Thu·Jun 4, 2015Thursday·June 4, 2015

1. 01*

   High x Structure Function of the Virtually Free Neutron

   Wim Cosyn🇧🇪 · Misak M. Sargsian🇺🇸

   The pole extrapolation method is applied to the semi-inclusive inelastic electron scattering off the deuteron with tagged spectator protons to extract the high-x structure function of the neutron. This approach is based on the extrapolation of the measured cross sections at different momenta of the spectator proton to the non-physical pole of the bound neutron in the deuteron. The advantage of the method is in the possibility of suppression of the nuclear effects in a maximally model-independent way. The neutron structure functions obtained in this way demonstrate a surprising x dependence at $x\ge 0.6$ and $1.6\le Q^2\le 3.38$ GeV${}^2$, indicating a possible rise of the neutron to proton structure function ratio. If the observed rise is valid in the true deep inelastic region then it may indicate new dynamics in the generation of high-x quarks in the nucleon. One such mechanism we discuss is the possible dominance of short-range isosinglet quark-quark correlations that can enhance the d-quark distribution in the proton.

   ↳ hep-phnucl-exnucl-thPRC(2016)·7 citations
2. 02*

   Role of the ${\Lambda }_c^{+}(2940)$ in the ${\pi }^{-}p\to D^{-}{D}^{0}p$ reaction close to threshold

   Ju-Jun Xie🇨🇳 · Yu-Bing Dong🇨🇳 · Xu Cao🇨🇳

   We report on a theoretical study of the ${\pi }^{-}p\to D^{-}{D}^{0}p$ reaction near threshold within an effective Lagrangian approach. The production process is described by $t$ channel $D^{\ast 0}$ meson exchange, $s$-channel nucleon pole, and $u$ channel ${\Sigma }_c^{++}$ exchange. In our work, the final $D^{0}p$ results from the ground ${\Lambda }_c^{+}(2286)$ state and also dominantly from the excited ${\Lambda }_c^{+}(2940)$ state which is assumed as a $D^{\ast 0}p$ molecular state with spin parity $J^P={\frac{1}{2}}^{+}$ or ${\frac{1}{2}}^{-}$. We calculate the total cross section of the ${\pi }^{-}p\to D^{-}{D}^{0}p$ reaction. It is shown that the spin parity assignment of ${\frac{1}{2}}^{-}$ for ${\Lambda }_c^{+}(2940)$ gives a sizable enhancement for the total cross section in comparison with a choice of $J^p={\frac{1}{2}}^{+}$. However, our theoretical result of the total cross section is sensitive to the value of the cutoff parameter involved in the form factor of the exchanged off-shell particles. Moreover, we also calculate the second order differential cross section and find it can be used to determine the parity of the ${\Lambda }_c^{+}(2940)$. It is expected that our model calculations can be tested by future experiments at J-PARC in Japan.

   ↳ hep-phhep-exnucl-exnucl-thPRD(2015)·45 citations
3. 03*

   Comment on "Lattice determination of $\Sigma$-$\Lambda$ mixing"

   Avraham Gal🇮🇱

   A recent lattice QCD (LQCD) calculation of $\Sigma$-$\Lambda$ mixing by the QCDSF-UKQCD Collaboration [Phys. Rev. D 91, 074512 (2015)] finds a mixing angle about half of that found from the Dalitz-von Hippel (DvH) flavor SU(3) mass formula which relates the $\Sigma$-$\Lambda$ mixing matrix element to known octet baryon mass differences and which has been used widely to evaluate charge symmetry breaking effects in $\Lambda$ hypernuclei. We show that the LQCD-calculated $\Sigma$-$\Lambda$ mixing matrix element and octet baryon masses satisfy the DvH mass formula, concluding thereby that a good LQCD evaluation of $\Sigma$-$\Lambda$ mixing requires an equally good reproduction of octet baryon mass differences which is yet to be demonstrated.

   ↳ nucl-thhep-lathep-phnucl-exPRD(2015)·13 citations
4. 04*

   Cancellation of the sigma meson in thermal models

   Wojciech Broniowski🇵🇱 · Francesco Giacosa🇩🇪 · Viktor Begun🇵🇱

   The by now well-established scalar-isoscalar resonance $f_0(500)$ (the $\sigma$ meson) seems potentially relevant in the evaluation of thermodynamic quantities of a hadronic gas, since its mass is low. However, we recall that its contribution to isospin-averaged observables is, to a surprising accuracy, canceled by the repulsion from the pion-pion scalar-isotensor channel. As a result, in practice one should not incorporate $f_0(500)$ in standard hadronic resonance-gas models for studies of isospin averaged quantities. In our analysis we use the formalism of the virial expansion, which allows one to calculate the thermal properties of an interacting hadron gas in terms of derivatives of the scattering phase shifts, hence in a model-independent way directly from experimentally accessible quantities. A similar cancellation mechanism occurs for the scalar kaonic interactions between the $I=1/2$ channel (containing the alleged $K_0^{\ast }(800)$ or the $\kappa$ meson) and the $I=3/2$ channel.

   ↳ nucl-thhep-phnucl-exPRC(2015)·85 citations
5. 05*

   A covariant model for the nucleon spin structure

   G. Ramalho🇧🇷

   We present the results of the covariant spectator quark model applied to the nucleon structure function $f(x)$ measured in unpolarized deep inelastic scattering, and the structure functions $g_1(x)$ and $g_2(x)$ measured in deep inelastic scattering using polarized beams and targets ($x$ is the Bjorken scaling variable). The nucleon is modeled by a valence quark-diquark structure with $S,P$ and $D$ components. The shape of the wave functions and the relative strength of each component are fixed by making fits to the deep inelastic scattering data for the structure functions $f(x)$ and $g_1(x)$. The model is then used to make predictions on the function $g_2(x)$ for the proton and neutron.

   ↳ hep-phhep-exnucl-exnucl-thProceedings of New Trends in High-Energy …·0 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.