Fermilab Antiproton Research Articles

A NEW EXPERIMENT TO STUDY HYPERON CP VIOLATION AND THE CHARMONIUM SYSTEM

Fermilab operates the world's most intense antiproton source, now exclusively dedicated to serving the needs of the Tevatron Collider. The anticipated 2009 shutdown of the Tevatron presents the opportunity for a world-leading low- and medium-energy antiproton program. We summarize the status of the Fermilab antiproton facility and review physics topics for which a future experiment could make the world's best measurements.

Measurement of the resonance parameters of the [formula omitted](1 3P 1) and [formula omitted](1 3P 2) states of charmonium formed in antiproton–proton annihilations

We have studied the 3P J ( χ c ) states of charmonium in formation by antiproton–proton annihilations in experiment E835 at the Fermilab Antiproton Source. We report new measurements of the mass, width, and B ( χ c J → p ¯ p ) Γ ( χ c J → J / ψ + anything ) for the χ c 1 and χ c 2 by means of the inclusive reaction p ¯ p → χ c J → J / ψ + anything → ( e + e − ) + anything . Using the subsample of events where χ c J → γ + J / ψ → γ + ( e + e − ) is fully reconstructed, we derive B ( χ c J → p ¯ p ) Γ ( χ c J → J / ψ + γ ) . We summarize the results of the E760 (updated) and E835 measurements of mass, width and B ( χ c J → p ¯ p ) Γ ( χ c J → J / ψ + γ ) ( J = 0 , 1 , 2 ) and discuss the significance of these measurements.

Experiment E835 at Fermilab

We provide a comprehensive description of experiment E835 at Fermilab, a high-precision experimental study of charmonium bound states. The c ̄ c states are formed in p ̄ p annihilations of cooled antiprotons stored in the Fermilab Antiproton Accumulator using a dense internal hydrogen gas-jet target. We describe the experimental strategies adopted for detecting the tiny c ̄ c resonant signals in the huge non-resonant hadronic background, and for measuring resonance parameters with high precision.

Charmonium states at the Fermilab antiproton accumulator. New results from E835

Experiment E835 has collected a large sample of charmonium states using a hydrogen jet and the virtually monoenergetic stochastically cooled antiproton beam. We present an improved measurement of the ξ c0 mass and width, preliminary results of analysis of the ξ c0 decay to μ 0 μ0 and γγ and the final value of our measurements of the η c parameters.

Beam decelerations with variable momentum compaction in the Fermilab Antiproton Accumulator

For the study of charmonium resonances above and including the χ c0 , Fermilab experiment E-835 required an intense and stochastically cooled antiproton beam with kinetic energies from 8 GeV (the injection energy of the Accumulator) down to 4 GeV . We developed a scheme in which the momentum compaction factor of the machine was changed as the antiprotons were decelerated, so that the energies of interest to the experiment were kept above transition. The scheme was used during the E-835 10-month run of the year 2000. Here we describe the design criteria, operational procedures and diagnostic tools we used to exploit the machine as an efficient antiproton decelerator. The machine performance during data taking is also discussed, in relation to the main experimental requirements.

Prospects for low-energy antiproton physics at Fermilab

Fermilab has long had the world's most intense antiproton source, but the opportunities for medium-energy antiproton physics have been limited, and those for low-energy antiproton physics nonexistent. The conclusion of E835 brings this era to an end. While the future of antiproton physics at Fermilab remains highly uncertain, developments are occurring that may lead to a low-energy program within the next several years, with the possibility of an improved medium-energy program thereafter. These issues were considered at the recent $\bar{p}2000$ Workshop at Illinois Institute of Technology. I summarize the current status of the Fermilab antiproton facility, review hyperon {\em CP} violation as an example of the physics that might be achievable, and discuss future possibilities.

Rotating band pion production targets for muon colliders and neutrino factories

An update is presented on a conceptual design for a pion production target station using a rotating cupronickel band and that was originally proposed for use at a muon collider facility with a 4 MW pulsed proton beam. After reviewing the salient design features and motivations for this target, ongoing studies are described that are attempting to benchmark the thermal stresses and radiation damage on the target band using data from the Fermilab antiproton source and other operating targets. Possible parameter optimizations and alternative technologies for the rotating band are surveyed, including discussion on the the various proton beam parameters that might be encountered for rotating band targets at either muon colliders or neutrino factories. Finally, an outline is proposed for a possible R&D path towards capability for the actual construction of rotating band pion production targets.

Time dependence and temperature stability of the permanent magnets for the Fermilab antiproton recycler ring

The Fermilab Recycler Ring, part of the Main Injector upgrade, is an 8 GeV storage ring consisting of 362 gradient magnets, 109 quadrupoles, 8 mirror magnets, and 5 Lambertsons. The field is driven by strontium ferrite permanent magnets and shaped by precision pole pieces. Temperature dependence of the ferrite is compensated by the use of Ni (30%) Fe (70%) alloy operating near its Curie point. Temperature stability is held to within 0.004%/spl deg/C rms. over the operating range of 25 to 35 C. Tighter stability requirements (0.001%/spl deg/C) for the high beta quadrupoles are met by active thermal control using heating blankets. Longitudinal uniformity is obtained by distribution of the compensator and ferrite throughout the magnet. Field strength in the magnets are adjusted to be within 0.05% of the design field. The higher harmonics contribute less than 0.01% of the primary field measured at a radius of 25.4 mm. For the gradient magnets custom end shims are made to adjust the harmonics; the field is adjusted by adding or subtracting ferrite. The loss of magnetization is logarithmic in time with a /spl Delta/(M/sub 2//M/sub 1/)=9.0/spl times/10/sup -4/ *log (t/sub 2//t/sub 1/), corresponding to a 0.35% loss of field over the expected operating life of 20 years.

Two photon decay widths of charmonium resonances

E835 studies resonant charmonium formation in the Fermilab Antiproton Accumulator. Preliminary measurements of the ground state η c (1 1 S 0) and the γγ partial width of the χ 2 ( 3 P 2) are presented. Also reported are the preliminary results of the search for the η c ′ (2 1 S 0) in the γγ decay channel.

New limit on CPT violation

A search for antiproton decay has been made at the Fermilab Antiproton Accumulator. Limits are placed on fifteen antiproton decay modes. The results are used to place limits on the characteristic mass scale m(X) that could be associated with CPT violation accompanied by baryon number violation.

High precision charmonium spectroscopy in [formula omitted] annihilations

Fermilab experiment E835 studies the direct formation of charmonium states in proton-antiproton annihilations, obtained by intersecting the p beam of the Fermilab Antiproton Accumulator with an internal hydrogen jet target. In this paper we report the preliminary results from the 1996/1997 run, in particular about η c mass and width, search for η′ c and first observation of the χ 0 state in pp annihilations.

A detector to search for antiproton decay at the Fermilab Antiproton Accumulator

We describe the experimental apparatus used by the APEX experiment (Experiment 868) at the Fermilab Antiproton Accumulator. The experiment is designed to search for decays of 8.9 GeV c antiprotons as they traverse a 3.7 m long evacuated decay tank inserted in a straight section of the Antiproton Accumulator ring. The detector components in the experimental set-up are discussed individually, and the performance of the experiment during data-taking is described.

The variable density gas jet internal target for Experiment 835 at Fermilab

The hydrogen Jet Target for Experiment 835 (Charmonium spectroscopy) at the Fermilab Antiproton Accumulator can provide a variable density cluster stream up to 3.2×10 14 atoms/cm 3 in order to allow an instantaneous luminosity greater than 2×10 31 cm −2 s −1. This result can be achieved due to the helium refrigerated expansion stage which provides the cluster stream and due to the pumping and the alignment system which significantly lower the background gas. Details on the construction and the performances, measured in the laboratory and during the run, are discussed.

Observation of Atomic Antihydrogen

We report the background-free observation of atomic antihydrogen, produced by interactions of an antiproton beam with a hydrogen gas jet target in the Fermilab Antiproton Accumulator. We measure the cross section of the reaction $\overline{p}p\ensuremath{\rightarrow}\overline{H}{e}^{\ensuremath{-}}p$ for $\overline{p}$ beam momenta between 5203 and 6232 MeV/ $c$ to be $1.12\ifmmode\pm\else\textpm\fi{}0.14\ifmmode\pm\else\textpm\fi{}0.09$ pb.

Charmonium Spectroscopy in $\bar{p}p$ Annihilations

We present a review of results from E760, a resonant charmonium formation experiment in the Fermilab Antiproton Accumulator. Experiment E835, a continuation of E760, and its physics goals are also presented.

Charmonium spectroscopy in p̄p annihilations

We present a review of results from E760, a resonant charmonium formation experiment in the Fermilab Antiproton Accumulator. Experiment E835, a continuation of E760, and its physics goals are also presented.

Charmonium spectroscopy in p¯p annihilations

We present a review of results from E760, a resonant charmonium formation experiment in the Fermilab Antiproton Accumulator. Experiment E835, a continuation of E760, and its physics goals are also presented.

Development of a cylindrical scintillating fiber tracker for experiment E835 at FNAL

A tracking detector made of scintillating fibers wound on a cylinder is being developed at FNAL, for the experiment E835 (study of the spectroscopy of charmonium formed in pp annihilations, at the Fermilab Antiproton Accumulator). The tracker will be used for the measurement of the polar angle, i.e. of the longitudinal coordinate. The small amount of light from the fibers will be detected by solid state devices (Visible Light Photon Counters) with very high QE, currently being developed and tested by the D0 Fiber Tracking Group at FNAL. This paper reports the performance of a prototype fiber tracker, as measured at FNAL. We present results on light yield/mip, attenuation, efficiency, homogeneity of response and cross-talk. The data are then compared with Monte Carlo predictions. We measured an average number of 14 photoelectrons per mip and a very low noise level. An efficiency greater than 99% is foreseen for the future double layered tracker.

New results from E760. Study of charmonium states at the fermilab accumulator

Experiment 760 at the Fermilab Antiproton Accumulator ring is mainly dedicated to a precision study of several charmonium states. In this paper, after a short description of the experimental method and a summary of the main results obtained, some recent measurements coming from further study of neutral decay and of angular distributions are presented.

Evidence for ηη resonances in antiproton-proton annihilations at [formula omitted

We present the first high-statistics study of the ηη system over the mass range 1000–3000 MeV/ c 2. The experiment was performed at the Fermilab Antiproton Accumulator, and the data sample consists of six-photon final states produced in antiproton-proton annihilations at s in the range 2950–3620 MeV. We find evidence for three states with masses 1488 ± 10 MeV/ c 2, 1748 ± 10 MeV/ c 2 and 2104 ± 20 MeV/ c 2 respectively.