Upper Limits in the Case That Zero Events are Observed: An Intuitive Solution to the Background Dependence Puzzle

We compare the ``unified approach'' for the estimation of upper limits with an approach based on the Bayes theory, in the special case that no events are observed. The ``unified approach'' predicts, in this case, an upper limit that decreases with the increase in the expected level of background. This seems absurd. On the other hand, the Bayesian approach leads to a result which is background independent. An explanation of the Bayesian result is presented, together with suggested reasons for the paradoxical result of the ``unified approach''.Comment: Latex file (compiled with cernrep.cls included) 5 pages, no figures. To appear in the Proceed. of the workshop on ''Confidence limits'' (CERN, Jan 2000). This paper and related papers also available at http://grwav3.roma1.infn.it

Energy spectrums for proton /200 eV + or = E + or = 1 MeV/ intensities in the outer radiation zone

Energy spectrums for proton intensities in outer radiation zon

Note on the Electron Energy Spectrum in the Inner Van Allen Belt

Electron energy spectrum in the inner van allen bel

Background Estimation in a Gravitational Wave Experiment

The problem to estimate the background due to accidental coincidences in the search for coincidences in gravitational wave experiments is discussed. The use of delayed coincidences obtained by orderly shifting the event times of one of the two detectors is shown to be the most correctComment: Latex file. 6 pages, 3 figures. Submitted to the proceeding of the 3 GWDAW workshop (Rome, dic 1999) (International journal of Modern physics D

Purity control of the XENON1T gas inventory prior to initial filling and studies of mixing properties of impurities in gaseous xenon

Dark matter composes 27% of the universe but its presence is inferred only from gravitational phenomena. Direct detection experiments, such as Xenon1T, attempt to detect the scattering of dark matter particles with the detector target, in this case xenon nuclei. The experiment Xenon1T employs 3.3 tonnes of liquid xenon in a Time Projection Chamber (TPC). The TPC is a detector that employs electromagnetic fields in a sensitive volume for 3-d position reconstruction and particle identification. Since dark matter scattering is a rare event, it is necessary to reduce the background to improve the sensitivity of the detector. It is necessary to monitor two kind of impurities in liquid xenon: radioactive impurities such as krypton (present in commercially available xenon at ppb level), since it increases the background, and electronegative molecules such as oxygen and water, since they lower the electron life-time and disrupts the well functioning of the TPC. In this work, the measurements of the xenon inventory prior to filling is presented using the technique of gas chromatography. Some of the bottles measurements are presented and the total purity is summarized. In the second part, a study of gas mixing as solution of inconsistency measurements in the previous part is presented, and different solutions to speed up the gas diffusion are tested. Finally, since gas chromatography is not sensitive to helium, a measurement of the helium concentration in the full xenon inventory is presented using the technique of mass spectrometry