George J. Igo

Intermediate Energy Experiment

Office: 5-137 Knudsen
Phone: (310) 825-1306
email

Educational Background:

• Ph.D., UC Berkeley, 1953

Research Interest:

Currently, the experimental program of the Igo-Whitten group covers three main areas: The CERN SMC (spin muon collaboration) program which has measured the spin structure of the neutron and of the proton by studying the asymmetry in the scattering of polarized muon beams (100-200 GeV) on polarized proton and deuteron targets. This experiment has tested the fundamental Bjorken sum rule for the first time and has achieved an accuracy of 10%. A violation of the Bjorken sum rule would require a restructuring of quantum chromodynamics(QCD), hence the importance of improving the accuracy of the test. Data has also been obtained at SLAC on this fundamental quantity and together with the SMC data provides a tighter bound (In 1995, members of the Igo-Whitten group will participate in the 50 GeV measurements at SLAC). During running periods in 1995 and 1996, the SMC will accumulate more data on the deuteron and proton respectively. The data on the proton and neutron seperately may be used to test the Ellis-Jaffee sum rule. This sum rule on the first moment of the spin structure functions has been calculated assuming that strange quarks do not contribute to the spin of the nucleon and neglects some effects associated with the gluons. A consequence of the Ellis-jaffee sum rule is that the intrinsic spins of the quarks and anti-quarks in the proton and neutron are responsible on average for about 60% of the spin 1/2 of the nucleon (the remainder could be ordinary orbital angular momentum or due to the intrinsic spin of the gluons). The deep inelastic scattering data of the SMC clearly shows that the Ellis-Jaffe sum rule is violated and in fact the quarks are responsible for a much smaller fraction of the nucleon spin. The SMC experiment is unique in its coverage of that part of the quark momentum spectrum, described in the Breit frame, in which the sea quarks are expected to predominate. Very interesting and subtle features are being investigated in this region by the SMC.

A second component of the Igo-Whitten research program is the study of relativistic collisions between Pb nuclei. This is Experiment NA-49 at CERN. This experiment is at the beginning of its data taking period which is seen to continue for approximately the next five years. The experiment is unique at this time in that it is possible to gain significant information on an event by event basis. Typically several thousand pions are produced in a "head-on" collision between two Pb nuclei with energy brought in by the projectile Pb nucleus onto the fixed target Pb nucleus of approx. 400,000 GeV. A Hanbury-Braun-Twist (HBT) nuclear analogue of the optical measurement (HBT) which can measure the size of a star or galaxy by looking at the spatial and energy correlations of photons can be performed on an event by event basis with pions playing the role of the photons in the nuclear case. A large collision volume is of special interest, it is thought, in searching for effects of the production for a fleeting moment of a quark-gluon plasma, thought to be an important component of the universe in the first microsecond. UCLA is very active in the present construction part of this experiment, specifically having essentially the responsibility for the construction of the external gas envelopes of the two large time projection chambers (TPC) which are with smaller vertex TPC'S the major detectors of NA-49. Additional research in the field of relativistic heavy ion collisions involve the investigation of dilepton production at the Bevalac and an h-zero search at the AGS accelerator at BNL.

A third component of the Igo-Whitten research program involves the Relativistic Heavy Ion Collider Facility under construction at the Brookhaven National Laboratory. In particular we are members of the STAR collaboration. STAR is a solenoidal detector with a cylindrical TPC surrounding a collision region of the two intersecting beams of heavy nuclei, each with and energy as high as 200,000 GeV. It is expected that quark-gluon matter will be produced in these collisions. The challenge will be to detect it with certainty. This will be interesting because of its possible implications about the beginning of time in the early universe. UCLA is building a major component of the TPC, the gated grid driver and its associated software as well as prototype phomultiplier tube bases. We have been active in the planning of an electromagnetic calorimeter for STAR.

Recent Selected Publications

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