80 research outputs found
Can new heavy gauge bosons be observed in ultra-high energy cosmic neutrino events?
A wide range of models beyond the Standard Model predict charged and neutral
resonances, generically called - and -bosons, respectively. In this
paper we study the impact of such resonances on the deep inelastic scattering
of ultra-high energy neutrinos as well as on the resonant charged current
scattering (Glashow resonance). We find that the effects of
such resonances can not be observed with the Pierre Auger Observatory or any
foreseeable upgrade of it.Comment: 5 pages, 2 figure
Strange Quark PDFs and Implications for Drell-Yan Boson Production at the LHC
Global analyses of Parton Distribution Functions (PDFs) have provided
incisive constraints on the up and down quark components of the proton, but
constraining the other flavor degrees of freedom is more challenging.
Higher-order theory predictions and new data sets have contributed to recent
improvements. Despite these efforts, the strange quark PDF has a sizable
uncertainty, particularly in the small x region. We examine the constraints
from experiment and theory, and investigate the impact of this uncertainty on
LHC observables. In particular, we study W/Z production to see how the s-quark
uncertainty propagates to these observables, and examine the extent to which
precise measurements at the LHC can provide additional information on the
proton flavor structure.Comment: 14 pages, 11 figures, added reference
Impact of heavy quark and quarkonium data on nuclear gluon PDFs
A clear understanding of nuclear parton distribution functions (nPDFs) plays
a crucial role in the interpretation of collider data taken at the Relativistic
Heavy Ion Collider (RHIC), the Large Hadron Collider (LHC) and in the near
future at the Electron-Ion Collider (EIC). Even with the recent inclusions of
vector boson and light meson production data, the uncertainty of the gluon PDF
remains substantial and limits the interpretation of heavy ion collision data.
To obtain new constraints on the nuclear gluon PDF, we extend our recent
nCTEQ15WZ+SIH analysis to inclusive quarkonium and open heavy-flavor meson
production data from the LHC. This vast new data set covers a wide kinematic
range and puts strong constraints on the nuclear gluon PDF down to . The theoretical predictions for these data sets are obtained from a
data-driven approach, where proton-proton data are used to determine effective
scattering matrix elements. This approach is validated with detailed
comparisons to existing next-to-leading order (NLO) calculations in
non-relativistic QCD (NRQCD) for quarkonia and in the general-mass
variable-flavor-number scheme (GMVFNS) for the open heavy-flavored mesons. In
addition, the uncertainties from the data-driven approach are determined using
the Hessian method and accounted for in the PDF fits. This extension of our
previous analyses represents an important step toward the next generation of
PDFs not only by including new data sets, but also by exploring new methods for
future analyses
Impact of LHC vector boson production in heavy ion collisions on strange PDFs
The extraction of the strange quark parton distribution function (PDF) poses a long-standing puzzle. Measurements from neutrino-nucleus deep inelastic scattering (DIS) experiments suggest the strange quark is suppressed compared to the light sea quarks, while recent studies of W^\pm /Z boson production at the LHC imply a larger strange component at small x values. As the parton flavor determination in the proton depends on nuclear corrections, e.g. from heavy-target DIS, LHC heavy ion measurements can provide a distinct perspective to help clarify this situation. In this investigation we extend the nCTEQ nPDFs to study the impact of the LHC proton-lead W^\pm /Z production data on both the flavor differentiation and nuclear corrections. This complementary data set provides new insights on both the LHC W^\pm /Z proton analyses and the neutrino-nucleus DIS data. We identify these new nPDFs as nCTEQWZ. Our calculations are performed using a new implementation of the nCTEQ code (nCTEQ++) based on C++ which enables us to easily interface to external programs such as HOPPET, APPLgrid and MCFM. Our results indicate that, as suggested by the proton data, the small x nuclear strange sea appears larger than previously expected, even when the normalization of the W^{\pm }/Z data is accommodated in the fit. Extending the nCTEQ analysis to include LHC W^\pm /Z data represents an important step as we advance toward the next generation of nPDFs
Impact of LHC vector boson production in heavy ion collisions on strange PDFs
The extraction of the strange quark parton distribution function (PDF) poses a long-standing puzzle. Measurements from neutrino-nucleus deep inelastic scattering (DIS) experiments suggest the strange quark is suppressed compared to the light sea quarks, while recent studies of W^\pm /Z boson production at the LHC imply a larger strange component at small x values. As the parton flavor determination in the proton depends on nuclear corrections, e.g. from heavy-target DIS, LHC heavy ion measurements can provide a distinct perspective to help clarify this situation. In this investigation we extend the nCTEQ nPDFs to study the impact of the LHC proton-lead W^\pm /Z production data on both the flavor differentiation and nuclear corrections. This complementary data set provides new insights on both the LHC W^\pm /Z proton analyses and the neutrino-nucleus DIS data. We identify these new nPDFs as nCTEQWZ. Our calculations are performed using a new implementation of the nCTEQ code (nCTEQ++) based on C++ which enables us to easily interface to external programs such as HOPPET, APPLgrid and MCFM. Our results indicate that, as suggested by the proton data, the small x nuclear strange sea appears larger than previously expected, even when the normalization of the W^{\pm }/Z data is accommodated in the fit. Extending the nCTEQ analysis to include LHC W^\pm /Z data represents an important step as we advance toward the next generation of nPDFs
Electroweak top-quark pair production at the LHC with Z ′ bosons to NLO QCD in POWHEG
NLO QCD+EW predictions for HV and HV +jet production including parton-shower effects
We present the first NLO QCD+EW predictions for Higgs boson production in association with a ℓνℓ or ℓ+ℓ− pair plus zero or one jets at the LHC. Fixed-order NLO QCD+EW calculations are combined with a QCD+QED parton shower using the recently developed resonance-aware method in the POWHEG framework. Moreover, applying the improved MiNLO technique to Hℓνℓ +jet and Hℓ+ℓ− +jet production at NLO QCD+EW, we obtain predictions that are NLO accurate for observables with both zero or one resolved jet. This approach permits also to capture higher-order effects associated with the interplay of EW corrections and QCD radiation. The behavior of EW corrections is studied for various kinematic distributions, relevant for experimental analyses of Higgsstrahlung processes at the 13 TeV LHC. Exact NLO EW corrections are complemented with approximate analytic formulae that account for the leading and next-to-leading Sudakov logarithms in the high-energy regime. In the tails of transverse-momentum distributions, relevant for analyses in the boosted Higgs regime, the Sudakov approximation works well, and NLO EW effects can largely exceed the ten percent level. Our predictions are based on the POWHEG BOX RES+OpenLoops framework in combination with the Pythia 8.1 parton shower
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