References of "Dixon, L. J."
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See detailMissing energy and jets for supersymmetry searches
Bern, Zvi; Diana, Giovanni UL; Dixon, L. J. et al

in Physical Review D (2013), 87(3), 034026

We extend our investigation of backgrounds to new physics signals, following CMS’s data-driven search for supersymmetry at the LHC. The aim is to use different sets of cuts in γ+3-jet production to ... [more ▼]

We extend our investigation of backgrounds to new physics signals, following CMS’s data-driven search for supersymmetry at the LHC. The aim is to use different sets of cuts in γ+3-jet production to predict the irreducible Z+3-jet background (with the Z boson decaying to neutrinos) to searches with E̸T+3-jet signal topologies. We compute ratios of Z+3-jet to γ+3-jet production cross sections and kinematic distributions at next-to-leading order (NLO) in αs. We compare these ratios with those obtained using a parton shower matched to leading-order matrix elements (ME+PS). This study extends our previous work [Bern et al., Phys. Rev. D 84 114002 (2011)] on the Z+2-jet to γ+2-jet ratio. We find excellent agreement with the ratio determined from the earlier NLO results involving two instead of three jets, and agreement to within 10% between the NLO and ME+PS results for the ratios. We also examine the possibility of large QCD logarithms in these processes. Ratios of Z+n-jet to γ+n-jet cross sections are plausibly less sensitive to such corrections than the cross sections themselves. Their effect on estimates of Z+3-jet to γ+3-jet ratios can be assessed experimentally by measuring the γ+3-jet to γ+2-jet production ratio in search regions. We partially address the question of potentially large electroweak logarithms by computing the real-emission part of the electroweak corrections to the ratio using ME+PS and find that it is 1% or less. Our estimate of the remaining theoretical uncertainties in the Z to γ ratio is in agreement with our earlier study. [less ▲]

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See detailNLO vector boson production with light jets
Bern, Z.; Diana, Giovanni UL; Dixon, L. J. et al

in Il Nuovo Cimento (2012), 35(3), 25-28

In this contribution we present recent progress in the computation of next-to-leading order (NLO) QCD corrections for the production of an electroweak vector boson in association with jets at hadron ... [more ▼]

In this contribution we present recent progress in the computation of next-to-leading order (NLO) QCD corrections for the production of an electroweak vector boson in association with jets at hadron colliders. We focus on results obtained using the virtual matrix element library BlackHat [1] in conjunction with SHERPA [2, 3, 4], focusing on results relevant to understanding the background to top production. [less ▲]

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See detailFour-jet production at the Large Hadron Collider at next-to-leading order in QCD
Bern, Z.; Diana, Giovanni UL; Dixon, L. J. et al

in Physical Review Letters (2012), 109(4), 042001

We present the cross sections for production of up to four jets at the Large Hadron Collider, at next-to-leading order in the QCD coupling. We use the BlackHat library in conjunction with SHERPA and a ... [more ▼]

We present the cross sections for production of up to four jets at the Large Hadron Collider, at next-to-leading order in the QCD coupling. We use the BlackHat library in conjunction with SHERPA and a recently developed algorithm for assembling primitive amplitudes into color-dressed amplitudes. We adopt the cuts used by ATLAS in their study of multijet events in pp collisions at √s=7  TeV. We include estimates of nonperturbative corrections and compare to ATLAS data. We store intermediate results in a framework that allows the inexpensive computation of additional results for different choices of scale or parton distributions. [less ▲]

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See detailDriving missing data at next-to-leading order
Bern, Zvi; Diana, Giovanni UL; Dixon, L. J. et al

in Physical Review D (2011), 84(11), 114002

The prediction of backgrounds to new-physics signals in topologies with large missing transverse energy and jets is important to new-physics searches at the LHC. Following a CMS study, we investigate ... [more ▼]

The prediction of backgrounds to new-physics signals in topologies with large missing transverse energy and jets is important to new-physics searches at the LHC. Following a CMS study, we investigate theoretical issues in using measurements of γ+2-jet production to predict the irreducible background to searches for missing energy plus two jets that originates from Z+2-jet production where the Z boson decays to neutrinos. We compute ratios of γ+2-jet to Z+2-jet production cross sections and kinematic distributions at next-to-leading order in αs, as well as using a parton shower matched to leading-order matrix elements. The former ratios rely on the first next-to-leading-order calculation of γ+2-jet production at a hadron collider. We find that the ratios obtained in the two approximations are quite similar, making γ+2-jet production a theoretically reliable estimator for the missing energy plus two jets background. We employ a Frixione-style photon isolation, but we also show that for isolated prompt-photon production at high transverse momentum the difference between this criterion and the standard-cone isolation used by CMS is small. [less ▲]

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See detailLeft-handed W bosons at the LHC
Bern, Z.; Diana, Giovanni UL; Dixon, L. J. et al

in Physical Review D (2011), 84(3), 034008

The production of W bosons in association with jets is an important background to new physics at the LHC. Events in which the W carries large transverse momentum and decays leptonically lead to large ... [more ▼]

The production of W bosons in association with jets is an important background to new physics at the LHC. Events in which the W carries large transverse momentum and decays leptonically lead to large missing energy and are of particular importance. We show that the left-handed nature of the W coupling, combined with valence quark domination at a pp machine, leads to a large left-handed polarization for both W+ and W- bosons at large transverse momenta. The polarization fractions are very stable with respect to QCD corrections. The leptonic decay of the W± bosons translates the common left-handed polarization into a strong asymmetry in transverse momentum distributions between positrons and electrons and between neutrinos and antineutrinos (missing transverse energy). Such asymmetries may provide an effective experimental handle on separating W+jets from top-quark production, which exhibits very little asymmetry due to C invariance, and from various types of new physics. [less ▲]

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