Utilizing recent neutrino dimuon production measurement from NuTeV the assumptions on the determination of the strangeness content of the nucleon within the dynamical approach to parton distributions are investigated. The data are found to be in good agreement with the predictions derived from our (GJR08) dynamical parton distributions, which have been generated entirely radiatively starting from vanishing strange input distributions at an optimally chosen low resolution scale. Further, the data induce an asymmetry in the strange sea which is found to be small and positive in agreement with previous results.
We have performed the first global QCD analysis to include the CCFR and NuTeV dimuon data, which provide direct constraints on the strange and anti-strange parton distributions, $s(x)$ and $\bar{s}(x)$. To explore the strangeness sector, we adopt a general parametrization of the non-perturbative $s(x), \bar{s}(x)$ functions satisfying basic QCD requirements. We find that the strangeness asymmetry, as represented by the momentum integral $[S^{-}]\equiv \int_0^1 x [s(x)-\bar{s}(x)] dx$, is sensitive to the dimuon data provided the theoretical QCD constraints are enforced. We use the Lagrange Mul…
We consider a hard jet production tagged by a muon pair in ultrarelativistic heavy ion collisions. The process cross section is calculated by the CompHEP Monte-Carlo generator taking into account full gamma*/Z interference pattern at LHC energies. We have found that reasonable statistics, ~1000 events per 1 month of LHC run with lead beams, can be expected for realistic geometrical acceptance and kinematic cuts. The transverse momentum imbalance due to interactions of jet partons in the medium is evaluated for mu+mu-pair+jet correlation, as well as for the correlation between mu+mu- pair and a…
Experimentally, the production of oppositely charged dimuon events by neutrino and anti-neutrino deep inelastic scattering (DIS) is used to determine the strangeness asymmetry inside a nucleon. Here we point out that the direct production of $D$-meson in DIS may make substantial influence to the measurement of nucleon strange distributions. The direct $D$-meson production is via the heavy quark recombination (HQR) and via the light quark fragmentation from perturbative QCD (LQF-P). To see the influence precisely, we compute the direct $D$-meson productions via HQR and LQF-P quantitatively and …
Dimuon production has been studied in a series of fixed-target experiments at Fermilab during the last two decades. Highlights from these experiments, together with recent results from the Fermilab E866 experiment, are presented. Future prospects for studying the parton distributions in the nucleons and nuclei using dimuon production are also discussed.
We present details on calculation of next-to-next-to-leading order QCD corrections to massive charged-current coefficient functions in deep-inelastic scattering. Especially we focus on the application to charm-quark production in neutrino scattering on fixed target that can be measured via the dimuon final state. We construct a fast interface to the calculation so for any parton distributions the cross sections can be evaluated within milliseconds by using the pre-generated interpolation grids. We discuss agreements of various theoretical predicitons with the NuTeV and CCFR dimuon data and the…
We present an analysis of the nucleon strange sea extracted from a global Parton Distribution Function fit including the neutrino and anti-neutrino dimuon data by the CCFR and NuTeV collaborations, the inclusive charged lepton-nucleon Deep Inelastic Scattering and Drell-Yan data. The (anti-)neutrino induced dimuon analysis is constrained by the semi-leptonic charmed-hadron branching ratio $B_μ=(8.8\pm0.5)%$, determined from the inclusive charmed hadron measurements performed by the FNAL-E531 and CHORUS neutrino emulsion experiments. Our analysis yields a strange sea suppression factor $κ(Q^2=2…
Neutrino induced deep inelastic charm production off strange sea partons in the nucleon is studied in the framework of the MSbar fixed flavor factorization scheme. The momentum (z) distributions of the produced D mesons as calculated in the next-to-leading order QCD analysis are presented and compared to their leading order counterparts. Perturbative stability within this formalism is demonstrated and the compatibility of recent next-to-leading order (NLO) strange quark distributions with available dimuon data is investigated. Our NLO (MSbar) results provide, for the first time, the tools requ…
Strangeness production was investigated during the equilibration of a gluon dominated parton plasma produced at RHIC and LHC energies. The time evolution of parton densities are followed by a set of rate equations in a 1-dimensional expanding system. The strangeness production will depend on the initial chemical equilibration level and in our case the parton densities will remain far from the full equilibrium. We investigate the influence of gluon fragmentation on final strangeness content.
The strangeness degrees of freedom in the parton structure of the nucleon are explored in the global analysis framework, using the new CTEQ6.5 implementation of the general mass perturbative QCD formalism of Collins. We systematically determine the constraining power of available hard scattering experimental data on the magnitude and shape of the strange quark and anti-quark parton distributions. We find that current data favor a distinct shape of the strange sea compared to the isoscalar non-strange sea. A new reference parton distribution set, CTEQ6.5S0, and representative sets spanning the …
We extend to the strange quarks and antiquarks, the statistical approach of parton distributions and we calculate the strange quark asymmetry $s-\bar s$. We find that the asymmetry is small, positive in the low $x$ region and negative in the high $x$ region. In this framework, the polarized strange quarks and antiquarks distributions, which are obtained simultaneously, are found to be both negative for all $x$ values.
Interest in the strange nucleon sea has been renewed when it was realized that the strangeness asymmetry $s^-=s-\bar{s}$ plays a prominent role in the interpretation of the NuTeV weak mixing angle anomaly. I review the NLO QCD calculation of the neutrino-production of opposite-sign dimuons as the experimental signature of the strange quark parton density. Results from a recent CTEQ fit are presented and discussed with respect to their stability under NLO corrections and their impact on the NuTeV measurement.
The dynamical parton distributions of the nucleon are generated radiatively from positive definite (valencelike) input distributions at an optimally chosen low resolution scale (Q_0^2 < 1 GeV^2). For the strange distribution in particular, it has been assumed that vanishing strange input distributions at this low scale is an appropriate choice. By confronting predictions derived from our (GJR08) NLO dynamical parton distributions with recent neutrino dimuon production measurement from NuTeV we show that this is indeed the case, and that little improvement is achieved by using a more general an…
Charm production as related to the determination of the strange sea density in deep inelastic charged current processes is studied predominantly in the framework of the $\overline{\rm{MS}}$ fixed flavor factorization scheme. Perturbative stability within this formalism is demonstrated. The compatibility of recent next-to-leading order strange quark distributions with the available dimuon and $F^{νN}_2$ data is investigated. It is shown that final conclusions concerning these distributions afford further analyses of presently available and/or forthcoming neutrino data.
A recently completed next-to-leading-order program to calculate neutrino cross sections, including power-suppressed mass correction terms, has been applied to evaluate the Paschos-Wolfenstein relation, in order to quantitatively assess the validity and significance of the NuTeV anomaly. In particular, we study the shift of $\sin^2 θ_{\mathrm{W}}$ obtained in calculations with a new generation of PDF sets that allow $s(x)\neq \bar{s}(x)$, enabled by recent neutrino dimuon data from CCFR and NuTeV, as compared to the previous $s = \bar{s}$ parton distribution functions like CTEQ6M. The extracted…
Dimuon production has been studied in a series of fixed-target experiments at Fermilab during the last two decades. Highlights from these experiments, together wih recent results from the Fermilab E866 experiment, are presented. Future prospects for studying the parton distributions in the nucleons and nuclei using dimuon production at Fermilab and J-PARC are also discussed.
We discuss the physics interest and the experimental feasibility for detecting high-mass dimuon pairs using the planned 50-GeV Proton Synchrotron (PS) at the KEK/JHF and JAERI/NSP joint accelerator project. The Drell-Yan measurement of $p+d$ versus $p+p$ at 50 GeV will provide unique information on the flavor asymmetry of proton's up and down sea-quark distributions in the large-$x$ region. A study of the nuclear dependences of Drell-Yan cross sections can reveal the modification of antiquark distributions in nuclei. Furthermore, the effect of energy loss for fast partons traversing nuclear me…
We use recent neutrino dimuon production data combined with a global deep-inelastic parton fit to construct a new parton set, NNPDF1.2, which includes a determination of the strange and antistrange distributions of the nucleon. The result is characterized by a faithful estimation of uncertainties thanks to the use of the NNPDF methodology, and is free of model or theoretical assumptions other than the use of NLO perturbative QCD and exact sum rules. Better control of the uncertainties of the strange and antistrange parton distributions allows us to reassess the determination of electroweak par…
We consider the collinear limit of QCD amplitudes at one-loop order, and their factorization properties directly in colour space. These results apply to the multiple collinear limit of an arbitrary number of QCD partons, and are a basic ingredient in many higher-order computations. In particular, we discuss the triple collinear limit and its relation to flavour asymmetries in the QCD evolution of parton densities at three loops. As a phenomenological consequence of this new effect, and of the fact that the nucleon has non-vanishing quark valence densities, we study the perturbative generation …
We present the CTEQ6HQ parton distribution set which is determined in the general variable flavor number scheme which incorporates heavy flavor mass effects; hence, this set provides advantages for precision observables which are sensitive to charm and bottom quark masses. We describe the analysis procedure, examine the predominant features of the new distributions, and compare with previous distributions. We also examine the uncertainties of the strange quark distribution and how the the recent NuTeV dimuon data constrains this quantity.
We present a preliminary set of updated NLO parton distributions. For the first time we have a quantitative extraction of the strange quark and antiquark distributions and their uncertainties determined from CCFR and NuTeV dimuon cross sections. Additional jet data from HERA and the Tevatron improve our gluon extraction. Lepton asymmetry data and neutrino structure functions improve the flavour separation, particularly constraining the down quark valence distribution.
CERN collaboration NA50 has measured charmonium and Drell-Yan dimuon production in Pb+Pb collisions. Parton scattering broadens the transverse momentum, p_T, distributions for these processes. We predict that the average p_T^{2} will flatten in Pb+Pb collisions as a function of the neutral transverse energy of hadrons, E_T, in contrast to the almost-linear rise seen in S+U - psi +X. If seen, such a flattening will support hadronic explanations of charmonium suppression. Figures 2 and 5 are improved and numerous typographical errors are corrected.
We present recent progress within the NNPDF parton analysis framework. After a brief review of the results from the DIS NNPDF analysis, NNPDF1.0, we discuss results from an updated analysis with independent parametrizations for the strange and anti-strange distributions, denoted by NNPDF1.1. We examine the phenomenological implications of this improved analysis for the strange PDFs.
We perform QCD fit of the nucleon strange and anti-strange sea distributions to the neutrino and anti-neutrino dimuon data by the CCFR and NuTeV collaborations, supplemented by the inclusive charged lepton-nucleon Deep Inelastic Scattering (DIS) and Drell-Yan data. The effective semi-leptonic charmed-hadron branching ratio is constrained from the inclusive charmed hadron measurements performed by the FNAL-E531 and CHORUS neutrino emulsion experiments as $B_μ=(8.8\pm0.5)%$. We obtain a strange sea suppression factor {$κ(20 {\rm GeV}^2)=0.62\pm0.04({\rm exp.})\pm0.03({\rm QCD})$}. An $x$-distrib…
A large class of polarized and unpolarized deep inelastic data is successfully described with Fermi-Dirac functions for the non-diffractive part of quark parton distributions. The NLO approach used here improves the agreement with experiment of the previous LO work. We get a broader distribution for the strange parton s(x) than for sbar(x).
The strange sea quarks distributions of nucleons obtained by two global analyses based on available structure function data of muon and neutrino deep inelastic scatterings are different from the strange sea quark distribution measured by the CCFR Collaboration from dimuon events in neutrino scattering. We discuss possible contributions to this discrepancy from the nuclear shadowing in the deuteron and from the isospin symmetry breaking in the sea between the neutron and the proton.
New data sets have recently become available for neutrino and antineutrino deep inelastic scattering on nuclear targets and for inclusive dimuon production in pp pd interactions. These data sets are sensitive to different combinations of parton distribution functions in the large-x region and, therefore, provide different constraints when incorporated into global parton distribution function fits. We compare and contrast the effects of these new data on parton distribution fits, with special emphasis on the effects at large x. The effects of the use of nuclear targets in the neutrino and antin…
In order to examine polarized strange quark distribution, semi-inclusive $D/\Dbar$ production in neutrino deep inelastic scattering is studied including ${\cal O}(α_s)$ corrections. Cross section and spin asymmetry are calculated by using various parametrizations of polarized parton distribution functions. It is found that $\Dbar$ production is promising to directly extract the polarized strange sea.
We reexamine the shapes of the strange quark parton distribution functions (PDFs) of the proton by means of quantum chromodynamics (QCD) analysis of {\hera} deep inelastic scattering cross section measurement at DESY, and inclusive gauge boson production and $W$ boson production associated with a charm quark from LHC at CERN. We find that there is an overall agreement on the strange quark distributions obtained from CMS $W$ + charm and ATLAS $W/Z$ data at the parton momentum fraction range $x \lesssim 10^{-2}$. Meanwhile, there is also a strong tension between these data towards large $x$. We …
We study the nuclear parton distribution functions on the basis of our recently developed semi-microscopic model, which takes into account a number of nuclear effects including nuclear shadowing, Fermi motion and nuclear binding, nuclear meson-exchange currents, and off-shell corrections to bound nucleon distributions. We discuss in detail the dependencies of nuclear effects on the type of parton distribution (nuclear sea vs valence), as well as on the parton flavor (isospin). We apply the resulting nuclear parton distributions to calculate ratios of cross sections for proton-induced Drell-Yan…
Recently a new set of Parton Distribution Functions (NNPDF1.2) has been produced and released by the NNPDF Collaboration. The inclusion of dimuon data in the analysis allows a determination of the strange content of the proton with faithful uncertainty estimation together with a precision determination of electroweak parameters. In this contribution, we discuss some of the implications of the NNPDF1.2 set, and in particular of its uncertainty determination of the strange PDFs, for LHC phenomenology. First of all, we study the impact on the electroweak boson production cross-section, with speci…
A detailed study of nucleon parton distribution functions is performed within a radiative Next-to-Next-to Leading Order (NNLO) parton model whose low-scale input is rigidly described by wave functions which include quarks and dressing meson-cloud. The light-front Hamiltonian dynamics fixes the three-quark wave functions and the meson cloud is introduced by means of high-order Fock component in time-ordered perturbation theory in the infinite momentum frame. Non-strange as well as strange mesons-baryon fluctuations are considered ($π$, $ρ$, $ω$, $K$ and $K^*$, together with $N$, $Δ$, $Λ$ and $Σ…
Dimuon production has been studied in a series of fixed-target experiments at Fermilab during the last two decades. Highlights from these experiments, together with recent results from the Fermilab E866 experiment, are presented. Future prospects for studying the parton distributions in the nucleons and nuclei using dimuon production are also discussed.
The current status of global QCD analysis of parton distribution functions of the nucleon is reviewed. Recent progress made in determining various features of the parton structure of the nucleon, as well as outstanding open questions are discussed. These include: the small-$x$ and large-$x$ behavior of the partons, particularly the gluon; the differentiation of $u$ and $d$ quarks; the strangeness sea ($s+\bar{s}$), the strangeness asymmetry ($s-\bar{s}$); and the heavy quark distributions $c$ and $b$. Important issues about assessing the uncertainties of parton distributions and their physical…
The HERMES collaboration in Phys. Rev. D89 (2014) 097101 extracted information about the strange quark density in the nucleon. One of the main results is an observation that the shape of the extracted density is very different from the shapes of the strange quark density from global QCD fits and also from that of the light antiquarks. In this paper systematic studies on the HERMES published multiplicity of pion and kaon data are presented. It is shown that the conclusions concerning the strange quark distribution in the nucleon reached in Phys. Rev. D89 (2014) 097101 are at the moment prematur…
A Comment on the recently published reevaluation of the polarization-averaged parton distribution of strange quarks in the nucleon using final data on the multiplicities of charged kaons in semi-inclusive deep-inelastic scattering is reviewed. Important features of the comparison of one-dimensional projections of the multidimensional HERMES data are pointed out. A test of the leading-order extraction of xS(x) using the difference between charged-kaon multiplicities is repeated. The results are consistent with leading-order predictions within the uncertainties in the input data, and do not inva…
Based on quantum fluctuations in momentum and of the proton into meson-baryon pairs, we develop a physical model for the non-perturbative x-shape of parton density functions in the proton. The model describes the proton structure function and gives a natural explanation of observed quark asymmetries, such as the difference between the anti-up and anti-down sea quark distributions and between the up and down valence distributions. An asymmetry in the momentum distribution of strange and anti-strange quarks in the nucleon is found to reduce the NuTeV anomaly to a level which does not give a sign…
The Parton-Hadron-String Dynamics (PHSD) transport approach consistently simulates the full evolution of a relativistic heavy-ion collision from the initial hard scatterings string formation through the dynamical deconfinement phase transition to the quark gluon plasma (QGP), to the hadronization and to subsequent interactions in the hadronic phase. The transport theoretical description of quarks and gluons is based on a dynamical quasiparticle model for partons matched to reproduce recent lattice QCD results in thermodynamic equilibrium. The transition from partonic to hadronic degrees of fre…
We calculate the energy--momentum distribution of the charmed quarks produced in neutrino reactions on protons, quantifying the importance of mass and current non--conservation effects. We study the strange and charm distributions probed in neutrino interactions in the presently accessible kinematical region. Some ambiguities inherent to the extraction of the parton densities from dimuon data are pointed out.
We perform the first simultaneous extraction of unpolarized parton distributions and fragmentation functions from a Monte Carlo analysis of inclusive and semi-inclusive deep-inelastic scattering, Drell-Yan lepton-pair production, and single-inclusive $e^+ e^-$ annihilation data. We use data resampling techniques to thoroughly explore the Bayesian posterior distribution of the extracted functions, and use $k$-means clustering on the parameter samples to identify the configurations that give the best description across all reactions. Inclusion of the semi-inclusive data reveals a strong suppress…
Semi-inclusive $D / \Dbar$ meson productions in neutrino deep inelastic scattering are studied including ${\cal O}(α_s)$ corrections. Supposing a future neutrino factory, cross sections and spin asymmetries in polarized processes are calculated by using various parametrization models of polarized parton distribution functions. We suggest that $\Dbar$ production is promising to directly extract the strange quark distribution.
This paper describes salient features of new sets of parton distributions obtained by the CTEQ Collaboration based on a comprehensive QCD global analysis of all available data. The accuracy of the new data on deep inelastic scattering structure functions obtained by the very high statistics NMC and CCFR experiments provides unprecedented sensitivity to the flavor dependence of the sea-quark distributions. In addition to much better determination of the small x dependence of all parton distributions, we found: (i) the strange quark distribution is much softer than the non-strange sea quarks and…
We consider determinations of the strange sea in the nucleon based on the QCD analyses of data collected at the LHC with focus on the recent high-statistics ATLAS measurement of the $W^\pm$- and $Z$-boson production. We study the effect of different functional forms for parameterization of the parton distribution functions and the combination of various data sets in the analysis. We compare to earlier strange sea determinations and discuss ways to improve them in the future.
Strangeness production is calculated in a pQCD-based model (including nuclear effects) in the high transverse momentum sector, where pQCD is expected to work well. We investigate pion, kaon, proton and lambda production in pp and heavy-ion collisions. Parton energy loss in AA collisions is taken into account. We compare strange-to-non-strange meson and baryon ratios to data at RHIC, and make predictions for the LHC. We find that these ratios significantly deviate from unity not only at RHIC but also at the LHC, indicating the special role of strangeness at both energies.
We present updated leading-order, next-to-leading order and next-to-next-to-leading order parton distribution functions ("MSTW 2008") determined from global analysis of hard-scattering data within the standard framework of leading-twist fixed-order collinear factorisation in the MSbar scheme. These parton distributions supersede the previously available "MRST" sets and should be used for the first LHC data-taking and for the associated theoretical calculations. New data sets fitted include CCFR/NuTeV dimuon cross sections, which constrain the strange quark and antiquark distributions, and Teva…
The present status of the (JR) dynamical parton distribution functions is reported. Different theoretical improvements, including the determination of the strange sea input distribution, the treatment of correlated errors and the inclusion of alternative data sets, are discussed. Highlights in the ongoing developments as well as (very) preliminary results in the determination of the strong coupling constant are presented.
We investigate the impact of parton distribution functions (PDFs) uncertainties on W/Z production at the LHC, concentrating on the strange quark PDF. Additionally we examine the extent to which precise measurements at the LHC can provide additional information on the proton flavor structure.
PACIAE, a parton and hadron cascade model, is utilized to systematically investigate strange particle production and strangeness enhancement in Au+Au collision and in Pb+Pb collision with the 200GeV at RHIC and 2.76TeV at LHC, respectively. The experimental results at different centrality, which come from the STAR collaboration and the ALICE collaboration, are well described by the PACIAE model. This may represent the importance of the parton and hadron rescatterings, as well as the reduction mechanism of strange quark suppression, added in the PACIAE model.
I discuss advances in the determination of strange, charm, and bottom quark parton distribution functions obtained in the CTEQ6.5 and CTEQ6.6 global analyses. These results affect electroweak precision observables and certain new physics searches at the Large Hadron Collider. I focus, in particular, on high-energy implications of the consistent treatment of heavy-quark threshold effects in DIS in the general-mass factorization scheme; an independent parametrization for the strangeness PDF; and the possible presence of nonperturbative ("intrinsic") charm.
The LHC has already provided many relevant measurements for the determination of parton distribution functions (PDFs). Measurements of the W and Z lepton distributions are of interest for flavor separation and in particular for the determination of the relatively poorly constrained strange quark distribution. In this contribution we shall discuss the computational developments that allow for the efficient inclusion of LHC data into the NNPDF framework consistently at NLO for all observables, and we study the constraints of the LHC W and Z data on the strangeness content of the proton.
A physical model for parton densities in hadrons, based on Gaussian momentum fluctuations of partons and hadronic baryon-meson fluctuations, is presented. The model has previously been shown to describe proton structure function data, and is now applied to sea quark asymmetries and shown to describe the dbar-ubar asymmetry of the proton. By considering fluctuations involving strange quarks, the model gives an asymmetry between the momentum distributions of s and sbar, which would reduce the significance of the NuTeV anomaly.
We calculate the parton distributions for both polarized and unpolarized octet and decuplet baryons, using the MIT bag, dressed by mesons. We show that the hyperfine interaction responsible for the $Δ- N$ and $Σ^0 - Λ$ splittings leads to large deviations from SU(3) and SU(6) predictions. For the $Λ$ we find significant polarized, non-strange parton distributions which lead to a sizable $Λ$ polarization in polarized, semi-inclusive $ep$ scattering. We also discuss the flavour symmetry violation arising from the meson-cloud associated with the chiral structure of baryons.
