scholarly journals Cuts for two-body decays at colliders

2021 ◽  
Vol 2021 (11) ◽  
Author(s):  
Gavin P. Salam ◽  
Emma Slade
Keyword(s):  
Cross Sections ◽  
Linear Dependence ◽  
Gluon Fusion ◽  
Perturbative Expansion ◽  
Perturbative Calculations ◽  
Perturbative Series ◽  
Quadratic Dependence ◽  
Poor Convergence ◽  
Fixed Order

Abstract Fixed-order perturbative calculations of fiducial cross sections for two-body decay processes at colliders show disturbing sensitivity to unphysically low momentum scales and, in the case of H → γγ in gluon fusion, poor convergence. Such problems have their origins in an interplay between the behaviour of standard experimental cuts at small transverse momenta (pt) and logarithmic perturbative contributions. We illustrate how this interplay leads to a factorially divergent structure in the perturbative series that sets in already from the first orders. We propose simple modifications of fiducial cuts to eliminate their key incriminating characteristic, a linear dependence of the acceptance on the Higgs or Z-boson pt, replacing it with quadratic dependence. This brings major improvements in the behaviour of the perturbative expansion. More elaborate cuts can achieve an acceptance that is independent of the Higgs pt at low pt, with a variety of consequent advantages.

scholarly journals PERTURBATIVE EXPANSION OF τ HADRONIC SPECTRAL FUNCTION MOMENTS

2014 ◽  
Vol 35 ◽  
pp. 1460442
Author(s):  
DIOGO BOITO
Keyword(s):  
Perturbation Theory ◽  
Renormalization Group ◽  
Systematic Study ◽  
Higher Order ◽  
Perturbative Expansion ◽  
Main Stream ◽  
Spectral Functions ◽  
Perturbative Series ◽  
Fixed Order ◽  
Adler Function

In the extraction of αs from hadronic τ decay data several moments of the spectral functions have been employed. Furthermore, different renormalization group improvement (RGI) frameworks have been advocated, leading to conflicting values of αs. Recently, we performed a systematic study of the perturbative behavior of these moments in the context of the two main-stream RGI frameworks: Fixed Order Perturbation Theory (FOPT) and Contour Improved Perturbation Theory (CIPT). The yet unknown higher order coefficients of the perturbative series were modelled using the available knowledge of the renormalon singularities of the QCD Adler function. We were able to show that within these RGI frameworks some of the commonly employed moments should be avoided due to their poor perturbative behavior. Furthermore, under reasonable assumptions about the higher order behavior of the perturbative series FOPT provides the preferred RGI framework.

scholarly journals Collinear expansion for color singlet cross sections

2020 ◽  
Vol 2020 (9) ◽  
Author(s):  
Markus A. Ebert ◽  
Bernhard Mistlberger ◽  
Gherardo Vita
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Production Cross ◽  
Gluon Fusion ◽  
Building Blocks ◽  
Color Singlet ◽  
Final State ◽  
Beam Function ◽  
Kinematic Limit ◽  
State Radiation

Abstract We demonstrate how to efficiently expand cross sections for color-singlet production at hadron colliders around the kinematic limit of all final state radiation being collinear to one of the incoming hadrons. This expansion is systematically improvable and applicable to a large class of physical observables. We demonstrate the viability of this technique by obtaining the first two terms in the collinear expansion of the rapidity distribution of the gluon fusion Higgs boson production cross section at next-to-next-to leading order (NNLO) in QCD perturbation theory. Furthermore, we illustrate how this technique is used to extract universal building blocks of scattering cross section like the N-jettiness and transverse momentum beam function at NNLO.

scholarly journals Fiducial cross sections for the lepton-pair-plus-photon decay mode in Higgs production up to NNLO QCD

2022 ◽  
Vol 2022 (1) ◽  
Author(s):  
X. Chen ◽  
T. Gehrmann ◽  
E. W. N. Glover ◽  
A. Huss
Keyword(s):  
Higgs Boson ◽  
Decay Mode ◽  
Cross Sections ◽  
Gluon Fusion ◽  
Lepton Pair ◽  
Distinctive Features ◽  
Photon Decay ◽  
Higgs Decay ◽  
Decay Products ◽  
Three Body

Abstract The rare three-body decay of a Higgs boson to a lepton-antilepton pair and a photon is starting to become experimentally accessible at the LHC. We investigate how higher-order QCD corrections to the dominant gluon-fusion production process impact on the fiducial cross sections in this specific Higgs decay mode for electrons and muons. Corrections up to NNLO QCD are found to be sizeable. They are generally uniform in kinematical variables related to the Higgs boson, but display several distinctive features in the kinematics of its individual decay products.

scholarly journals PROBING THE ANOMALOUS COUPLINGS OF THE TOP QUARK WITH GLUON AT THE LHC AND TEVATRON

2013 ◽  
Vol 28 (37) ◽  
pp. 1350170 ◽  
Author(s):  
HODA HESARI ◽  
MOJTABA MOHAMMADI NAJAFABADI
Keyword(s):  
Production Rate ◽  
Cross Sections ◽  
Top Quark ◽  
Dipole Moments ◽  
Gluon Fusion ◽  
Fusion Process ◽  
Small Range ◽  
Anomalous Couplings ◽  
Text Production ◽  
Measured Ratio

In this paper, we study the sensitivity of the fraction of [Formula: see text] events arising from gluon–gluon fusion to the chromoelectric and chromomagnetic dipole moments (CEDM and CMDM) as well as the total and differential [Formula: see text] cross-sections at the LHC and Tevatron. The sensitivity of measured charged asymmetry at the LHC to CEDM and CMDM is also studied. We find that at the Tevatron and the LHC, nonzero values of CMDM could suppress the [Formula: see text] production rate. It is shown that the ratio of [Formula: see text] at the Tevatron is more sensitive to CEDM and CMDM than the LHC case. The presence of CEDM always increases the contribution of gluon–gluon fusion process in top pair rate at the Tevatron and LHC. Except for a small range of CMDM, the presence of CEDM and CMDM can increase the fraction of gluon–gluon fusion at the Tevatron and LHC. The measured ratio of [Formula: see text] at the Tevatron is used to derive bounds on the chromoelectric and chromomagnetic dipole moments as well as the total and differential [Formula: see text] cross-sections at the LHC and Tevatron, and the measured charged asymmetry at the LHC. The combination of [Formula: see text] and σ LHC provides stringent limits on CMDM and CEDM.

scholarly journals Production of prompt photons associated with jets at LHC in kT-factorization

2019 ◽  
Vol 222 ◽  
pp. 03015
Author(s):  
Maxim Malyshev ◽  
Artem Lipatov ◽  
Hannes Jung
Keyword(s):  
Monte Carlo ◽  
Cross Sections ◽  
Parton Shower ◽  
Gluon Fusion ◽  
Monte Carlo Generator ◽  
Hadronic Jets ◽  
Factorization Approach ◽  
Associated Production ◽  
Parton Showering ◽  
Collinear Limit

We use the kT–factorization approach to calculate total and differential cross sections of associated production of prompt photons and hadronic jets at the LHC energies. Our consideration relies on the pegasus Monte-Carlo generator with implemented ℴ(αα2s) off-shell gluon–gluon fusion subprocess g*g* → γqq− and several subleading quark-initiated contributions from ℴ(ααs) and ℴ(αα2s) subprocesses, taken into account in the collinear limit. Using Monte-Carlo generators CASCADE and PYTHIA, we investigate parton showering effects and compare our predictions with the data, taken by CMS and ATLAS collaborations at the LHC. We demostrate reasonabledescription of the data and the importance of parton shower effects in the kT–factorization.

scholarly journals Measurements of top-quark pair spin correlations in the $$e\mu $$ channel at $$\sqrt{s} = 13$$ TeV using pp collisions in the ATLAS detector

2020 ◽  
Vol 80 (8) ◽  
Author(s):  
M. Aaboud ◽  
◽  
G. Aad ◽  
B. Abbott ◽  
D. C. Abbott ◽  
...  
Keyword(s):  
Cross Sections ◽  
Differential Cross ◽  
Top Quark ◽  
Hadron Collider ◽  
Atlas Detector ◽  
Absolute Difference ◽  
Opening Angle ◽  
Differential Cross Sections ◽  
Spin Correlations ◽  
Fixed Order

Abstract A measurement of observables sensitive to spin correlations in $$t\bar{t}$$tt¯ production is presented, using 36.1 $$\hbox {fb}^{-1}$$fb-1 of pp collision data at $$\sqrt{s} = 13$$s=13 TeV recorded with the ATLAS detector at the Large Hadron Collider. Differential cross-sections are measured in events with exactly one electron and one muon with opposite-sign electric charge as a function of the azimuthal opening angle and the absolute difference in pseudorapidity between the electron and muon candidates in the laboratory frame. The azimuthal opening angle is also measured as a function of the invariant mass of the $$t\bar{t}$$tt¯ system. The measured differential cross-sections are compared to predictions by several NLO Monte Carlo generators and fixed-order calculations. The observed degree of spin correlation is somewhat higher than predicted by the generators used. The data are consistent with the prediction of one of the fixed-order calculations at NLO, but agree less well with higher-order predictions. Using these leptonic observables, a search is performed for pair production of supersymmetric top squarks decaying into Standard Model top quarks and light neutralinos. Top squark masses between 170 and 230 GeV are largely excluded at the 95% confidence level for kinematically allowed values of the neutralino mass.

Dissociation and Charge Transfer of CO21+ and CO22+ Ions in Collisions with Neutral Atoms and Molecules

1977 ◽  
Vol 32 (6) ◽  
pp. 555-557 ◽  
Author(s):  
A. Müller ◽  
E. Salzborn
Keyword(s):  
Charge Transfer ◽  
Electron Capture ◽  
Cross Section ◽  
Cross Sections ◽  
Impact Energy ◽  
Linear Dependence ◽  
Hard Sphere ◽  
Single Electron Capture ◽  
Target Particle ◽  
Total Collision

AbstractCross sections for single electron capture by CO22+ ions as well as total collision cross sections σi,tot (i=1, 2) for CO21+ and CO22+ ions in He, Ne, Ar, Kr, Xe, H2, O2, N2, CH4 and CO2 gases have been measured at 10 keV impact energy. σ2,1 varies between 4.5·10-17cm2 for the He and 1.8·10·15cm2 for the CO, target. On the average, σ2,1,tot is 1.6 times larger than σ1,tot and shows a nearly linear dependence on the gaskinetic hard sphere cross section of the target particle. The largest observed value of σ2,tot is 9.4·10-15cm2 for the CO2 target.

The relation between the undercooling and the growth rate of YBa2Cu3O6+x superconductive oxide

1996 ◽  
Vol 11 (5) ◽  
pp. 1094-1100 ◽  
Author(s):  
Y. Nakamura ◽  
A. Endo ◽  
Y. Shiohara
Keyword(s):  
Growth Rate ◽  
Crystal Growth ◽  
Linear Dependence ◽  
Mass Flux ◽  
Peritectic Reaction ◽  
Screw Dislocations ◽  
Quadratic Dependence

To clarify the effect of undercooling on the crystal growth of Y-123, the growth rate was measured with different undercoolings. The growth rate of the {100} face shows a quadratic dependence of undercooling, while that of the {001} face shows a linear dependence in the sample with nominal 123 composition. In the case with 211-rich composition, the growth rate of each face was larger than that compared with nominal 123 composition since the mass flux from 211 particle for peritectic reaction becomes large. Addition of excess 211 alters the undercooling dependence of Ra from quadratic to linear. It is considered that the entrapment of 211 particles into 123 crystals supplies step sources beside screw dislocations. The growth rate of the {001} face is larger than that of the {100} face up to 26° of undercooling.

GLUON SATURATION AND THE TOTAL PROTON-AIR CROSS SECTION

2010 ◽  
Vol 19 (08n10) ◽  
pp. 1685-1689
Author(s):  
F. CARVALHO ◽  
F. O. DURÃES ◽  
S. SZPIGEL ◽  
F. S. NAVARRA
Keyword(s):  
Simple Model ◽  
Cross Section ◽  
Cross Sections ◽  
Cosmic Ray ◽  
Dipole Model ◽  
Perturbative Calculations ◽  
Experimental Cross ◽  
Energy Behavior ◽  
Gluon Saturation

In this work we propose a simple model for the total proton-air cross section, which is an improvement of the minijet model with the inclusion of a window in the pT-spectrum associated to the saturation physics. Our approach introduces a natural cutoff for the perturbative calculations which modifies the energy behavior of this component. The saturated component is calculated with a dipole model. The results are compared with experimental cross sections measured in cosmic ray experiments.

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