E. Pauli

Determination of the electric and magnetic form factors of the proton in the time-like region

The s dependence of the electromagnetic proton form factors in the time-like region has been determined from the threshold (s = 4Mp2) up to s = 4.2 GeV2. Data were collected in a dedicated experiment performed at the LEAR antiproton ring at CERN, increasing by one order of magnitude the available statistics. Total and differential cross section of the pp → e−e+ reaction have been measured. The electric and magnetic form factors are found to have comparable value. The observed form factor shows a clear steep s dependence close to the threshold.

Measurement of the proton electromagnetic form factor near threshold in the time-like region

The rate of the reaction pp→e+e− has been measured in liquid hydrogen for antiprotons at momentum values between 150 and 300 MeV/c. New precise values of the proton electromagnetic form factor in the time-like region have been obtained assuming |Ge|=|Gm| in the investigated region. The q2 dependence of the form factor close to threshold is found to have a steeper slope than indicated by existing calculations based on vector dominance models.

Study of the production of a strange (S = −1) dibaryon in the interactions of K− and π+ on deuterium below 1.5GeV/c

Abstract The production of a strange dibaryonic system called H+1 (M = 2.13 GeV/c2, S = −1), has been studied with a missing mass spectrometer, at the CERN Proton Synchrotron, in the reaction K−d → π−H+1 and in the line-reversed reaction π+d → K+H+1 between 0.9 and 1.4 GeV/c. The reactions K − d → π − X + , π d → K + X + , have been studied in a missing mass spectrometer at CERN. The experiment (PS159) is well adapted to search for a signal in the missing mass X+ (B = 2, S = −1) produced in the backward c.m.s. direction, between 2.0 and 2.3 GeV/c2. The two reactions have been analysed at three different beam settings: 1.4, 1.06 and 0.92 GeV/c for reaction (1) and 1.4, 1.2 and 1.06 GeV/c for reaction (2).

Precise determination of the electromagnetic form factor of the proton in the time-like region up to s = 4.2 GeV2

Abstract The s dependence of the proton form factor in the time-like region has been determined up to s=4.2 GeV2, assuming the validity of the |Ge| = |Gm| = |G| hypothesis. Data were taken in a dedicated experiment performed at the LEAR antiproton ring at CERN, increasing by one order of magnitude the available statistics on the proton form factor near threshold in the time-like region. Our result consist of cross section measurements of the p p → e + e − reaction for different beam momenta in the kinematical r 3.6⩽s⩽4.2 GeV2. The observed s dependence of the form factor close to threshold differs appreciably from the one suggested by previous experiments.

A large solid angle magnetic detector for precision studies of e.m. processes in low-energy p interactions

The detector presented is designed to measure the proton e.m. form factors by measuring e+e− pairs produced in pp annihilations at low energy or at rest. In this paper the apparatus is described in detail, with emphasis on how to achieve a suppression factor of about 1010 of the hadronic background.

Search for strange (S = −2) dibaryons in the reaction K− + d → K+ + MM at 1.4 GeV/c

The reaction K− + d → K+ + MM has been studied at 1.4 GeV/c, to search for Q = −1, S = −2 dibaryonic states, in the mass range ≈ 2.1–2.5 GeV/c2. No evidence for the presence of structures has been found and upper limits for the backward production differential cross section for narrow states are established.

Study of the missing-mass spectra in the reactions π−d → K+ + MM and K−d → π+ + MM at 1.4 GeV/c to search for strange dibaryon states

Abstract The reactions π − d → K + + MM and K − d → π + + MM have been studied at 1.4 GeV / c to search for strange dibaryon states with quantum numbers Q = −1, and S = −1. No structures are found which could indicate the production of such states and upper limits for the cross sections are established.

A measurement of the pp→π+π− reaction for 158⩽p(p)⩽275 MeV/c

Abstract A measurement of the total cross section for the reaction p p → π+π− has been performed for seven values of the incident momentum between 158 and 275 MeV/c. The values obtained, if compared with previous results at higher momenta, agree with a 1/s dependence. The differential cross section sssumed over the whole incident momentum range has also been measured and the result of a fit by Legendre polynomials is given.

Silica aerogel Cherenkov counter in a missing-mass experiment K−d → K+ + X at 1.4 GeV/c

Abstract Two Cherenkov counters, C 0 and C 1 , are being used in an experiment to search for dibaryon candidates in the reaction K − d → K + + X at 1.4 GeV/ c . They have useful cross-sections of 10 × 8 cm 2 and 30 × 15 cm 2 , respectively. Each counter is a diffusing box surrounding the aerogel sample and can be examined by two photomultipliers. The mean number of photoelectrons collected is equal to 17 in C 0 and 21 in C 1 for β = 1 incident particles. Below threshold, the residual scintillation corresponds to 0.12 photoelectrons. The role of each otheter in the trigger logic for the K − d → K + + X experiment is carefully studied.

Search for CP-violation in K0 → π+π−π0 decays

Abstract We have studied the time distribution of π + π − π o decays of the neutral K meson produced in the reaction K + p → K o pπ + with K + momenta at 1.4 and 1.7 GeV/ c . Within our fiducial volume we have 98 uniquely identified π + π − π o decays with proper times between 0.04 and 20 K s lifetimes. For the ratio η +− o of the amplitude K s → π + π − π o to the amplitude K L → π + π − π o , it is found that: Re η +−0 = 0.01 ± 0.22 0.20 , Im η +−o = 0.33 ± 0.42 0.50 . This result is consistent with no CP -violation. Assuming η +− o = 0, we find the rate Г( K L → π + π − π o ) = (2.5 ± 0.3) 10 6 sec −1 .