3,391 research outputs found
Feasibility of top quark measurements at LHCb and constraints on the large- gluon PDF
The forward LHCb acceptance opens interesting possibilities of studying
precision Standard Model hard processes in a kinematical region beyond the
reach of ATLAS and CMS. In this paper we perform a feasibility study for
cross-section measurements of top quark pairs with the LHCb detector, with an
analysis of signal and background rates for selected final states, and
determine the potential precision achievable at 7 and 14~TeV. We
then study the dependence of theoretical uncertainties on the pseudorapidity
distribution of top quarks produced in pair production at NLO, and observe that
a cross-section measurement at high pseudorapidity has enhanced sensitivity to
probe the high- gluon PDF as compared to measurements in the central-region.
Based on simulated pseudodata, the impact of a 14~TeV cross-section measurement
on the gluon PDF and charge asymmetry is quantified.Comment: 25 pages, 14 figures, 8 tables. Extended PDF analysis to include
ABM11 5flv nlo. Added summary plots of LHCb cross-sections. Include shift of
gluon PDF central value for CT10, NNPDF sets assuming different pseudodata
values. Matches version to be published in JHE
Understanding forward hadron production
The LHCb collaboration has recently performed a measurement of the production
rate of inclusive hadron production () at both 7 and 13~TeV
centre-of-mass (CoM) energies. As part of this measurement, the ratio of these
two cross section measurements has been presented differentially in hadron
pseudorapidity within the range of . A large tension
() is observed for the ratio measurement in the lower pseudorapidity
range of , where the data is observed to exceed
theoretical predictions, while consistency is found at larger values.
This behaviour is not expected within perturbative QCD, and can only be
achieved by introducing ad-hoc features into the structure of the
non-perturbative gluon PDF within the region of .
Specifically, the gluon PDF must grow extremely quickly with decreasing
within this kinematic range, closely followed by a period of decelerated
growth. However, such behaviour is highly disfavoured by global fits to proton
structure. Further studies of the available LHCb and hadron cross
section data, available for a range of CoM energies, indicate systematic
tension in the (pseudo)rapidity region of .Comment: 31 page
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