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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:201609.00900 [pdf]

Energy dependence of direct-quarkonium production in $pp$ collisions from fixed-target to LHC energies: complete one-loop analysis

Yu Feng; Jean-Philippe Lansberg; Jian-XiongWang
Subjects: Physics >> Nuclear Physics

We compute the energy dependence of the P_T-integrated cross section of directly produced quarkonia in pp collisions at next-to-leading order (NLO), namely up to alpha_s^3, within nonrelativistic QCD (NRQCD). Our analysis is based on the idea that the P_T-integrated and the P_T-differential cross sections can be treated as two different observables. The colour-octet NRQCD parameters needed to predict the P_T-integrated yield can thus be extracted from the fits of the P_T-differential cross sections at mid and large P_T. For the first time, the total cross section is evaluated in NRQCD at full NLO accuracy using the recent NLO fits of the P_T-differential yields at RHIC, the Tevatron and the LHC. Both the normalisation and the energy dependence of the J/psi, psi' and Upsilon(1S), we obtained, are in disagreement with the data irrespective of the fit method. The same is true if one uses CEM-like colour-octet NRQCD parameters. If, on the contrary, one disregards the colour-octet contribution, the existing data in the TeV range are well described by the alpha_s^3 contribution in the colour-singlet model --which, at alpha_s^4, however shows an unphysical energy dependence. A similar observation is made for eta(c,b). This calls for a full NNLO or for a resummation of the initial-state radiation in this channel. In any case, past claims that colour-octet transitions are dominantly responsible for low-P_T quarkonium production are not supported by our results. This may impact the interpretation of quarkonium suppression in high-energy proton-nucleus and nucleus-nucleus collisions.

submitted time 2016-09-13 Hits297Downloads160 Comment 0

3. chinaXiv:201609.00830 [pdf]

Measurement of differential and integrated fiducial cross sections for Higgs boson production in the four-lepton decay channel in pp collisions at $ \sqrt{s}=$ 7 and 8 TeV

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

Integrated fiducial cross sections for the production of four leptons via the H to 4l decays (l = e, mu) are measured in pp collisions at sqrt(s) = 7 and 8 TeV. Measurements are performed with data corresponding to integrated luminosities of 5.1 inverse femtobarns at 7 TeV, and 19.7 inverse femtobarns at 8 TeV, collected with the CMS experiment at the LHC. Differential cross sections are measured using the 8 TeV data, and are determined as functions of the transverse momentum and rapidity of the four-lepton system, accompanying jet multiplicity, transverse momentum of the leading jet, and difference in rapidity between the Higgs boson candidate and the leading jet. A measurement of the Z to 4l cross section, and its ratio to the H to 4l cross section is also performed. All cross sections are measured within a fiducial phase space defined by the requirements on lepton kinematics and event topology. The integrated H to 4l fiducial cross section is measured to be 0.56 +0.67-0.44 (stat) +0.21-0.06 (syst) fb at 7 TeV, and 1.11 +0.41-0.35 (stat) +0.14-0.10 (syst) fb at 8 TeV. The measurements are found to be compatible with theoretical calculations based on the standard model.

submitted time 2016-09-12 Hits1302Downloads748 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:201609.00823 [pdf]

Study of Z boson production in pPb collisions at $\sqrt{s} NN $=5.02TeV

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

The production of Z bosons in pPb collisions at sqrt(s[NN]) = 5.02 TeV is studied by the CMS experiment via the electron and muon decay channels. The inclusive cross section is compared to pp collision predictions, and found to scale with the number of elementary nucleon-nucleon collisions. The differential cross sections as a function of the Z boson rapidity and transverse momentum are measured. Though they are found to be consistent within uncertainty with theoretical predictions both with and without nuclear effects, the forward-backward asymmetry suggests the presence of nuclear effects at large rapidities. These results provide new data for constraining nuclear parton distribution functions.

submitted time 2016-09-12 Hits1271Downloads741 Comment 0

6. chinaXiv:201609.00822 [pdf]

Measurement of the inclusive jet cross section in pp collisions at $\sqrt{s} =$ 2.76 TeV

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

The double-differential inclusive jet cross section is measured as a function of jet transverse momentum pT and absolute rapidity y, using proton-proton collision data collected with the CMS experiment at the LHC, at a center-of-mass energy of sqrt(s) = 2.76 TeV and corresponding to an integrated luminosity of 5.43 inverse picoboarns. Jets are reconstructed within the pT range of 74 to 592 GeV and the rapidity range |y| < 3.0. The reconstructed jet spectrum is corrected for detector resolution. The measurements are compared to the theoretical prediction at next-to-leading-order QCD using different sets of parton distribution functions. This inclusive cross section measurement explores a new kinematic region and is consistent with QCD predictions.

submitted time 2016-09-12 Hits1281Downloads731 Comment 0

7. 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

8. chinaXiv:201609.00818 [pdf]

Measurement of the $ZZ$ Production Cross Section in $pp$ Collisions at $\sqrt{s} =$ 8 TeV with the ATLAS Detector

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

The?ZZ?production cross section in proton-proton collisions at 13 TeV center-of-mass energy is measured using 3.2 fb?1?of data recorded with the ATLAS detector at the Large Hadron Collider. The considered?Z?boson candidates decay to an electron or muon pair of mass 66-116 GeV. The cross section is measured in a fiducial phase space reflecting the detector acceptance. It is also extrapolated to a total phase space for?Z?bosons in the same mass range and of all decay modes, giving?16.7+2.2?2.0(stat.)+0.9?0.7(syst.)+1.0?0.7(lumi.) pb. The results agree with standard model predictions.

submitted time 2016-09-12 Hits1374Downloads772 Comment 0

9. chinaXiv:201609.00817 [pdf]

Combination of searches for $WW$, $WZ$, and $ZZ$ resonances in pp collisions at $\sqrt{s} =$ 8 TeV with the ATLAS detector

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

The ATLAS experiment at the CERN Large Hadron Collider has performed searches for new, heavy bosons decaying to?WW,?WZ?and?ZZ?final states in multiple decay channels using 20.3 fb?1?of?pp?collision data at?s√=8?TeV. In the current study, the results of these searches are combined to provide a more stringent test of models predicting heavy resonances with couplings to vector bosons. Direct searches for a charged diboson resonance decaying to WZ in the??ν?′?′?(?=μ,e) ,???qq?,??νqq??and fully hadronic final states are combined and upper limits on the rate of production times branching ratio to the?WZ?bosons are compared with predictions of an extended gauge model with a heavy?W′?boson. In addition, direct searches for a neutral diboson resonance decaying to?WW?and?ZZ?in the???qq?,??νqq?, and fully hadronic final states are combined and upper limits on the rate of production times branching ratio to the?WW?and?ZZ?bosons are compared with predictions for a heavy, spin-2 graviton in an extended Randall--Sundrum model where the Standard Model fields are allowed to propagate in the bulk of the extra dimension.

submitted time 2016-09-12 Hits1207Downloads717 Comment 0

10. chinaXiv:201609.00816 [pdf]

Search for charged Higgs bosons in the $H^\pm \rightarrow tb$ decay channel in $pp$ collisions at $\sqrt{s}=8 $ TeV using the ATLAS detector

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

Charged Higgs bosons heavier than the top quark and decaying via?H±→tb?are searched for in proton--proton collisions measured with the ATLAS experiment at?s√=8?TeV corresponding to an integrated luminosity of 20.3 fb?1. The production of a charged Higgs boson in association with a top quark,?gb→tH±, is explored in the mass range 200 to 600 GeV using multi-jet final states with one electron or muon. In order to separate the signal from the Standard Model background, analysis techniques combining several kinematic variables are employed. An excess of events above the background-only hypothesis is observed across a wide mass range, amounting to up to 2.4 standard deviations. Upper limits are set on the?gb→tH±?production cross section times the branching fraction?BR(H±→tb). Additionally, the complementary?s-channel production,?qq′→H±, is investigated through a reinterpretation of?W′→tb?searches in ATLAS. Final states with one electron or muon are relevant for?H±?masses from 0.4 to 2.0 TeV, whereas the all-hadronic final state covers the range 1.5 to 3.0 TeV. In these search channels, no significant excesses from the predictions of the Standard Model are observed, and upper limits are placed on the?qq′→H±?production cross section times the branching fraction BR(H±→tb).

submitted time 2016-09-12 Hits1267Downloads720 Comment 0

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