J.D. Davies

The scintillation efficiency of sodium and iodine recoils in a NaI(Tl) detector for dark matter searches

Abstract Searches for weakly interacting massive particles that may constitute the Galactic dark matter can be based on the detection of nuclear recoil events in NaI(Tl) scintillation detectors. For this purpose it is necessary to know the relative scintillation efficiency for nuclear recoil events. Presented here are the results of measurements of the efficiency for conversion of low energy I and Na nuclear recoil events into scintillation light in NaI(Tl). The experiments were performed using elastic scattering of monoenergetic neutrons of energy 3.2–5.5 MeV. The relative scintillation efficiency was found to be about 30% for Na recoils, down to 15 keV, and 8% for I recoils, down to 27 keV.

Measurement of strong interaction effects in Σ atoms

Abstract X-rays produced by Σ-atoms in targets of O, Mg, Al, Si and S have been observed. The shifts, widths and yields of the last observed X-ray due to the strong interaction have been measured. A fit to the data using the optical model gives a value for the effective scattering length which appears to differ significantly from the free value.

Observation of kaonic hydrogen atom X-rays

Abstract A special liquid-hydrogen target has been used with a stopping kaon beam in order to search for the X-rays from kaonic hydrogen atoms. A peak at 6.52 ± 0.06 keV, consistent with the unshifted energy of 2p-1s X-rays from K − −p atoms, has been observed with a yield of about 0.1%. The energy shift would imply rather small values for the real K − −p scattering length at threshold.

Measurement of kaonic and pionic X-rays from liquid helium

Abstract The strong interaction widths, shifts and relative intensities have been measured for the last observed X-ray transitions in kaonic and pionic helium. The effect of the strong interaction on the 2p level in kaonic helium was much larger than anticipated from optical-model calculations. The energy shift of the 2p level was determined to be −35±12eV and the natural line width 30±30eV, whereas optical-model calculations predicted a shift and width of approximately 0.1 eV and 2.0 eV, respectively.

The scintillation efficiency for calcium and fluorine recoils in CaF2 and carbon and fluorine recoils in C6F6 for dark matter searches

Abstract Results are presented of neutron scattering experiments to measure the relative scintillation effeciency of low energy calcium and fluorine recoils in a CaF 2 (Eu) scintillator, and carbon and fluorine recoils in a C 6 F 6 scintillator. These measurements are needed to calibrate these fluorine-containing scintillators for uses as possible detectors of weakly interacting massive particles (WIMPs) that may constitute the dark matter of the Universe. The relative scintillation efficiency of CaF 2 (0.5% Eu) below 100 keV was found to be about 12% for fluorine recoils and 8% for calcium recoils. In C 6 F 6 quenching of the scintillation was found to be very severe, limiting the efficiency relative to electrons for carbon recoils to 0.7%, with a limit for fluorine recoils of

Measurement of X-rays from anti-protonic hydrogen and deuterium

Abstract The yields of K and L series X-rays from pp atoms and of the L series X-rays from pd atoms have been measured at gas densities of 0.25, 0.92, 2.0 and 10.0ρ STP . For pp atoms the strong interaction shift and width for the 1s state and the width of the 2p state have been measured. The results are in good agreement with the predictions of potential models.

Strong interaction effects in pionic atoms

Abstract Strong-interaction shifts and widths in pionic atoms of Al, Si, S, Ca, Fe, Cu, Zn, Ag, Cd, Pb, Bi and U have been measured. Various forms for an effective pion-nucleus potential have been fitted to the data for 2p levels and the predictions of these potentials compared with the results for 3d and 4f levels. The predictions have also been compared with available data for 1s states. The effects on pionic atoms of strongly bound pionic states, which it has recently been suggested might exist, are discussed.

K-series X-rays from anti-protonic hydrogen and deuterium

Abstract Energies and yields of K-series X-rays from pp atoms have been measured with two gas scintillation proportional detectors at target gas densities of 0.25 and 0.92 ρ STP . Values for the strong interaction shift and width of the 1s state obtained from the X-ray spectra are compared with the predictions of a variety of theoretical models. Upper limits for the yield of K-series X-rays from pd atoms have also been obtained.

Liquid xenon as a dark matter detector. Prospects for nuclear recoil discrimination by photon timing

Abstract Two mechanisms lead to liquid xenon scintillatlon, and are excited differently by incident electrons and by heavy charged nuclei. This could be used to discriminate nuclear recoil events from radioactive background in a search for hypothetical Galactic dark matter particles. To achieve low energy threshold a likelihood analysis is proposed using the time intervals between detected photons. Results are presented of Monte Carlo simulations, showing the background rejection achievable as a function of the number of detected photons. Some comments are included on background discrimination by simultaneous measurement of scintillation and ionization signals.

Measurement of the spin and temperature dependence of ddµ molecule formation rate in solid and liquid deuterium

The ddµ molecule formation rate is experimentally measured for the two hyperfine states of the dµ-atom in the temperature range of 5–30 K. Results are consistent with a preliminary measurement by the TRIUMF group and contradict theoretical predictions. The work has been performed on the JINR phasotron (Dubna).