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F. Halzen

Publications and source records attributed to F. Halzen.

137 records · Page 8Linked to original sources

14th International Workshop on Weak Interactions: Concluding Remarks

This superbly organized workshop invited the participants to focus on four outstanding questions in weak interactions: i) is the electroweak model correct at the quantum level? ii)supersymmetry? iii) neutrino mass? iv) what is the nature of CP-violation? The meeting demonstrated how weak-interaction physics has become a terrain successfully covered by accelerator and non-accelerator experiments in a very complimentary way.

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The Charm Content of W+1 Jet Events as a Probe of the Strange Quark Distribution Function

We investigate the prospects for measuring the strange quark distribution function of the proton in associated $W$ plus charm quark production at the Tevatron. The $W+c$ quark signal produced by strange quark -- gluon fusion, $sg\rightarrow W^-c$ and $\bar sg\rightarrow W^+\bar c$, is approximately 5\% of the inclusive $W+1$ jet cross section for jets with a transverse momentum $p_T(j)>10$~GeV. We study the sensitivity of the $W$ plus charm quark cross section to the parametrization of the strange quark distribution function, and evaluate the various background processes. Strategies to identify charm quarks in CDF and DØ\ are discussed. For a charm tagging efficiency of about 10\% and an integrated luminosity of 30~pb$^{-1}$ or more, it should be possible to constrain the strange quark distribution function from $W+c$ production at the Tevatron.

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High Energy Neutrino Telescopes Detect Supernovae

We have simulated the response of a high energy neutrino telescope to the stream of low energy neutrinos produced by a supernova. The nominal threshold of such detectors is in the GeV energy range. The passage of a large flux of MeV neutrinos during a period of seconds will nevertheless be detected as an excess of single counting rates in all individual optical modules. Detectors under construction, which consist of roughly 200 modules, will be able to detect a galactic supernova at or above the 5 $σ$ level. The rate of fake signals is, however, too large for the telescope to serve as a neutrino watch. Such capability requires detectors with roughly 3 times the number of optical modules, thus within easy reach of the next generation detectors.

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Blois V: Summary Talk

Although we have a theory of strong interactions, its implications for the physics of average hadron collisions, which is the focus of this series of conferences, are far from obvious. QCD has nevertheless been a very powerful guide and I will argue that a consensus description of ``soft" hadronic physics is emerging at least at the phenomenological level, even though the message is hidden by a myriad of competing models such as the Lipatov Pomeron, the jet model, dual topological unitarization, etc. Understanding this physics is a high priority not only because it is intrinsically interesting (e.g.\ the search for chiral condensates or for point-like structure of the Pomeron), but because it dictates the structure of the backgrounds and underlying events in any hadron collider experiment. In the not so distant future most of particle physics will rely on such machines and I will therefore emphasize issues associated with the physics exploitation of future colliders (e.g.\ rapidity gaps). This is also the first Blois meeting after HERA and the experiments have already contributed significant novel information on the physics discussed at this meeting.

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Measurement of the Strange Quark Distribution Function in W + Charm Quark Events

We investigate the prospects of measuring the strange quark distribution function at the Tevatron, using $W$ plus charm quark events. The $W$ plus charm quark signal produced by strange quark--gluon fusion, $sg\rightarrow W^-c$ and $\bar sg\rightarrow W^+\bar c$, is approximately 5\% of the inclusive $W+1$ jet cross section for jets with a transverse momentum $p_T(j)>10$~GeV. We study the sensitivity of the $W$ plus charm quark cross section to the parametrization of the strange quark distribution function, and evaluate the various background processes. Strategies to identify charm quarks in CDF and D$0\llap/$ are briefly described.

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Hadronic $W$ production and the Gottfried Sum Rule

The difference in production rate between $W^+$ and $W^-$ at hadron colliders is very sensitive to the the difference between up- and down-quark distributions in the proton. This sensitivity allows for a variety of useful measurements. We consider the difference $d_s(x,Q^2) - u_s(x,Q^2)$ in the sea distributions and the difference $Δu(x,Q^2) - Δd(x,Q^2)$ in the polarized parton distribution functions. In both cases we construct an asymmetry to reduce systematic uncertainties. Although we discuss measurements at the Tevatron and future hadron colliders, we find that the Brookhaven Relativistic Heavy Ion Collider (RHIC) is the most appropriate hadron collider for these measurements.

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Diffraction and the Gluon Mass

We recently proposed a QCD-Pomeron described by the exchange of two non-perturbative gluons characterized by a dynamically generated gluon mass. It is here shown that data on elastic scattering, exclusive $ρ$ production in deep inelastic scattering and the $J/Ψ$-nucleon total cross-section can be successfully described in terms of a single gluon mass $m_g\simeq0.37$~GeV. We observe that the total cross sections of hadrons with small radii, such as $J/Ψ$, have a marked dependence on the effective gluon mass.

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Measuring the Gamma-Gamma Coupling of the Higgs at Linear Colliders

Observing the production of the Higgs particle in the $γ$-$γ$ mode of a linear $e^+e^-$ collider allows for the measurement of the $Hγγ$ coupling. We point out that for the intermediate Higgs mass range this measurement is considerably more challenging than previously believed. The $b \bar b$ signature receives a large background from the production of heavy quark pairs by resolved photons. We quantify the experimental requirements needed to make a meaningful measurement in the presence of this background.

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Empirical Determination of the Very High Energy Heavy Quark Cross Section from Non-Accelerator Data

To cosmic rays incident near the horizon the Earth's atmosphere represents a beam dump with a slant depth reaching 36000~g~cm$^{-2}$ at $90^\circ$. The prompt decay of a heavy quark produced by very high energy cosmic ray showers will leave an unmistakable signature in this dump. We translate the failure of experiments to detect such a signal into an upper limit on the heavy quark hadroproduction cross section in the energy region beyond existing accelerators. Our results disfavor any rapid growth of the cross section or the gluon structure function beyond very conservative estimates based on perturbative QCD.

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$J/ψ$ at small-$x$

It has been suggested that the suppression of $J/ψ$ production in heavy nuclei is a signature of the formation of quark-gluon plasma. We here show that this phenomenon can be understood in terms of conventional physics, {\it i.e.} {\it i)} perturbative QCD, {\it ii)} the parton recombination implementation of shadowing in the initial state, and {\it iii)} final state interactions with the hadronic debris of the nuclear target. Unlike previous calculations we include both the direct $J/ψ$ production and its production via radiative $χ$ decays ($χ_J \to J/ψ+ γ$). We are able to reproduce the experimental data including their small-$x$ behavior. We emphasize the importance of studying the $x_2$-dependence of the ratio $σ(b A)/σ(b N)$, where $b$ designates the beam and $x_2$ is the momentum fraction of the parton from the nuclear target.

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Threshold Effects on Heavy Quark Production in $γγ$ Interactions

The exchange of gluons between heavy quarks produced in $e^+e^-$ interactions results in an enhancement of their production near threshold. We study QCD threshold effects in $γγ$ collisions. The results are relevant to heavy quark production by beamstrahlung and laser back-scattering in future linear collider experiments. Detailed predictions for top, bottom and charm production are presented.

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