67 research outputs found
Probing top quark FCNC couplings in the triple-top signal at the high energy LHC and future circular collider
Our main aim in this paper is to present detailed studies to probe the top
quark flavor changing neutral current (FCNC) interactions at , ,
and vertices in the triple-top
signal at the high energy proposal of
Large Hadron Collider (HE-LHC) and future circular hadron-hadron collider
(FCC-hh). To this end, we investigate the production of three top quarks which
arises from the FCNC couplings taken into account the fast simulation at
TeV of HE-LHC and 100 TeV of FCC-hh considering the integrated
luminosities of 10, 15 and 20 ab. All the relevant backgrounds are
considered in a cut based analysis to obtain the limits on the anomalous
couplings and the corresponding branching ratios. The obtained exclusion limits
on the coupling strengths and the branching ratios are summarized and compared
in details with the results in the literature, namely the most recent direct
LHC experimental limits and HL-LHC projections as well. We show that, for
higher energy phase of LHC, a dedicated search for the top quark FCNC couplings
can achieve much better sensitivities to the triple-top signal than other top
quark production scenarios. We found that the limits for the branching ratios
of and transitions could reach an impressive sensitivity and the
obtained 95\% CL limits are at least three orders of magnitude better than the
current LHC experimental results as well as the existing projections of HL-LHC.Comment: 18 pages, 8 figures and 6 Tables; Final version accepted for
publication in Nuclear Physics
First global QCD analysis of charged hadron fragmentation functions and their uncertainties at next-to-next-to-leading order
In this paper, we present FFs, a first global QCD analysis of
parton-to-{\it unidentified} charged hadrons fragmentation functions (FFs) at
next-to-next-to-leading order (NNLO) accuracy in perturbative QCD. This
analysis is based on single-inclusive charged hadron production in
electron-positron () annihilation. The uncertainties in the extraction
of FFs as well as the corresponding observables are estimated
using the "Hessian" technique. We study the quality of the {\tt SGK18} FFs
determined in this analysis by comparing with the recent results in literature.
We also show how {\tt SGK18} FFs results describe the available data for
single-inclusive unidentified charged hadron production in
annihilation. We demonstrate that the theoretical uncertainties due to the
variation of the renormalization and factorization scales improve when NNLO QCD
corrections are considered. We find that the resulting {\tt SGK18} FFs are in
good agreement with all data analyzed and the inclusion of NNLO corrections
tends to improve the data description with somewhat smaller uncertainty.Comment: 17 pages, 6 figures and 3 Table
Impact of unidentified light charged hadron data on the determination of pion fragmentation functions
In this paper a new comprehensive analysis of parton-to-pion fragmentation
functions (FFs) is performed for the first time by including all experimental
data sets on single inclusive pion as well as unidentified light charged hadron
production in electron-positron () annihilation. We determine the pion
FFs along with their uncertainties using the standard "Hessian" technique at
next-to-leading order (NLO) and next-to-next-to leading order (NNLO) in
perturabative QCD. It is shown that the determination of pion FFs using
simultaneously the data sets from pion and unidentified light charged hadron
productions leads to the reduction of all pion FFs uncertainties especially for
the case of strange quark and gluon FFs by significant factors. In this study,
we have quantified the constraints that these data sets could impose on the
extracted pion FFs. Our results also illustrate the significant improvement in
the precision of FFs fits achievable by inclusion of higher order corrections.
The improvements on both FFs uncertainties as well as fit quality have been
clearly discussed.Comment: 34 pages, 9 figures and 3 table
Single top quark production as a probe of anomalous and couplings at the FCC-ee
In this paper, a detailed study to probe the top quark Flavour-Changing
Neutral Currents (FCNC) and at the future
collider FCC-ee in three different center-of-mass energies of 240, 350 and 500
GeV is presented. A set of useful variables are proposed and used in a
multivariate technique to separate signal from standard model background
processes. The study includes a fast detector simulation based on the {\sc
delphes} package to consider the detector effects. The discovery
regions and the upper limits on the FCNC branching ratios at 95\% confidence
level (CL) in terms of the integrated luminosity are presented. It is shown
that with 300 fb of integrated luminosity of data, FCC-ee would be able
to exclude the effective coupling strengths above
which is corresponding to branching fraction of \%. We
show that moving to a high-luminosity regime leads to a significant improvement
on the upper bounds on the top quark FCNC couplings to a photon or a boson.Comment: 21 Pages, 6 Figures, 8 Table
Effect of symmetry breaking of polarized light sea quarks on the nucleon and nuclear structure functions, and sum rules
In this study, we performed calculations and analyses of the structure
functions of polarized nucleons and light nuclei, specifically He and
H, using second-order Feynman diagrams. Our investigation focused on two
main aspects: Firstly, we examined the symmetry properties of polarized light
sea quarks. Secondly, we conducted a detailed investigation into the impacts of
symmetry breaking on the structure functions of both nucleons and nuclei. To
achieve this, we utilized the existing polarized Parton Distribution Functions
(polarized PDFs) available in the literature. These PDFs were used to calculate
and compare the polarized structure functions and of the nuclei.
Additionally, we examined and analyzed the Bjorken and Efremov-Leader-Teryaev
sum rules by utilizing the moments of the polarized structure functions. The
Lorentz color force components, namely and , are
determined using the twist-2, twist-3, and twist-4 matrix elements. When
symmetry breaking is applied, it is observed that they have similar magnitudes
but opposite signs. Our theoretical predictions for the polarized structure
functions of nucleons and light nuclei, taking into account the symmetry
breaking of light sea quarks, exhibit better agreement with experimental data.Comment: 13 pages, 12 figures, 3 table
Probing four-fermion operators in the triple top production at future hadron colliders
In this paper, we study the triple top quark production at the future high-energy proton-proton colliders to probe the four-fermion interactions involving three top quarks. We employ the Standard Model Effective Field Theory (SMEFT) to find the upper limits at 95% CL on the Wilson coefficients of these kinds of four-fermion operators. We consider a detailed analysis with a unique signal signature of two same-sign leptons. A full simulation chain includes all the relevant backgrounds, realistic detector simulations, and a cut-based technique are taken into account. This study is presented for the HE-LHC working at the center of mass energy of 27 TeV with 15 ab −1 and FCC-hh working at the center of mass energy of 100 TeV with 30 ab −1 . We show that the future high-energy proton-proton colliders could reach an impressive sensitivity to four-fermion contact interactions involving three top quarks
Global analysis of nuclear parton distribution functions and their uncertainties at next-to-next-to-leading order
We perform a next-to-next-to-leading order (NNLO) analysis of nuclear parton distribution functions (nPDFs) using neutral current charged-lepton (ℓ±+nucleus) deeply inelastic scattering (DIS) data and Drell-Yan (DY) cross-section ratios σADY/σA′DY
for several nuclear targets. We study in detail the parametrizations and the atomic mass (A) dependence of the nuclear PDFs at this order. The present nuclear PDFs global analysis provides us a complete set of nuclear PDFs, f
(A,Z)i(x,Q2) , with a full functional dependence on x , A, Q 2
. The uncertainties of the obtained nuclear modification factors for each parton flavour are estimated using the well-known Hessian method. The nuclear charm quark distributions are also added into the analysis. We compare the parametrization results with the available data and the results of other nuclear PDFs groups. We found our nuclear PDFs to be in reasonably good agreement with them. The estimates of errors provided by our global analysis are rather smaller than those of other groups. In general, a very good agreement is achieved. We also briefly review the recent heavy-ion collisions data including the first experimental data from the LHC
proton + lead and lead + lead
run which can be used in the global fits of nuclear PDFs. We highlight different aspects of the high luminosity Pb–Pb and p–Pb data which have been recorded by the CMS Collaboration
Constraining Higgs boson effective couplings at electron-positron colliders
We probe the dimension-six operators contributing to Higgs production in association with a Z boson at
the future high-luminosity electron-positron colliders. Potential constraints on dimension-six operators in
the Higgs sector are determined by performing a shape analysis on the differential angular distribution
of the Higgs and Z boson decay products. The analysis is performed at the center-of-mass energies of 350
and 500 GeV including a realistic detector simulation and the main sources of background processes. The
68% and 95% confidence level upper limits are obtained on the contributing anomalous couplings
considering only the decay of the Higgs boson into a pair of b-quarks and leptonic Z boson decay. Our
results show that angular observables provide a great sensitivity to anomalous couplings, in particular,
at the high-luminosity regime
Effects of next-to-leading order DGLAP evolution on generalized parton distributions of the proton and deeply virtual Compton scattering at high energy
We studied the effects of NLO Q2 evolution of generalized parton distributions (GPDs) using the aligned-jet model for the singlet quark and gluon GPDs at an initial evolution scale. We found that the skewness ratio for quarks is a slow logarithmic function of Q2, reaching rS=1.5−2 at Q2=100 GeV2 and rg≈1 for gluons in a wide range of Q2. Using the resulting GPDs, we calculated the DVCS cross section on the proton in NLO pQCD and found that this model in conjunction with modern parameterizations of proton PDFs (CJ15 and CT14) provides a good description of the available H1 and ZEUS data in a wide kinematic range
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