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Exclusive $J/psi$ and $Upsilon$ photoproduction and the low $x$ gluon | | S.P. Jones
; A.D. Martin
; M.G. Ryskin
; T. Teubner
; | | Date: |
24 Jul 2015 | | Abstract: | We study exclusive vector meson photoproduction, $gamma p o V + p$ with
$V=J/psi$ or $Upsilon$, at NLO in collinear factorisation, in order to
examine what may be learnt about the gluon distribution at very low $x$. We
examine the factorisation scale dependence of the predictions. We argue that,
using knowledge of the NLO corrections, terms enhanced by a large $ln(1/xi)$
can be reabsorbed in the LO part by a choice of the factorisation scale. (In
these exclusive processes $xi$ takes the role of Bjorken-$x$.) Then, the scale
dependence coming from the remaining NLO contributions has no $ln(1/xi)$
enhancements. As a result, we find that predictions for the amplitude of
$Upsilon$ production are stable to within about $pm 15\%$. This will allow
data for the exclusive process $p p o pUpsilon p$ at the LHC, particularly
from LHCb, to be included in global parton analyses to constrain the gluon PDF
down to $xsim 10^{-5}$. Moreover, the study of exclusive $J/psi$
photoproduction indicates that the gluon density found in the recent global PDF
analyses is too small at low $x$ and low scales. | | Source: | arXiv, 1507.6942 | | Services: | Forum | Review | PDF | Favorites | |
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