132 research outputs found
Fully hadronic tt cross section with the ATLAS detector
A measurement of the tt production cross section in the all-hadronic decay
mode is presented using 4.7 fb-1 of proton-proton collisions at a centre of
mass energy of 7 TeV collected by the ATLAS experiment in 2011. Events are
selected using a multi-jet trigger. Kinematic and b-tagging requirements are
then applied to identify tt event candidates. A kinematic fit reconstructs the
event topology of the final state extracting the top-quark mass which is then
used to measure the production cross section with an unbinned likelihood fit.
The result is found in good agreement with the Standard Model prediction for a
top-quark mass of 172.5 GeV.Comment: 4 pages, 4 figures, TOP 2012 (5th International Workshop on Top Quark
Physics
Usage of vertex detectors in the ATLAS trigger software
The challenging environment in which the Large Hadron Collider (LHC) experiments are going to operate implies a sophisticated trigger system, capable of real-time track and vertex reconstruc- tion. In the ATLAS experiment, the first selection stage where these ingredients are available is the software-based High-Level Trigger (HLT), which reduces its 75 kHz input to âŒ200 Hz in two subsequent steps: the LVL2 and the Event Filter (EF) triggers. In this contribution we present algorithms for fast reconstruction of charged tracks in the HLT framework, including common extrapolation and fitting tools. Their application to different trig- ger selections and in particular to b-jet selections, used to improve the flexibility of the trigger scheme and extend its physics performance, is also discussed. Examples of performance of the presented algorithms on simulation and cosmic-ray data are given. Efficient and robust tracking capabilities are demonstrated to be achievable with average execution times well within the trigger requirements
Fast Neural Network Inference on FPGAs for Triggering on Long-Lived Particles at Colliders
Experimental particle physics demands a sophisticated trigger and acquisition
system capable to efficiently retain the collisions of interest for further
investigation. Heterogeneous computing with the employment of FPGA cards may
emerge as a trending technology for the triggering strategy of the upcoming
high-luminosity program of the Large Hadron Collider at CERN. In this context,
we present two machine-learning algorithms for selecting events where neutral
long-lived particles decay within the detector volume studying their accuracy
and inference time when accelerated on commercially available Xilinx FPGA
accelerator cards. The inference time is also confronted with a CPU- and
GPU-based hardware setup. The proposed new algorithms are proven efficient for
the considered benchmark physics scenario and their accuracy is found to not
degrade when accelerated on the FPGA cards. The results indicate that all
tested architectures fit within the latency requirements of a second-level
trigger farm and that exploiting accelerator technologies for real-time
processing of particle-physics collisions is a promising research field that
deserves additional investigations, in particular with machine-learning models
with a large number of trainable parameters.Comment: 12 pages, 9 figures, 2 table
Displaced vertices from pseudo-Dirac dark matter
Displaced vertices are relatively unusual signatures for dark matter searches at the LHC. We revisit the model of pseudo-Dirac dark matter (pDDM), which can accommodate the correct relic density, evade direct detection constraints, and generically provide observable collider signatures in the form of displaced vertices. We use this model as a benchmark to illustrate the general techniques involved in the analysis, the complementarity between monojet and displaced vertex searches, and provide a comprehensive study of the current bounds and prospective reach
Epidemiologic and clinical updates on impulse control disorders: a critical review
The article reviews the current knowledge about the impulse control disorders (ICDs) with specific emphasis on epidemiological and pharmacological advances. In addition to the traditional ICDs present in the DSM-IVâpathological gambling, trichotillomania, kleptomania, pyromania and intermittent explosive disorderâa brief description of the new proposed ICDsâcompulsiveâimpulsive (CâI) Internet usage disorder, CâI sexual behaviors, CâI skin picking and CâI shoppingâis provided. Specifically, the article summarizes the phenomenology, epidemiology and comorbidity of the ICDs. Particular attention is paid to the relationship between ICDs and obsessiveâcompulsive disorder (OCD). Finally, current pharmacological options for treating ICDs are presented and discussed
First Direct Observation of Collider Neutrinos with FASER at the LHC
We report the first direct observation of neutrino interactions at a particle
collider experiment. Neutrino candidate events are identified in a 13.6 TeV
center-of-mass energy collision data set of 35.4 fb using the
active electronic components of the FASER detector at the Large Hadron
Collider. The candidates are required to have a track propagating through the
entire length of the FASER detector and be consistent with a muon neutrino
charged-current interaction. We infer neutrino interactions
with a significance of 16 standard deviations above the background-only
hypothesis. These events are consistent with the characteristics expected from
neutrino interactions in terms of secondary particle production and spatial
distribution, and they imply the observation of both neutrinos and
anti-neutrinos with an incident neutrino energy of significantly above 200 GeV.Comment: Submitted to PRL on March 24 202
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
Search for dark matter produced in association with bottom or top quarks in âs = 13 TeV pp collisions with the ATLAS detector
A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fbâ1 of protonâproton collision data recorded by the ATLAS experiment at âs = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements
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