Sub-leading contributions to the intrinsic charm of the nucleon

We discuss corrections to the simple intrinsic charm model due to both quark and nucleon masses via ζ-scaling and mass-dependent radiative QCD contributions, and, in addition, take appropriate account of threshold effects. The recent EMC data are shown not to conflict with the basic idea of intrinsic charm but to suggest that a normalisation of 1% may overestimate the charm content of the nucleon; the large experimental uncertainties inx mean that the simple photon-gluon fusion mechanism alone cannot be ruled out.     

Intrinsic charm and photon-gluon fusion contributions to muoproduction of charm

The charm muoproduction data has been analysed in terms of the intrinsic charm and the γG fusion contributions, in order to estimate the intrinsic charm content of the nucleon. Unfortunately the result is sensitive to the choices of fragmentation function and the energy scale of α_s, that one makes for the fusion contribution. Nonetheless, there is one solution with a hard intrinsic charm spectrum—very similar to that suggested by the recent hadroproduction data.     

Neutrino scattering bound on intrinsic charm of nucleon

The uudc$\text{c}$ five-quark Fock component of the proton, recently proposed by Brodsky et al., is compatible with the CDHS upper bound on wrong-sign ν → μ⁺ events if the integrated charm probability per nucleon is at the suggested level λ = 0.01. With various realistic assumptions, the CDHS bound may be interpreted as λ < 0.025 with 90% confidence.     

A nonperturbative component in muoproduction of charm

A nonperturbative C component in the quark fragmentation function, as suggested by the neutrino-induced like-sign dimuon data, contributes appreciably to muoproduction of charm. It is comparable in size to the perturbative QCD (photon-gluon fusion) contribution; and its inclusion gives a better fit to the charm muoproduction (muon-induced dimuon) data.     

Probing nucleon strange asymmetry from charm production in neutrino deep inelastic scattering

We propose a means to detect the nucleon strange quark-antiquark asymmetry, which is predicted as a non-perturbative effect, but still unchecked directly by available experiments. The difference for the and meson production cross sections in neutrino and antineutrino induced charged current deep inelastic scattering is illustrated to be sensitive to the nucleon strange asymmetry. A prospect is given and the effect due to the light quark fragmentation is also discussed for the extraction of the strange asymmetry in future experiments.Received: 23 April 2005, Published online: 27 July 2005PACS: 14.60.Pq, 12.15.Ff     

Determination of the strange quark content of the nucleon from a next-to-leading-order QCD analysis of neutrino charm production

We present the first next-to-leading-order QCD analysis of neutrino charm production, using a sample of 6090 ^– and -induced opposite-sign dimuon events observed in the CCFR detector at the Fermilab Tevatron. We find that the nucleon strange quark content is suppressed with respect to the non-strange sea quarks by a factor =0.477 _–0.053 ^+0.063 , where the error includes statistical, systematic and QCD scale uncertainties. In contrast to previous leading order analyses, we find that the strange seax-dependence is similar to that of the non-strange sea, and that the measured charm quark mass,m _c =1.70±0.19 GeV/c², is larger and consistent with that determined in other processes. Further analysis finds that the difference inx-distributions betweenxs(x) and is small. A measurement of the Cabibbo-Kobayashi-Maskawa matrix element |V _cd |=0.232 _–0.020 ^+0.018 is also presented.     

Intrinsic charm production of doubly charmed baryons:Collider vs. fixed-target

The LHCb Collaboration has measured the doubly charmed baryon,■^++cc(ucc),through two different decay channels[1,2]in p+p collisions at center-of-mass energies of 7,8 and 13 TeV.While they have performed similar searches for the doubly charmed baryon ■^+cc(dcc),it has not yet been observed by LHCb[3].However,the fixed-target experiment,SELEX,at Fermilab,reported the observation of the ■^+cc in two different decay channels with a 600 GeV charged hyperon beam[4,5].The beam was composed of an admixture of π^±,p,p components as well as the Σ^- hyperon.Much discussion has arisen over the fact that the fixed-target observations have not been easily reproduced by the collider experiments at higher energies,where one might have expected the production rates to be much higher due to the orders of magnitude increase in the center of mass energy with LHCb.     

Veneziano model for nucleon nucleon and nucleon antinucleon scattering. I

The thermal conductivity has been measured on two niobium samples of different purity (ratio of mean free path to coherence length 220 and 10, respectively), in the mixed state, with heat current parallel (k _∥) and normal (k _⊥) to the magnetic field. The experimental results are compared with theories; the range of validity is discussed. Maki's relation (k-k _n) ～ (H _c2 -H)^1/2 could be verified only for the purer sample in the field range (H _c2 -H)?140 Oe. The relationsk _∥/k ₁>1 forT?T _c andk _∥/k ₁<1 forT?T _c were found to be valid for the whole range of fields in the mixed state.     

Intrinsic fragment spins generated in the reactions of 20Ne with 197Au and 238U at 12.6 MeV/nucleon

The average magnitude and alignment of the intrinsic spin of the heavy partner from the reaction of 252 MeV ²⁰Ne with ¹⁹⁷Au and ²³⁸U were determined as a function of Q-value. These spin values were extracted from sequential fission angular distributions obtained in coincidence with projectile-like products. For all Q-values a large out-of-plane anisotropy was observed, while for large negative Q-values an in-plane anisotropy was observed. A very large entrance-channel mass-asymmetry was chosen to provide a stringent test of equilibrium statistical model predictions for the spin alignment. The importance of determining the direction of the line-of-centers of the dinuclear system at scission is discussed. Large values of P_ZZ were deduced for all Q- values. P_XY was observed to be positive in the quasielastic region and negative in the deep-inelastic region. The extracted alignment data are compared to equilibrium statistical model calculations.     

Soliton models for the nucleon and predictions for the nucleon spin structure

In these lectures the three flavor soliton approach for baryons is reviewed. Effects of flavor symmetry breaking in the baryon wave functions on axial current matrix elements are discussed. A bosonized chiral quark model is considered to outline the computation of spin dependent nucleon structure functions in the soliton picture.     

Charm in the nucleon

A next-to-leading order analysis of inelastic electroproduction of charm is performed using an interpolating scheme which maps smoothly onto massless QCD evolution at large and photon–gluon fusion at small . In contrast with earlier analyses, this scheme allows the inclusion of quark and target mass effects and heavy quark thresholds, as well as possible non-perturbative, or intrinsic, charm contributions. We find no conclusive evidence in favor of an intrinsic charm component in the nucleon, although several data points which disagree with perturbative QCD expectations will need to be checked by future experiments. Received: 22 March 1999 / Revised version: 11 June 1999 / Published online: 3 November 1999