Abstract:We present phenomenological results for vector boson pair production at the LHC, obtained using the parton-level next-to-leading order program MCFM. We include the implementation of a new process in the code, pp → γγ, and important updates to existing processes. We incorporate fragmentation contributions in order to allow for the experimental isolation of photons in γγ, W γ, and Zγ production and also account for gluon-gluon initial state contributions for all relevant processes. We present results for a varie… Show more
“…Cross sections are calculated for the dominant diboson and top-quark processes as follows: the inclusive WW cross section is calculated to NLO in α S with MCFM [51]; nonresonant gluon fusion is calculated and modeled to leading order (LO) in α S with GG2VV, including both WW and ZZ production and their interference; tt production is normalized to the calculation at next-to-next-to-leading order (NNLO) in α S with resummation of higher-order terms to the next-to-next-to-leading logarithms (NNLL), evaluated with TOP++2.0 [52]; and single-top processes are normalized to NNLL following the calculations from Refs. [53][54][55] for the s-channel, t-channel, and Wt processes, respectively.…”
We report the observation of Higgs boson decays to WW Ã based on an excess over background of 6.1 standard deviations in the dilepton final state, where the Standard Model expectation is 5.8 standard deviations. Evidence for the vector-boson fusion (VBF) production process is obtained with a significance of 3.2 standard deviations. The results are obtained from a data sample corresponding to an integrated luminosity of 25 fb −1 from ffiffi ffi s p ¼ 7 and 8 TeV pp collisions recorded by the ATLAS detector at the LHC. For a Higgs boson mass of 125.36 GeV, the ratio of the measured value to the expected value of the total production cross section times branching fraction is 1.09 þ0.
“…Cross sections are calculated for the dominant diboson and top-quark processes as follows: the inclusive WW cross section is calculated to NLO in α S with MCFM [51]; nonresonant gluon fusion is calculated and modeled to leading order (LO) in α S with GG2VV, including both WW and ZZ production and their interference; tt production is normalized to the calculation at next-to-next-to-leading order (NNLO) in α S with resummation of higher-order terms to the next-to-next-to-leading logarithms (NNLL), evaluated with TOP++2.0 [52]; and single-top processes are normalized to NNLL following the calculations from Refs. [53][54][55] for the s-channel, t-channel, and Wt processes, respectively.…”
We report the observation of Higgs boson decays to WW Ã based on an excess over background of 6.1 standard deviations in the dilepton final state, where the Standard Model expectation is 5.8 standard deviations. Evidence for the vector-boson fusion (VBF) production process is obtained with a significance of 3.2 standard deviations. The results are obtained from a data sample corresponding to an integrated luminosity of 25 fb −1 from ffiffi ffi s p ¼ 7 and 8 TeV pp collisions recorded by the ATLAS detector at the LHC. For a Higgs boson mass of 125.36 GeV, the ratio of the measured value to the expected value of the total production cross section times branching fraction is 1.09 þ0.
“…We reconstruct jets using the anti-k T algorithm from FastJet [53][54][55] with R anti−k T = 0.4, which gives us a very moderate geometric separation of two jets. When dealing with photons in a QCD environment some familiar subtleties have to be considered [56][57][58][59][60][61]: a photon can arise from non-perturbative fragmentation. Those photons are not useful in our case since our focus is obviously not on QED corrections to multi-jet production rates.…”
Staircase and Poisson scaling are two typical patterns we observe for the exclusive number of jets at high energy hadron colliders. We examine these scaling properties for photon plus jets production at the LHC and find that this channel is well suited to study these features. We illustrate and discuss when to expect each of the two patterns, how to induce a transition through kinematic cuts, and how photons are related to heavy gauge bosons. Measurements of photon+jets production is therefore providing valuable information on exclusive jet scaling, which is going to help to eventually understand the theoretical origin of exclusive jet scaling properties in more detail.
“…For the same rapidity range, the POWHEG+PYTHIA pp simulation predicts 94.0 ± 4.7 nb after scaling with the number of nucleons in the Pb nucleus (A = 208), which agrees with the measured value. The left hand-side of Figure 2 shows the differential cross section of Z boson production as a function of rapidity in the center-of-mass frame compared to predictions from MCFM generator [17]. The MCFM predictions are calculated with MSTW2008NLO [18] free proton PDF set with and without the nuclear modification from EPS09 [19] or DSSZ [20] nPDF sets and scaled by A.…”
The electroweak boson production is an important benchmark measurement in ultra-relativistic heavyion collisions which can provide constraints on the nuclear parton distribution functions. In this paper the first results from the proton-lead collision data taken in early 2013 are presented. The Z boson production cross section is measured in the muon decay channel in bins of transverse momentum and rapidity together with the forward-backward ratio. The W production is studied in the muon and electron decay channels and the differential cross sections, lepton-charge and forward-backward asymmetries are computed as a function of the lepton pseudorapidity. All results are compared with theory predictions with and without nuclear modification of the parton distribution functions showing hints of nuclear effects.
Presented at QM2014 Quark Matter 2014Nuclear Physics A 00 (2014)
AbstractThe electroweak boson production is an important benchmark measurement in ultra-relativistic heavy-ion collisions which can provide constraints on the nuclear parton distribution functions. In this paper the first results from the proton-lead collision data taken in early 2013 are presented. The Z boson production cross section is measured in the muon decay channel in bins of transverse momentum and rapidity together with the forward-backward ratio. The W production is studied in the muon and electron decay channels and the differential cross sections, lepton-charge and forward-backward asymmetries are computed as a function of the lepton pseudorapidity. All results are compared with theory predictions with and without nuclear modification of the parton distribution functions showing hints of nuclear effects.
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