Charged particle tracking is essential in order to investigate the new physics expected at the SSC. The Tracking Group studied radiation damage and rate limitations to tracking devices, vertex detectors, and central tracking. The Group concluded that silicon strips and large wire tracking chambers with small cells can probably survive at the design luminosity of 10/sup 33/ cm/sup -2/ sec/sup -1/; however, the presently designed electronics for silicon strip vertex detectors can withstand a luminosity of only 10/sup 31/ cm/sup -2/ sec/sup -1/. Wire chambers at a radius of less than about 25 cm can withstand a luminosity of less than or equal to 10/sup 32/ cm/sup -2/ sec/sup -1/ only. Actual tracking and pattern recognition in central tracking chambers at a luminosity of 10/sup 33/ cm/sup -2/ sec/sup -1/ will be very difficult because of multiple interactions within the resolving time of the chambers; detailed simulations are needed in order to decide whether tracking is indeed possible at this luminosity. Scintillating glass fibers are an interesting possibility both for vertex detectors and for central trackers, but much research and development is still needed both on the fibers themselves and on the readout.

We report measurements of the lifetimes of the D, D+, and D,+ (F+) mesons produced in e+e collisions at a center-of-mass energy of 29 GeV. The decay vertex distribution in the processes D ~K rr+, D+~E n+n+, and . D+~Prr+ were made using a vertex chamber installed in the High Resolution Spectrometer at the SLAC storage ring PEP. The measured lifetimes are ~ 0=(4.4+1.0%0.6)X10 ' s, w +=(9.2+,'3+1.6)X10 " s, and r +=(3.1+20+0.5)X10 " s. S In addition the lifetime of the B meson is determined assuming that only the B and not the B decays to a D*+ meson. The B is not directly observed. The lifetime w 0 is estimated indirectly to be (8.2+3 7+2.7) X 10

Results from recent observations with the Whipple Observatory gamma-ray telescope are reported; after the successful detection of Markarian (Mkn) 421 particular emphasis was put on the observation of nearby Bl Lacs. The Bl Lac, Mkn 501, which is similar to Mkn 421 in many ways, was detected for the first time as a gamma-ray source. Extensive coverage of Mkn 421 this season revealed unusual variability; one episode of intensity change in April, 1995 was measured with high statistical significance. Upper limits were found for a number of Bl Lacs with z < 0.1.

The detection of gamma rays of energy greater than 300 GeV from the BL Lacertae object Mrk 501 demonstrates that extragalactic TeV emission is not unique to Mrk 421. During 66 hr of observations between 1995 March and July we measured an average flux of 8.1 ± 1.4 × 10-12 cm-2 s-1 above 300 GeV, a flux that is only 20% of the average Mrk 421 flux. The new gamma-ray source has not been reported by the Compton Gamma Ray Observatory as an emitter of gamma rays at lower energies. There is evidence for variability on timescales of days.

In this paper we compare various methods of deriving a Conversion between ADC counts and detected photoelectrons for the photomultiplier tubes comprising the Whipple air-Cherenkov imaging camera. When applied to the same data set, these methods are found to be in excellent agreement within the uncertainties associated with each method.

The results of a search for TeV gamma-ray emission from 35 active galactic nuclei (AGNs) using the Whipple Observatory High Resolution Atmospheric Cerenkov Camera are reported. Fifteen of these objects have been detected at GeV energies by the EGRET experiment on the Compton Gamma Ray Observatory. None of the 35 objects gave a signal at the 3 sigma level; Mrk 421 remains the only AGN detected at TeV energies. The absence of a TeV signal may imply a change in the primary source spectrum and/or the effect of absorption by pair production on intergalactic infrared photons.

Measurements of the gamma ray flux from a number of nearby, radio-bright supernova remnants (SNRs) at energies above similar to 300 GeV have been made with the Whipple imaging air Cerenkov detector. Such observations of the gamma-ray emission of SNRs provide a constraint on SNR-shock acceleration models of cosmic ray origin.

An upper bound to the energy density of infra-red background radiation is derived from considering the effect of gamma-gamma interactions on the observed TeV gamma-ray spectrum of the active galaxy Markarian 421. This upper bound proves to be the most restrictive for the wavelength range of 10 - 12 mu m. These constraints are presently limited by the uncertainty of extrapolating the source spectrum from 5 to 500 GeV. Observations in the regime less than 100 GeV would significantly improve these limits, allowing for a wide range of IR production models to be constrained.

A TeV flare from the BL Lac object Mrk 421 was detected in May of 1994 by the Whipple Observatory air Cherenkov experiment during which the flux above 250 GeV increased by nearly an order of magnitude over a 2-day period. Contemporaneous observations by ASCA showed the X-ray flux to be in a very high state. We present these results, combined with the first ever simultaneous or nearly simultaneous observations at GeV gamma-ray, UV, IR, mm, and radio energies for this nearest BL Lac object. While the GeV gamma-ray flux increased slightly, there is little evidence for variability comparable to that seen at TeV and X-ray energies. Other wavelengths show even less variability. This provides important constraints on the emission mechanisms at work. We present the multiwavelength spectrum of this gamma-ray blazar for both quiescent and flaring states and discuss the data in terms of current models of blazar emission.

The Whipple Observatory Gamma Ray Telescope has been used to observe 30 of the sources listed in the First EGRET Catalog of gamma-ray sources. Flux limits for 17 of these objects are reported here. The energy threshold was 300 GeV and the flux sensitivity was typically 10% that of the Crab flux.

Very high energy gamma-ray emission from the BL Lac object Markarian 421 has been monitored for more than 100 hours since 1992. For observations taken during the current season the detection significance is 38.7 sigma. A strong flare [1], 15 May 1994, nearly simultaneous with a strong X-ray flare [2], showed an increase of similar to 9 over a quiescent level, although contemporaneous EGRET observations [3] show no evidence for such a strong increase.

Markarian 421, an active galactic nucleus (AGN) of the BL Lacertae type, is the closest EGRET-detected AGN. It has been monitored by the Whipple Observatory very high energy gamma-ray telescope since its discovery at TeV energies (Punch et al. 1992), for approximately 90 nights, totaling 130 hours of observation. Observations from 1993 December 23 to 1994 May 10 showed an average source flux only half that of its 1992 discovery level. However, observations on 1994 May 14 and 15 show an increase in flux above this quiescent level by a factor of approximately 10. The timescale of this increase provides the best geometric constraint on the extent of TeV photon emission regions within AGNs. The observation of the high TeV flux occurred 1 day prior to the observation by ASCA of a very high 2-10 keV X-ray flux (Takahashi et al. 1994). This strong TeV outburst is reminiscent of the behavior seen for the stronger 100 MeV-GeV EGRET sources (e.g., 3C 279; Kniffen et al. 1993) but was not anticipated in view of the fact that the six EGRET observations of Mrk 421 from 1991 June to 1993 July (Lin et al. 1994) showed no evidence for variability.

TeV energy gamma ray emission from the blazar Markarian 421 was detected with the Whipple 10 meter imaging Cherenkov telescope initially during the observation period March‐June 1992 at an average photon flux of 1.5×10−11 cm2 s−1. The photon spectrum in the TeV range lies on the extrapolation of the data points observed by EGRET during viewing phase I and indicates that the emission follows an unchanged power law between 100 MeV and 10 TeV with no significant intergalactic absorption. More recent observations from the spring of 1993 confirm the 1992 measurements. Here we give an update on the status of the observations, the analysis for time variability, and the results from the analysis to determine the spectral index for Markarian 421 at TeV energies.The search for TeV emission from other extragalactic sources detected by the EGRET instrument on the Compton Gamma Ray Observatory at GeV energies have so far been negative.

The results of four years of observation of the Crab Nebula at TeV energies by the Whipple group are discussed and the status of the Crab Nebula as a standard candle for TeV astronomy is reviewed.

We have searched the Whipple 1988-89 canonical Crab Nebula database for evidence of a possible geomagnetic field effect on the sensitivity of the atmospheric Cherenkov imaging technique. At the present sensitivity of the imaging technique, the selection of gamma-ray-like events on the basis of image characteristics appears to be unaffected by the transverse field strength. We are unable to detect any broadening of shower images or any increase in integrated light content.