121947981
Modified frequentist analysis of search results (The CL(s) method)
The statistical analysis of direct Higgs searches at LEP is described. The likelihood ratio with respect to the background-only hypothesis (or a related teststatistic) is used to order experimental results. The ratio of the confidences in the signal+background to background hypotheses, so-called “CLs”, is used to set lower bounds on the Higgs boson mass. The excluded mass interval which results has an untraditional but useful interpretation which differs both from frequentist intervals which require coverage and from Bayesian credible intervals. Issues such as flip-flopping, experimental uncertainties, discovery significance and the transition to measurement are discussed. The interpretation of results of searches for new particles and phenomena near the sensitivity limit of an experiment is a common problem in particle physics. The loss of sensitivity may be due to a combination of small signal rates, the presence of background comparable to the expected signal, and the loss of discrimination between two models due to insufficient experimental resolution. The search for Higgs bosons at LEP is such an experiment. The LEP experiments have separately, and in collaboration through the LEP working group for Higgs boson searches, developed a nearly common strategy for carrying out and reporting the results of their direct searches. For the time being no significant evidence of Higgs production at LEP has been observed and lower bounds on Higgs masses have been reported. In this report I hope to explain how the lower bound is derived with the so-called CLs method, why this method is used, and how to interpret the result. Since the SM Higgs search has the lowest number of free parameters (1) it will be used to illustrate the features of the CLs method. The generalization to models with several parameters (e.g. the MSSM) is straightforward if more time-consuming in practice. The techniques described in this talk are in fact successfully used in general scans over the many-parameter space of the MSSM in searches for the h and A neutral bosons, in 2-parameter searches for charged Higgs bosons of a general 2-doublet Higgs model, and in combined searches for sparticles by the LEP working group for SUSY particle searches. The individual LEP experiments use either the likelihood ratio, a close approximation of the likelihood ratio, or the integral of the likelihood function as their test-statistics in Higgs searches. Exhaustive studies [1] have shown that they have similar performances for exclusion. To simplify my presentation I only described the likelihood ratio and I will do the same here. I will also show how the CLs method can be applied in other contexts with an example of a hypothetical search for new physics via deviations of a parameter which is measured with normal-distributed uncertainty.
35536172
In-orbit performance of the EPIC-MOS detectors on XMM-Newton
XMM-Newton was launched into space on a highly eccentric 48 hour orbit on December 10th 1999. XMM-Newton is now in its fifth year of operation and has been an outstanding success, observing the Cosmos with imaging, spectroscopy and timing capabilities in the X-ray and optical wavebands. The EPIC-MOS CCD X-ray detectors comprise two out of three of the focal plane instruments on XMM-Newton. In this paper we discuss key aspects of the current status and performance history of the charge transfer ineffiency (CTI), energy resolution and spectral redistribution function (rmf) of EPIC-MOS in its fifth year of operation.
120705876
Presentation of search results: the CLs technique
I describe a framework for the presentation of search results which is motivated by frequentist statistics. The most well-known use of this framework is for the combined search for the Higgs boson at LEP. A toy neutrino oscillations experiment is used to illustrate the rich information available in the framework for exclusion and discovery. I argue that the so-called CLs technique for setting limits is appropriate for determining exclusion intervals while the determination of confidence intervals advocated by Feldman and Cousins' method is more appropriate for treating established signals, i.e. going beyond discovery to measurement. (From the workshop 'Advanced Statistical Techniques in Particle Physics', 18–22 March 2002)
123487894
The small angle tile calorimeter in the DELPHI experiment
Abstract The Small angle TIle Calorimeter (STIC) provides calorimetric coverage in the very forward region of the DELPHI experiment at the CERN LEP collider. The structure of the calorimeters, built with a so-called “shashlik” technique, gives a perfectly hermetic calorimeter and still allows for the insertion of tracking detectors within the sampling structure to measure the direction of the showering particle. A charged-particle veto system, composed of two scintillator layers, makes it possible to trigger on single photon events and provides e–γ separation. Results are presented from the extensive studies of these detectors in the CERN testbeams prior of installation and of the detector performance at LEP.
64455357
Normalization in DELPHI
110699804
The small angle tile calorimeter project in DELPHI
The new Small Angle TIIe Calorimeter (STIC) covers the forward regions in DELPHI. The main motivation for its construction was to achieve a systematic error of 0.1% on the luminosity determination. This detector consists of a “shashlik” type calorimeter, equipped with two planes of silicon pad detectors placed respectively after 4 and 7.4 radiation lengths. A veto counter, composed of two scintillator planes, covers the front of the calorimeter to allow ϱ − γ separation and to provide a neutral energy trigger. The physics motivations for this project, results from extensive testbeam measurements and the performance during the 1994 LEP run are reported here.
123088836
Search for short-lived particles in high-energy neutrino interactions identified using a hybrid emulsion-spark-chamber arrangement
Seventeen litres of nuclear photographic emulsion have been exposed to the wide-band neutrino beam at Fermilab. Tracks of secondaries from neutrino interactions in the emulsion were observed in a wide-gap spark chamber and a system of narrow-gap spark chambers and counters down beam. From measurements on the tracks in the wide-gap chamber the positions of vertices from which the secondaries diverged were predicted and 37 neutrino interactions in emulsion were located. Factors affecting the efficiency of location of events searched for (approx.20% in this experiment) are assessed and conclusions drawn about means of optimizing the design of experiments employing emulsion hybrid techniques. In one of the interactions a secondary track gave rise to three tracks after a distance of 182 ..mu..m. Further measurements made on this event do not alter the previous conclusion of its most likely interpretation as the decay of a short-lived particle of lifetime approx.6 x 10/sup -13/ sec.
124083721
SOME ASPECTS OF TARGETING SYSTEMS FOR A SLOW EXTRACTED BEAM AT THE AGS.
122023821
Measurement of the double-spin asymmetry ALL for inclusive multi-γ pair production with 200 GeV/c polarized proton beam and polarized proton target
The invariant double-differential cross section, E1E2d6 delta/dp(1)3dp(2)3, and the double-spin asymmetry, A(LL), for inclusive multi-gamma pair production in which gamma-rays came from neutral mesons were measured with a 200 GeV/c longitudinally-polarized proton beam and a longitudinally-polarized proton target. Most of the multi-gamma pairs comes from two-jet type events which are sensitive to partonic interaction. The A(LL) values were found to be consistent with zero. The invariant double-differential cross section for inclusive pi0pi0 production was also measured. These measured cross sections are consistent with LUND Monte Carlo simulations. Using the LUND Monte Carlo simulation package with the Carlitz-Kaur model of spin dependent distribution functions of valence quarks, the A(LL) values have been compared with theoretical predictions of gluon polarization, DELTAG/G. The results put restrictions on the size of DELTAG/G in the region of 0.05 less-than-or-similar-to x less-than-or-similar-to 0.35.
123662576
Observation of a likely example of the decay of a charmed particle produced in a high energy neutrino interaction
Abstract In a study of neutrino interactions occurring in nuclear emulsion, an event has been found that is most readily interpreted as the decay of a charmed particle with lifetime a few times 10 −13 s.
123035937
The design and performance of the FNAL high-energy polarized beam facility
We describe a new polarized-proton and -antiproton beam with 185-GeV/c momentum in the Fermilab MP beam line which is currently operational. The design uses the parity-conserving decay of lambda and antilambda hyperons to produce polarized protons and antiprotons, respectively. A beam-transport system minimizes depolarization effects and uses a set of 12 dipole magnets that rotate the beam-particle spin direction. A beam-tagging system determines the momentum and polarization of individual beam particles, allowing a selection of particles in definite intervals at momentum and polarization. We measured polarization of the beam by using two types of polarimeters, which verified the determination of polarization by a beam-particle tagging system. Two of these processes are the inverse-Primakoff effect and the Coulomb-nuclear interference (CNI) in elastic proton-proton scattering. Another experiment measured the {pi}{sup 0} production asymmetry of large-x{sub F} values; this process may now be used as an on-line beam polarimeter. 9 refs., 9 figs.