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.
The azimuthal correlation,
Δ
ϕ
12
, of high transverse momentum jets in pp collisions at
s
=
13
TeV is studied by applying PB-TMD distributions to NLO calculations via MCatNLO together with the ...PB-TMD parton shower. A very good description of the cross section as a function of
Δ
ϕ
12
is observed. In the back-to-back region of
Δ
ϕ
12
→
π
, a very good agreement is observed with the PB-TMD Set 2 distributions while significant deviations are obtained with the PB-TMD Set 1 distributions. Set 1 uses the evolution scale while Set 2 uses transverse momentum as an argument in
α
s
, and the above observation therefore confirms the importance of an appropriate soft-gluon coupling in angular ordered parton evolution. The total uncertainties of the predictions are dominated by the scale uncertainties of the matrix element, while the uncertainties coming from the PB-TMDs and the corresponding PB-TMD shower are very small. The
Δ
ϕ
12
measurements are also compared with predictions using MCatNLO together
Pythia
8, illustrating the importance of details of the parton shower evolution.
Azimuthal correlations in
Z
+
jet production at large transverse momenta are computed by matching Parton-Branching (PB) TMD parton distributions and showers with NLO calculations via MCatNLO. The ...predictions are compared with those for dijet production in the same kinematic range. The azimuthal correlations
Δ
ϕ
between the Z boson and the leading jet are steeper compared to those in dijet production at transverse momenta
O
(
100
)
GeV , while they become similar for very high transverse momenta
O
(
1000
)
GeV . The different patterns of
Z
+
jet and dijet azimuthal correlations can be used to search for potential
factorization-breaking
effects in the back-to-back region, which depend on the different color and spin structure of the final states and their interferences with the initial states. In order to investigate these effects experimentally, we propose to measure the ratio of the distributions in
Δ
ϕ
for
Z
+
jet- and multijet production at low and at high transverse momenta, and compare the results to predictions obtained assuming factorization. We examine the role of theoretical uncertainties by performing variations of the factorization scale, renormalization scale and matching scale. In particular, we present a comparative study of matching scale uncertainties in the cases of PB-TMD and collinear parton showers.
Abstract Azimuthal correlations in $$\mathrm {Z} +$$ Z + jet production at large transverse momenta are computed by matching Parton-Branching (PB) TMD parton distributions and showers with NLO ...calculations via MCatNLO. The predictions are compared with those for dijet production in the same kinematic range. The azimuthal correlations $$\Delta \phi $$ Δ ϕ between the Z boson and the leading jet are steeper compared to those in dijet production at transverse momenta $$\mathcal{O}(100)$$ O ( 100 ) GeV , while they become similar for very high transverse momenta $${{\mathcal {O}}}(1000)$$ O ( 1000 ) GeV . The different patterns of $$\mathrm {Z} +$$ Z + jet and dijet azimuthal correlations can be used to search for potential factorization-breaking effects in the back-to-back region, which depend on the different color and spin structure of the final states and their interferences with the initial states. In order to investigate these effects experimentally, we propose to measure the ratio of the distributions in $$\Delta \phi $$ Δ ϕ for $$\mathrm {Z} +$$ Z + jet- and multijet production at low and at high transverse momenta, and compare the results to predictions obtained assuming factorization. We examine the role of theoretical uncertainties by performing variations of the factorization scale, renormalization scale and matching scale. In particular, we present a comparative study of matching scale uncertainties in the cases of PB-TMD and collinear parton showers.
Azimuthal correlations in Formula omittedjet production at large transverse momenta are computed by matching Parton-Branching (PB) TMD parton distributions and showers with NLO calculations via ...MCatNLO. The predictions are compared with those for dijet production in the same kinematic range. The azimuthal correlations Formula omitted between the Z boson and the leading jet are steeper compared to those in dijet production at transverse momenta Formula omitted GeV, while they become similar for very high transverse momenta Formula omitted GeV . The different patterns of Formula omittedjet and dijet azimuthal correlations can be used to search for potential factorization-breaking effects in the back-to-back region, which depend on the different color and spin structure of the final states and their interferences with the initial states. In order to investigate these effects experimentally, we propose to measure the ratio of the distributions in Formula omitted for Formula omittedjet- and multijet production at low and at high transverse momenta, and compare the results to predictions obtained assuming factorization. We examine the role of theoretical uncertainties by performing variations of the factorization scale, renormalization scale and matching scale. In particular, we present a comparative study of matching scale uncertainties in the cases of PB-TMD and collinear parton showers.
Abstract
Azimuthal correlations in
$$\mathrm {Z} +$$
Z
+
jet production at large transverse momenta are computed by matching Parton-Branching (PB) TMD parton distributions and showers with NLO ...calculations via MCatNLO. The predictions are compared with those for dijet production in the same kinematic range. The azimuthal correlations
$$\Delta \phi $$
Δ
ϕ
between the Z boson and the leading jet are steeper compared to those in dijet production at transverse momenta
$$\mathcal{O}(100)$$
O
(
100
)
GeV , while they become similar for very high transverse momenta
$${{\mathcal {O}}}(1000)$$
O
(
1000
)
GeV . The different patterns of
$$\mathrm {Z} +$$
Z
+
jet and dijet azimuthal correlations can be used to search for potential
factorization-breaking
effects in the back-to-back region, which depend on the different color and spin structure of the final states and their interferences with the initial states. In order to investigate these effects experimentally, we propose to measure the ratio of the distributions in
$$\Delta \phi $$
Δ
ϕ
for
$$\mathrm {Z} +$$
Z
+
jet- and multijet production at low and at high transverse momenta, and compare the results to predictions obtained assuming factorization. We examine the role of theoretical uncertainties by performing variations of the factorization scale, renormalization scale and matching scale. In particular, we present a comparative study of matching scale uncertainties in the cases of PB-TMD and collinear parton showers.
In this study, we present our latest findings regarding azimuthal
distributions in vector boson + jets and multi-jet production at the Large
Hadron Collider (LHC). These findings result from matching ...next-to-leading
order (NLO) perturbative matrix elements with transverse momentum dependent
(TMD) parton branching. We conduct a comprehensive comparative analysis of
azimuthal correlations between Z boson-jet and jet-jet systems in the
back-to-back region. These distinct azimuthal correlation patterns can help
identify potential factorization-breaking effects in this region. Such effects
depend on the different color and spin structures of the final states and their
interactions with the initial states.
We discuss our recent results on azimuthal distributions in vector boson + jets and multi-jet production at the LHC, obtained from the matching of next-to-leading order (NLO) perturbative matrix ...elements with transverse momentum dependent (TMD) parton branching. We present a comparative analysis of boson-jet and jet-jet correlations in the back to-back region, and a study of the theoretical systematic uncertainties associated with the matching scale in the cases of TMD and collinear parton showers.
Azimuthal correlations in Z+jet production at large transverse momenta are computed by matching Parton - Branching (PB) TMD parton distributions and showers with NLO calculations via MCatNLO. The ...predictions are compared with those for dijet production in the same kinematic range. The azimuthal correlations \(\Delta\phi\) between the Z boson and the leading jet are steeper compared to those in dijet production at transverse momenta \({\cal O}(100)\) GeV, while they become similar for very high transverse momenta \({\cal O}(1000)\) GeV. The different patterns of Z+jet and dijet azimuthal correlations can be used to search for potential {\it factorization - breaking} effects in the back-to-back region, which depend on the different color and spin structure of the final states and their interferences with the initial states. In order to investigate these effects experimentally, we propose to measure the ratio of the distributions in \(\Delta\phi\) for Z+jet - and multijet production at low and at high transverse momenta, and compare the results to predictions obtained assuming factorization. We examine the role of theoretical uncertainties by performing variations of the factorization scale, renormalization scale and matching scale. In particular, we present a comparative study of matching scale uncertainties in the cases of PB-TMD and collinear parton showers.
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