Precision determination of electroweak parameters and the strange content of the proton from neutrino deep-inelastic scattering

100

The production of a W boson in association with a single charm quark is studied using 4.6 fb −1 of pp collision data at √ s = 7 TeV collected with the ATLAS detector at the Large Hadron Collider. In events in which a W boson decays to an electron or muon, the charm quark is tagged either by its semileptonic decay to a muon or by the presence of a charmed meson. The integrated and differential cross sections as a function of the pseudorapidity of the lepton from the W -boson decay are measured. Results are compared to the predictions of next-to-leading-order QCD calculations obtained from various parton distribution function parameterisations. The ratio of the strange-to-down sea-quark distributions is determined to be 0.96 +0.26−0.30 at Q 2 = 1.9 GeV 2 , which supports the hypothesis of an SU(3)-symmetric composition of the light-quark sea. Additionally, the cross-section ratio σ(W + +c)/σ(W − +c) is compared to the predictions obtained using parton distribution function parameterisations with different assumptions about the s-s quark asymmetry.Keywords: Electroweak interaction, Hadron-Hadron Scattering, Charm physics Conclusion 43The ATLAS collaboration 50 IntroductionThe production of a W boson in association with a single charm quark in proton-proton collisions is described at leading order (LO) in perturbative quantum chromodynamics (QCD) by the scattering of a gluon and a down-type quark (d, s, b). The relative contribution from each of the three families in the initial state is determined by the parton distribution functions (PDF) of the proton and by the quark-mixing matrix elements V cd , V cs and V cb . In proton-proton collisions at a centre-of-mass energy of √ s = 7 TeV, gs → W − c and gs → W +c production channels are dominant, while the reaction initiated by a d-quark contributes about 10% [1], being suppressed by the quark-mixing matrix element V cd . The contribution of processes that include b-quarks is negligible. The next-to-leading-order (NLO) QCD terms [2] are dominated by one-loop corrections to the subprocess gs → W c and the tree-level 2 → 3 processes gg → sW c and qs → qW c. Processes with charm quarks in the initial state are not considered for this analysis as explained in section 9.2. Since the gs → W c process and its higher-order corrections are dominant, the pp → W cX production is directly sensitive to the s-quark distribution function in the proton at momentum-transfer values on the order of the W -boson mass (m W ).The s-quark PDF has been determined by neutrino-nucleon deep inelastic scattering (DIS) experiments [3,4] at momentum transfer squared Q 2 ∼ 10 GeV 2 and momentum fraction x ∼ 0.1. However, the interpretation of these data is sensitive to the modelling of c-quark fragmentation and nuclear corrections; some analyses [5][6][7] indicate that the squark sea is suppressed relative to the d-quark sea at all values of x while others [8] suggest that SU(3) symmetry is restored as x decreases. A recent joint analysis of inclusive W and -1 - JHEP05(2014)068Z producti...

Section: Jhep05(2014)068mentioning

confidence: 98%

mentioning

confidence: 98%

Measurement of the production of a W boson in association with a charm quark in pp collisions at $ \sqrt{s} $ = 7 TeV with the ATLAS detector

Aad

Abajyan

Abbott

et al. 2014

100

“…In a series of papers [3][4][5][6][7][8][9][10][11][12][13] we have introduced a methodology aimed at reducing as much as possible this procedural uncertainty, up to the point that it can be neglected in comparison to the remaining data and theory uncertainty. However, as data become more abundant and precise, and theoretical calculations more accurate, a full characterization of the procedural uncertainties becomes necessary.…”

Section: Jhep04(2015)040mentioning

confidence: 99%

Parton distributions for the LHC run II

Ball

Bertone

Carrazza

et al. 2015

Self Cite

1,950

1,814

We present NNPDF3.0, the first set of parton distribution functions (PDFs) determined with a methodology validated by a closure test. NNPDF3.0 uses a global dataset including HERA-II deep-inelastic inclusive cross-sections, the combined HERA charm data, jet production from ATLAS and CMS, vector boson rapidity and transverse momentum distributions from ATLAS, CMS and LHCb, W +c data from CMS and top quark pair production total cross sections from ATLAS and CMS. Results are based on LO, NLO and NNLO QCD theory and also include electroweak corrections. To validate our methodology, we show that PDFs determined from pseudo-data generated from a known underlying law correctly reproduce the statistical distributions expected on the basis of JHEP04(2015)040the assumed experimental uncertainties. This closure test ensures that our methodological uncertainties are negligible in comparison to the generic theoretical and experimental uncertainties of PDF determination. This enables us to determine with confidence PDFs at different perturbative orders and using a variety of experimental datasets ranging from HERA-only up to a global set including the latest LHC results, all using precisely the same validated methodology. We explore some of the phenomenological implications of our results for the upcoming 13 TeV Run of the LHC, in particular for Higgs production cross-sections.

“…As can be seen, while the differences in the cross sections are moderate in the low 9 As we make the choice of using parton cross sections and PDFs that are consistently taken at the same perturbative order, we will not consider two other parameterizations, CTEQ [83] and NNPDF [84], which provide PDF sets only at NLO. 10 The NNLO PDF sets can be found at [87].…”

Section: Jhep03(2011)055mentioning

confidence: 99%

Higgs production at the lHC

Baglio

Djouadi

2011

172

194

Abstract:We analyze the production of Higgs particles at the early stage of the CERN large Hadron Collider with a 7 TeV center of mass energy (lHC). We first consider the case of the Standard Model Higgs boson that is mainly produced in the gluon-gluon fusion channel and to be detected in its decays into electroweak gauge bosons, gg → H → W W, ZZ, γγ. The production cross sections at √ s = 7 TeV and the decay branching ratios, including all relevant higher order QCD and electroweak corrections, are evaluated. An emphasis is put on the various theoretical uncertainties that affect the production rates: the significant uncertainties from scale variation and from the parametrization of the parton distribution functions as well as the uncertainties which arise due to the use of an effective field theory in the calculation of the next-to-next-to-leading order corrections. The parametric uncertainties stemming from the values of the strong coupling constant and the heavy quark masses in the Higgs decay branching ratios, which turn out to be non-negligible, are also discussed. The implications for different center of mass energies of the proton collider, √ s = 8-10 TeV as well as for the design energy √ s = 14 TeV, are briefly summarized. We then discuss the production of the neutral Higgs particles of the Minimal Supersymmetric extension of the Standard Model in the two main channels: gluon-gluon and bottom quark fusion leading to Higgs bosons which subsequently decay into tau lepton or b-quark pairs, gg, bb → Higgs → τ + τ − , bb. The Higgs production cross sections at the lHC and the decay branching ratios are analyzed. The associated theoretical uncertainties are found to be rather large and will have a significant impact on the parameter space of the model that can be probed.