7. Hyperons and Neutrinos
In the beginning, at Fermilab, there were neutrinos and hyperons created by beams from the Main Ring. Among the first experiments proposed, approved, and run were E1A, and E21, the first generation of Fermilab electronic neutrino detectors, and E8 the first generation Fermilab hyperon beam experiment. There were also several bubble chamber exposures in the neutrino beam. These approaches matured into complete programs of experiments in the Tevatron fixed target era.
The common physics thread shared by these two rather different beam particles is the weak interaction. Neutrinos are particles which feel only the weak force. This makes them excellent probes of complicated structures, like protons and neutrons. Some of the Tevatron neutrino experiments were so sharply focused in the area, that they have been included in the section on proton, neutron, and meson structure rather than here. Neutrinos are also excellent places to study the weak interaction itself. They don’t do anything else, so they are a clean weak interaction laboratory. Neutrino scattering cross-sections (the probability that they will actually hit something in a given target) increase linearly with the neutrino energy. This made the 400 GeV Fermilab Main Ring good for doing neutrino physics, and the 800 GeV/c Tevraton even better.
The hyperons are the particles in the same family as the proton and the neutron, but containing one or more strange valence quarks. Only the weak interaction does not conserve strangeness; it is the only way a hyperon can decay. This makes hyperons live 1014 times longer than their non-strange cousins, the excited non-strange proton and neutron states. This is long enough to make hyperon beams that will go many meters at Tevatron energies before most of the hyperons decay. Hyperons, like protons, are particles of spin ½. This makes it possible to have polarized hyperon beams; something which is impossible with a spin 0 K meson beam. Polarization is a delicate and sensitive probe of both the weak interaction controlling the hyperon’s decay and the structure of the quarks and other stuff which makes up the hyperon itself. E8 discovered in 1976 that hyperons were produced with significant polarization. Tom Devlin, of Rutgers University, and Lee Pondrom, of the University of Wisconsin, were subsequently awarded the Panofsky prize for this discovery and the sequence of experiments it enabled.
Typically only one process happens at a time in weak interactions, one quark decays to another, or a neutrino hits just one quark in a target proton. The combination of the cleanliness of the weak interaction and the high intensity beams of both neutrinos and hyperons available at the Tevatron allowed a set of experiments of unprecedented precision.
A carefully crafted experiment can isolate just one particular aspect of the structure of a proton in order to study it carefully. For example, the E632 dimuon result focused in on the charmed quark content of the proton - which only exists in the sea of virtual quark antiquark pairs inside the proton. In a similar but different example, in a series of experiments all the hyperon magnetic moments were measured with high precision, including the W- (by E800) which is made of three strange valence quarks. The results are sufficiently precise to both confirm our basic understanding of the structure of the baryons (the family to which protons, neutrons and hyperons belong) and to confound theoretical description anywhere close to the present experimental uncertainties.
E815/NuTeV will make a precision measurement of the Weinberg angle, sin2(qW), a fundamental electro-weak parameter more normally associated with the very high energy scales of e+e- and hadron colliders. E872 is seeking to observe the last fundamental fermion, the t neutrino.
Birmingham (Great Britain), UC/Berkeley, CERN (Switzerland), Fermilab,
Hawaii, IHEP/Serpukhov (Russia), IIT, Imperial College (Great Britain), ITEP
(Russia),
Jammu (India), Libre (Belgium), MPI (Germany), Moscow State (Russia),
Oxford (Great Britain), Panjab (India), Rutgers, Saclay (France), Stevens, Tufts
E632 was the only Bubble Chamber experiment to study neutrinos at Tevatron energies. These neutrinos were produced by 800 GeV/c protons, using a quadrupole triplet beam. A moderately heavy neon-hydrogen mix was selected to increase both the event rate and detection of gammas, electrons, and pi-zeros. Holography and a high resolution camera improved heavy flavor detection in the central portion of the fiducial volume. The new External Muon Identifier and Internal Picket Fence helped separate charged and neutral currents and select dilepton events. Bubble Chambers use the same fluid for both target and detector, which provides unbiased detection of secondaries in all directions and down to short distances.
In addition to searching for new phenomena in the higher energy region, dimuon, neutral current, strange and charmed particle production were studied. Other topics were coherent pion and r-meson production and nuclear effects in experiments using neon.
E632 Degree Recipients
Homaira Akbari Ph.D. Tufts University
V.
Jain Ph.D. University of Hawaii
Douglas Francis DeProspo Ph.D. Rutgers University
Mary Anne Lauko Ph.D. Rutgers University
P.R. Nailor Ph.D. Imperial College - London
Elena Vataga Ph.D. Moscow State University
L. Verluyten Ph.D. Universiteit Antwerpen
Stephane Willocq Ph.D. Tufts University
E632 Publications
Coherent Production of p Mesons by Charged Current Interactions of Neutrinos and Antineutrinos on Neon Nuclei at the Tevatron., M. Aderholz, et al., Phys. Rev. Lett. 63, 2349 (1989).
Dimuon Production by Neutrinos in the Fermilab 15-foot Bubble Chamber at the Tevatron., V. Jain, et al., Phys. Rev. D41, 2057 (1990).
Study of High Energy Neutrino Neutral Current Interactions., M. Aderholz, et al., Phys. Rev. D45, 2232 (1992).
Coherent production of single pions and rho mesons in charged-current interactions of neutrinos and antineutrinos on neon nuclei at the Fermilab Tevatron., S. Willocq, et al., Phys. Rev. D47, 2661 (1993).
Neutral strange particle production in neutrino and antineutrino charged-current interactions on neon., D. DeProspo, et al., Phys. Rev. D50, 6691 (1994).
Production of D*+(2010) mesons by high energy neutrinos from the Tevatron., A.E. Asratian, et al., Z. Phys. C76, 647 (1997).
7.3
E715
- PRECISION MEASURMENT OF S ‾ ® n e‾ n
University of Chicago, Elmhurst College, Fermi National Accelerator Laboratory, Iowa State University, Leningrad Institute of Nuclear Physics (USSR) Yale University
The Charged Hyperon Collaboration was one of the groups using high energy hyperon beams at the Tevatron to study the mechanisms by which hyperons are produced and decay. These three experiments, E715, E761, and E781, shared a largely constant set of, now senior physicists and the the Proton Center charged hyperon beam which was built in the Main Ring era for the original hyperon experiment, E497.
A hyperon is a baryon, a relative of the proton, which contains at least one strange quark and decays by the weak interaction. The decays of these particles provide insights into the structure of the baryon family that are inaccessible with other techniques. The fundamental questions are basic: "what are these things made of and how are they put together?" The discovery, by E8 in 1976, that hyperons are produced polarized makes the hyperon beam a sensitive and unique probe for this type of physics. E715, the first experiment to use the Tevatron during its 400 GeV commissioning run in 1983, resolved a long standing and potentially serious anomaly in the beta decay of the S‾ hyperon; S‾® ne‾ n. In four previous measurements, the angular correlation of the electron direction relative to the S‾ spin had the "wrong" sign. If these observations were confirmed, then the decay was either due to a new weak interaction (right handed W's, in the jargon) or the accepted spin structure of the S‾, and by extension the whole baryon family, was just wrong. Never-mind. With 100 times the previous world's data, E715 contradicted the old measurements and got the expected sign and magnitude of the electron correlation. E715 also made precision measurements of the magnetic moments of both the S‾ and X‾, and made significant contributions to the development of transition radiation detectors (TRDs) as high performance electron identifiers.
E715 Degree Recipients
Shao Hsueh Ph.D. University of Chicago
Panos Andreo Razis Ph.D. Yale University
L.H. Trost M.S. University of Iowa
G. Zapalac Ph.D. University of Chicago
E715 Publications
Measurement of the Electron Asymmetry in the Beta Decay of Polarized S ‾ Hyperons. ,
S.Y. Hsueh, et al., Phys. Rev. Lett. 54, 2399 (1985).
A Measurement of the S ‾ Magnetic Moment Using the S ‾® ne‾n and S ‾® np ‾ Decay Modes., G. Zapalac, et al., Phys. Rev. Lett. 57, 1526 (1986).
A High Precision Measurement of Polarized S ‾ Beta Decay., S.Y. Hsueh, et al., Phys. Rev. D38, 2056 (1988).
New Measurement of the Production Polarization and Magnetic Moment of the X ‾ Hyperon., L.H. Trost, et al., Phys. Rev. D40, 1703 (1989).
7.4 E756 -
Magnetic Moment of the W ‾ Hyperon
Fermilab,
Michigan, Minnesota, Rutgers, Washington
In E756, polarizations of the omega minus and the other charged hyperons inclusively produced by 800 GeV protons were measured. Contrary to predictions, E756 discovered that anti-cascade plus was signficantly polarized when produced in these interactions. This remains one of the mysteries in strong interactions. The details of the cascade minus polarization were also studied. We found it has a different behavior from that of the lambda hyperon. With these polarized cascade minus events and their anti-particles, E756 measured and compared their magnetic moments. E756 also performed the first CP-violation search in charged-cascade decay.
On the other hand, omega-minus hyperons created by protons did not get polarized. Another approach was employed. With a polarized neutral beam, a polarized sample of omega minus's was obtained, and the magnetic moment of the omega minus was measured for the first time. E756 also collected about 2000 anti-omega plus decays, with which E756 determined the lifetime, decay parameter, and mass of this rare anti-hyperon.
E756 Degree Recipients
Herman Thomas Diehl III Ph.D. Rutgers University
Jeffrey Walton Duryea Ph.D. University of Minnesota
Pak Ming Ho Ph.D. University of Michigan
An Nguyen Ph.D. University of Michigan
E800 Publications
Production Polarization of Magnetic Moment of X + Antihyperons Produced by 800 GeV/c Protons., P.M. Ho, et al., Phys. Rev. Lett. 65, 1713 (1990).
Measurement of the W ‾ Magnetic Moment. , H.T. Diehl, et al., Phys. Rev. Lett. 67, 804 (1991).
Polarization of X ‾ Produced by 800 GeV Protons., J. Duryea, et al., Phys. Rev. Lett. 67, 1193 (1991).
Measurement of the Polarization and Magnetic Moment of X +Antihyperons Produced by 800-GeV/c Protons., P.M. Ho, et al., Phys. Rev. D44, 3402 (1991).
Precise Measurement of the X ‾ Magnetic Moment., J. Duryea et al., Phys. Rev. Lett. 68, 768 (1992).
Production Polarization of W ‾ Hyperons in 800 GeV Proton-Beryllium Collisions., K.B. Luk, et al., Phys. Rev. Lett. 70, 900 (1993).
Measurement of the Properties of the W +and W ‾ Hyperons., A. Chan, et al., Phys. Rev. D58, 072002 (1998).
7.5 E761 -
An Electroweak Enigma: Hyperon
Radiative Decays
Bristol (Great Britain), CBPF (Brazil),
Fermilab, IHEP/Beijing (PRC),
Iowa, ITEP/Moscow (Russia), PNPI
(Russia), Rio de Janeiro (Brazil),
Sao Paulo (Brazil), Yale
E761 was the third experiment done by the Charged Hyperon Collaboration in the series E497, E715, E761, E781. It built upon the previous two experiments in several ways. The techniques of producing, reversing, and measuring the polarization of charged hyperon beams had been well developed and applied to rare S‾ decays in E715. The members of the collaboration had also advanced the state of the art in electron-pion separation using transition radiation detectors (TRDs), applying these techniques to make a tracking photon detector for radiative hyperon decays. The high energy decay photons from the hyperon radiative decays were converted in steel plates, and the resulting shower centroid was tracked using TRDs to sense the high energy electrons and the positrons. The main interest was in the S+ radiative decay. Since to the positive S+ hyperon occurs as only a few percent of a beam which is mostly protons we had to handle significantly higher rates through the apparatus than in E715. Advances in data acquisition made this relatively straight forward by 1990 when E761 took it data.
The decay modes studied in E761 were the hyperon radiative decays; S+ ® p g, X‾ ® S‾ g and W‾ ® X‾ g. These decays require Strong, weak and electro-magnetic interactions. The parity violation observed here is very large and difficult to understand theoretically. E761 made the most precise measurements of the branching ratio and asymmetry parameter in both S+ and X‾ radiative decays. It also set an upper limit on the branching ratio of the W‾ radiative decay. In addition to the largest samples of these unusual decay modes E715 also made precision measurements of the production polarization, magnetic moments and lifetimes of the S+ hyperon and its anti particle. E715 saw that the anti-S+ was produced polarized, an effect even more surprising than hyperon polarization. E715 has also made the first experimental observation of the magnetic moment precession of S+ hyperons channeled in bent crystals, and even a search for supersymmetric hyperons.
E761 Degree Recipients
Ivone Alburquerque Ph.D. University of Sao Paulo
Ricardo .F. Barbosa M.S. University of Sao Paulo
Dong Chen Ph.D. State University of New York at
Albany
Tim Dubbs Ph.D. University of Iowa
Maurice Emile Foucher Ph.D. Yale University
Gery Langlund Ph.D. University of Iowa
Jose Roberto Pinheiro Mahon Ph.D. University of Sao Paulo
Antonio Morelos Pineda Ph.D. Cinvestav
Steve Timm Ph.D. Carnegie Mellon University
Measurement of the asymmetry parameter in the hyperon radiative decay S +® pg., M. Foucher et al., Phys. Rev. Lett. 68, 3004 (1992).
First observation of magnetic moment precession of channeled particles in bent crystals., D. Chen, et al., Phys. Rev. Lett. 69, 3286 (1992).
Polarization of S +and anti-S ‾ hyperons hyperons produced by 800-GeV/c protons., A. Morelos, et al., Phys. Rev. Lett. 71, 2172 (1993).
Measurement of the branching ratio for X ‾®S ‾g radiative decay., T. Dubbs, et al., Phys. Rev. Lett. 72, 808 (1994).
Measurement of the magnetic moments of S + and anti-S ‾., A. Morelos, et al., Phys. Rev. Lett. 71, 3417 (1993).
Pt and XF dependence of the polarization of S + hyperons produced by 800 GeV/c protons., A. Morelos, et al., Phys. Rev. D52, 3777 (1995).
New upper limit for the branching ratio of the W ‾® X ‾ g radiative decay., I.F. Albuquerque, et al., Phys. Rev. D50, 18 (1994).
Measurement of the branching ratio and asymmetry parameter for S +® pg radiative decay., S. Timm, et al., Phys. Rev. D51, 4638 (1995).
A Search for light supersymmetric baryons, I.F. Albuquerque, et al., Phys.Rev.Lett.78, 3252 (1997).
Measurement of the anti-S + lifetime and direct comparison with the S + lifetime., R.F. Barbosa, et al., Phys. Rev. D61, 031101 (2000).
7.6 E800 - High Precision Measurement of
the W ‾ Minus Magnetic Moment
Arizona,
Depauw, Fermilab, Michigan, Minnesota
The primary goal of E800 was to make a precision measurment of the W‾ hyperon magnetic moment. The simple quark and spin structure of the W‾ (three strange quarks with spins aligned) makes it an ideal testing ground for theories that describe the behaviour of quarks inside hadrons. Polarized W‾'s were produced by a new technique that involved using a secondary, unpolarized neutral hyperon beam to create them. Spin precession of this polarized W‾ - sample was then used to determine the W‾ magnetic moment.
Using a sample of 2.35 x 105 polarized W‾, the W‾ magnetic moment was measured to be m = - 2.024 ± 0.056 n.m. Other physics results produced by the experiment include detailed studies of the polarization processes in hyperon production and a measurement of the W‾ decay asymmetry parameters.
E800 Degree Recipients
Gerald Michael Guglielmo Ph.D. University of Minnesota
Noah Benjamin Wallace Ph.D. University of Minnesota
D.M. Woods Ph.D. University of Minnesota
E800 Publications
Precision Measurement of the W ‾ Magnetic Moment, N.B. Wallace, et al., Phys. Rev. Lett. 74, 3732 (1995).
Polarization of the X ‾ and W ‾ Hyperons Produced by Neutral Beams., D.M. Woods, et al., Phys. Rev. D54, 6610 (1996).
7.7 E815/NuTev - Precision Neutrino /
Antineutrino Deep Inelastic Scattering Experiment
Cincinnati, Columbia, Fermilab, Kansas
State,
Northwestern, Oregon, Rochester, Xavier
To make progress on precision tests of the standard model after E744/770 required the use of a new technique, employing separate neutrino and antineutrino beams. Measuring the weak mixing angle using these separate beams was a major goal of E815, the NuTeV experiment. The beam was delivered by the sign-selected quadrupole train (SSQT) beamline. This chain of magnets generated a beam made up either solely of neutrinos or solely of antineutrinos, produced by focusing either positively-charged secondaries (which decay into neutrinos) or negative ones, (which yield a beam of antineutrinos). The new beamline was matched to a refurbished Lab E detector, provided with new scintillator oil and photomultiplier tubes in the calorimeter, and an instrumented decay channel upstream of the main detector to look for new particles outside the standard theory. To establish the energy scale of the calorimeter and continuously calibrate its response, a second beam line was constructed to deliver a test beam of electrons, muons, and pions to the detector.
NuTeV collected data during the 1996-1997 Tevatron Fixed Target run. Analysis of the data is currently well underway. By comparing the relative event rates of neutral current (Z-exchange) and charged current (W-exchange) interactions in neutrino and antineutrino beams, NuTeV has measured the weak mixing angle with a precision comparable to collider measurements. (See G. Zeller et al., DPF99, hep-ex/9906024.) The fact that NuTeV's result is consistent with those from very different processes provides an impressive confirmation of the standard model across many momentum scales, and imposes an important constraint on new physics. First results have also recently been published on the search for heavy neutrinos that are expected in many theoretical models. No indication of such neutrinos was seen in the mass region below 2.2 GeV. Another search has placed limits on the existence of a new particle suggested by an anomaly observed in the KARMEN experiment in England.
In addition to the main goal of NuTev, many other physics topics are being studied, including setting competitive limits on neutrino oscillations for muon to electron neutrinos; measuring the distribution of strange quarks in the nucleon (the "strange sea"); and determining cosmic ray muon energies in a new way. The measurements of quark momentum distributions from CCFR/NuTeV's nucleon structure function determinations provide an important fundamental input to theory and to other experiments.
This trio of neutrino experiments using the Lab E detector has contributed greatly to present understandings of both the weak and the stong interactions, and has searched for new phenomena beyond the current standard theory. The extraordinary vitality and success of this program is evident in the depth and breadth of physics topics it has addressed.
E815 Degree Recipients
Artur Vaitaitis Ph.D. Columbia University
E815 Publications
Search for Neutral Heavy Leptons in a High-Energy Neutrino Beam., A. Vaitaitis, et al., Phys. Rev. Lett. 83, 4943 (1999).
Evidence for Diffractive Charm Production in nm Fe and anti-nm Fe Scattering at the Tevatron., T. Adams, et al., Phys. Rev. D61, 92001 (2000).
Search for a 33.9 Mev/c2 Neutral Particle in Pion Decay., J.A. Formaggio, et al., Submitted to Phys. Rev. Lett. 84, 4043 (2000).
7.8 E872 - Measurement
of t Production from the Process nt + N → t
Aichi
(Japan), Athens (Greece), UC/Davis, Changwon Nat'l (Korea),
Coll. de
France (France), Fermilab, Gyeongsang (Korea), Kansas State,
Kobe (Japan),
Kon-kuk (Korea), Korean Nat'l (Korea), Minnesota,
Nagoya
(Japan), Osaka Sci. Ed. Inst. (Japan), Pittsburgh, South Carolina,
Toho (Japan),
Tufts, Utsunomiya (Japan)
This experiment was designed with one main objective: to recognize and analyze t neutrino interactions for the first time.
Neutrinos are very low-mass or zero-mass, chargeless fermions. The first to be seen was associated with the electron. Soon another electron-like particle, another lepton, was found. It was called the "muon," and it too had a distinct neutrino partner. After the third lepton, the tau, was discovered, it was expected that its neutrino partner, the t neutrino, must exist.
There are several reasons why the t neutrino had not been observed in the same manner as the electron and muon neutrinos. First, although electron neutrinos are extremely common particles (they are radiated by the sun and by nuclear reactors), it is much more difficult to produce suitable t neutrinos at a laboratory. Secondly, only one t neutrino out of 1014 will interact with ordinary matter, so one needs to produce a very large number of neutrinos. Third, the interaction can be identified as coming from a t neutrino only if the detector spatial resolutions are very good, down to 1/1000 of a millimeter.
In the DONUT experiment, the t neutrinos interact in 260 kilogram stacks of nuclear emulsion, much like photographic film, so that a very detailed microscopic record of each interaction is made. These emulsions are analyzed not by eye, but by digitizing cameras that record the tracks emerging from the interaction as computer files for study later. The experiment has been searching the emulsion data for 2 years, and we have several events that are most likely from tau neutrinos, but an additional set of data is being examined to confirm this. About 20 t neutrino interactions should be in this data set.
Experimental neutrino physics is a difficult endeavor, requiring a lot of technology and resources, which only a laboratory like Fermilab can provide. It is no surprise that we have had to wait as many years after the tau lepton was seen (1976), as it took to see the first neutrino (1956) after it was hypothesized (1933).
E872 Degree Recipients
H. Iinuma M.S. Nagoya University
N. Itoh M.S. Nagoya University
E872 Conference Proceedings
Results from DONUT., M. Nakamura, 18th Intl. Conf. on Neutrino Physics and Astrophysics (Neutrino 98), Nucl. Phys. Proc. Suppl. 77, 259 (1999).
Chorus and DONUT., O. Sato, Intl Workshop on JHF Science, Tsukuba, Japan, 4 Mar 1998
JHF Science 2, 89 (1998).
E872, The Direct Observation of the nt., T.Kafka, 5th Intl Workshop on Topics in Astroparticle and Underground Physics, Gran Sasso, Italy 7 Sep 1997, Nucl. Phys. Proc. Suppl. 70, 204 (1999).
