Thu·Apr 16, 2015Thursday·April 16, 2015

1. 01*

   Is $\hat{q}$ a physical quantity or just a parameter? and other unanswered questions in High-$p_T$ Physics

   M. J. Tannenbaum🇺🇸

   The many different theoretical studies of energy loss of a quark or gluon traversing a medium have one thing in common: the transport coefficient of a gluon in the medium, $\hat{q}$, which is defined as the mean 4-momentum transfer${}^2$, $⟨q^2⟩$, by a gluon to the medium per gluon mean free path, ${\lambda }_{\mathrm{mfp}}$. In the original BDMPSZ formalism, the energy loss of an outgoing parton, $-dE/dx$, per unit length ($x$) of a medium with total length $L$, due to coherent gluon bremsstrahlung, is proportional to the $⟨q^2⟩$ and takes the form: $-dE/dx\simeq {\alpha }_s⟨q^2(L)⟩={\alpha }_s{\mu }^{2}L/{\lambda }_{\mathrm{mfp}}={\alpha }_s\hat{q}L$ , where $\mu$, is the mean momentum transfer per collision. Thus, the total energy loss in the medium goes like $L^2$. Additionally, the accumulated momentum${}^2$, $⟨k_{\perp }^2⟩$, transverse to a gluon traversing a length $L$ in the medium is well approximated by $⟨k_{\perp }^2⟩\approx ⟨q^2(L)⟩=\hat{q}L$. A simple estimate shows that the $⟨k_{\perp }^2⟩\approx \hat{q}L$ should be observable at RHIC at $\sqrt{s_{NN}}=200$ GeV via the broadening of di-hadron azimuthal correlations resulting in an azimuthal width $\sim \sqrt{2}$ larger in Au$+$Au than in $p+p$ collisions . Measurements relevant to this issue will be discussed as well as recent STAR jet results presented at QM2014. Other topics to be discussed include the danger of using forward energy to define centrality in $p(d)+$A collisions for high $p_T$ measurements, the danger of not using comparison $p+p$ data at the same $\sqrt{s}$ in the same detector for $R_{AA}$ or lately for $R_{pA}$ measurements.

   nucl-exJ.Phys.Conf.Ser.(2017)·0 citations
2. 02*

   Evidence of Cluster Structure of ${}^9$Be from ${}^3$He+${}^9$Be Reaction

   S.M. Lukyanov (1)🇷🇺 · M.N. Harakeh (2)🇳🇱 · M.A. Naumenko (1) · Yi Xu (3) · W.H. Trzaska (4)🇫🇮 · V. Burjan (3)🇨🇿 · V. Kroha (3) · J. Mrazek (3)🇨🇿 · V. Glagolev (3)🇷🇺 · Š. Piskoř (3) · E.I. Voskoboynik (1) · S.V. Khlebnikov (5) and 6 other authors

   The study of inelastic scattering and multi-nucleon transfer reactions was performed by bombarding a ${}^9$Be target with a ${}^3$He beam at an incident energy of 30 MeV. Angular distributions for ${}^9$Be(${}^3$He,${}^3$He)${}^9$Be, ${}^9$Be(${}^3$He,${}^4$He)${}^8$Be, ${}^9$Be(${}^3$He,${}^5$He)${}^7$Be, ${}^9$Be(${}^3$He,${}^6$Li)${}^6$Li and ${}^9$Be(${}^3$He,${}^5$Li)${}^7$Li reaction channels were measured. Experimental angular distributions for the corresponding ground states (g.s.) were analysed within the framework of the optical model, the coupled-channel approach and the distorted-wave Born approximation. Cross sections for channels leading to unbound ${}^5$He${}_{g.s.}$, ${}^5$Li${}_{g.s.}$ and ${}^8$Be systems were obtained from singles measurements where the relationship between the energy and the scattering angle of the observed stable ejectile is constrained by two-body kinematics. Information on the cluster structure of ${}^9$Be was obtained from the transfer channels. It was concluded that cluster transfer is an important mechanism in the investigated nuclear reactions. In the present work an attempt was made to estimate the relative strengths of the interesting ${}^8$Be+$n$ and ${}^5$He+$\alpha$ cluster configurations in ${}^9$Be. The branching ratios have been determined confirming that the ${}^5$He+$\alpha$ configuration plays an important role. The configuration of ${}^9$Be consisting of two bound helium clusters ${}^3$He+${}^6$He is significantly suppressed, whereas the two-body configurations ${}^8$Be+$n$ and ${}^5$He+$\alpha$ including unbound ${}^8$Be and ${}^5$He are found more probable.

   nucl-exJ.Phys.Conf.Ser.(2016)·13 citations
3. 03*

   Semi-microscopic modeling of heavy-ion fusion reactions with multi-reference covariant density functional theory

   K. Hagino🇯🇵 · J.M. Yao🇯🇵

   We describe low-lying collective excitations of atomic nuclei with the multi-reference covariant density functional theory, and combine them with coupled-channels calculations for heavy-ion fusion reactions at energies around the Coulomb barrier. To this end, we use the calculated transition strengths among several collective states as inputs to the coupled-channels calculations. This approach provides a natural way to describe anharmonic multi-phonon excitations as well as a deviation of rotational excitations from a simple rigid rotor. We apply this method to subbarrier fusion reactions of ${}^{58}$Ni+${}^{58}$Ni, ${}^{58}$Ni+${}^{60}$Ni and ${}^{40}$Ca+${}^{58}$Ni systems. We find that the effect of anharmonicity tends to smear the fusion barrier distributions, better reproducing the experimental data compared to the calculations in the harmonic oscillator limit.

   ↳ nucl-thnucl-exPRC(2015)·14 citations
4. 04*

   Quark-hadron duality constraints on \gamma Z box corrections to parity-violating elastic scattering

   N. L. Hall🇦🇺 · P. G. Blunden🇨🇦 · W. Melnitchouk🇺🇸 · A. W. Thomas🇦🇺 · R. D. Young🇦🇺

   We examine the interference \gamma Z box corrections to parity-violating elastic electron--proton scattering in the light of the recent observation of quark-hadron duality in parity-violating deep-inelastic scattering from the deuteron, and the approximate isospin independence of duality in the electromagnetic nucleon structure functions down to Q^2 \approx 1 GeV^2. Assuming that a similar behavior also holds for the \gamma Z proton structure functions, we find that duality constrains the \gamma Z box correction to the proton's weak charge to be \Re e\, \square_{\gamma Z}^V = (5.4 \pm 0.4) \times 10^{-3} at the kinematics of the Q_{\text{weak}} experiment. Within the same model we also provide estimates of the \gamma Z corrections for future parity-violating experiments, such as MOLLER at Jefferson Lab and MESA at Mainz.

   ↳ nucl-thhep-phnucl-exPLB(2016)·29 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.