A
bstract
We investigate the discovery potential for long-lived particles produced in association with a top-antitop quark pair at the (High-Luminosity) LHC. Compared to inclusive searches for a ...displaced vertex, top-associated signals offer new trigger options and an extra handle to suppress background. We design a search strategy for a displaced di-muon vertex in the tracking detectors, in association with a reconstructed top-antitop pair. For axion-like particles with masses above the di-muon threshold, we find that the (High-Luminosity) LHC can probe effective top-quark couplings as small as |
c
tt
|/
f
a
= 0
.
03 (0
.
002)/TeV and proper decay lengths as long as 20 (300) m, assuming a cross section of 1 fb, with data corresponding to an integrated luminosity of 150 fb
−
1
(3 ab
−
1
). Our predictions suggest that searches for top-associated displaced di-muons will explore new terrain in the current sensitivity gap between searches for prompt di-muons and missing energy.
One burden of high energy physics data analysis is uncertainty within the measurement, both systematically and statistically. Even with sophisticated neural network techniques that are used to assist ...in high energy physics measurements, the resulting measurement may suffer from both types of uncertainties. Fortunately, most types of systematic uncertainties are based on knowledge from information such as theoretical assumptions, for which the range and behaviour are known. It has been proposed to mitigate such systematic uncertainties by using a new type of neural network called adversarial neural network (ANN) that would make the discriminator less sensitive to these uncertainties, but this has not yet been demonstrated in a real-life LHC analysis. This work investigates ANNs using as a benchmark the search for the production of four top quarks, an extremely rare physics process at the LHC and one of the important processes that can prove or disprove the Standard Model. The search for four top quarks in some cases is sensitive to large systematic uncertainties. The expected cross section upper limit for four top quark production is calculated using traditional neural networks and adversarial neural networks based on simulated proton-proton collisions within the Compact Muon Solenoid detector within Large Hadron Collider, and are compared to existing results. The improvement and further considerations to the search for rare processes at the LHC will be discussed.
The D0 Silicon Microstrip Tracker Ahmed, S.N.; Aoki, M.; Åsman, B. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
04/2011, Letnik:
634, Številka:
1
Journal Article
Recenzirano
Odprti dostop
This paper describes the mechanical design, the readout chain, the production, testing and the installation of the Silicon Microstrip Tracker of the D0 experiment at the Fermilab Tevatron collider. ...In addition, we describe the performance and operational experience of the detector during the experiment data collection between 2001 and 2010.
(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image).Results are presented from a search for the electroweak production of supersymmetric particles in pp collisions in final ...states with two tau leptons. The data sample corresponds to an integrated luminosity between 18.1 fb super(-1) and 19.6 fb super(-1) depending on the final state of tau lepton decays, at ... TeV, collected by the CMS experiment at the LHC. The observed event yields in the signal regions are consistent with the expected standard model backgrounds. The results are interpreted using simplified models describing the pair production and decays of charginos or tau sleptons. For models describing the pair production of the lightest chargino, exclusion regions are obtained in the plane of chargino mass vs. neutralino mass under the following assumptions: the chargino decays into third-generation sleptons, which are taken to be the lightest sleptons, and the sleptons masses lie midway between those of the chargino and the neutralino. Chargino masses below 420 GeV are excluded at a 95% confidence level in the limit of a massless neutralino, and for neutralino masses up to 100 GeV, chargino masses up to 325 GeV are excluded at 95% confidence level. Constraints are also placed on the cross section for pair production of tau sleptons as a function of mass, assuming a massless neutralino. Figure not available: see fulltext.
(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image).Cross sections for the production of a Z boson in association with jets in proton-proton collisions at a centre-of-mass ...energy of ... TeV are measured using a data sample collected by the CMS experiment at the LHC corresponding to 19.6 fb super(-1). Differential cross sections are presented as functions of up to three observables that describe the jet kinematics and the jet activity. Correlations between the azimuthal directions and the rapidities of the jets and the Z boson are studied in detail. The predictions of a number of multileg generators with leading or next-to-leading order accuracy are compared with the measurements. The comparison shows the importance of including multi-parton contributions in the matrix elements and the improvement in the predictions when next-to-leading order terms are included. Figure not available: see fulltext.
(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image).The spectra of charged particles produced within the pseudorapidity window | eta | < 1 at ... TeV are measured using 404 mu ...b super(-1) of PbPb and 27.4 pb super(-1) of pp data collected by the CMS detector at the LHC in 2015. The spectra are presented over the transverse momentum ranges spanning 0.5 < p sub(T) < 400 GeV in pp and 0.7 < p sub(T) < 400 GeV in PbPb collisions. The corresponding nuclear modification factor, R sub(AA), is measured in bins of collision centrality. The R sub(AA) in the 5% most central collisions shows a maximal suppression by a factor of 7-8 in the p sub(T) region of 6-9 GeV. This dip is followed by an increase, which continues up to the highest p sub(T) measured, and approaches unity in the vicinity of p sub(T) = 200 GeV. The R sub(AA) is compared to theoretical predictions and earlier experimental results at lower collision energies. The newly measured pp spectrum is combined with the pPb spectrum previously published by the CMS collaboration to construct the pPb nuclear modification factor, R sub(pA), up to 120 GeV. For p sub(T) > 20 GeV, R sub(pA) exhibits weak momentum dependence and shows a moderate enhancement above unity. Figure not available: see fulltext.
(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image).A measurement of the double-differential inclusive jet cross section as a function of the jet transverse momentum p sub(T) ...and the absolute jet rapidity |y| is presented. Data from LHC proton-proton collisions at ... TeV, corresponding to an integrated luminosity of 19.7 fb super(-1), have been collected with the CMS detector. Jets are reconstructed using the anti-k sub(T) clustering algorithm with a size parameter of 0.7 in a phase space region covering jet p sub(T) from 74 GeV up to 2.5 TeV and jet absolute rapidity up to |y| = 3.0. The low-p sub(T) jet range between 21 and 74 GeV is also studied up to |y| = 4.7, using a dedicated data sample corresponding to an integrated luminosity of 5.6 pb super(-1). The measured jet cross section is corrected for detector effects and compared with the predictions from perturbative QCD at next-to-leading order (NLO) using various sets of parton distribution functions (PDF). Cross section ratios to the corresponding measurements performed at 2.76 and 7 TeV are presented. From the measured double-differential jet cross section, the value of the strong coupling constant evaluated at the Z mass is alpha sub(S)(M sub(Z))=0.1164 sub(-0.0043) super(+0.0060), where the errors include the PDF, scale, nonperturbative effects and experimental uncertainties, using the CT10 NLO PDFs. Improved constraints on PDFs based on the inclusive jet cross section measurement are presented. Figure not available: see fulltext.
(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image).The results of a first search for CP violation in the production and decay of top quark-antiquark (...) pairs are ...presented. The search is based on asymmetries in T-odd, triple-product correlation observables, where T is the time-reversal operator. The analysis uses a sample of proton-proton collisions at ... TeV collected by the CMS experiment, corresponding to an integrated luminosity of 19.7 fb super(-1). Events are selected having one electron or muon and at least four jets. The T-odd observables are measured using four-momentum vectors associated with ... production and decay. The measured asymmetries exhibit no evidence for CP-violating effects, consistent with the expectation from the standard model. Figure not available: see fulltext.
The cross section for Higgs boson production in pp collisions is studied using the H arrow right W super(+)W super(-) decay mode, followed by leptonic decays of the W bosons to an oppositely charged ...electron-muon pair in the final state. The measurements are performed using data collected by the CMS experiment at the LHC at a centre-of-mass energy of 8 TeV, corresponding to an integrated luminosity of 19.4 fb super(-1). The Higgs boson transverse momentum (p sub(T)) is reconstructed using the lepton pair p sub(T) and missing p sub(T). The differential cross section times branching fraction is measured as a function of the Higgs boson p sub(T) in a fiducial phase space defined to match the experimental acceptance in terms of the lepton kinematics and event topology. The production cross section times branching fraction in the fiducial phase space is measured to be 39 plus or minus 8 (stat) plus or minus 9 (syst) fb. The measurements are found to agree, within experimental uncertainties, with theoretical calculations based on the standard model. Figure not available: see fulltext.
(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image).A search for new particles has been conducted using events with two high transverse momentum (p sub(T)) tau leptons that ...decay hadronically, at least two high-p sub(T) jets, and missing transverse energy from the tau lepton decays. The analysis is performed using data from proton-proton collisions, collected by the CMS experiment in 2015 at ... TeV, corresponding to an integrated luminosity of 2.1 fb super(-1). The results are interpreted in two physics models. The first model involves heavy right-handed neutrinos, N sub() ( = e, mu , tau ), and right-handed charged bosons, W sub(R), arising in a left-right symmetric extension of the standard model. Masses of the W sub(R) boson below 2.35 (1.63) TeV are excluded at 95% confidence level, assuming the N sub( ) tau mass is 0.8 (0.2) times the mass of the W sub(R) boson and that only the N sub( ) tau flavor contributes to the W sub(R) decay width. In the second model, pair production of third-generation scalar leptoquarks that decay into tau tau bb is considered. Third-generation scalar leptoquarks with masses below 740 GeV are excluded, assuming a 100% branching fraction for the leptoquark decay to a tau lepton and a bottom quark. This is the first search at hadron colliders for the third-generation Majorana neutrino, as well as the first search for third-generation leptoquarks in the final state with a pair of hadronically decaying tau leptons and jets. Figure not available: see fulltext.
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