124580471
The data acquisition and calibration system for the ATLAS Semiconductor Tracker
The SemiConductor Tracker (SCT) data acquisition (DAQ) system will calibrate, configure, and control the approximately six million front-end channels of the ATLAS silicon strip detector. It will provide a synchronized bunch-crossing clock to the front-end modules, communicate first-level triggers to the front-end chips, and transfer information about hit strips to the ATLAS high-level trigger system. The system has been used extensively for calibration and quality assurance during SCT barrel and endcap assembly and for performance confirmation tests after transport of the barrels and endcaps to CERN. Operating in data-taking mode, the DAQ has recorded nearly twenty million synchronously-triggered events during commissioning tests including almost a million cosmic ray triggered events. In this paper we describe the components of the data acquisition system, discuss its operation in calibration and data-taking modes and present some detector performance results from these tests
209521249
Search for long-lived, heavy particles in final states with a muon and multi-track displaced vertex in proton-proton collisions at √s=7 TeV with the ATLAS detector
Many extensions of the Standard Model posit the existence of heavy particles with long lifetimes. In this Letter, results are presented of a search for events containing one or more such particles, which decay at a significant distance from their production point, using a final state containing charged hadrons and an associated muon. This analysis uses a data sample of proton-proton collisions at root s = 7 TeV corresponding to an integrated luminosity of 4.4 fb(-1) collected in 2011 by the ATLAS detector operating at the Large Hadron Collider. Results are interpreted in the context of R-parity violating supersymmetric scenarios. No events in the signal region are observed and limits are set on the production cross section for pair production of supersymmetric particles, multiplied by the square of the branching fraction for a neutralino to decay to charged hadrons and a muon, based on the scenario where both of the produced supersymmetric particles give rise to neutralinos that decay in this way. However, since the search strategy is based on triggering on and reconstructing the decay products of individual long-lived particles, irrespective of the rest of the event, these limits can easily be reinterpreted in scenarios with different numbers of long-lived particles per event. The limits are presented as a function of neutralino lifetime, and for a range of squark and neutralino masses.
121864227
Progress with the single-sided module prototypes for the ATLAS tracker upgrade stave
Abstract The ATLAS experiment is preparing for the planned luminosity upgrade of the LHC (the super-luminous LHC or sLHC) with a programme of development for tracking able to withstand an order of greater magnitude radiation fluence and much greater hit occupancy rates than the current detector. This has led to the concept of an all-silicon tracker with an enhanced performance pixel-based inner region and short-strips for much of the higher radii. Both sub-systems employ many common technologies, including the proposed “stave” concept for integrated cooling and support. For the short-strip region, use of this integrated stave concept requires single-sided modules mounted on either side of a thin central lightweight support. Each sensor is divided into four rows of 23.82 mm length strips; within each row, there are 1280 strips of 74.5μm pitch. Well over a hundred prototype sensors are being delivered by Hamamatsu Photonics (HPK) to Japan, Europe and the US. We present results of the first 20 chip ABCN25 ASIC hybrids for these sensors, results of the first prototype 5120 strip module built with 40 ABCN25 read-out ASICs, and the status of the hybrids and modules being developed for the ATLAS tracker upgrade stave programme.
113198029
Triggering on Long-Lived Neutral Particles in the ATLAS Detector
Neutral particles with long decay paths that decay to many-particle final states represent, from an experimental point of view, a challenge both for the trigger and for the reconstruction capabilities of the ATLAS apparatus. The Hidden Valley scenario serves as an excellent setting for the purpose of exploring the challenges to the trigger posed by long-lived particles.
9225555
The barrel modules of the ATLAS semiconductor tracker.
This paper describes the silicon microstrip modules in the barrel section of the SemiConductor Tracker (SCT) of the ATLAS experiment at the CERN Large Hadron Collider (LHC). The module requirements, components and assembly techniques are given, as well as first results of the module performance on the fully assembled barrels that make up the detector being installed in the ATLAS experiment.
56087669
The detector control system of the ATLAS SemiConductor Tracker during macro-assembly and integration
The ATLAS SemiConductor Tracker (SCT) is one of the largest existing semiconductor detectors. It is situated between the Pixel detector and the Transition Radiation Tracker at one of the four interaction points of the Large Hadron Collider (LHC). During 2006-2007 the detector was lowered into the ATLAS cavern and installed in its final position. For the assembly, integration and commissioning phase, a complete Detector Control System (DCS) was developed to ensure the safe operation of the tracker. This included control of the individual powering of the silicon modules, a bi-phase cooling system and various types of sensors monitoring the SCT environment and the surrounding test enclosure. The DCS software architecture, performance and operational experience will be presented in the view of a validation of the DCS for the final SCT installation and operation phase.
118624969
KeV warm dark matter and composite neutrinos
A bstractElementary keV sterile Dirac neutrinos can be a natural ingredient of the composite neutrino scenario. For a certain class of composite neutrino theories, these sterile neutrinos naturally have the appropriate mixing angles to be resonantly produced warm dark matter (WDM). Alternatively, we show these sterile neutrinos can be WDM produced by an entropy-diluted thermal freeze-out, with the necessary entropy production arising not from an out-of-equilibrium decay, but rather from the confinement of the composite neutrino sector, provided there is sufficient supercooling.
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.
118476252
More flavor SU(3) tests for new physics in CP violating B decays
A bstractThe recent LHCb measurements of the Bs → K−π+ and Bs → K+K− rates and CP asymmetries are in agreement with U-spin expectations from Bd → K+π− and Bd → π+π− results. We derive the complete set of isospin, U-spin, and SU(3) relations among the CP asymmetries in two-body charmless B → PP and B → PV decays, some of which are novel. To go beyond the unbroken SU(3) limit, we present relations which are properly defined and normalized to allow incorporation of SU(3) breaking in the simplest manner. We show that there are no CP relations beyond first order in SU(3) and isospin breaking. We also consider the corresponding relations for charm decays. Comparing parametrizations of the leading order sum rules with data can shed light on the applicability and limitations of both the flavor symmetry and factorization-based descriptions of SU(3) breaking. Two factorization relations can already be tested, and we show they agree with current data.
117823450
Linear in temperature resistivity of scalar fermions: application to high Tc cuprates
no longer applicable
55385081
Dynamical framework for KeV Dirac neutrino warm dark matter
If the source of the reported $3.5$ keV x-ray line is a sterile neutrino, comprising an $\mathcal{O}(1)$ fraction of the dark matter (DM), then it exhibits the property that its mass times mixing angle is $\sim \mbox{few} \times 10^{-2}$ eV, a plausible mass scale for the active neutrinos. This property is a common feature of Dirac neutrino mixing. We present a framework that dynamically produces light active and keV sterile Dirac neutrinos, with appropriate mixing angles to be the x-ray line source. The central idea is that the right-handed active neutrino is a composite state, while elementary sterile neutrinos gain keV masses similarly to the quarks in extended Technicolor. The entire framework is fixed by just two dynamical scales and may automatically exhibit a warm dark matter (WDM) production mechanism -- dilution of thermal relics from late decays of a heavy composite neutrino -- such that the keV neutrinos may comprise an $\mathcal{O}(1)$ fraction of the DM. In this framework, the WDM is typically quite cool and within structure formation bounds, with temperature $\sim \mbox{few}\times 10^{-2}~T_\nu$ and free-streaming length $\sim$ few kpc. A toy model that exhibits the central features of the framework is also presented.