Mon·Sep 7, 2015Monday·September 7, 2015

1. 01*

   Search for $\eta$-mesic helium via $dd\to {}^3\mathrm{He}n{\pi }^0$ reaction by means of the WASA-at-COSY facility

   Magdalena Skurzok🇵🇱

   In November 2010, we performed a search for a ${}^4\text{mbox}He$-$\eta$ bound state by measuring the excitation function for the $dd\to$ ${}^3\text{mbox}Hen\pi {}^0$ and $dd\to$ ${}^3\text{mbox}Hep\pi {}^{-}$ reactions in the vicinity of the $\eta$ production threshold with the WASA detector.~The experiment was carried out using a deuteron COSY beam and deuteron pellet target. The beam momentum varied continuously in each of acceleration cycle from 2.127 GeV/c to 2.422 GeV/c, which corresponds to a range of excess energy $Q$ $\in$(-70,30)MeV. This dissertation is about the search for ${}^4\text{mbox}He$-$\eta$ bound state in $dd\to$ ${}^3\text{mbox}Hen\pi {}^0$ reaction. The excitation function for the process was determined after identification of all outgoing particles and the application of the selection conditions based on Monte Carlo simulations of $\eta$-mesic helium production and its decay via excitation of the $N^{\ast }$ resonance. No narrow structure of the $\eta$-mesic helium was observed in the excitation function. The upper limit of the total cross section for the bound state formation and its decay in $dd\to ({}^4\text{mbox}He$-$\eta {)}_{bound}\to$ ${}^3\text{mbox}Hen\pi {}^0$ process was determined on the 90% confidence level. It varies from 21 to 36 nb for the bound state width ranging from 5 MeV to 50 MeV, respectively. However, an indication for a broad state was observed. The kinematic region, where we expect the evidence of the signal from the bound state, cannot be fully described only by the combination of the considered background processes. In contrast, the experimental excitation function is very well fitted by the background contributions for the region where the signal is not expected.

   nucl-ex10 citations
2. 02*

   Measurements of charged particle spectra and nuclear modification factor in p+Pb collisions with the ATLAS detector

   Petr Balek (for the ATLAS Collaboration)🇨🇿

   The ATLAS detector at the LHC obtained the sample of p+Pb data at $\sqrt{s_{NN}}=$5.02TeV with integrated luminosity of 25nb${}^{-1}$, which can be compared to the pp data obtained by interpolating pp measurements at $\sqrt{s}=$2.76TeV and 7TeV. Due to the excellent capabilities of the ATLAS detector, and its stable operation in heavy ion as well as proton-proton physics runs, the data allow measurements of the nuclear modification factor, ratio of heavy ion charged particle spectra divided by pp reference, in different centrality classes over a wide range of rapidity. The charged particle nuclear modification factor is found to vary significantly as a function of transverse momentum with a stronger dependence in more peripheral collisions.

   ↳ hep-exnucl-exNPA(2014)·5 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.