C. A. Baker

Revised experimental upper limit on the electric dipole moment of the neutron

We present for the first time a detailed and comprehensive analysis of the experimental results that set the current world sensitivity limit on the magnitude of the electric dipole moment (EDM) of the neutron. We have extended and enhanced our earlier analysis to include recent developments in the understanding of the effects of gravity in depolarizing ultracold neutrons; an improved calculation of the spectrum of the neutrons; and conservative estimates of other possible systematic errors, which are also shown to be consistent with more recent measurements undertaken with the apparatus. We obtain a net result of dn=−0.21±1.82×10−26  e cm, which may be interpreted as a slightly revised upper limit on the magnitude of the EDM of 3.0×10−26  e cm (90% C.L.) or 3.6×10−26  e cm (95% C.L.).

Observation of two JPC=0++ isoscalar resonances at 1365 and 1520 MeV

From a simultaneous analysis of data on pp → π0π0π0 and pp → ηηπ0 at rest, two I = 0, JPC = 0++ resonances are identified above 1 GeV. The first has mass M = 1365−55+20 MeV and width г = 268 ± 70 MeV, close to the ƒ0(1400) of the Particle Data Group. The second has M = 1520 ± 25 MeV, г = 148−25+20 MeV.

High-statistics study of f0(1500) decay into π0π0

Abstract A partial-wave analysis of the reaction p p →π 0 π 0 π 0 has been performed using a high-quality high-statistics data set of 712 000 events. In addition to the f0(975) and f0(1300), the scalar resonance with mass m = (1500 ± 15) MeV and width Γ = (120 ± 25) MeV is necessary to describe the data.

Coupled channel analysis of pp annihilation into π0π0π0, π0ηη and π0π0η

We confirm the existence of the two IG(JPC) = 0+(0++) resonances f0(1370) and f0(1500) reported by us in earlier analyses. The analysis presented here couples the final states π0π0π0, π0π0η and π0ηη of pp annihilation at rest. It is based on a 3 × 3 K-matrix. We find masses and widths of M = (1390±30) MeV, Γ = (380±80) MeV; and M = (1500±10) MeV, Γ = (154 ± 30) MeV, respectively. The product branching ratios for the production and decay into π0π0 and ηη of the f0(1500) are (1.27 ± 0.33) · 10−3 and (0.60 ± 0.17) · 10−3, respectively.

Observation of a new IG(JPC)=1−(0++) resonance at 1450 MeV

Abstract A new IG=1− JPC=0++πη resonance is observed in pp annihilation at rest into π0π0η. It has a mass M=(1450±40)MeV and a width Γ=(270±40)MeV.

Observation of a 2+ + resonance at 1515 MeV in proton-antiproton annihilations into 3π0

Abstract Antiproton-proton annihilations at rest into 3 π 0 are analyzed in terms of π 0 π 0 final state interactions. A J PC = 2 + + resonance at a mass of 1515 ± 10 MeV with a width of 120 ± 10 MeV is required to explain the data. This result is supported by previous observations made on the ππ system in p p and p n annihilations which show that the resonance has I = 0. This resonance is practically degenerate in mass with the f′ 2 (1525) but the two resonances have very different production and decay characteristics.

The pseudoscalar mixing angle ΘPS from ν and ν′ production in p annihiltion at rest

Abstract We have determined ratios of branching ratios for p p annihilations at rest into π 0 η and π 0 η ′, into ηη and ηη ′, and into ωη and ωη ′. All reactins are observed in two different all-neutral final states. The ratios permit a determination of the pseudoscalar mixing angle. We find Θ PS = −(17.3±1.8)°.

Proton-antiproton annihilation into ηηπ-observation of a scalar resonance decaying into ηη

Abstract The results of a measurement of pp annihilation at rest into ηηπ 0 are presented. Assuming a resonance dominated model for the annihilation process an isoscalar J PC =0 ++ resonance decaying into ηη is observed with a mass of 1560±25 MeV/ c 2 and a width of 245±50 MeV/ c 2 .

Search for a neutron electric dipole moment

In 1950 at a time when parity conservation was almost universally believed, PURCELL and RAMSEY [1] pointed out that such an assumption must be based on experiment and that there was little experimental evidence for the assumption at that time. We further noted that a search for a neutron electric dipole moment would provide such a test since a dipole moment is forbidden under parity symmetry and the test would be particularly sensitive since the neutron has no electric charge and is consequently not accelerated out of the observation region when a strong external electric field is applied.

P- versus S-wave pp-annihilation at rest in LH2

Abstract The annihilation p p →π 0 π 0 was measured for antiprotons stopped in liquid hydrogen (LH2). This reaction is only allowed from odd angular momentum states of the p p - atom . The resulting branching ratio BR ( p p →π 0 π 0 ) LH 2 =(6.93±0.22 stat ±0.37 syst )×10 −4 , combined with a previous measurement of the branching ratio BR ( p p →π + π − ) 2 P in gas from the 2P-state of p p suggests a fraction of P-wave annihilation in LH2 of (28.8±3.5)%, much larger than the values obtained from other annihilation channels. A method of reconciling the contradictory results is discussed.