arXiv subjects

D. Gill

Publications and source records attributed to D. Gill.

5 recordsLinked to original sources

arXiv2024

Kohn-Sham-Proca equations for ultrafast exciton dynamics

A long standing problem in time dependent density functional theory (TD-DFT) has been the absence of a functional able to capture excitonic physics under laser pump conditions. Here we introduce a Kohn-Sham-Proca scheme that we demonstrate reproduces both linear response excitonic effects in the absorption in excellent agreement with experiment for a wide range of materials, but also captures excitonic physics in the highly non-linear regime of ultrafast laser pumping, in particular laser fluence dependent "bleaching" (i.e. reduction) of the excitonic weight and the appearance of excitonic side bands. The approach is a procedural functional -- the Kohn-Sham and Proca equations are simultaneously time propagated -- allowing the straight-forward inclusion of, for example, lattice and spin degrees of freedom into excitonic physics.

cond-mat.mtrl-sci↗

arXiv2022

New determination of the branching ratio of the structure dependent radiative $K^{+} \to e^{+} \nu_{e} \gamma$ decay

The branching ratio of the structure dependent (SD) radiative $K^{+} \to e^{+} \nu_{e} \gamma$ decay relative to that of the $K^+\rightarrow e^+ \nu_{e} (\gamma)$ decay including the internal bremsstrahlung (IB) process ($K_{e2(\gamma)}$) has been measured in the J-PARC E36 experiment using plastic scintillator/lead sandwich detectors. In the analysis, the effect of IB was also taken into account in the SD radiative decay as $K_{e2\gamma(\gamma)}^{\rm SD}$. By combining the new data with the previously reported result of the E36 experiment using a CsI(Tl) calorimeter after revision for the IB correction for $K_{e2\gamma(\gamma)}^{\rm SD}$, a new value $Br(K_{e2\gamma(\gamma)}^{\rm SD})/Br(K_{e2(\gamma)})=1.20\pm0.07$ has been determined, which is consistent with a recent lattice QCD calculation, but larger than the expectation of Chiral Perturbation Theory (ChPT) at order $O(p^4)$ and the previous KLOE value. Also, using the method to relate form factor and branching ratio described in the KLOE paper, the present result is consistent with the form factor prediction based on a gauged nonlocal chiral quark model, but larger than ChPT at order $O(p^6)$.

hep-ex↗

arXiv2021

Measurement of structure dependent radiative $K^{+} \rightarrow e^{+} \nu \gamma$ decays using stopped positive kaons

The structure dependent radiative $K^+ \rightarrow e^+ \nu \gamma$ ($K_{e2\gamma}^{\rm SD^+}$) decay was investigated with stopped positive kaons. The $e^+$ momentum spectra containing 574$\pm$30 $K_{e2\gamma}^{\rm SD^+}$ events with a $K^+ \rightarrow \mu^+ \nu$ ($K_{\mu2}$) background of 28$\pm$19 events were measured with and without a photon in coincidence and analyzed with Monte Carlo simulations for acceptance and detector response to extract the ratio of the branching ratio of the $K_{e2\gamma}^{\rm SD^+}$ decay and the $K^+ \rightarrow e^+ \nu$ decay including the internal bremsstrahlung process ($K_{e2(\gamma)}$). A value of $Br(K_{e2\gamma}^{\rm SD^+}) / Br(K_{e2(\gamma)}) = 1.12\pm0.07_{\rm stat} \pm 0.04_{\rm syst}$ was obtained. This indicates a partial branching ratio, $Br(K_{e2\gamma}^{\rm SD^+}, ~{p_e>200~{\rm MeV}/c}, ~{E_\gamma>10~{\rm MeV}})/Br(K_{\mu2}) =(1.85 \pm 0.11_{\rm{stat}} \pm 0.07_{\rm{syst}}) \times10^{-5}$, which is $25\%(\sim$2.5$\sigma)$ higher than the previous experimental result.

hep-ex↗

arXiv1999

K$^-$ Meson Production in the Proton-Proton Reaction at 3.67 GeV/c

The total cross section of the reaction $pp\to ppK^+K^-$ has been determined for proton--proton reactions with $p_{beam}=3.67 GeV/c$. This represents the first cross section measurement of the $pp \to ppK^-K^+$ channel near threshold, and is equivalent to the inclusive $pp\to ppK^-X$ cross section at this beam momentum. The cross section determined at this beam momentum is about a factor 20 lower than that for inclusive $pp\to ppK^+X$ meson production at the same CM energy above the corresponding threshold. This large difference in the $K^+$ and $K^-$ meson inclusive production cross sections in proton-proton reactions is in strong contrast to cross sections measured in sub-threshold heavy ion collisions, which are similar in magnitude at the same energy per nucleon below the respective thresholds.

nucl-ex↗

arXiv1999

Spin Transfer in Exclusive Lambda Production from pp Collisions at 3.67 GeV/c

We report the first polarization transfer measurements for exclusive hyperon production reactions. The normal spin transfer coefficient DNN for pp -> p K+ Lambda is large and negative for forward Lambda production at a beam momentum of 3.67 GeV/c, a result qualitatively consistent with expectations for a mechanism dominated by kaon-exchange and rescattering. The sign of DNN is opposite to that observed in the fragmentation regime for inclusive Lambda production at much higher energies.

nucl-ex↗