12181544
PROTOTYPE TESTS FOR A VERTEX CHAMBER
We describe the design parameters for a pressurized drift chamber under construction for use with the MAC detector at PEP to operate within 3 cm of the beam line. The chamber is constructed of 7 mm diameter tubes of aluminized mylar with wall thickness of 0.10 mm. The tracking device incorporating these tubes is particularly simple to construct and can be configured so that any malfunctioning tube cau be remotely disconnected without affecting overall og erations. Resolution studies made in a SLAC test beam with a prototype over a wide range of gases and operating conditions are reported. The resolutions obtained were in the 10-40 micron range. It was found that the chamber could be operated satisfactorily, using heavily quenched gases, at high pressures (~4 atm) and operating voltages of ~4 kV in a mode for which saturated streamers were initiated with high efficiency by single electrons. Single electron gains for this mode were -108. The streamers were confined to a region of the wire with dimension of the order of a few hundred microns and count rates in excess of lo4 Hz/cm could be sustained with low dead-times. Further studies are in progress on chamber lifetimes with a variety of gas Elliogs. For our specific application this is of particular importance as the vertex chamber is expected to run in regions of high radiation backgrounds. As was expected for a chamber with extended cathodes, lifetimes were good. Actual lifetimes observed to date with our tube configurations have ranged from 0.05 coul/cm integrated current on the anode for 50:50 argon-isobutane to ~1 coul/cm for a mix of 49% A: 50% CO2: 1% C&. The results of these tests show our design goals to be achievable. Additionally they provide a basis on which to design high precision tracking devices particularly in applications where the device is to be operated in regions of difficult physical access or high ambient radiation levels.
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.
123179979
The discovery and measurements of a Higgs boson
The discovery of a Higgs-like boson with a mass of approximately 125?GeV by the ATLAS and CMS experiments at the Large Hadron Collider was announced at CERN on 4 July 2012. The data-set of 5?fb?1 of proton?proton collisions with collected during 2011 and 6?fb?1 with collected in 2012 up to the July discovery was supplemented by an additional 15?fb?1 of data with collected during the rest of 2012. The measurements of the properties of the new boson with the combined data-set have substantially strengthened the evidence that this new particle is indeed the Higgs boson predicted to exist as a consequence of the Brout?Englert?Higgs-mechanism that takes responsibility for generating masses of fundamental particles and for the electroweak symmetry breaking.
64455357
Normalization in DELPHI
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)
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.
121757543
Measurement of single spin asymmetry for direct photon production in pp collisions at 200 GeV/c
The single spin asymmetry for inclusive direct-photon production has been measured using a polarized proton beam of 200 GeV/c with an unpolarized proton target at −0.15 < xf < 0.15 and 2.5 < pt < 3.1 GeV/c at Fermilab. The data on the cross section for pp → γX at 2.5 < pt < 3.8 GeV/c are also provided. The measurement was done using lead-glass calorimeters and photon detectors which surrounded the fiducial area of the calorimeters. Background rejection has been done using these surrounding photon detectors. The cross section obtained is consistent with the results of previous measurements assuming a nuclear dependence of A1.0. The single spin asymmetry, AN, for the direct-photon production is consistent with zero within experimental uncertainty.
123280964
High-energy elastic scattering of pi-plus-minus, k-minus, and anti-p on hydrogen at c.m. angles from 22 degrees to 180 degrees
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.
124067127
PROGRESS REPORT ON THE 200-GeV ACCELERATOR OF THE NATIONAL ACCELERATOR LABORATORY.
123415460
Rationale for a Choice of Secondary Particle Beams at NAL