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1. chinaXiv:201609.01016 [pdf]

Next-to-Leading Order Differential Cross Sections for J/ψ,ψ(2S), and Υ Production in Proton-Proton Collisions at a Fixed-Target Experiment Using the LHC Beams (AFTER@LHC)

Yu Feng; Jian-Xiong Wang
Subjects: Physics >> Nuclear Physics

Using nonrelativistic QCD (NRQCD) factorization, we calculate the yields for?J/ψ,?ψ(2S)?and?Υ(1S)hadroproduction at?s√=?72 GeV and 115 GeV including the next-to-leading order QCD corrections. Both these center-of-mass energies correspond to those obtained with 7~TeV and 2.76~TeV nucleon beam impinging a fixed target. We study the cross section integrated in?pt?as a function of the rapidity as well as the?pt?differential cross section in the central rapidity region. Using different NLO fit results of the NRQCD long-distance matrix elements, we evaluate a theoretical uncertainty which is certainly much larger than the projected experimental uncertainties with the expected 20 fb?1?to be collected per year with AFTER@LHC.

submitted time 2016-09-14 Hits289Downloads169 Comment 0

2. chinaXiv:201609.00971 [pdf]

Concept for a Future Super Proton-Proton Collider

Jingyu Tang; J. Scott Berg; Weiping Chai; Fusan Chen; Nian Chen; Weiren Chou; HaiyiDong; Jie Gao; Tao Han; Yongbin Leng; Guangrui Li; Ramesh Gupta; Peng Li; Zhihui Li; Baiqi Liu; Yudong Liu; Xinchou Lou; Qing Luo; Ernie Malamud; Lijun Mao
Subjects: Physics >> Nuclear Physics

Following the discovery of the Higgs boson at LHC, new large colliders are being studied by the international high-energy community to explore Higgs physics in detail and new physics beyond the Standard Model. In China, a two-stage circular collider project CEPC-SPPC is proposed, with the first stage CEPC (Circular Electron Positron Collier, a so-called Higgs factory) focused on Higgs physics, and the second stage SPPC (Super Proton-Proton Collider) focused on new physics beyond the Standard Model. This paper discusses this second stage.

submitted time 2016-09-14 Hits652Downloads393 Comment 0

3. chinaXiv:201609.00886 [pdf]

Method study of parameter choice for a circular proton–proton collider

SU Feng; GAO Jie; XIAO Ming; WANG Dou; WANG Yi-Wei; BAI Sha; BIAN Tian-Jian
Subjects: Physics >> Nuclear Physics

In this paper we showed a systematic method of appropriate parameter choice for a circular pp collider by using analytical expression of beam-beam tune shift limit started from given design goal and technical limitations. A parameter space has been explored. Based on parameters scan and considerations from RF systems, a set of appropriate parameter designed for a 50Km and a 100Km circular proton-proton collider was proposed.

submitted time 2016-09-13 Hits602Downloads350 Comment 0

4. chinaXiv:201609.00829 [pdf]

Search for supersymmetry in events with soft leptons, low jet multiplicity, and missing transverse energy in proton–proton collisions at $\sqrt{s}$=8?TeV

Khachatryan, Vardan and others
Subjects: Physics >> Nuclear Physics

Results are presented from a search for supersymmetric particles in scenarios with a compressed mass spectrum. The data sample corresponds to 19.7 inverse femtobarns of proton-proton collisions recorded by the CMS experiment at sqrt(s) = 8 TeV. The search targets top squark pair production in scenarios with mass differences Delta m = m(top squark) - m(neutralino) below the W-boson mass and with top-squark decays in the four-body mode (top squark to b l nu neutralino), where the neutralino is assumed to be the lightest supersymmetric particle (LSP). The signature includes a high transverse momentum (pt) jet associated with initial-state radiation, one or two low-pt leptons, and significant missing transverse energy. The event yields observed in data are consistent with the expected background contributions from standard model processes. Limits are set on the cross section for top squark pair production as a function of the top squark and LSP masses. Assuming a 100% branching fraction for the four-body decay mode, top-squark masses below 316 GeV are excluded for Delta m = 25 GeV at 95% CL. The dilepton data are also interpreted under the assumption of chargino-neutralino production, with subsequent decays to sleptons or sneutrinos. Assuming a difference between the common lightest chargino/next lightest neutralino mass and the LSP mass of 20 GeV and a tau-enriched decay scenario, masses in the range m(chargino) < 307 GeV are excluded at 95% CL.

submitted time 2016-09-12 Hits1175Downloads691 Comment 0

5. chinaXiv:201609.00819 [pdf]

Search for new phenomena with photon+jet events in proton-proton collisions at $ \sqrt{s}=13 $ TeV with the ATLAS detector

Aad, Georges and others
Subjects: Physics >> Nuclear Physics

A search is performed for the production of high-mass resonances decaying into a photon and a jet in 3.2 fb?1?of proton--proton collisions at a centre-of-mass energy of?s√=13?TeV collected by the ATLAS detector at the Large Hadron Collider. Selected events have an isolated photon and a jet, each with transverse momentum above 150 GeV. No significant deviation of the?γ+jet invariant mass distribution from the background-only hypothesis is found. Limits are set at 95% confidence level on the cross sections of generic Gaussian-shaped signals and of a few benchmark phenomena beyond the Standard Model: excited quarks with vector-like couplings to the Standard Model particles, and non-thermal quantum black holes in two models of extra spatial dimensions. The minimum excluded visible cross sections for Gaussian-shaped resonances with width-to-mass ratios of 2% decrease from about 6 fb for a mass of 1.5 TeV to about 0.8 fb for a mass of 5 TeV. The minimum excluded visible cross sections for Gaussian-shaped resonances with width-to-mass ratios of 15% decrease from about 50 fb for a mass of 1.5 TeV to about 1.0 fb for a mass of 5 TeV. Excited quarks are excluded below masses of 4.4 TeV, and non-thermal quantum black holes are excluded below masses of 3.8 (6.2) TeV for Randall--Sundrum (Arkani-Hamed--Dimopoulous--Dvali) models with one (six) extra dimensions.

submitted time 2016-09-12 Hits1349Downloads754 Comment 0

6. chinaXiv:201609.00809 [pdf]

Measurement of the transverse momentum and $\phi ^*_\eta $ distributions of Drell–Yan lepton pairs in proton–proton collisions at $\sqrt{s}=8$ ?TeV with the ATLAS detector

Aad, Georges and others
Subjects: Physics >> Nuclear Physics

Distributions of transverse momentum?pllT?and the angular variable???η?of Drell--Yan lepton pairs are measured in 20.3 fb?1?of proton--proton collisions at?s√=8?TeV with the ATLAS detector at the LHC. Measurements in electron-pair and muon-pair final states are corrected for detector effects and combined. Compared to previous measurements in proton--proton collisions at?s√=7?TeV, these new measurements benefit from a larger data sample and improved control of systematic uncertainties. Measurements are performed in bins of lepton-pair mass above, around and below the Z-boson mass peak. The data are compared to predictions from perturbative and resummed QCD calculations. For values of???η<1?the predictions from the Monte Carlo generator ResBos are generally consistent with the data within the theoretical uncertainties. However, at larger values of???η?this is not generally the case. Monte Carlo generators based on the parton-shower approach are unable to describe the data over the full range of?pllT?and the fixed-order prediction of DYNNLO falls below the data at high values of?pllT. ResBos and the parton-shower Monte Carlo generators provide a much better description of the evolution of the???η?and?pllT?distributions as a function of lepton-pair mass and rapidity.

submitted time 2016-09-12 Hits1343Downloads764 Comment 0

7. chinaXiv:201609.00804 [pdf]

Search for narrow resonances decaying to dijets in proton-proton collisions at $\sqrt{s} =$ 13 TeV

Khachatryan, Vardan and others
Subjects: Physics >> Nuclear Physics

A search for narrow resonances in proton-proton collisions at sqrt(s) = 13 TeV is presented. The invariant mass distribution of the two leading jets is measured with the CMS detector using a data set corresponding to an integrated luminosity of 2.4 inverse femtobarns. The highest observed dijet mass is 6.1 TeV. The distribution is smooth and no evidence for resonant particles is observed. Upper limits at 95% confidence level are set on the production cross section for narrow resonances with masses above 1.5 TeV. When interpreted in the context of specific models, the limits exclude string resonances with masses below 7.0 TeV, scalar diquarks below 6.0 TeV, axigluons and colorons below 5.1 TeV, excited quarks below 5.0 TeV, color-octet scalars below 3.1 TeV, and W' bosons below 2.6 TeV. These results significantly extend previously published limits.

submitted time 2016-09-12 Hits1246Downloads713 Comment 0

8. chinaXiv:201609.00801 [pdf]

Measurement of the dependence of transverse energy production at large pseudorapidity on the hard-scattering kinematics of proton-proton collisions at $\sqrt{s} = 2.76$ TeV with ATLAS

Aad, Georges and others
Subjects: Physics >> Nuclear Physics

The relationship between jet production in the central region and the underlying-event activity in a pseudorapidity-separated region is studied in 4.0 pb?1?of?s√=2.76?TeV?pp?collision data recorded with the ATLAS detector at the LHC. The underlying event is characterised through measurements of the average value of the sum of the transverse energy at large pseudorapidity downstream of one of the protons, which are reported here as a function of hard-scattering kinematic variables. The hard scattering is characterised by the average transverse momentum and pseudorapidity of the two highest transverse momentum jets in the event. The dijet kinematics are used to estimate, on an event-by-event basis, the scaled longitudinal momenta of the hard-scattered partons in the target and projectile beam-protons moving toward and away from the region measuring transverse energy, respectively. Transverse energy production at large pseudorapidity is observed to decrease with a linear dependence on the longitudinal momentum fraction in the target proton and to depend only weakly on that in the projectile proton. The results are compared to the predictions of various Monte Carlo event generators, which qualitatively reproduce the trends observed in data but generally underpredict the overall level of transverse energy at forward pseudorapidity.

submitted time 2016-09-12 Hits206Downloads118 Comment 0

9. chinaXiv:201609.00800 [pdf]

Search for dark matter and unparticles produced in association with a Z boson in proton-proton collisions at $\sqrt{s}=$ 8??TeV

Khachatryan, Vardan and others
Subjects: Physics >> Nuclear Physics

A search for evidence of particle dark matter (DM) and unparticle production at the LHC has been performed using events containing two charged leptons, consistent with the decay of a Z boson, and large missing transverse momentum. This study is based on data collected with the CMS detector corresponding to an integrated luminosity of 19.7 inverse femtobarns of pp collisions at the LHC at a center-of-mass energy of 8 TeV. No significant excess of events is observed above the number expected from the standard model contributions. The results are interpreted in terms of 90% confidence level limits on the DM-nucleon scattering cross section, as a function of the DM particle mass, for both spin-dependent and spin-independent scenarios. Limits are set on the effective cutoff scale Lambda, and on the annihilation rate for DM particles, assuming that their branching fraction to quarks is 100%. Additionally, the most stringent 95% confidence level limits to date on the unparticle model parameters are obtained.

submitted time 2016-09-12 Hits1312Downloads730 Comment 0

10. chinaXiv:201609.00795 [pdf]

Evidence for single top-quark production in the $s$-channel in proton-proton collisions at $\sqrt{s}=$8 TeV with the ATLAS detector using the Matrix Element Method

Aad, Georges and others
Subjects: Physics >> Nuclear Physics

This Letter presents evidence for single top-quark production in the?s-channel using proton-proton collisions at a centre-of-mass energy of 8 TeV with the ATLAS detector at the CERN Large Hadron Collider. The analysis is performed on events containing one isolated electron or muon, large missing transverse momentum and exactly two?b-tagged jets in the final state. The analysed data set corresponds to an integrated luminosity of 20.3 fb?1. The signal is extracted using a maximum-likelihood fit of a discriminant which is based on the matrix element method and optimized in order to separate single-top-quark?s-channel events from the main background contributions, which are top-quark pair production and?W?boson production in association with heavy-flavour jets. The measurement leads to an observed signal significance of 3.2 standard deviations and a measured cross-section of?σs=4.8±0.8(stat.)+1.6?1.3(syst.) pb, which is consistent with the Standard Model expectation. The expected significance for the analysis is 3.9 standard deviations.

submitted time 2016-09-12 Hits368Downloads194 Comment 0

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