H. E. Henrikson

Limits on cold dark matter from the Gotthard Ge experiment

Abstract Data from a high purity Ge detector operated in the Gotthard underground laboratory, corresponding to 51.6 kg day, were used to set limits on cold dark matter. In particular, Dirac neutrinos with masses between 10 and 2400 GeV are ruled out. A new lower limit on the half-life for the decay of the electron into weakly interacting particles of 1.9 × 1023 yr at 68% CL was also derived.

Search for ββ decay in 136Xe: new results from the Gotthard experiment

Abstract The Gotthard Xe experiment has taken an additional 6013 hours of data with an upgraded readout system. Lower limits for the half-life of the double beta decay in 136 Xe are T 1/2 0 ν >4.4×10 23 yr (including 6830 hours taken in an earlier phase), T 1/2 0 νχ 0 >0.72×10 22 yr and T 1/2 2 ν >3.6×10 20 yr at 90% confidence level. Alpha spectroscopy, as well as βα and αα coincidence techniques lead to a determination of the activity of the gas of 10 −12 g/g effective of 232 Th and 238 U. Evaluations of background strongly suggest that an appreciable fraction of the ββ -candidates comes from the allowed 2 ν decay.

Low background study of the neutrinoless double beta decay of 76-GE and upper limit for neutrino mass

Abstract A Ge detector system was built possessing significnt reduced background, from natural radioactivities, notably 208-TI (2.6 MeV line). After a 2600 h measuring period a lower limit for the half life of the neutrinoless double beta decay in 76- Ge of T( 1 2 o ν) > 1.7 × 10 22 yr (1σ) was obtained, corresponding to a neutrino mass upper limit of 22 eV.

Experimental study of neutrino oscillations at a fission reactor

Abstract The electron-antineutrino spectrum has been measured at a position 8.75 m from the “point-like” core of the ILL 235 U fission reactor, using the reaction ν e + p → e + + n. Positrons and neutrons were detected in coincidence by means of a low-background liquid scintillator and a 3 He detector system. The observed neutron correlated positron spectrum is consistent with theoretical predictions assuming no neutrino oscillations. Upper limits for the oscillation parameter are presented.

A search for double beta decay in 76Ge

This thesis describes a search for the double beta (ββ) decay of ⁷⁶Ge using an array of eight high purity, high resolution germanium detectors containing a total of 3.9 x 10²⁴ ⁷⁶Ge nuclei. There are three modes of ββ decay: neutrinoless (0ѵ)ββ decay, ββ decay with Majoron emission (x⁰ββ decay) and two neutrino (2ѵ)ββ decay. The first two modes violate lepton number conservation, while the third is allowed by the Standard Model. 0ѵββ decay may take place to the ground state of the daughter nucleus (0⁺ → 0⁺ transition) or to an excited state of the daughter nucleus (0⁺ → 2⁺ transition). The detector was operated for a total time of 2033 h (0.23 y) which translates to 1.30 kg-y. The background at the ββ decay transition energy was 0.53 counts keV⁻¹ y⁻¹ (10²³ ⁷⁶Ge nuclei)⁻¹. No evidence for double beta decay of any sort was found and the half life limits are T0ѵ½(0⁺ → 0⁺) > 1.2 x 10²³ y, T0ѵ½(0⁺ → 2⁺) > 2 x 10²² y, Tχo½ > 8 x 10²⁰ y, and T2ѵ½ > 2 x 10²⁰ y, all at 90% c.l. The limit for the neutrinoless mode translates to an upper limit of between 16 and 1.6 eV on the Majorana mass of the neutrino, depending on the nuclear matrix element used.

Limit on double beta decay with majoron emission

Abstract A search for majoron emission accompanying neutrinoles double beta decay in 76 Ge was conducted with a low background germanium detector in the St. Gotthard underground laboratory. No evidence for neutrinoless double beta decay with or without majoron emission was found, with a lower limit for the half life of the majoron branch of t 1 2 > 1.2 × 10 21 yr at 90% confidence level.

Investigations of fast neutron production by 190 GeV/c muon interactions on different targets

AbstractThe production of fast neutrons (1 MeV - 1 GeV) in high energy muon-nucleusinteractions is poorly understood, yet it is fundamental to the understanding of thebackground in many underground experiments. The aim of the present experiment(CERN NA55) was to measure spallation neutrons produced by 190 GeV/c muonsscattering on carbon target. We have investigated the energy spectrum and angulardistribution of spallation neutrons, and we report the result of our measurement ofthe neutron production di erential cross section. Key words: underground neutron flux, fast neutron production, muon-nucleusinteraction, time-of-flight PACS: 25.30.Mr, 25.20.-x, 25.40.Sc, 28.20.-v 1 IntroductionNeutrons are an important source of background in many low rate under-ground experiments. Detectors such as the Palo Verde detector [1], theKamiokandedetector[2],theEdelweiss detector[3],theStanfordUnderground corresponding author. Email address: verene.chazal@unine.ch (V. Chazal ). 1 Present address: Jet Propulsion Laboratory, Pasadena CA 91109, U.S.A.

A point focusing graphite spectrometer for low energy X-rays☆

Abstract A point-focusing graphite crystal spectrometer has been developed for the 2–10 keV X-ray range. With an efficiency of 10−5 and an energy resolution of 1%, it is a suitable instrument for the study of X-rays from light pionic atoms.

Experimental determination of the relativistic fine structure splitting in a pionic atom

Abstract Using a high-resolution crystal spectrometer, we have measured the energy splitting of the pionic 5g-4f and 5f-4d transitions in Ti. The observed fine structure splitting agrees, within experimental error of 3%, with the splitting arising from the calculated relativistic term and other small corrections for spinless particles.

Investigations of fast neutron production by 190-GeV/c muon interactions on graphite target

AbstractThe production of fast neutrons (1 MeV - 1 GeV) in high energy muon-nucleusinteractions is poorly understood, yet it is fundamental to the understanding of thebackground in many underground experiments. The aim of the present experiment(CERN NA55) was to measure spallation neutrons produced by 190 GeV/c muonsscattering on carbon target. We have investigated the energy spectrum and angulardistribution of spallation neutrons, and we report the result of our measurement ofthe neutron production di erential cross section. Key words: underground neutron flux, fast neutron production, muon-nucleusinteraction, time-of-flight PACS: 25.30.Mr, 25.20.-x, 25.40.Sc, 28.20.-v 1 IntroductionNeutrons are an important source of background in many low rate under-ground experiments. Detectors such as the Palo Verde detector [1], theKamiokandedetector[2],theEdelweiss detector[3],theStanfordUnderground corresponding author. Email address: verene.chazal@unine.ch (V. Chazal ). 1 Present address: Jet Propulsion Laboratory, Pasadena CA 91109, U.S.A.