We present a LO evaluation of helicity densities of valence, Δu_v+Δd_v, non-strange sea, Δ\bar{u}+Δ\bar{d}, and strange quarks, Δs (assumed to be equal to Δ\bar{s}). They have been obtained from the inclusive asymmetry A_{3,d} and the semi-inclusive asymmetries A^{π+}_{1,d}, A^{π-}_{1,d}, A^{K+}_{1,d}, A^{K-}_{1,d} measured in polarised deep inelastic muon-deuteron scattering. The full deuteron statistics of COMPASS (years 2002-2004 and 2006) has been used. The data cover the range Q^2 > 1 (GeV/c)^2 and 0.004<x<0.3. Both non-strange densities are found to be in a good agreement with previous measurements. The distribution of Δs(x) is compatible with zero in the whole measured range, in contrast to the shape of the strange quark helicity distribution obtained in most LO and NLO QCD fits. The sensitivity of the values of Δs(x) upon the choice of fragmentation functions used in the derivation is discussed.
Double-spin asymmetries for production of charged pions and kaons in semi-inclusive deep-inelastic muon scattering have been measured by the COMPASS experiment at CERN. The data, obtained by scattering a 160 GeV muon beam off a longitudinally polarised NH_3 target, cover a range of the Bjorken variable x between 0.004 and 0.7. A leading order evaluation of the helicity distributions for the three lightest quarks and antiquark flavours derived from these asymmetries and from our previous deuteron data is presented. The resulting values of the sea quark distributions are small and do not show an…
The momentum and helicity density distributions of the strange quark sea in the nucleon are obtained in leading order from charged-kaon production in deep-inelastic scattering on the deuteron. The distributions are extracted from spin-averaged K+/- multiplicities, and from K+/- and inclusive double-spin asymmetries for scattering of polarized positrons by a polarized deuterium target. The shape of the momentum distribution is softer than that of the average of the ubar and dbar quarks. In the region of measurement 0.02 < x < 0.6 and Q^2 > 1.0 GeV^2, the helicity distribution is zero within exp…
The strange quark helicity distribution Delta s(x)is derived at LO from the semi-inclusive and inclusive spin asymmetries measured by the COMPASS experiment at CERN. The significance of the results is found to depend critically on the ratio of the sbar and u quark fragmentation functions into positive kaons.
Polarization properties of high energy photodisintegration of the deuteron are studied within the framework of the hard rescattering mechanism~(HRM). In HRM, a quark of one nucleon knocked-out by the incoming photon rescatters with a quark of the other nucleon leading to the production of two nucleons with high relative momentum. Summation of all relevant quark rescattering amplitudes allows us to express the scattering amplitude of the reaction through the convolution of a hard photon-quark interaction vertex, the large angle p-n scattering amplitude and the low momentum deuteron wave functio…
The HERMES experiment has measured double spin asymmetries of inclusive and semi-inclusive cross sections for the production of charged hadrons in deep-inelastic scattering of polarised positrons on polarised hydrogen and deuterium targets, in the kinematic range 0.023 < x < 0.6, and 1 GeV^2 < Q^2 < 15 GeV^2. For the data taken on the deuterium target, a RICH detector provides the complete identification of charged pions and kaons. From the inclusive measurements on deuterium, the polarised structure function g_1^d has been extracted with high precision. Together with the semi-inclusive measur…
Nucleon spin structure functions have been investigated mainly by longitudinally-polarized ones for finding the origin of the nucleon spin. Other types of spin structure functions are transversely-polarized ones. In particular, quark transversity distributions in the nucleons have very different properties from the longitudinally-polarized quark distribution functions, especially in scaling violation, because they are decoupled from the gluon transversity, due to the fact that they are helicity-flip (chiral-odd) distributions. Such studies are valuable for finding not only the origin of the nu…
Azimuthal asymmetries in exclusive electroproduction of a real photon from an unpolarized deuterium target are measured with respect to beam helicity and charge. They appear in the distribution of these photons in the azimuthal angle phi around the virtual-photon direction, relative to the lepton scattering plane. The extracted asymmetries are attributed to either the deeply virtual Compton scattering process or its interference with the Bethe-Heitler process. They are compared with earlier results on the proton target. In the measured kinematic region, the beam-charge asymmetry amplitudes and…
New experiments in polarised deep inelastic scattering will mainly concentrate on the measurement of semi-inclusive asymmetries. Especially, the upgraded HERMES experiment at DESY and the newly build COMPASS experiment at CERN will investigate the gluon polarisation via open charm and high p_T hadron pair production, study in detail the flavour decomposition of the quark helicity distributions and measure the tranversity distributions with tranversely polarised targets.
We report the first lattice quantum chromodynamics (QCD) study of deuteron($np$)-like dibaryons with heavy quark flavours. These include particles with following dibaryon structures and valence quark contents: $Σ_cΞ_{cc} (uucucc)$, $Ω_cΩ_{cc} (sscscc)$, $Σ_bΞ_{bb} (uububb)$, $Ω_bΩ_{bb} (ssbsbb)$ and $Ω_{ccb}Ω_{cbb} (ccbcbb)$, and with spin ($J$)-parity ($P$), $J^{P} \equiv 1^{+}$. Using a state-of-the art lattice QCD calculation, after controlling relevant systematic errors, we unambiguously find that the ground state masses of dibaryons $Ω_cΩ_{cc} (sscscc)$, $Ω_bΩ_{bb} (ssbsbb)$ and $Ω_{ccb}Ω…
Understanding how sea quarks behave inside a nucleon is one of the most important physics goals of the proposed Electron-Ion Collider in China (EicC), which is designed to have 3.5 GeV polarized electron beam (80% polarization) colliding with 20 GeV polarized proton beam (70% polarization) at instantaneous luminosity of $2 \times 10^{33} {\rm cm}^{-2} {\rm s}^{-1}$. A specific topic at EicC is to understand the polarization of individual quarks inside a longitudinally polarized nucleon. The potential of various future EicC data, including the inclusive and semi-inclusive deep inelastic scatter…
A comprehensive collection of results on longitudinal double-spin asymmetries is presented for charged pions and kaons produced in semi-inclusive deep-inelastic scattering of electrons and positrons on the proton and deuteron, based on the full HERMES data set. The dependence of the asymmetries on hadron transverse momentum and azimuthal angle extends the sensitivity to the flavor structure of the nucleon beyond the distribution functions accessible in the collinear framework. No strong dependence on those variables is observed. In addition, the hadron charge-difference asymmetry is presented,…
The inclusive A_1,p and hadron double-spin asymmetries A_p^pi+, A_p^pi-, A_p^K+, A_p^K- measured at COMPASS (CERN SPS) in deep-inelastic scattering of a polarized muon beam off a polarized NH_3 solid target are presented. The results have been obtained with the full statistics collected in 2007 for the longitudinal target polarization. Proton asymmetries have been combined with the published deuteron ones. An evaluation of the non-singlet spin-dependent structure function g_1^NS(x,Q^2) and its first moment, which confirms the validity of the Bjorken sum-rule, is presented. A LO evaluation of p…
In the leading order of QCD parton model of Semi Inclusive Deep Inelastic Scattering (SIDIS) the double spin asymmetry $A_{LT}$ arises due to the longitudinal polarization of quarks in the transversely polarized nucleon. The corresponding $k_T^2$ weighted distribution function $g^{(1)}_{1T}$ can be related to ordinary helicity distribution $g_1(x)$ measured in DIS. Using recent parameterizations for (un)polarized distribution and fragmentation functions we calculated $A_{LT}$ asymmetry on transversely polarized proton and deuteron targets for different types hadron production. The predictions …
Twelve years after the discovery of the Top quark, the CDF detector has collected large samples of tt-bar events with integrated luminosities up to 1-1.7 fb^-1, where we are able to probe our knowledge of the Standard Model Top quark. This article will focuss on those analysis results dedicated to find new physics in the Top quark production: measurement of relative fractions of Top pair production mechanisms, searches for a massive resonant state decaying to tt-bar pairs as well as a heavy Top-like quark decaying as the Standard Model Top quark. Besides its production, the Top quark decay is …
