Measurements of top-quark pair to $Z$-boson cross-section ratios at $\sqrt s = 13, 8, 7$TeV with the ATLAS detector
M. Aaboud
,
G. Aad
(1)
,
M. Alstaty
(1)
,
M. Barbero
(1)
,
A. Calandri
(1)
,
T.P. Calvet
(1)
,
Y. Coadou
(1)
,
C. Diaconu
(1)
,
F. Djama
(1)
,
V. Ellajosyula
(1)
,
L. Feligioni
(1)
,
A. Hadef
(1)
,
G.D. Hallewell
(1)
,
F. Hubaut
(1)
,
S.J. Kahn
(1)
,
E. B. F. G. Knoops
(1)
,
E. Le Guirriec
(1)
,
K. Liu
(1)
,
D. Madaffari
(1)
,
E. Monnier
(1)
,
S. Muanza
(1)
,
E. Nagy
(1)
,
P. Pralavorio
(1)
,
Y. Rodina
(1)
,
A. Rozanov
(1)
,
M. Talby
(1)
,
T. Theveneaux-Pelzer
(1)
,
R.E. Ticse Torres
(1)
,
S. Tisserant
(1)
,
J. Toth
(1)
,
F. Touchard
(1)
,
L. Vacavant
(1)
,
R. Wolff
(1)
,
D. Boumediene
(2)
,
E. Busato
(2)
,
D. Calvet
(2)
,
S. Calvet
(2)
,
A.R. Chomont
(2)
,
J. Donini
(2)
,
S. Ganguly
(2)
,
Ph. Gris
(2)
,
R. Madar
(2)
,
D. Pallin
(2)
,
S.M. Romano Saez
(2)
,
C. Santoni
(2)
,
F. Vazeille
(2)
,
N. Berger
(3)
,
A.M. Burger
(3)
,
M. Delmastro
(3)
,
L. Di Ciaccio
(3)
,
S. Elles
(3)
,
K. Grevtsov
(3)
,
T. Guillemin
(3)
,
T. Hryn’ova
(3)
,
S. Jézéquel
(3)
,
I. Koletsou
(3)
,
R. Lafaye
(3)
,
Jérémy Lévêque
(3)
,
P. Mastrandea
(3)
,
E. Sauvan
(3)
,
B.H. Smart
(3)
,
I. Wingerter-Seez
(3)
,
E. Yatsenko
(3)
,
S. Berlendis
(4)
,
A. Bethani
(4)
,
C. Camincher
(4)
,
J. Collot
(4)
,
S. Crépé-Renaudin
(4)
,
P.A. Delsart
(4)
,
C. Gabaldon
(4)
,
M.H. Genest
(4)
,
P.O.J. Gradin
(4)
,
J.Y. Hostachy
(4)
,
F. Ledroit-Guillon
(4)
,
A. Lleres
(4)
,
A. Lucotte
(4)
,
F. Malek
(4)
,
E. Petit
(4)
,
J. Stark
(4)
,
B. Trocmé
(4)
,
M. Wu
(4)
,
G. Rahal
(5)
M. Aaboud
- Fonction : Auteur
G. Aad
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Y. Coadou
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D. Calvet
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N. Berger
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T. Hryn’ova
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S. Jézéquel
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S. Crépé-Renaudin
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M.H. Genest
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F. Ledroit-Guillon
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F. Malek
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B. Trocmé
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- IdRef : 139039872
Résumé
Ratios of top-quark pair to $Z$-boson cross sections measured from proton--proton collisions at the LHC centre-of-mass energies of $\sqrt s=13$TeV, 8TeV, and 7TeV are presented by the ATLAS Collaboration. Single ratios, at a given $\sqrt s$ for the two processes and at different $\sqrt s$ for each process, as well as double ratios of the two processes at different $\sqrt s$, are evaluated. The ratios are constructed using previously published ATLAS measurements of the $t\overline{t}$ and $Z$-boson production cross sections, corrected to a common phase space where required, and a new analysis of $Z \rightarrow \ell^+ \ell^-$ where $\ell=e,\mu$ at $\sqrt s=13$TeV performed with data collected in 2015 with an integrated luminosity of $3.2$fb$^{-1}$. Correlations of systematic uncertainties are taken into account when evaluating the uncertainties in the ratios. The correlation model is also used to evaluate the combined cross section of the $Z\rightarrow e^+e^-$ and the $Z\rightarrow \mu^+ \mu^-$ channels for each $\sqrt s$ value. The results are compared to calculations performed at next-to-next-to-leading-order accuracy using recent sets of parton distribution functions. The data demonstrate significant power to constrain the gluon distribution function for the Bjorken-$x$ values near 0.1 and the light-quark sea for $x<0.02$.