CASCADE3 A Monte Carlo event generator based on TMDs Baranov, S.; Bermudez Martinez, A.; Estevez Banos, L. I. ...
The European physical journal. C, Particles and fields,
05/2021, Letnik:
81, Številka:
5
Journal Article
Recenzirano
Odprti dostop
The
Cascade3
Monte Carlo event generator based on Transverse Momentum Dependent (TMD) parton densities is described. Hard processes which are generated in collinear factorization with LO multileg or ...NLO parton level generators are extended by adding transverse momenta to the initial partons according to TMD densities and applying dedicated TMD parton showers and hadronization. Processes with off-shell kinematics within
k
t
-factorization, either internally implemented or from external packages via LHE files, can be processed for parton showering and hadronization. The initial state parton shower is tied to the TMD parton distribution, with all parameters fixed by the TMD distribution.
It has been observed in the literature that measurements of low-mass Drell–Yan (DY) transverse momentum spectra at low center-of-mass energies
s
are not well described by perturbative QCD ...calculations in collinear factorization in the region where transverse momenta are comparable with the DY mass. We examine this issue from the standpoint of the Parton Branching (PB) method, combining next-to-leading-order (NLO) calculations of the hard process with the evolution of transverse momentum dependent (TMD) parton distributions. We compare our predictions with experimental measurements at low DY mass, and find very good agreement. In addition we use the low mass DY measurements at low
s
to determine the width
q
s
of the intrinsic Gauss distribution of the PB-TMDs at low evolution scales. We find values close to what has earlier been used in applications of PB-TMDs to high-energy processes at the Large Hadron Collider (LHC) and HERA. We find that at low DY mass and low
s
even in the region of
p
T
/
m
DY
∼
1
the contribution of multiple soft gluon emissions (included in the PB-TMDs) is essential to describe the measurements, while at larger masses (
m
DY
∼
m
Z
) and LHC energies the contribution from soft gluons in the region of
p
T
/
m
DY
∼
1
is small.
Transverse momentum dependent (TMD) parton distributions obtained from the parton branching (PB) method are combined with next-to-leading-order (NLO) calculations of Drell-Yan (DY) production. We ...apply the MC@NLO method for the hard process calculation and matching with the PB TMDs. We compute predictions for the transverse momentum, rapidity, and ϕ* spectra of Z-bosons. We find that the theoretical uncertainties of the predictions are dominated by the renormalization and factorization scale dependence, while the impact of TMD uncertainties is moderate. The theoretical predictions agree well, within uncertainties, with measurements at the Large Hadron Collider (LHC). In particular, we study the region of lowest transverse momenta at the LHC, and comment on its sensitivity to nonperturbative TMD contributions.
A common library, TMDlib2, for Transverse-Momentum-Dependent distributions (TMDs) and unintegrated parton distributions (uPDFs) is described, which allows for easy access of commonly used TMDs and ...uPDFs, providing a three-dimensional (3D) picture of the partonic structure of hadrons. The tool TMDplotter allows for web-based plotting of distributions implemented in TMDlib2, together with collinear pdfs as available in LHAPDF.
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