We present the new nCTEQ15 set of nuclear parton distribution functions (nPDFs) with uncertainties. This fit extends the CTEQ proton PDFs to include the nuclear dependence using data on nuclei all the way up to 208 Pb. The uncertainties are determined using the Hessian method with an optimal rescaling of the eigenvectors to accurately represent the uncertainties for the chosen tolerance criteria. In addition to the Deep Inelastic Scattering (DIS) and Drell-Yan (DY) processes, we also include inclusive pion production data from RHIC to help constrain the nuclear gluon PDF. Furthermore, we investigate the correlation of the data sets with specific nPDF flavor components, and asses the impact of individual experiments. We also provide comparisons of the nCTEQ15 set with recent fits from other groups.
We present a review of the state of the art of our understanding of the intrinsic charm and bottom content of the nucleon. We discuss theoretical calculations, constraints from global analyses, and collider observables sensitive to the intrinsic heavy quark distributions. A particular emphasis is put on the potential of a high energy and high luminosity fixed target experiment using the LHC beams (AFTER@LHC) to search for intrinsic charm.
We provide a comprehensive comparison of W ± /Z vector boson production data in pPb and PbPb collisions at the LHC with predictions obtained using the nCTEQ15 PDFs. We identify the measurements which have the largest potential impact on the PDFs, and estimate the effect of including these data using a Bayesian reweighting method. We find this data set can provide information as regards both the nuclear corrections and the heavy flavor (strange quark) PDF components. As for the proton, the parton flavor determination/separation is dependent on nuclear corrections (from heavy target DIS, for example), this information can also help improve the proton PDFs.
Renormalization group equations are an essential tool for the description of
theories accross different energy scales. Even though their expressions at
two-loop for an arbitrary gauge field theory have been known for more than
thirty years, deriving the full set of equations for a given model by hand is
very challenging and prone to errors. To tackle this issue, we have introduced
in [1] a Python tool called PyR@TE; Python Renormalization group equations @
Two-loop for Everyone. With PyR@TE, it is easy to implement a given Lagrangian
and derive the complete set of two-loop RGEs for all the parameters of the
theory. In this paper, we present the new version of this code, PyR@TE 2, which
brings many new features and in particular it incorporates kinetic mixing when
several $\mathrm{U}(1)$ gauge groups are involved. In addition, the group
theory part has been greatly improved as we introduced a new Python module
dubbed PyLie that deals with all the group theoretical aspects required for the
calculation of the RGEs as well as providing very useful model building
capabilities. This allows the use of any irreducible representation of the
$\mathrm{SU}(n)$, $\mathrm{SO}(2n)$ and $\mathrm{SO(2n+1)}$ groups. %
Furthermore, it is now possible to implement terms in the Lagrangian involving
fields which can be contracted into gauge singlets in more than one way. As a
byproduct, results for a popular model (SM+complex triplet) for which, to our
knowledge, the complete set of two-loop RGEs has not been calculated before are
presented in this paper. Finally, the two-loop RGEs for the anomalous dimension
of the scalar and fermion fields have been implemented as well. It is now
possible to export the coupled system of beta functions into a numerical C++
function, leading to a consequent speed up in solving them.Comment: 26 page
Baryon and lepton numbers being accidental global symmetries of the Standard Model (SM), it is natural to promote them to local symmetries. However, to preserve anomaly-freedom, only combinations of B-L are viable. In this spirit, we investigate possible dark matter realizations in the context of the U (1) B−L model: (i) Dirac fermion with unbroken B-L; (ii) Dirac fermion with broken B-L; (iii) scalar dark matter; (iv) two-component dark matter. We compute the relic abundance, direct and indirect detection observables and confront them with recent results from Planck, LUX-2016, and Fermi-LAT and prospects from XENON1T. In addition to the well-known LEP bound M Z /g BL 7 TeV, we include often ignored LHC bounds using 13 TeV dilepton (dimuon + dielectron) data at next-to-leading order plus nextto-leading logarithmic accuracy. We show that, for gauge couplings smaller than 0.4, the LHC gives rise to the strongest collider limit. In particular, we find M Z /g BL > 8.7 TeV for g BL = 0.3. We conclude that the NLO+NLL corrections improve the dilepton bounds on the Z mass and that both dark matter candidates are only viable in the Z resonance region, with the parameter space for scalar dark matter being fully probed by XENON1T. Lastly, we show that one can successfully have a minimal two-component dark matter model.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.