scholarly journals C-parameter hadronisation in the symmetric 3-jet limit and impact on $$\alpha _s$$ fits

2021 ◽  
Vol 81 (2) ◽  
Author(s):  
Gionata Luisoni ◽  
Pier Francesco Monni ◽  
Gavin P. Salam
Keyword(s):  
Strong Coupling ◽  
Event Shape ◽  
Coupling Constant ◽  
Dominant Effect ◽  
Perturbative Methods ◽  
Lepton Colliders ◽  
Range Of Functions ◽  
New Perspective ◽  
The Impact ◽  
Soft Radiation

AbstractHadronisation corrections are crucial in extractions of the strong coupling constant ($$\alpha _s$$ α s ) from event-shape distributions at lepton colliders. Although their dynamics cannot be understood rigorously using perturbative methods, their dominant effect on physical observables can be estimated in singular configurations sensitive to the emission of soft radiation. The differential distributions of some event-shape variables, notably the C parameter, feature two such singular points. We analytically compute the leading non-perturbative correction in the symmetric three-jet limit for the C parameter, and find that it differs by more than a factor of two from the known result in the two-jet limit. We estimate the impact of this result on strong coupling extractions, considering a range of functions to interpolate the hadronisation correction in the region between the 2 and 3-jet limits. Fitting data from ALEPH and JADE, we find that most interpolation choices increase the extracted $$\alpha _{s}$$ α s , with effects of up to $$4\%$$ 4 % relative to standard fits. This brings a new perspective on the long-standing discrepancy between certain event-shape $$\alpha _s$$ α s fits and the world average.

Comparison of coupling constant by using momentum spectra and event shape variables in different interactions

2020 ◽  
Vol 98 (10) ◽  
pp. 900-906
Author(s):  
R. Saleh-Moghaddam ◽  
M.E. Zomorrodian
Keyword(s):  
Quantum Chromodynamics ◽  
Strong Coupling ◽  
Event Shape ◽  
Coupling Constant ◽  
Main Text ◽  
Shape Distribution ◽  
Electron Positron ◽  
Momentum Spectra ◽  
Dispersive Model ◽  
Event Shape Distribution

We describe in this paper the quantum chromodynamics prediction to calculate the strong coupling constant by using event shape variables as well as momentum spectra. By fitting the dispersive model and employing our parameters on event shape distribution, we obtain the perturbative value of [Formula: see text] = 0.1305 ± 0.0474 and also the non-perturbative value of α0 = 0.5246 ± 0.0516 GeV for electron–proton interactions. Next, by using momentum spectra for the same interactions, we obtain αs = 0.1572 ± 0.029. Our values in both methods are consistent with those obtained from electron–positron annihilations measured previously. When we find coupling constant for different flavours, we observe that they do not affect our results considerably. This is in accordance with quantum chromodynamics theory. All these features will be explained in the main text.

Measurement of strong coupling constant from transverse momentum

2009 ◽  
Vol 87 (11) ◽  
pp. 1151-1158 ◽  
Author(s):  
Alireza Sepehri ◽  
Tooraj Ghaffary ◽  
Mohammad Ebrahim Zomorrodian
Keyword(s):  
Strong Coupling ◽  
Clustering Algorithm ◽  
Center Of Mass ◽  
Parton Model ◽  
Energy Scale ◽  
Strong Coupling Constant ◽  
Event Shape ◽  
Coupling Constant ◽  
Center Of Mass Energy ◽  
Gluon Bremsstrahlung

Data from e+e– annihilation into hadrons at the center of mass energy of 60 GeV are used to study the distribution of momentum components with respect to the jet axis. At high energies, the gluon emission that leads to three jet structures represents a gross violation of the parton model without gluons and finds a most natural interpretation if gluon bremsstrahlung is included. The coupling constant, αs, is measured by two different methods, first by employing the jet clustering algorithm introduced by the JADE group. Using this method, the strong coupling constant is found to be 0.123 ± 0.004. Next, from the event shape distributions, we extract the strong coupling constant, αs, and test its evaluation with energy scale. The results are consistent with the running of αs, expected from QCD predictions. Averaging over different observables, the value of αs is determined to be 0.121 ± 0.007.

scholarly journals Constraints on parton distributions and the strong coupling from LHC jet data

2015 ◽  
Vol 30 (31) ◽  
pp. 1546005 ◽  
Author(s):  
Juan Rojo
Keyword(s):  
Strong Coupling ◽  
State Of The Art ◽  
Distribution Functions ◽  
Coupling Constant ◽  
Hadron Colliders ◽  
Parton Distribution Functions ◽  
Jet Production ◽  
Future Developments ◽  
The Impact ◽  
First Time

Jet production at hadron colliders provides powerful constraints on the parton distribution functions (PDFs) of the proton, in particular on the gluon PDF. Jet production can also be used to extract the QCD coupling [Formula: see text] and to test its running with the momentum transfer up to the TeV region. In this review, I summarize the information on PDFs and the strong coupling that has been provided by Run I LHC jet data. First of all, I discuss why jet production is directly sensitive to the gluon and quark PDFs at large-x, and then review the state-of-the-art perturbative calculations for jet production at hadron colliders and the corresponding fast calculations required for PDF fitting. Then I present the results of various recent studies on the impact on PDFs, in particular the gluon, that have been performed using as input jet measurements from ATLAS and CMS. I also review the available determinations of the strong coupling constant based on ATLAS and CMS jet data, with emphasis on the fact that LHC jet data provides, for the first time, a direct test of the [Formula: see text] running at the TeV scale. I conclude with a brief outlook on possible future developments.

scholarly journals Measurement of the strong coupling constant αs from global event-shape variables of hadronic Z decays

1991 ◽  
Vol 255 (4) ◽  
pp. 623-633 ◽  
Author(s):  
D. Decampo ◽  
B. Deschizeaux ◽  
C. Goy ◽  
J.-P. Lees ◽  
M.-N. Minard ◽  
...  
Keyword(s):  
Strong Coupling ◽  
Strong Coupling Constant ◽  
Event Shape ◽  
Coupling Constant ◽  
Global Event ◽  
Z Decays ◽  
Hadronic Z Decays

scholarly journals THE QCD COUPLING AND PARTON DISTRIBUTIONS AT HIGH PRECISION

2010 ◽  
Vol 25 (31) ◽  
pp. 2621-2636 ◽  
Author(s):  
JOHANNES BLÜMLEIN
Keyword(s):  
Strong Coupling ◽  
High Precision ◽  
Present Status ◽  
Strong Coupling Constant ◽  
Precision Measurements ◽  
Coupling Constant ◽  
Hadron Colliders ◽  
Parton Distributions ◽  
Precision Observables ◽  
The Impact

A survey is given on the present status of the nucleon parton distributions and related precision calculations and precision measurements of the strong coupling constant [Formula: see text]. We also discuss the impact of these quantities on precision observables at hadron colliders.

scholarly journals Measurement of Strong Coupling Constant by Using Event Shape Moments in Perturbative Theory

2014 ◽  
Vol 45 (5) ◽  
pp. 1077 ◽  
Author(s):  
L. Khajooee ◽  
T. Kalalian ◽  
R. Saleh-Moghaddam ◽  
A. Sepehri ◽  
M.E. Zomorrodian
Keyword(s):  
Strong Coupling ◽  
Strong Coupling Constant ◽  
Event Shape ◽  
Coupling Constant

scholarly journals Determination of $$\alpha _{S}$$ beyond NNLO using event shape averages

2021 ◽  
Vol 81 (4) ◽  
Author(s):  
Adam Kardos ◽  
Gábor Somogyi ◽  
Andrii Verbytskyi
Keyword(s):  
Monte Carlo ◽  
Perturbative Qcd ◽  
Strong Coupling ◽  
Higher Order ◽  
Strong Coupling Constant ◽  
Monte Carlo Event ◽  
Event Shape ◽  
Coupling Constant

AbstractWe consider a method for determining the QCD strong coupling constant using fits of perturbative predictions for event shape averages to data collected at the LEP, PETRA, PEP and TRISTAN colliders. To obtain highest accuracy predictions we use a combination of perturbative $${{{\mathcal {O}}}}(\alpha _{S}^{3})$$ O ( α S 3 ) calculations and estimations of the $${{{\mathcal {O}}}}(\alpha _{S}^{4})$$ O ( α S 4 ) perturbative coefficients from data. We account for non-perturbative effects using modern Monte Carlo event generators and analytic hadronization models. The obtained results show that the total precision of the $$\alpha _{S}$$ α S determination cannot be improved significantly with the higher-order perturbative QCD corrections alone, but primarily requires a deeper understanding of the non-perturbative effects.

Exchange-Correlation Energy Densities and Response Potentials: Connection Between Two Definitions and Analytical Model for the Strong-Coupling Limit of a Stretched Bond

2019 ◽  
Author(s):  
S. Giarrusso ◽  
Paola Gori-Giorgi
Keyword(s):  
Density Functional Theory ◽  
Strong Coupling ◽  
Density Functional ◽  
Correlation Energy ◽  
Order Term ◽  
Strong Coupling Limit ◽  
Local Form ◽  
Coupling Constant ◽  
Functional Theory ◽  
Exchange Correlation

We analyze in depth two widely used definitions (from the theory of conditional probablity amplitudes and from the adiabatic connection formalism) of the exchange-correlation energy density and of the response potential of Kohn-Sham density functional theory. We introduce a local form of the coupling-constant-dependent Hohenberg-Kohn functional, showing that the difference between the two definitions is due to a corresponding local first-order term in the coupling constant, which disappears globally (when integrated over all space), but not locally. We also design an analytic representation for the response potential in the strong-coupling limit of density functional theory for a model single stretched bond.<br>

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