general some of these symmetries may survive confinement, and in particular, one of them manifests itself at low energy as an exact B − L symmetry. Dirac neutrinos are therefore produced. The neutrinos are naturally light due to compositeness. In general, sterile states are present in the model, some of them can naturally be warm dark matter candidates.
118549709
Galactic center gamma-ray excess through a dark shower
The reported excess of $\gamma$-rays, emitted from an extended region around the galactic center, has a distribution and rate suggestive of an origin in dark matter (DM) annihilations. The conventional annihilation channels into standard model (SM) $b$ quarks or $\tau$ leptons may, however, be in tension with various experimental constraints on antiproton and positron fluxes. We present a framework that is free from such constraints. The key idea is that the mediators between the dark matter and the SM are themselves part of a strongly coupled sector: a hidden valley. In this scenario, the dark matter particles annihilate only into hidden quarks that subsequently shower and hadronize. Hidden quark effective couplings to SM hypercharge allow the lightest hidden bound states to subsequently decay into SM photons, producing the observed photon energy spectrum. Associated production of SM fermions is, in contrast, suppressed by electroweak, loop or helicity effects. We find that, generically, $\sim$ 10 GeV DM and a confinement scale $\sim$ 1 GeV provide a good fit to the observed spectrum. An $SU(2)$ hidden confining group is preferred over $SU(3)$ or higher rank gauge groups, up to uncertainties in the extraction of the astrophysical background. An explicit realization of this framework is also presented, and its phenomenology is discussed in detail, along with pertinent cosmological, astrophysical and collider bounds. This framework may be probed by model-independent searches, including future beam-dump experiments.
117823450
Linear in temperature resistivity of scalar fermions: application to high Tc cuprates
no longer applicable
118518738
Flavor oscillation from the two-point function
We present a formalism for the flavor oscillation of unstable particles that relies only upon the structure of the time Fourier-transformed two-point Green's function. We derive exact oscillation probability and integrated oscillation probability formulae, and verify that our results reproduce the known results for both neutrino and neutral meson oscillation in the expected regimes of parameter space. The generality of our approach permits us to investigate flavor oscillation in exotic parameter regimes, and present the corresponding oscillation formulae.
118492998
SU(3) sum rules for charm decay
A bstractWe present flavor SU(3) sum rules for D → PP and D → PV decay amplitudes, that are valid to second order in symmetry breaking by the strange quark mass spurion. Decay rate sum rules are also computed to this order. Particular attention is given to sum rules arising from the isospin and U-spin subgroups, the former providing sensitive tests for alternative sources of SU(3) breaking. We apply the latter together with the postulated ΔU = 0 rule for the large penguin picture to predict the ratio and difference of the direct CP asymmetries for D → KK∗ and D → πρ.
115170899
Lorentz symmetric quantum field theory for symplectic fermions
A free quantum field theory with Lorentz symmetry is derived for spin-half symplectic fermions in 2+1 dimensions. In particular, we show that fermionic spin-half fields may be canonically quantized in a free theory with a Klein–Gordon Lagrangian. This theory is shown to have all the required properties of a consistent free quantum field theory, namely, causality, unitarity, adherence to the spin-statistics theorem, CPT symmetry, and the Hermiticity and positive definiteness of the Hamiltonian. The global symmetry of the free theory is Sp(4)≃SO(5). Possible interacting theories of both the pseudo-Hermitian and Hermitian variety are then examined briefly.
123014224
A neural network clustering algorithm for the ATLAS silicon pixel detector
A novel technique to identify and split clusters created by multiple charged particles in the ATLAS pixel detector using a set of artificial neural networks is presented. Such merged clusters are a common feature of tracks originating from highly energetic objects, such as jets. Neural networks are trained using Monte Carlo samples produced with a detailed detector simulation. This technique replaces the former clustering approach based on a connected component analysis and charge interpolation. The performance of the neural network splitting technique is quantified using data from proton-proton collisions at the LHC collected by the ATLAS detector in 2011 and from Monte Carlo simulations. This technique reduces the number of clusters shared between tracks in highly energetic jets by up to a factor of three. It also provides more precise position and error estimates of the clusters in both the transverse and longitudinal impact parameter resolution.
110162019
Engineering for the ATLAS SemiConductor Tracker (SCT) end-cap
The ATLAS SemiConductor Tracker (SCT) is a silicon-strip tracking detector which forms part of the ATLAS inner detector. The SCT is designed to track charged particles produced in proton-proton collisions at the Large Hadron Collider (LHC) at CERN at an energy of 14 TeV. The tracker is made up of a central barrel and two identical end-caps. The barrel contains 2112 silicon modules, while each end-cap contains 988 modules. The overall tracking performance depends not only on the intrinsic measurement precision of the modules but also on the characteristics of the whole assembly, in particular, the stability and the total material budget. This paper describes the engineering design and construction of the SCT end-caps, which are required to support mechanically the silicon modules, supply services to them and provide a suitable environment within the inner detector. Critical engineering choices are highlighted and innovative solutions are presented – these will be of interest to other builders of large-scale tracking detectors. The SCT end-caps will be fully connected at the start of 2008. Further commissioning will continue, to be ready for proton-proton collision data in 2008.
18380644
Construction and performance of the ATLAS silicon microstrip barrel modules
Abstract The ATLAS Semiconductor Tracker (SCT) consists of four barrel cylinders and 18 end-cap disks. This paper describes the SCT modules of the barrel region, of which more than 2000 are about to be constructed. The module design is fixed. Its design concept is given together with the electrical, thermal and mechanical specifications. The pre-series production of the barrel modules is underway using mass-production procedures and jigs. The pre-series modules have given satisfactory performances on noise, noise occupancy, electrical as well as mechanical and thermal properties. In addition, irradiated modules were demonstrated to work successfully. Also first results from a 10-module system test are given.
202105722
Search for strong gravity signatures in same-sign dimuon final states using the ATLAS detector at the LHC
A search for microscopic black holes has been performed in a same-sign dimuon final state using 1.3 fb(-1) of proton-proton collision data collected with the ATLAS detector at a centre of mass energy of 7 TeV at the CERN Large Hadron Collider. The data are found to be consistent with the expectation from the Standard Model and the results are used to derive exclusion contours in the context of a low scale gravity model.
209834301
Search for supersymmetry in events with photons, bottom quarks, and missing transverse momentum in proton–proton collisions at a centre-of-mass energy of 7 TeV with the ATLAS detector
A search has been performed for the experimental signature of an isolated photon with high transverse momentum, at least one jet identified as originating from a bottom quark, and high missing transverse momentum. Such a final state may originate from supersymmetric models with gauge-mediated supersymmetry breaking in events in which one of a pair of higgsino-like neutralinos decays into a photon and a gravitino while the other decays into a Higgs boson and a gravitino. The search is performed using the full dataset of 7 TeV proton–proton collisions recorded with the ATLAS detector at the LHC in 2011, corresponding to an integrated luminosity of 4.7 fb−1. A total of 7 candidate events are observed while 7.5±2.2 events are expected from the Standard Model background. The results of the search are interpreted in the context of general gauge mediation to exclude certain regions of a benchmark plane for higgsino-like neutralino production.