Feasibility of top quark measurements at LHCb and constraints on the large-xx 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 $\sqrt{s} =$ 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-$x$ 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 BB hadron production

The LHCb collaboration has recently performed a measurement of the production rate of inclusive $B$ hadron production ($pp\to BX$) 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 $B$ hadron pseudorapidity within the range of $\eta_B \in [2.0,5.0]$. A large tension ($4\sigma$) is observed for the ratio measurement in the lower pseudorapidity range of $\eta_B \in [2.0,3.0]$, where the data is observed to exceed theoretical predictions, while consistency is found at larger $\eta_B$ 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 $x\in[10^{-3},10^{-4}]$. Specifically, the gluon PDF must grow extremely quickly with decreasing $x$ 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 $B$ and $D$ hadron cross section data, available for a range of CoM energies, indicate systematic tension in the (pseudo)rapidity region of $[2.0,2.5]$.Comment: 31 page

Working Group 5: Physics with Heavy Flavours

This paper summarises a few selected topics discussed during Working Group 5 of the Deep Inelastic Scattering 2017 conference, Physics with Heavy Flavours, related to the study of charm, bottom, and top quark physics. While the programme of this Working Group was structured by thematic areas, this conference was the occasion for intense cross-pollination between traditionally disjoint research lines. The four LHC experiments all contribute to heavy-flavour physics, with some degree of overlap in most areas, while experiments at other accelerators provide vital input in complimentary kinematic regions. Theorists now have the possibility to take inputs from more sources, and experimentalists focus on measurements that maximise utility. The interplay of LHC heavy quark cross-section measurements with DIS expertise is greatly improving PDF precision, leading to much improved models that, amongst other things, better inform the prospects for future colliders.Comment: 14 pages, 11 figures, to appear in the proceedings of 25th International Workshop on Deep Inelastic Scattering and Related Topics (DIS 2017), 3-7 April 2017, University of Birmingham, U

The small-x gluon from forward charm production: implications for a 100 TeV proton collider

We review the constraints on the small-x gluon PDF that can be derived by exploiting the forward D meson production data from the LHCb experiment at $\sqrt{s}=5,7$ and 13 TeV. We then discuss the phenomenological implications of the resulting improved small-x gluon for ultra-high energy astrophysics, in particular neutrino telescopes, as well as for the proposed Future Circular Collider (FCC) with $\sqrt{s}=100$ TeV. We illustrate how at the FCC even electroweak scale cross-sections can become sensitive to the small-x region of the quark and gluon PDFs, and then demonstrate how the addition of the LHCb heavy meson production measurements leads to a reduction of PDF uncertainties for various benchmark cross-sections.Comment: 5 pages, 4 figures, to appear in the proceedings of the XXV International Workshop on Deep-Inelastic Scattering and Related Subjects, 3-7 April 2017, University of Birmingham, U

An explicit Z'-boson explanation of the B->K*mu+mu- anomaly

A global fit to the recent B->K*mu+mu- data shows indications for a large new-physics contribution to the Wilson coefficient of the semi-leptonic vector operator. In this article we consider a simple Z'-boson model of 3-3-1 type that can accommodate such an effect without violating any other constraint from quark-flavour physics. Implications for yet unobserved decay modes such as B->Xsnunubar and longstanding puzzles like B->piK are also discussed. The Z'-boson masses required to address the observed anomaly lie in the range of 7 TeV. Such heavy Z' bosons evade the existing bounds from precision data and direct searches, and will remain difficult to discover even at a high-luminosity LHC. The potential of an ILC as well as the next generation of low-energy parity-violation experiments in constraining the Z'-boson parameter space is also examined.Comment: 20 pages, 5 figures; v2: Eqs. (9.2), (9.4) and (9.5) corrected, typos fixed and references added; matches version published in JHE

Flavor Identification of Reconstructed Hadronic Jets

Identifying the flavor of reconstructed hadronic jets is critical for precision phenomenology and the search for new physics at collider experiments, as it allows one to pinpoint specific scattering processes and reject backgrounds. Jet measurements at the LHC are almost universally performed using the anti-kT algorithm; however, no approach exists to define the jet flavor for this algorithm that is infrared and collinear safe. We propose a new approach, a flavor-dressing algorithm, that is infrared and collinear safe in perturbation theory and can be combined with any definition of a jet. We test the algorithm in an e+e- environment and consider the pp→Z+b-jet process as a practical application at hadron colliders