3,282 research outputs found
New sensitivity of LHC measurements to composite dark matter models
We present sensitivity of LHC differential cross-section measurements to
so-called "stealth dark matter" scenarios occurring in an SU(N) dark gauge
group, where constituents are charged under the Standard Model and N=2 or 4.
The low-energy theory contains mesons which can be produced at the LHC, and a
scalar baryon dark matter (DM) candidate which cannot. We evaluate the impact
of LHC measurements on the dark meson masses. Using existing lattice results,
we then connect the LHC explorations to DM phenomenology, in particular
considering direct-detection experiments. We show that current LHC measurements
constrain DM masses in the region of 10 TeV. We discuss potential pathways to
explore these models further at the LHC
New sensitivity of current LHC measurements to vector-like quarks
Quark partners with non-chiral couplings appear in several extensions of the
Standard Model. They may have non-trivial generational structure to their
couplings, and may be produced either in pairs via the strong and EM
interactions, or singly via the new couplings of the model. Their decays often
produce heavy quarks and gauge bosons, which will contribute to a variety of
already-measured "Standard Model" cross-sections at the LHC. We present a study
of the sensitivity of such published LHC measurements to vector-like quarks,
first comparing to limits already obtained from dedicated searches, and then
broadening to some so-far unstudied parameter regions
Testing new-physics models with global comparisons to collider measurements: the Contur toolkit
Measurements at particle collider experiments, even if primarily aimed at
understanding Standard Model processes, can have a high degree of model
independence, and implicitly contain information about potential contributions
from physics beyond the Standard Model. The Contur package allows users to
benefit from the hundreds of measurements preserved in the Rivet library to
test new models against the bank of LHC measurements to date. This method has
proven to be very effective in several recent publications from the Contur
team, but ultimately, for this approach to be successful, the authors believe
that the Contur tool needs to be accessible to the wider high energy physics
community. As such, this manual accompanies the first user-facing version:
Contur v2. It describes the design choices that have been made, as well as
detailing pitfalls and common issues to avoid. The authors hope that with the
help of this documentation, external groups will be able to run their own
Contur studies, for example when proposing a new model, or pitching a new
search
Destructive breakdown studies of irradiated LGADs at beam tests for the ATLAS HGTD
In the past years, it has been observed at several beam test campaigns that
irradiated LGAD sensors break with a typical star shaped burn mark when
operated at voltages much lower than those at which they were safely operated
during laboratory tests. The study presented in this paper was designed to
determine the safe operating voltage that these sensors can withstand. Many
irradiated sensors from various producers were tested in two test beam
facilities, DESY (Hamburg) and CERN-SPS (Geneva), as part of ATLAS High
Granularity Timing Detector (HGTD) beam tests. The samples were placed in the
beam and kept under bias over a long period of time in order to reach a high
number of particles crossing each sensor. Both beam tests lead to a similar
conclusion, that these destructive events begin to occur when the average
electric field in the sensor becomes larger than 12 Volts per micrometre.Comment: Published versio
Interaction of amisulpride with GLUT1 at the blood-brain barrier. Relevance to Alzheimer’s disease
Blood-brain barrier (BBB) dysfunction may be involved in the increased sensitivity of Alzheimer's disease (AD) patients to antipsychotics, including amisulpride. Studies indicate that antipsychotics interact with facilitated glucose transporters (GLUT), including GLUT1, and that GLUT1 BBB expression decreases in AD. We tested the hypotheses that amisulpride (charge: +1) interacts with GLUT1, and that BBB transport of amisulpride is compromised in AD. GLUT1 substrates, GLUT1 inhibitors and GLUT-interacting antipsychotics were identified by literature review and their physicochemical characteristics summarised. Interactions between amisulpride and GLUT1 were studied using in silico approaches and the human cerebral endothelial cell line, hCMEC/D3. Brain distribution of [3H]amisulpride was determined using in situ perfusion in wild type (WT) and 5xFamilial AD (5xFAD) mice. With transmission electron microscopy (TEM) we investigated brain capillary degeneration in WT mice, 5xFAD mice and human samples. Western blots determined BBB transporter expression in mouse and human. Literature review revealed that, although D-glucose has no charge, charged molecules can interact with GLUT1. GLUT1 substrates are smaller (184.95±6.45g/mol) than inhibitors (325.50±14.40g/mol) and GLUT-interacting antipsychotics (369.38±16.04). Molecular docking showed beta-D-glucose (free energy binding: -15.39kcal/mol) and amisulpride (-29.04kcal/mol) interact with GLUT1. Amisulpride did not affect [14C]D-glucose hCMEC/D3 accumulation. [3H]amisulpride uptake into the brain (except supernatant) of 5xFAD mice compared to WT remained unchanged. TEM revealed brain capillary degeneration in human AD. There was no difference in GLUT1 or P-glycoprotein BBB expression between WT and 5xFAD mice. In contrast, caudate P-glycoprotein, but not GLUT1, expression was decreased in human AD capillaries versus controls. This study provides new details about the BBB transport of amisulpride, evidence that amisulpride interacts with GLUT1 and that BBB transporter expression is altered in AD. This suggests that antipsychotics could potentially exacerbate the cerebral hypometabolism in AD. Further research into the mechanism of amisulpride transport by GLUT1 is important for improving antipsychotics safety
Measurement of the cross-section and charge asymmetry of bosons produced in proton-proton collisions at TeV with the ATLAS detector
This paper presents measurements of the and cross-sections and the associated charge asymmetry as a
function of the absolute pseudorapidity of the decay muon. The data were
collected in proton--proton collisions at a centre-of-mass energy of 8 TeV with
the ATLAS experiment at the LHC and correspond to a total integrated luminosity
of 20.2~\mbox{fb^{-1}}. The precision of the cross-section measurements
varies between 0.8% to 1.5% as a function of the pseudorapidity, excluding the
1.9% uncertainty on the integrated luminosity. The charge asymmetry is measured
with an uncertainty between 0.002 and 0.003. The results are compared with
predictions based on next-to-next-to-leading-order calculations with various
parton distribution functions and have the sensitivity to discriminate between
them.Comment: 38 pages in total, author list starting page 22, 5 figures, 4 tables,
submitted to EPJC. All figures including auxiliary figures are available at
https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/STDM-2017-13
Search for chargino-neutralino production with mass splittings near the electroweak scale in three-lepton final states in √s=13 TeV pp collisions with the ATLAS detector
A search for supersymmetry through the pair production of electroweakinos with mass splittings near the electroweak scale and decaying via on-shell W and Z bosons is presented for a three-lepton final state. The analyzed proton-proton collision data taken at a center-of-mass energy of √s=13 TeV were collected between 2015 and 2018 by the ATLAS experiment at the Large Hadron Collider, corresponding to an integrated luminosity of 139 fb−1. A search, emulating the recursive jigsaw reconstruction technique with easily reproducible laboratory-frame variables, is performed. The two excesses observed in the 2015–2016 data recursive jigsaw analysis in the low-mass three-lepton phase space are reproduced. Results with the full data set are in agreement with the Standard Model expectations. They are interpreted to set exclusion limits at the 95% confidence level on simplified models of chargino-neutralino pair production for masses up to 345 GeV
Performance of a front-end prototype ASIC for the ATLAS High Granularity Timing Detector
This paper presents the design and characterisation of a front-end prototype
ASIC for the ATLAS High Granularity Timing Detector, which is planned for the
High-Luminosity phase of the LHC. This prototype, called ALTIROC1, consists of
a 55-pad matrix and contains the analog part of the single-channel
readout (preamplifier, discriminator, two TDCs and SRAM). Two preamplifier
architectures (transimpedance and voltage) were implemented and tested. The
ASIC was characterised both alone and as a module when connected to a
55-pad array of LGAD sensors. In calibration measurements, the ASIC
operating alone was found to satisfy the technical requirements for the
project, with similar performances for both preamplifier types. In particular,
the jitter was found to be 151~ps (351~ps) for an injected charge of
10~fC (4~fC). A degradation in performance was observed when the ASIC was
connected to the LGAD array. This is attributed to digital couplings at the
entrance of the preamplifiers. When the ASIC is connected to the LGAD array,
the lowest detectable charge increased from 1.5~fC to 3.4~fC. As a consequence,
the jitter increased for an injected charge of 4~fC. Despite this increase,
ALTIROC1 still satisfies the maximum jitter specification (below 65~ps) for the
HGTD project. This coupling issue also affects the time over threshold
measurements and the time-walk correction can only be performed with
transimpedance preamplifiers. Beam test measurements with a pion beam at CERN
were also undertaken to evaluate the performance of the module. The best time
resolution obtained using only ALTIROC TDC data was 46.30.7~ps for a
restricted time of arrival range where the coupling issue is minimized. The
residual time-walk contribution is equal to 23~ps and is the dominant
electronic noise contribution to the time resolution at 15~fC.Comment: 20 pages, 15 figures Second version submitted to JINST including
minor changes applied to address journal's comment
Search for new phenomena in final states with an energetic jet and large missing transverse momentum in pp collisions at √ s = 8 TeV with the ATLAS detector
Results of a search for new phenomena in final states with an energetic jet and large missing transverse momentum are reported. The search uses 20.3 fb−1 of √ s = 8 TeV data collected in 2012 with the ATLAS detector at the LHC. Events are required to have at least one jet with pT > 120 GeV and no leptons. Nine signal regions are considered with increasing missing transverse momentum requirements between Emiss T > 150 GeV and Emiss T > 700 GeV. Good agreement is observed between the number of events in data and Standard Model expectations. The results are translated into exclusion limits on models with either large extra spatial dimensions, pair production of weakly interacting dark matter candidates, or production of very light gravitinos in a gauge-mediated supersymmetric model. In addition, limits on the production of an invisibly decaying Higgs-like boson leading to similar topologies in the final state are presente
Reinterpretation of LHC results for new physics: Status and recommendations after run 2
We report on the status of efforts to improve the reinterpretation of searches and measurements at the LHC in terms of models for new physics, in the context of the LHC Reinterpretation Forum. We detail current experimental offerings in direct searches for new particles, measurements, technical implementations and Open Data, and provide a set of recommendations for further improving the presentation of LHC results in order to better enable reinterpretation in the future. We also provide a brief description of existing software reinterpretation frameworks and recent global analyses of new physics that make use of the current data
- …