A Study of Snippet Length and Informativeness: Behaviour, Performance and User Experience

The design and presentation of a Search Engine Results Page (SERP) has been subject to much research. With many contemporary aspects of the SERP now under scrutiny, work still remains in investigating more traditional SERP components, such as the result summary. Prior studies have examined a variety of different aspects of result summaries, but in this paper we investigate the influence of result summary length on search behaviour, performance and user experience. To this end, we designed and conducted a within-subjects experiment using the TREC AQUAINT news collection with 53 participants. Using Kullback-Leibler distance as a measure of information gain, we examined result summaries of different lengths and selected four conditions where the change in information gain was the greatest: (i) title only; (ii) title plus one snippet; (iii) title plus two snippets; and (iv) title plus four snippets. Findings show that participants broadly preferred longer result summaries, as they were perceived to be more informative. However, their performance in terms of correctly identifying relevant documents was similar across all four conditions. Furthermore, while the participants felt that longer summaries were more informative, empirical observations suggest otherwise; while participants were more likely to click on relevant items given longer summaries, they also were more likely to click on non-relevant items. This shows that longer is not necessarily better, though participants perceived that to be the case - and second, they reveal a positive relationship between the length and informativeness of summaries and their attractiveness (i.e. clickthrough rates). These findings show that there are tensions between perception and performance when designing result summaries that need to be taken into account

B Physics at the Tevatron: Run II and Beyond

This report provides a comprehensive overview of the prospects for B physics at the Tevatron. The work was carried out during a series of workshops starting in September 1999. There were four working groups: 1) CP Violation, 2) Rare and Semileptonic Decays, 3) Mixing and Lifetimes, 4) Production, Fragmentation and Spectroscopy. The report also includes introductory chapters on theoretical and experimental tools emphasizing aspects of B physics specific to hadron colliders, as well as overviews of the CDF, D0, and BTeV detectors, and a Summary.Comment: 583 pages. Further information on the workshops, including transparencies, can be found at the workshop's homepage: http://www-theory.lbl.gov/Brun2/. The report is also available in 2-up http://www-theory.lbl.gov/Brun2/report/report2.ps.gz or chapter-by-chapter http://www-theory.lbl.gov/Brun2/report

Measurement of the diffractive structure function in deep inelastic scattering at HERA

This paper presents an analysis of the inclusive properties of diffractive deep inelastic scattering events produced in $ep$ interactions at HERA. The events are characterised by a rapidity gap between the outgoing proton system and the remaining hadronic system. Inclusive distributions are presented and compared with Monte Carlo models for diffractive processes. The data are consistent with models where the pomeron structure function has a hard and a soft contribution. The diffractive structure function is measured as a function of \xpom, the momentum fraction lost by the proton, of $\beta$, the momentum fraction of the struck quark with respect to \xpom, and of $Q^2$. The \xpom dependence is consistent with the form \xpoma where $a~=~1.30~\pm~0.08~(stat)~^{+~0.08}_{-~0.14}~(sys)$ in all bins of $\beta$ and $Q^2$. In the measured $Q^2$ range, the diffractive structure function approximately scales with $Q^2$ at fixed $\beta$. In an Ingelman-Schlein type model, where commonly used pomeron flux factor normalisations are assumed, it is found that the quarks within the pomeron do not saturate the momentum sum rule.Comment: 36 pages, latex, 11 figures appended as uuencoded fil

Search for the Higgs boson in events with missing transverse energy and b quark jets produced in proton-antiproton collisions at s**(1/2)=1.96 TeV

We search for the standard model Higgs boson produced in association with an electroweak vector boson in events with no identified charged leptons, large imbalance in transverse momentum, and two jets where at least one contains a secondary vertex consistent with the decay of b hadrons. We use ~1 fb-1 integrated luminosity of proton-antiproton collisions at s**(1/2)=1.96 TeV recorded by the CDF II experiment at the Tevatron. We find 268 (16) single (double) b-tagged candidate events, where 248 +/- 43 (14.4 +/- 2.7) are expected from standard model background processes. We place 95% confidence level upper limits on the Higgs boson production cross section for several Higgs boson masses ranging from 110 GeV/c2 to 140 GeV/c2. For a mass of 115 GeV/c2 the observed (expected) limit is 20.4 (14.2) times the standard model prediction.Comment: 8 pages, 2 figures, submitted to Phys. Rev. Let

Observation and Mass Measurement of the Baryon Ξb−\Xi^-_b

We report the observation and measurement of the mass of the bottom, strange baryon $\Xi^-_b$ through the decay chain $\Xi^-_b \to J/\psi \Xi^-$, where $J/\psi \to \mu^+ \mu^-$, $\Xi^- \to \Lambda \pi^-$, and $\Lambda \to p \pi^-$. Evidence for observation is based on a signal whose probability of arising from the estimated background is 6.6 x 10^{-15}, or 7.7 Gaussian standard deviations. The $\Xi^-_b$ mass is measured to be $5792.9\pm 2.5$ (stat.) $\pm 1.7$ (syst.) MeV/$c^2$.Comment: Minor text changes for the second version. Accepted by Phys. Rev. Let

Polarizations of J/psi and psi(2S) Mesons Produced in ppbar Collisions at 1.96 TeV

We have measured the polarizations of \jpsi and \psiprime mesons as functions of their transverse momentum \pt when they are produced promptly in the rapidity range $|y|<0.6$ with \pt \geq 5 \pgev. The analysis is performed using a data sample with an integrated luminosity of about 800 \ipb collected by the CDF II detector. For both vector mesons, we find that the polarizations become increasingly longitudinal as \pt increases from 5 to 30 \pgev. These results are compared to the predictions of nonrelativistic quantum chromodynamics and other contemporary models. The effective polarizations of \jpsi and \psiprime mesons from $B$-hadron decays are also reported.Comment: 8 pages, 7 figures, published in Physical Review Letter

Search for Third Generation Vector Leptoquarks in p anti-p Collisions at sqrt(s) = 1.96 TeV

We describe a search for a third generation vector leptoquark (VLQ3) that decays to a b quark and tau lepton using the CDF II detector and 322 pb^(-1) of integrated luminosity from the Fermilab Tevatron. Vector leptoquarks have been proposed in many extensions of the standard model (SM). Observing a number of events in agreement with SM expectations, assuming Yang-Mills (minimal) couplings, we obtain the most stringent upper limit on the VLQ3 pair production cross section of 344 fb (493 fb) and lower limit on the VLQ3 mass of 317 GeV/c^2 (251 GeV/c^2) at 95% C.L.Comment: 7 pages, 2 figures, submitted to PR

Precise measurement of the top quark mass in the lepton+jets topology at CDF II

We present a measurement of the mass of the top quark from proton-antiproton collisions recorded at the CDF experiment in Run II of the Fermilab Tevatron. We analyze events from the single lepton plus jets final state ($t\bar t\to W^+bW^-\bar b\to l\nu b q \bar q'\bar b$). The top quark mass is extracted using a direct calculation of the probability density that each event corresponds to the $t\bar t$ final state. The probability is a function of both the mass of the top quark and the energy scale of the calorimeter jets, which is constrained {\it in situ} by the hadronic $W$ boson mass. Using 167 events observed in 955 pb$^{{-}1}$ of integrated luminosity, we achieve the single most precise measurement of the top quark mass, 170.8 $\pm$ 2.2 (stat.) $\pm$ 1.4 (syst.) GeV/$c^2$.Comment: accepted by Phys. Rev. Let

Searches for Direct Pair Production of Supersymmetric Top and Supersymmetric Bottom Quarks in p-pbar Collisions at sqrt(s)=1.96 TeV

We search for direct pair production of supersymmetric top quarks and supersymmetric bottom quarks in proton-antiproton collisions at sqrt(s)=1.96 TeV, using 295 pb^-1 of data recorded by the Collider Detector at Fermilab (CDF II) experiment. The supersymmetric top (supersymmetric bottom) quarks are selected by reconstructing their decay into a charm (bottom) quark and a neutralino, which is assumed to be the lightest supersymmetric particle. The signature of such processes is two energetic heavy-flavor jets and missing transverse energy. The number of events that pass our selection for each search process is consistent with the expected standard model background. By comparing our results to the theoretical production cross sections of the supersymmetric top and supersymmetric bottom quarks in the minimal supersymmetric standard model, we exclude, at a 95% confidence level in the frame of that model, a supersymmetric top quark mass up to 132 GeV/c^2 for a neutralino mass of 48 GeV/c^2, and a supersymmetric bottom quark mass up to 193 GeV/c^2 for a neutralino mass of 40 GeV/c^2.Comment: 12 pages, 5 figures, submitted to Phys. Rev.