2,733 research outputs found
Polarization Effects in Standard Model Parton Distributions at Very High Energies
We update the earlier work of Refs. arXiv:1703.08562 and arXiv:1712.07147 on
parton distribution functions in the full Standard Model to include gauge boson
polarization, non-zero input electroweak boson PDFs and next-to-leading-order
resummation of large logarithms.Comment: 24 pages, 7 Figures. arXiv admin note: text overlap with
arXiv:1703.08562, arXiv:1806.1015
Standard Model Parton Distributions at Very High Energies
We compute the leading-order evolution of parton distribution functions for
all the Standard Model fermions and bosons up to energy scales far above the
electroweak scale, where electroweak symmetry is restored. Our results include
the 52 PDFs of the unpolarized proton, evolving according to the SU(3), SU(2),
U(1), mixed SU(2) x U(1) and Yukawa interactions. We illustrate the numerical
effects on parton distributions at large energies, and show that this can lead
to important corrections to parton luminosities at a future 100 TeV collider.Comment: 30 pages, 7 figures. Improved treatment of input PDFs at 100 GeV.
Adjusted plotting style to show features more clearly. Main results and
conclusions unchange
Standard Model Fragmentation Functions at Very High Energies
We compute the leading-order evolution of parton fragmentation functions for
all the Standard Model fermions and bosons up to energies far above the
electroweak scale, where electroweak symmetry is restored. We discuss the
difference between double-logarithmic and leading-logarithmic resummation, and
show how the latter can be implemented through a scale choice in the SU(2)
coupling. We present results for a wide range of partonic center-of-mass
energies, including the polarization of fermion and vector boson fragmentation
functions induced by electroweak evolution.Comment: 32 pages, 4 figure
Factorization and Resummation for Dijet Invariant Mass Spectra
Multijet cross sections at the LHC and Tevatron are sensitive to several
distinct kinematic energy scales. When measuring the dijet invariant mass m_jj
between two signal jets produced in association with other jets or weak bosons,
m_jj will typically be much smaller than the total partonic center-of-mass
energy Q, but larger than the individual jet masses m, such that there can be a
hierarchy of scales m << m_jj << Q. This situation arises in many new-physics
analyses at the LHC, where the invariant mass between jets is used to gain
access to the masses of new-physics particles in a decay chain. At present, the
logarithms arising from such a hierarchy of kinematic scales can only be summed
at the leading-logarithmic level provided by parton-shower programs. We
construct an effective field theory, SCET+, which is an extension of
soft-collinear effective theory that applies to this situation of hierarchical
jets. It allows for a rigorous separation of different scales in a multiscale
soft function and for a systematic resummation of logarithms of both m_jj/Q and
m/Q. As an explicit example, we consider the invariant mass spectrum of the two
closest jets in e+e- -> 3 jets. We also give the generalization to pp -> N jets
plus leptons relevant for the LHC.Comment: 37 pages, 6 figures; v2: journal versio
Drell-Yan Production at NNLL'+NNLO Matched to Parton Showers
We present results for Drell-Yan production from the GENEVA Monte-Carlo
framework. We combine the fully-differential NNLO calculation with higher-order
resummation in the 0-jettiness resolution variable. The resulting parton-level
events are further combined with parton showering and hadronization provided by
PYTHIA8. The 0-jettiness resummation is carried out to NNLL', which
consistently incorporates all singular virtual and real NNLO corrections. It
thus provides a natural perturbative connection between the NNLO calculation
and the parton shower regime, including a systematic assessment of perturbative
uncertainties. In this way, inclusive observables are correct to NNLO, up to
small power corrections in the resolution cutoff. Furthermore, the perturbative
accuracy of 0-jet-like resummation variables is significantly improved beyond
the parton shower approximation. We provide comparisons with LHC measurements
of Drell-Yan production at 7 TeV from ATLAS, CMS, and LHCb. As already observed
in collisions, for resummation-sensitive observables, the agreement
with data is noticeably improved by using a lower value of .Comment: 26 pages, 20 figure
Factorization and Endpoint Singularities in Heavy-to-Light decays
We prove a factorization theorem for heavy-to-light form factors. Our result
differs in several important ways from previous proposals. A proper separation
of scales gives hard kernels that are free of endpoint singularities. A general
procedure is described for including soft effects usually associated with the
tail of wavefunctions in hard exclusive processes. We give an operator
formulation of these soft effects using the soft-collinear effective theory,
and show that they appear at the same order in the power counting as the hard
spectator contribution.Comment: 5 pages, Added details on comparison with the literatur
- …