H. R. Gustafson

Neutron Total Cross-Sections on Nuclei at Fermilab Energies

We have measured total cross sections for neutrons on protons, deuteriom, beryllium, carbon, aluminium, iron, copper, cadmium, tungsten, lead, and uranium for momenta between 30 and 300 GeV/c. The measurements were carried out in a small-angle neutral beam at Fermilab. Typical accuracy of the data is 0.5 to 1%. The cross sections are consistent with an A0.77±0.01 dependence over the entire momentum range. The cross sections are compared with theoretical predictions. Agreement is found only if inelastic screening is included. Nuclear radii obtained from our data are in good agreement with previous determinations.

Evidence for the decay sigma+ --> pmu+ mu-.

We report the first evidence for the decay Sigma(+)-->pmu(+)mu(-) from data taken by the HyperCP (E871) experiment at Fermilab. Based on three observed events, the branching ratio is B(Sigma(+)-->pmu(+)mu(-))=[8.6(+6.6)(-5.4)(stat)+/-5.5(syst)]x10(-8). The narrow range of dimuon masses may indicate that the decay proceeds via a neutral intermediate state, Sigma(+)-->pP(0),P0-->mu(+)mu(-) with a P0 mass of 214.3+/-0.5 MeV/c(2) and branching ratio B(Sigma(+)-->pP(0),P0-->mu(+)mu(-))=[3.1(+2.4)(-1.9)(stat)+/-1.5(syst)]x10(-8).

Search for Chameleon Particles Using a Photon-Regeneration Technique

We report the first results from the GammeV search for chameleon particles, which may be created via photon-photon interactions within a strong magnetic field. Chameleons are hypothesized scalar fields that could explain the dark energy problem. We implement a novel technique to create and trap the reflective particles within a jar and to detect them later via their afterglow as they slowly convert back into photons. These measurements provide the first experimental constraints on the couplings of chameleons to photons.

Observation of the decay K- ---> pi- mu+ mu- and measurements of the branching ratios for K+- ---> pi+- mu+ mu-

Using data collected with the HyperCP (E871) spectrometer during the 1997 fixed-target run at Fermilab, we report the first observation of the decay K--->pi(-)mu(+)mu(-) and new measurements of the branching ratios for K+/--->pi(+/-)mu(+)mu(-). By combining the branching ratios for the decays K+-->pi(+)mu(+)mu(-) and K--->pi(-)mu(+)mu(-), we measure Gamma(K+/--->pi(+/-)mu(+)mu(-))/Gamma(K+/--->all) = (9.8+/-1.0+/-0.5)x10(-8). The CP asymmetry between the rates of the two decay modes is [Gamma(K+-->pi(+)mu(+)mu(-))-Gamma(K--->pi(-)mu(+)mu(-))]/[Gamma(K+-->pi(+)mu(+)mu(-))+Gamma(K--->pi(-)mu(+)mu(-))] = -0.02+/-0.11+/-0.04.

Neutron-nucleus inelastic cross sections from 160 to 375 GeV/c

Abstract We habe measured inelastic cross sections of neutrons on 14 nuclei ranging from hydrogen to uranium for neutron energies between 160 and 375 GeV. The measurements were made with a total absorption calorimeter and have an accuracy of 1%. The results are compared to other data and predictions of the Glauber model. Interaction lengths for high-energy neutrons in composite materials of practical interest are also given.

Forward Neutron Production at the Fermilab Main Injector

We have measured cross sections for forward neutron production from a variety of targets using proton beams from the Fermilab Main Injector. Measurements were performed for proton beam momenta of 58, 84, and 120 GeV/c. The cross section dependence on the atomic weight (A) of the targets was found to vary as A{sup {alpha}}, where {alpha} is 0.46{+-}0.06 for a beam momentum of 58 GeV/c and 0.54{+-}0.05 for 120 GeV/c. The cross sections show reasonable agreement with FLUKA and DPMJET Monte Carlos. Comparisons have also been made with the LAQGSM Monte Carlo.

High statistics search for the θ+(1.54) pentaquark state

We have searched for Theta+(1.54) -> K0,p decays using data from the 1999 run of the HyperCP experiment at Fermilab. We see no evidence for a narrow peak in the K0,p mass distribution near 1.54 GeV/c among 106,000 K0,p candidates, and obtain an upper limit for the fraction of Theta+(1.54) to K0,p candidates of <0.3% at 90% confidence.

Search for CP violation in charged-Xi and Lambda hyperon decays.

We have compared the p and p angular distributions in 117 x 10(6) Xi- -->Lambdapi- -->ppi-pi- and 41 x 10(6) Xi+ -->Lambda pi+ -->p pi+pi+ decays using a subset of the data from the HyperCP experiment (E871) at Fermilab. We find no evidence of CP violation, with the direct-CP-violating parameter AXiLambda identical with (alphaXialphaLambda-alpha Xialpha Lambda)/(alphaXialphaLambda+alphaXialphaLambda)=[0.0+/-5.1(stat)+/-4.4(syst)] x 10(-4).

Search for direct CP violation in Λ and Ξ hyperon decays

A sensitive search for direct CP violation in Ξ− (Ξ+) and Λ (Λ) decays is underway at FNAL. Experiment E871 (HyperCP) intends to perform a precision measurement of the angular distribution of protons (anti-protons) with respect to the helicity axis in the rest frame of the Λ (Λ). The slopes of these distributions give the decay parameters αΞαΛ and αΞαΛ. An asymmetry parameter A in terms of these decay parameters has been defined for which a non-zero value would be unambiguous evidence for direct CP violation. Theoretical predictions for A range from no asymmetry up to ∼ 10−3. HyperCP expects to measure A with an uncertainty of ∼ 2 × 10−4.

Neutron-proton differential cross sections in the range 70 to 400 GeV/c

Abstract We report the results of an experiment which measured np elastic scattering differential cross sections over a range in − t from 0.15 to ∼3.6 (GeV/ c ) 2 for incident neutron momenta from 70 to 400 GeV/ c . We find the logarithmic slope parameter, evaluated at − t = 0.2 (GeV/ c ) 2 , to be consistent with existing proton-proton parametrizations. The data exhibit a dip in the cross section near − t = 1.4 (GeV/ c ) 2 for incident neutron momenta above 200 GeV/ c . For neutron momenta less than 280 GeV/ c , the neutron-proton cross sections are found to be higher than existing proton-proton data in the range 0.7 ⩽ − t ⩽ 1.3 (GeV/ c ) 2 which is in contradiction to most Regge predictions.