Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userThe photon PDF within the CT18 global analysis
75
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Building upon the most recent CT18 global fit, we present a new calculation of the photon content of the proton based on an application of the LUX formalism. In this work, we explore two principal variations of the LUX ansatz. In one approach, which we designate CT18lux, the photon PDF is calculated directly using the LUX formula for all scales, $mu$. In an alternative realization, CT18qed, we instead initialize the photon PDF in terms of the LUX formulation at a lower scale, $mu! sim! mu_0$, and evolve to higher scales with a combined QED+QCD kernel at $mathcal{O}(alpha),~mathcal{O}(alphaalpha_s)$ and $mathcal{O}(alpha^2)$. While we find these two approaches generally agree, especially at intermediate $x$ ($10^{-3}lesssim xlesssim0.3$), we discuss some moderate discrepancies that can occur toward the end-point regions at very high or low $x$. We also study effects that follow from variations of the inputs to the LUX calculation originating outside the pure deeply-inelastic scattering (DIS) region, including from elastic form factors and other contributions to the photon PDF. Finally, we investigate the phenomenological implications of these photon PDFs for the LHC, including high-mass Drell-Yan, vector-boson pair, top-quark pair, and Higgs associated with vector-boson production.
rate research
Read More
Recently, two photon PDF sets based on implementations of the LUX ansatz into the CT18 global analysis were released. In CT18lux, the photon PDF is calculated directly using the LUX master formula for all scales, $mu$. In an alternative realization, CT18qed, the photon PDF is initialized at the starting scale, $mu_0$, using the LUX formulation and evolved to higher scales $mu(>mu_0)$ with a combined QED+QCD kernel at $mathcal{O}(alpha),~mathcal{O}(alphaalpha_s)$ and $mathcal{O}(alpha^2)$. In the small-$x$ region, the photon PDF uncertainty is mainly induced by the quark and gluon PDFs, through the perturbative DIS structure functions. In comparison, the large-$x$ photon uncertainty comes from various low-energy, nonperturbative contributions, including variations of the inelastic structure functions in the resonance and continuum regions, higher-twist and target-mass corrections, and elastic electromagnetic form factors of the proton. We take the production of doubly-charged Higgs pairs, $(H^{++}H^{--})$, as an example of scenarios beyond the Standard Model to illustrate the phenomenological implications of these photon PDFs at the LHC.
We discuss implementation of the LHC experimental data sets in the new CT18 global analysis of quantum chromodynamics (QCD) at the next-to-next-leading order of the QCD coupling strength. New methodological developments in the fitting methodology are discussed. Behavior of the CT18 NNLO PDFs for the conventional and saturation-inspired factorization scales in deep-inelastic scattering is reviewed. Four new families of (N)NLO CTEQ-TEA PDFs are presented: CT18, A, X, and Z.
Direct photon production in hadronic collisions provides a handle on the gluon PDF by means of the QCD Compton scattering process. In this work we revisit the impact of direct photon production on a global PDF analysis, motivated by the recent availability of the next-to-next-to-leading (NNLO) calculation for this process. We demonstrate that the inclusion of NNLO QCD and leading-logarithmic electroweak corrections leads to a good quantitative agreement with the ATLAS measurements at 8 TeV and 13 TeV, except for the most forward rapidity region in the former case. By including the ATLAS 8 TeV direct photon production data in the NNPDF3.1 NNLO global analysis, we assess its impact on the medium-x gluon. We also study the constraining power of the direct photon production measurements on PDF fits based on different datasets, in particular on the NNPDF3.1 no-LHC and collider-only fits. We also present updated NNLO theoretical predictions for direct photon production at 13 TeV that include the constraints from the 8 TeV measurements.
We present the new parton distribution functions (PDFs) from the CTEQ-TEA collaboration, obtained using a wide variety of high-precision Large Hadron Collider (LHC) data, in addition to the combined HERA I+II deep-inelastic scattering data set, along with the data sets present in the CT14 global QCD analysis. New LHC measurements in single-inclusive jet production with the full rapidity coverage, as well as production of Drell-Yan pairs, top-quark pairs, and high-$p_T$ $Z$ bosons, are included to achieve the greatest sensitivity to the PDFs. The parton distributions are determined at NLO and NNLO, with each of these PDFs accompanied by error sets determined using the Hessian method. Fast PDF survey techniques, based on the Hessian representation and the Lagrange Multiplier method, are used to quantify the preference of each data set to quantities such as $alpha_s(m_Z)$, and the gluon and strange quark distributions. We designate the main resulting PDF set as CT18. The ATLAS 7 TeV precision $W/Z$ data are not included in CT18, due to their tension with other data sets in the global fit. Alternate PDF sets are generated including the ATLAS precision 7 TeV $W/Z$ data (CT18A), a new scale choice for low-$x$ DIS data (CT18X), or all of the above with a slightly higher choice for the charm mass (CT18Z). Theoretical calculations of standard candle cross sections at the LHC (such as the $gg$ fusion Higgs boson cross section) are presented.
Particle and nuclear physics are moving toward a new generation of experiments to stress-test the Standard Model (SM), search for novel degrees of freedom, and comprehensively map the internal structure of hadrons. Due to the complex nature of QCD and wide array of past, present, and possible future experiments, measurements taken at these next-generation facilities will inhabit an expansive space of high-energy data. Maximizing the impact of each future collider program will depend on identifying its place within this sprawling landscape. As an initial exploration, we use the recently-developed PDFSense framework to assess the PDF sensitivity of two future high-energy facilities --- the high-luminosity upgrade to the LHC (HL-LHC) and the Large Hadron-electron Collider (LHeC) proposal --- as well as the electron-ion collider (EIC) proposed to map the few-GeV quark-hadron transition region. We report that each of these experimental facilities occupies a unique place in the kinematical parameter space with specialized pulls on particular collinear quantities. As such, there is a clear complementarity among these programs, with an opportunity for each to mutually reinforce and inform the others.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
