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MIT-CTP 4150 SB/F/380-10
Saclay IPhT T10/???
Vector Boson + Jets with BlackHat and Sherpa
C. F. Berger', Z. Bernb, L. J. Dixonc, F. Febres Corderod, D. Fordeef, T. Gleisbergc, H. Itab,
D. A. Kosowerg, D. Maitre h*
'Center for Theoretical Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
bDepartment of Physics and Astronomy, UCLA, Los Angeles, CA 90095-1547, USA
CSLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94309, USA
dUniversidad Simon Bolivar, Departamento de Fisica, Caracas 1080A, Venezuela
'Theory Division, Physics Department, CERN, CH 1211 Geneva 23, Switzerland
fNIKHEF Theory Group, Science Park 105, NL 1098 XG Amsterdam, The Netherlands
gInstitut de Physique Th6orique, CEA Saclay, F 91191 Gif-sur-Yvette cedex, France
hDepartment of Physics, University of Durham, DH1 3LE, UK
We review recent NLO QCD results for W, Z+3-jet production at hadron colliders, computing using BLACKHAT
and SHERPA, and including also some new results for Z + 3-jet production for the LHC at 7 TeV. We report
new progress towards the NLO cross section for W + 4-jet production. In particular, we show that the virtual
matrix elements produced by BLACKHAT are numerically stable. We also show that with an improved integrator
and tree-level matrix elements from BLACKHAT, SHERPA produces well-behaved real-emission contributions.
As an illustration, we present the real-emission contributions including dipole-subtraction terms to the PT
distribution of the fourth jet, for a single subprocess with the maximum number of gluons.
In the coming years a major theoretical task
will be to provide reliable predictions for hard-
scattering processes at the LHC. The start of the
LHC era in particle physics opens new opportu-
nities to confront data with theoretical predic-
tions at scales well beyond those probed in pre-
vious colliders. The first observation at the LHC
of W-boson production in association with jets
marks an important milestone. Processes involv-
ing vector bosons are central to the physics pro-
gram of the LHC. They are backgrounds to Higgs
and top physics, as well as to many signals of
new physics. Theoretical predictions can play an
important role in experimentally-driven determi-
nations of backgrounds, improving extrapolations
to signal regions. Z and W production can play
complementary roles in such determinations of
backgrounds. At low luminosity, W production
can be used to calibrate estimates of Z produc-
tion, because its cross section is higher; while at
high luminosity, Z production can be used to cal-
ibrate W production because of the cleanliness
of measuring lepton pairs. The good theoretical
understanding of vector-boson production also al-
lows its use to measure the luminosity.
Next-to-leading-order (NLO) QCD is a key tool
for confronting theory with experiment. This or-
der in perturbation theory is the first to provide
quantitatively reliable results, as it is the first
order at which quantum corrections compensate
the renormalization- and factorization-scale de-
pendence in the strong coupling a8. That scale
dependence in leading-order (LO) predictions in-
creases with the number of jets because of the
increasing number of powers of a,. At LO the
scale dependence can be quite large, on the order
of 50% for three or more jets. Furthermore, LO
results may not model the shapes of distributions
correctly. Although NLO computations are more
challenging, in general they yield results with bet-
ter reliability and agreement with measurements
Work supported in part by US Department of Energy contract DE-AC02-76SF00515.
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Berger, C.F.; /MIT, LNS; Bern, Z.; /UCLA; Dixon, Lance J.; /SLAC et al. Vector Boson Jets with BlackHat and Sherpa, article, August 25, 2010; [California]. (https://digital.library.unt.edu/ark:/67531/metadc1012228/m1/1/: accessed March 24, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.