5. PHYSICS OF CHARM AND BEAUTY
Two of the fundamental particles of the standard model are the charm quark and the beauty quark, the latter sometimes known as the bottom quark. In spite of their quaint names, these quarks have both played, and continue to play critical roles in particle physics research. The charm quark was the real spark for the acceptance of the whole picture of the quark-lepton sub-structure of matter. The bottom quark is now the focus of extensive studies around the world, studies which aim at understanding the details of standard-model CP violation and of the matter-antimatter asymmetry observed in experiments. More hopefully, these studies may find a glimpse of what lies beyond the standard model. Fermilab fixed-target experiments on particles containing charm quarks have provided guideposts in the understanding of CP violation. Given that the standard model explanation for the CP violation seen in the laboratory cannot explain the mysterious asymmetry in the matter-antimatter balance in the universe, there must be something beyond the standard model. Charm and beauty studies may hold the key to this and other tantalizing questions in particle physics. The mixing of charm particle and antiparticle, and the searches for rare and forbidden decays may open unexpected doors. Also, we may hope that a detailed study of physics involving charm and bottom quarks, when combined with the study of the other quarks, will lead to an understanding of why nature has arranged the quarks into three generations, with each generation containing two sometimes quite different quarks.
Even in the area of standard-model physics, there are important questions to which fixed-target experiments at Fermilab have contributed answers: how quarks are produced in high-energy interactions, how those quarks turn into the particles seen in the laboratory, and the dynamics leading to the decay of particles containing charm quarks. For example, since the charm and bottom quarks are produced dominantly by the fusion of bits of the glue that binds quarks within the particles that are seen directly in the laboratory, charm quark production properties may be used to study the distribution of the glue in particles. Also, the decay of charm particles provides a particularly clean environment in which to study the characteristics of those particles into which the charm particles decay. The recent charm experiments are providing answers that have eluded physicists for decades. The copious decays observed in Fermilab fixed-target experiments provide a unique way of studying the low-mass resonances of pairs of pions and of pions and kaons. These measurements complement those made historically in scattering experiments at lower energies.
Major contributions from the charm and beauty fixed target program also have been in the areas of detector development, and data acquisition and computing. The rarity of charm and beauty quarks in fixed target interactions and the unique decay properties of these quarks led experimenters to implement silicon microstrip detectors, trigger processors, fiber readout of scintillating plastics, high speed data readout, and web-based monitoring. Creativity, trying non-standard techniques, and diverse and innovative beams have marked this fixed target program. Each experiment tried a different wrinkle to advance the science.
5.2 E400 -
charmed particle production by neutrons
University of Bologna (Italy), University of Colorado, Fermi National Accelerator Laboratory, University of Illinois, INFN, Milano (Italy), University of Pavia (Italy), Yale University
E400 was designed to study the neutron production and
properties of charm particles. E400
featured a novel, high resolution MWPC called the D5 to enable the experiment
to tag charm particles through their very short, but finite lifetime. The D5 was a precursor to much finer pitched
microstrip detectors which emerged in the next generation of charm experiments
a few years later and revolutionized charm particle reconstruction in fixed
target environments. E400 was able to confirm the first evidence for the
existence of the Xc+ baryon, the first
baryon observed that has both charm and strange quark content.
E400 also measured the Xc+ lifetime with greater precision than known previously. Another E400 highlight was the first observation of the neutral D meson decaying into a final state consisting of two Kso mesons. This is an especially interesting final state. It is not expected to occur directly because of an interesting cancellation of contributions. It is likely to be produced through final-state re-scattering in other, direct decays.
E400 Degree Recipients
F. Bossi Ph.D. University of Pavia
Janice Enagonio Ph.D. University of Colorado
John Eugene Filaseta Ph.D. University of Illinois at
Urbana-Champaign
Thomas Knight Kroc Ph.D. University of Illinois at
Urbana-Champaign
Raymond Ladbury Ph.D. University of Colorado
Calvin L. Shipbaugh Ph.D. University of Illinois at
Urbana-Champaign
E400 Publications
Production of the charmed strange baryon X + by neutrons., P. Coteus et. al., Phys. Rev. Lett. 59, 1530 (1987).
Measurements of the S c° - L c+ and S c +- L c + mass differences., M. Diesburg, et. al., Phys. Rev. Lett. 59, 2711 (1987).
The first observation of D° → K° anti-K°., J.P. Cumulat, et. al., Phys. Lett. B210, 253 (1988).
Production of the Ds± by high energy neutrons., C. Shipbaugh, et. al., Phys. Rev. Lett. 60, 2117 (1988).
5.3 E653 - Charm and Beauty Decays in a Hybrid
Emulsion Spectrometer
Aichi (Japan), UC/Davis,
Carnegie-Mellon, Chonnam National (Korea), Fermilab,
Gifu (Japan), Gyeongsang National
(Korea), Joenbug (Korea), Kinki (Japan), Kobe
(Japan ), Korea (Korea), Nagoya (Japan),
Nagoya Inst. of Tech. (Japan), Ohio State,
Okayama (Japan), Oklahoma, Osaka City
(Japan), Osaka Sci. Ed. Center. (Japan),
Toho (Japan), Utsunomiya (Japan),
Yokohama National (Japan), Won Kwang (Korea)
E653 studied short-lived charm and beauty particles produced by high-energy pion and proton beams. The experiment’s unique feature incorporated a hybrid of emulsion target and conventional spectrometer. Decay candidate events to be scanned in the emulsion were selected and located with a silicon microstrip vertex detector. The emulsion target allowed the chosen events to be examined with sub-micron resolution. E653 had exceptionally good muon identification, and used a muon trigger to enrich the recorded sample of beauty events and of semimuonic and purely muonic decays of charm. The experiment used nine fully-reconstructed beauty quark-antiquark pairs to study production properties at fixed-target energies and to measure beauty lifetimes. It made an excellent measurement of semileptonic decay form factors for D+ → anti-K*o(892) m nm , made the first observation of D+ → r m nm , and the first form factor measurements for Ds+ → f m nm. The experiment used its hybrid capabilities to full advantage to do physics otherwise inaccessible: good limits for flavor-changing neutral current decays of charm in multineutral modes, and for possible four- and five-body semileptonic decays of charm; and a study of Ds+ → m nm. This very interesting purely leptonic decay is very difficult to study in conventional spectrometers because of its one-prong "kink" topology, but is ideally suited to E653's hybrid emulsion technique.
E653 Degree Recipients
T. Abe Ph.D. Kobe University
M. Adachi M.S. Toho University
James M. Dunlea Ph.D. Ohio State University
K. Ebara M.E. Utsunomiya University
Arne P. Freyberger Ph.D. Carnegie Melon University
K. Fujiwara M.S. Kobe University
O. Fukuda M.E. Utsunomiya University
K. Horie M.E. Utsunomiya University
S. Ikegami M.S. Toho University
N. Itou M.S. Kobe University
M. Kamiya M.E. Utsunomiya University
M. Komatsu M.S. Nagoya University
M. Komatsu Ph.D. Nagoya University
T. Koya M.S. Toho University
Akbar Mokhtarani Ph.D. University of California at Davis
William R. Nichols Ph.D. Carnegie Melon University
E. Niu M.S. Toho University
E. Niu Ph.D. Toho University
I. Ohtsuka M.E. Utsunomiya University
Gene A. Oleynik Ph.D. Ohio State University
Vittorio Paolone Ph.D. University of California at Davis
M. Seshimo M.E. Utsunomiya University
A. Suzuki M.S. Osaka City University
K. Suzuki M.E. Utsunomiya University
M. Takeda M.S. Kobe University
K. Taruma Ph.D. Kobe University
S. Torikai M.S. Aichi University of Education
K. Umemura M.S. Osaka City University
S. Watanabe M.S. Toho University
S. Watanabe Ph.D. Toho University
O'Hara Wilcox Ph.D. University of California at Davis
M. Yamaki M.E. Utsunomiya University
S. Yoshida M.S. Nagoya University
S. Yoshida Ph.D. Nagoya University
E653 Publications
Measurement of the Relative Branching Fraction G (Do → K m nm) / G (Do → m X)., K. Kodama, et al., Phys. Rev. Lett. 66, 1819 (1991).
Charm Meson Production in 800 GeV/c Proton-Emulsion Interactions., K. Kodama, et al., Phys. Lett. B263, 573 (1991).
Charm Pair Correlations in 800 GeV/c Proton-Emulsion Interactions., K. Kodama, et al., Phys. Lett. B263, 579 (1991).
Charm Meson Production in 600 GeV/c p- Interactions., K. Kodama, et al., Phys. Lett. B284, 461 (1992).
Measurement of the Form Factor Ratios in the Decay D+ → anti-K*o(892) m+ n., K. Kodama, et al., Phys. Lett. B274, 246 (1992).
Measurement of the Branching Ratio for D+ → anti-K*o(892) m+ n., K. Kodama, et al., Phys. Lett. B286, 187 (1992).
Measurement of the Lifetimes of Charged and Neutral Beauty Hadrons., K. Kodama, et al., Prog. Theo. Phys. 89, 679 (1993).
Measurement of Beauty Hadron Pair Production in 600 GeV/c p- Emulsion Interactions., K. Kodama, et al., Phys. Lett. B303, 359 (1993).
A Study of Semimuonic Decays of the DS,. K. Kodama, et al., Phys. Lett. B309, 483 (1993).
Limits for Four- and Five-Prong Semileptonic Charm Meson Decays., K. Kodama, et al., Phys. Lett. B313, 260 (1993).
Search for Diffractive Charm Production in 800 GeV/c Proton-Silicon Interactions., K. Kodama, et al., Phys. Lett. B316, 188 (1993).
Observation of D+→ ro(770) m+ n., K. Kodama, et al., Phys. Lett. B316, 455 (1993).
Measurement
of G
( Do → K -m+
n)
/ G (
Do →
m+
X) using a D* tag., K. Kodama, et
al., Phys. Lett. B336, 605 (1994).
Upper Limits for Charm Hadron Decays to Two Muons Plus a Hadron., K. Kodama, et al., Phys. Lett. B345, 85 (1995).
Direct Measurement of the Pseudoscalar Decay Constant of the D., K. Kodama, et al., Phys. Lett. B382, 299 (1996).
5.4 E672 - Hadronic Final States in Association with
High Mass Dimuons
Fermilab, IHEP/Protvino (Russia),
Illinois/Chicago,
Indiana, Louisville, Michigan/Flint
The production of beauty quarks in hadronic collisions is a subject of persistent theoretical and experimental interest. The comparison of the measured beauty-quark production cross section with the Next-to-Leading Order Quantum Chromodynamic (NLO QCD) calculations reveals the underlying dynamics. In addition to the lowest order beauty quark-antiquark pair production processes via gluon fusion or quark exchange, sizable contributions come from diagrams including the gluon exchanges with subsequent gluon splitting, and flavor excitation in which a gluon virtual fluctuation to a beauty quark-antiquark pair is put on-mass shell by an interaction. It is known that the measured inclusive beauty-quark cross sections at the Tevatron collider exceed the NLO QCD predictions by a factor of about 2.5 to 3. The NLO QCD calculations for the beauty quark-antiquark pair production are expected to be more reliable at fixed-target energies.
Renewed interest in the charmonium and bottomonium production originated with the observation by the CDF Collaboration that the direct J/y and y(2S) production exceeds expectations based on the color singlet model (CSM) of charmonium production by a factor of about 50. This observation led to a development of the color octet model (COM), nonperturbative parameters of which were fitted to match the CDF data. In the color singlet model, the charmonium meson retains the quantum numbers of the produced charm quark-antiquark pair, and thus each J/y state can only be directly produced via the corresponding hard scattering color singlet subprocess. The color octet mechanism extends the color singlet approach by taking into account the production of charm quark-antiquark pairs in a color octet configuration accompanied by a gluon. The color octet state evolves into a color singlet state via emission of a soft gluon. The inclusion of the color octet mechanism leads to a prediction that directly produced y charmonia will be increasingly transversely polarized at high transverse momentum. The polarization prediction is the most likely effect to help distinguish the COM model from the multiple soft gluon exchanges (color evaporation) model.
E672 was an open geometry experiment, the aim of which was to study hadronic processes yielding high-mass dimuons (the trigger) and associated particles, using proton and pion beams at momenta up to 800 GeV/c striking various nuclear targets. The specific goals, which are all related to experimental tests of Quantum Chromodynamics (QCD), included hadroproduction of: (i) beauty quarks observed through inclusive and exclusive decays to J/y, (ii) charmonium cc states observed via their radiative decays into J/y g, and (iii) y(2S) states observed in its m+ m- and J/y p+ p- decay modes.
Experiment E672 shared the Meson West beamline and spectrometer with the experiment E706 studying direct photon production. The data from the two experiments were written to shared tapes, and then independently analyzed. Most of the E672 publications were joint publications with E706 colleagues.
E672 measured beauty-quark production in pion-beryllium collisions at 515 GeV/c by identifying events with J/y originating from secondary vertices. In addition to inclusive J/y + X decays, the experiment reported five events of exclusive J/y K or J/y K* decays. The measured cross section, although with a large uncertainty, indicated an excess of data over the theory predictions.
E672 studied charmonium production in pion-beryllium and proton-beryllium collisions at 515 GeV/c and 800 GeV/c. The results included differential J/y cross sections and fractions of J/y produced either directly or as products of y(2s) and radiative c1 and c2 states decays. The measured xF distributions were used for an extensive comparison with the color-octet model predictions. All values of the required non-perturbative matrix elements were derived from other experiments, primarily from charmonium photoproduction data and from J/y production data from the Tevatron. In general, the parameter-free predictions of the model for xF - distributions agree with the proton and pion induced data both in magnitude and shape. On the other hand, the E672 data are consistent with unpolarized J/y production, contrary to expectations from the color octet model, but in agreement with the color evaporation model.
In addition, E672 was one of the first experiments to analyze the absorption of J/y particles in nuclear matter.
In its earlier incarnation (1984), E672 was also concerned with the production of jets in 800 GeV/c proton-nucleus interactions. There are several reasons for studying such interactions. First, measurements of secondary particles produced in these processes can provide unique information about the space-time development of proton-nucleon interactions. The nucleus serves as a short-range detector which interferes with the intermediate hadronic state produced in the primary proton-nucleon interaction, before that state can materialize into the observed particles. Second, results from proton-nucleus interactions help in understanding the properties of nuclear matter at high energy densities, a topic of considerable interest for the current quark-gluon plasma investigations.
The E557/E672 trigger required a deposition of large transverse energy (ET) in a large coverage calorimeter centered around 90 degrees in the proton-nucleon center of mass system. The experiment observed a nuclear enhancement in producing events with large ET and studied its dependence on the event topology. We were also able to separate effects associated with the jet production from nuclei.
E672 Degree Recipients
Paul Draper Ph.D. Indiana University
Richard Jesik Ph.D. University of Illinois at Chicago
Circle
Rui Li Ph.D. Indiana University
Sheila Markham M.S. Indiana University
Aditya K. Sambamurti Ph.D. Indiana University
Donald A. Stewart Jr. Ph.D. Indiana University
Francisco Vaca Ph.D. University of Illinois at Chicago
Circle
Guan Wu Ph.D. University of Illinois at Chicago
Circle
E557/E672 Publications
A Measurement of Nuclear Enhancement in High-ET and Jet Event Production., R. Gomez, et al., Phys Rev. D35, 2736 (1987).
A Dependence
of Highly Inelastic p Nucleus Collisions., A. Sambamurti, et al., Phys Rev D41, 1371(1990).
Production of High pt Jets in proton-Nucleus Collisions.,
D. Stewart, et al., Phys Rev. D42, 11 (1990).
A Dependence of J/y
Production in p- Nucleus Collisions at 530 Gev/c., S.
Kartik, et al., Phys. Rev. D41, 1 (1990).
Bottom
Production in p- Be
at 515 GeV/c., R. Jesik, et al.,
Phys. Rev. Letters 74, 495 (1995). J/y and y(2s) Production in p- Be at 515 GeV/c., A. Gribushin, et al., Phys. Rev. D53, 4723 (1996).
Production of Charmonium States in p- Be at 515 GeV/c.,
V. Koreshev, et al., Phys. Rev.
Letters, 77, 4294 (1996).
Differential Cross Sections of J/y in p Be Collisions at 530 and 800 GeV/c., A. Gribushin, et al., Phys. Rev. D61, 1120XX (2000).
5.5 E687 -
Photoproduction of Charm and Beauty
INFN/Bologna (Italy), UC/Davis,
Colorado, Fermilab, INFN/Frascati (Italy),
Illinois, Korea (Korea), INFN/Milano
(Italy), Milano (Italy), North Carolina,
Northwestern, Notre Dame, Pavia (Italy),
Puerto Rico/Mayaguez,
South Carolina, Tennessee, Western
Kentucky, Vanderbilt
Experiment E687 was an experiment studying the production and decay of charm particles in the Wideband Photon Beam in the Proton Area. The spectrometer was based on two large analysis magnets, which provided a large charged particle acceptance covering the entire forward hemisphere. The spectrometer was instrumented with twelve planes of silicon microstrip detectors, totaling 8256 pulse height analyzed strips, which provided primary and secondary vertex reconstruction; three threshold Cerenkov counters of about 100 cells each to provide charged hadron identification; a 10 meter neutral Vee decay volume; small and wide angle electromagnetic calorimeters providing excellent g and po identification; and muon identification based on scintillators and proportional tubes. Hadron calorimeters permit one to trigger on photoproduced events with hadrons in the final state.
The E687 Collaboration had three data-taking periods. The first occurred from December 1987- February 1988. During this period a total of 60 million triggers were written on tape. The second running period was from March 1990 until August 1990, when 300 million events were accumulated. The third running period began in June 1991 and lasted until January 1992. During this third running period we accumulated another 200 million triggers giving the experiment a total of 500 million triggers for the 1990-1991 running period.
This experiment had many important results, including obtaining the best lifetime measurements for all of the weakly decaying charm particles, D+, Do, Ds, Lc, Xc+ ; the discovery of the Wco ; charm baryon and measurement of its lifetime; and detailed study of the semileptonic form factors of Do, D+, and Ds. Many of the measurements made by the E687 collaboration remain as the defining numbers in the compilations of the Particle Data Group.
Vicenzo Arena Ph.D. University of Pavia
Stefano Bianco Ph.D. University of Roma
Kathleen Danyo Blackett Ph.D. University of Tennessee
Gavin Reed Blackett Ph.D. University of Tennessee
Christopher W. Bogart Ph.D. University of Colorado