789 research outputs found
Parallelizations on products of spheres and octonionic geometry
No full textA classical theoremof Kervaire states that products of spheres are parallelizable if and only if at least one of the factors has odd dimension. Two explicit parallelizations on Sm × S2h−1 seem to be quite natural, and have been previously studied by the first named author in [32]. The present paper is devoted to the three choices G = G2, Spin(7), Spin(9) of G-structures on Sm × S2h−1, respectively with m + 2h − 1 = 7, 8, 16 and related with octonionic geometry
Multi-Parton Interactions at the LHC.
Get PDFWe review the recent progress in the theoretical description and experimental observation of multiple parton interactions. Subjects covered include experimental measurements of minimum bias in- teractions and of the underlying event, models of soft physics implemented in Monte Carlo generators, developments in the theoretical description of multiple parton interactions and phenomenological studies of double parton scattering. This article stems from contributions presented at the Helmholtz Alliance workshop on ”Multi-Parton Interactions at the LHC”, DESY Hamburg, 13-15 September 2010
Monte Carlo studies of BFKL Physics
Get PDFWe study the properties of the BFKL evolution of a (-channel gluon exchange in the high-energy limit. In particular we formulate a solution to the BFKL evolution equation in terms of an explicit sum over emitted gluons, which allows for a Monte Carlo integration of the resulting rapidity ordered multi-gluon phase space. This formulation allows for an introduction of the running of the coupling to the BFKL evolution. More importantly, the Monte Carlo implementation of the solution to the BFKL evolution equation allows for studies of the exclusive final states resulting from the exchange. The full control over the gluon radiation allows for energy and momentum conservation to be observed when calculating the hadronic cross sections. This is in contrast to the standard analytic approach to BFKL physics, which solves the BFKL equation by effectively summing over any number of gluons emitted and integrating over the full rapidity ordered allowed phase space. It is therefore impossible to reconstruct the parton momentum fractions exactly, and thus energy and longitudinal momentum conservation is violated. Although the effect is indeed formally subleading, we show that the numerical impact at present and planned collider energies is very significant. The reduction in parton flux due to the increased energy consumption by the BFKL evolution is sufficient to change the parton level result of an exponential rise of the dijet cross section as a function of the rapidity separation of the leading dijets to a situation much like the LO case. However, we identify the azimuthal correlation between the dijets as an observable sensitive to BFKL effects but more stable under the observation of energy and momentum conservation. We also apply the BFKL MC to a study of dijets at the Tevatron. Finally we consider W + 2-jet production, a process which in the limit of large rapidity separation between the two jets exhibit the same factorisation into two impact factors and a (-channel gluon exchange as dijet production. We identify observables in this setup, for which BFKL effects could be important
Inclusive Jet Cross Sections in Proton-Proton Collisions at 7.0 TeV Center-of-Mass Energy with the ATLAS Detector at the Large Hadron Collider
Get PDFInclusive jet cross sections are measured using the full 2010 ATLAS data set, corresponding to approximately 37 pb-1 of proton-proton collisions at a center-of-mass energy of 7 TeV provided by the Large Hadron Collider. The cross sections are dened using the anti-kt algorithm with two jet size parameters, R = 0.6 and R = 0.4, and shown as a function of jet transverse momentum and rapidity. The measurements extend to a maximum transverse momentum of 1.5 TeV and a maximum absolute rapidity of 4.4, far surpassing previous inclusive jet analyses. The cross sections are corrected for detector effects and compared to predictions from next-to-leading order perturbative quantum chromodynamics that are corrected for the non-perturbative eects of hadronization and underlying event. Comparisons are made to predictions obtained from a variety of modern parton distribution functions. Good agreement is seen across the full measured range, validating the theory in a new kinematic region. Small discrepancies in the high transverse momentum and high rapidity regions indicate the utility of including this data in the derivation of future parton distribution functions
Inclusive W and Z production in the forward region at √s=7TeV
Get PDFMeasurements of inclusive W and Z boson production cross-sections in pp collisions at s√=7TeV using final states containing muons are presented. The data sample corresponds to an integrated luminosity of 37 pb−1 collected with the LHCb detector. The W and Z bosons are reconstructed from muons with a transverse momentum above 20 GeV/c and pseudorapidity between 2.0 and 4.5, and, in the case of the Z cross-section, a dimuon invariant mass between 60 and 120 GeV/c2. The cross-sections are measured to be 831 ± 9 ± 27 ± 29pb for W +, 656 ± 8 ± 19 ± 23 for W − and 76.7 ± 1.7 ± 3.3 ± 2.7pb for Z, where the first uncertainty is statistical, the second is systematic and the third is due to the luminosity. Differential cross-sections, W and Z cross-section ratios and the lepton charge asymmetry are also measured in the same kinematic region. The ratios are determined to be σW+→μ+ν/σW−→μ−ν−=1.27±0.02±0.01 and (σW+→μ+ν+σW−→μ−ν−)/σZ→μμ=19.4±0.5±0.9 . The results are in general agreement with theoretical predictions, performed at next-to-next-to-leading order in QCD using recently calculated parton distribution functions
Richard Clayderman
No full text1.Autumn leaves /Cosma - Mercier - Prevert +2.Desperado /P. de Senneville +3.We are the world /L. Ritchie - M. Jackson +4.Let it be /Lennon - McCartney +5.I will always love you /Dolly Parton +6.Ballade pour Adeline /P. de Senneville +7.Moonlight sonata /Beethoven +8.(Everything I do) I do it for you /Adams - Lange - Kamen +9.Up where we belong /Jennings - Saint Marie - Nitzsche +10.Unchained melody /Zaret - Mitchell - North +11.Don't cry for me Argentina /A.L. Webber - Tim Rice +12.West side story /Bernstein - Sondhei
Evidence for the 125 GeV Higgs boson decaying to a pair of τ leptons
Get PDFOpen Access. This article is distributed under the terms of the Creative Commons Attribution License (CC-BY 4.0), which permits any use, distribution and reproduction in any medium, provided the original author(s) and source are credited.A search for a standard model Higgs boson decaying into a pair of τ leptons is performed using events recorded by the CMS experiment at the LHC in 2011 and 2012. The dataset corresponds to an integrated luminosity of 4.9 fb−1 at a centre-of-mass energy of 7 TeV and 19.7 fb−1 at 8 TeV. Each τ lepton decays hadronically or leptonically to an electron or a muon, leading to six different final states for the τ -lepton pair, all considered in this analysis. An excess of events is observed over the expected background contributions, with a local significance larger than 3 standard deviations for m H values between 115 and 130 GeV. The best fit of the observed H → τ τ signal cross section times branching fraction for m H = 125 GeV is 0.78 ± 0.27 times the standard model expectation. These observations constitute evidence for the 125 GeV Higgs boson decaying to a pair of τ leptons
A parton branching with transverse momentum dependent splitting functions
No full textAbstract: Off-shell, transverse-momentum dependent splitting functions can be defined from the high-energy limit of partonic decay amplitudes. Based on these splitting functions, we construct Sudakov form factors and formulate a new parton branching algorithm. We present a first Monte Carlo implementation of the algorithm. We use the numerical results to verify explicitly momentum sum rules for TMD parton distributions. (C) 2022 The Author(s). Published by Elsevier B.V
Parton distributions with threshold resummation
Get PDFWe construct a set of parton distribution functions (PDFs) in which fixed-order NLO and NNLO calculations are supplemented with soft-gluon (threshold) resummation up to NLL and NNLL accuracy respectively, suitable for use in conjunction with any QCD calculation in which threshold resummation is included at the level of partonic cross sections. These resummed PDF sets, based on the NNPDF3.0 analysis, are extracted from deep-inelastic scattering, Drell-Yan, and top quark pair production data, for which resummed calculations can be consistently used. We find that, close to threshold, the inclusion of resummed PDFs can partially compensate the enhancement in resummed matrix elements, leading to resummed hadronic cross-sections closer to the fixed-order calculation. On the other hand, far from threshold, resummed PDFs reduce to their fixed-order counterparts. Our results demonstrate the need for a consistent use of resummed PDFs in resummed calculations.We construct a set of parton distribution functions (PDFs) in which fixed-order NLO and NNLO calculations are supplemented with soft-gluon (threshold) resummation up to NLL and NNLL accuracy respectively, suitable for use in conjunction with any QCD calculation in which threshold resummation is included at the level of partonic cross sections. These resummed PDF sets, based on the NNPDF3.0 analysis, are extracted from deep-inelastic scattering, Drell-Yan, and top quark pair production data, for which resummed calculations can be consistently used. We find that, close to threshold, the inclusion of resummed PDFs can partially compensate the enhancement in resummed matrix elements, leading to resummed hadronic cross-sections closer to the fixed-order calculations. On the other hand, far from threshold, resummed PDFs reduce to their fixed-order counterparts. Our results demonstrate the need for a consistent use of resummed PDFs in resummed calculations.We construct a set of parton distribution functions (PDFs) in which fixed-order NLO and NNLO calculations are supplemented with soft-gluon (threshold) resummation up to NLL and NNLL accuracy respectively, suitable for use in conjunction with any QCD calculation in which threshold resummation is included at the level of partonic cross sections. These resummed PDF sets, based on the NNPDF3.0 analysis, are extracted from deep-inelastic scattering, Drell-Yan, and top quark pair production data, for which resummed calculations can be consistently used. We find that, close to threshold, the inclusion of resummed PDFs can partially compensate the enhancement in resummed matrix elements, leading to resummed hadronic cross-sections closer to the fixed-order calculation. On the other hand, far from threshold, resummed PDFs reduce to their fixed-order counterparts. Our results demonstrate the need for a consistent use of resummed PDFs in resummed calculations
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