We present the new nCTEQ15 set of nuclear parton distribution functions (PDFs) with uncertainties. This fit extends the CTEQ proton PDFs to include the nuclear dependence using data on nuclei all the ...way up to super(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 and Drell-Yan processes, we also include inclusive pion production data from the Relativistic Heavy Ion Collider to help constrain the nuclear gluon PDF. Furthermore, we investigate the correlation of the data sets with specific nuclear PDF flavor components and asses the impact of individual experiments. We also provide comparisons of the nCTEQ15 set with recent fits from other groups.
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.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
A precise knowledge of nuclear parton distribution functions (nPDFs) is—among other things—important for the unambiguous interpretation of hard process data taken in pA and AA collisions at the ...Relativistic Heavy Ion Collider (RHIC) and the LHC. The available fixed target data for deep inelastic scattering (DIS) and Drell-Yan (DY) lepton pair production mainly constrain the light quark distributions. It is hence crucial to include more and more collider data in global analyses of nPDFs in order to better pin down the different parton flavors, in particular the gluon distribution at small x . To help constrain the nuclear gluon PDF, we extend the nCTEQ15 analysis by including single inclusive hadron (SIH) production data from RHIC (PHENIX and STAR) and LHC (ALICE). In addition to the DIS, DY, and SIH datasets, we will also include LHC W/Z production data. As the SIH calculation is dependent on hadronic fragmentation functions (FFs), we use a variety of FFs available in the literature to properly estimate this source of uncertainty. We study the impact of these data on the PDFs and compare with both the nCTEQ15 and nCTEQ15WZ sets. The calculations are performed using a new implementation of the nCTEQ code (ncteq++) including a modified version of incnlo, which allows faster calculations using precomputed grids. The extension of the nCTEQ15 analysis to include the SIH data represents an important step toward the next generation of PDFs.
A clear understanding of nuclear parton distribution functions (nPDFs) plays a crucial role in the interpretation of collider data taken at the Relativistic Heavy Ion Collider, the Large Hadron ...Collider (LHC), and in the near future at the Electron-Ion Collider. Even with the recent inclusions of vector boson and light meson production data, the uncertainty of the gluon PDF remains substantial and limits the interpretation of heavy ion collision data. To obtain new constraints on the nuclear gluon PDF, we extend our recent nCTEQ15WZ+SIH analysis to inclusive quarkonium and open heavy-flavor meson production data from the LHC. This vast new data set covers a wide kinematic range and puts strong constraints on the nuclear gluon PDF down to x≲10-5 . The theoretical predictions for these data sets are obtained from a data-driven approach, where proton-proton data are used to determine effective scattering matrix elements. This approach is validated with detailed comparisons to existing next-to-leading order calculations in nonrelativistic QCD for quarkonia and in the general-mass variable-flavor-number scheme for the open heavy-flavored mesons. In addition, the uncertainties from the data-driven approach are determined using the Hessian method and accounted for in the PDF fits. This extension of our previous analyses represents an important step toward the next generation of PDFs not only by including new data sets, but also by exploring new methods for future analyses.
Global analyses of parton distribution functions (PDFs) have provided incisive constraints on the up and down quark components of the proton, but constraining the other flavor degrees of freedom is ...more challenging. Higher-order theory predictions and new data sets have contributed to recent improvements. Despite these efforts, the strange quark parton distribution function has a sizable uncertainty, particularly in the small x region. We examine the constraints from experiment and theory, and investigate the impact of this uncertainty on LHC observables. In particular, we study W/Z production to see how the s quark uncertainty propagates to these observables, and examine the extent to which precise measurements at the LHC can provide additional information on the proton flavor structure.
Motivated by the wide range of kinematics covered by current and planned deep-inelastic scattering (DIS) facilities, we revisit the formalism, practical implementation, and numerical impact of target ...mass corrections (TMCs) for DIS on unpolarized nuclear targets. An important aspect is that we only use nuclear and later partonic degrees of freedom, carefully avoiding a picture of the nucleus in terms of nucleons. After establishing that formulae used for individual nucleon targets (p,n), derived in the Operator Product Expansion (OPE) formalism, are indeed applicable to nuclear targets, we rewrite expressions for nuclear TMCs in terms of re-scaled (or averaged) kinematic variables. As a consequence, we find a representation for nuclear TMCs that is approximately independent of the nuclear target. We go on to construct a single-parameter fit for all nuclear targets that is in good numerical agreement with full computations of TMCs. We discuss in detail qualitative and quantitative differences between nuclear TMCs built in the OPE and the parton model formalisms, as well as give numerical predictions for current and future facilities.
We introduce a hybrid variable flavor number scheme for heavy flavors, denoted H-VFNS, which incorporates the advantages of both the traditional variable flavor number scheme as well as the fixed ...flavor number scheme (FFNS). By including an explicit N sub(F) dependence in both the parton distribution functions (PDFs) and the strong coupling constant alpha sub(S), we generate coexisting sets of PDFs and alpha sub(S) for N sub(F) = {3, 4, 5, 6} at any scale mu that are related analytically by the MS matching conditions. The H-VFNS resums the heavy quark contributions and provides the freedom to choose the optimal N sub(F) for each particular data set. Thus, we can fit selected HERA data in a FFNS framework, while retaining the benefits of the VFNS to analyze LHC data at high scales. We illustrate how such a fit can be implemented for the case of both HERA and LHC data.
We analyze the properties of the Aivazis-Collins-Olness-Tung (ACOT) scheme for heavy quark production and make use of the MS massless results at next-to-next-to-leading order and N super(3) LO for ...the structure functions F sub(2) and F sub(L)in neutral current deep-inelastic scattering to estimate the higher order corrections. For this purpose we decouple the heavy quark mass entering the phase space from the one entering the dynamics of the short distance cross section. We show numerically that the phase space mass is generally more important. Therefore, the dominant heavy quark mass effects at higher orders can be taken into account using the massless Wilson coefficients together with an appropriate slow-rescaling prescription implementing the phase space constraints. Combining the exact ACOT scheme at next-to-leading order with these expressions should provide a good approximation to the missing full calculation in the ACOT scheme at next-to-next-to-leading order and N super(3) LO.
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