The total cross section for the π−p→π−π+n reaction has been measured at incident pion kinetic energies of 200, 190, 184, and 180 MeV. In addition, the π+p→π+π+n reaction was measured at 200 and 184 MeV. A fit of the cross sections by heavy baryon chiral perturbation theory yields values of 8.5±0.6(mπ−3) and 2.5±0.1(mπ−3) for the reaction matrix elements A10 and A32, which correspond to values for the s-wave isospin-0 and isospin-2 π−π scattering lengths of a0=0.23±0.08(mπ−1) and a2=−0.031±0.008(mπ−1), respectively.
No description provided.
The reaction p ̄ p→K + K − π 0 was analysed for antiproton annihilations at rest at three hydrogen target densities. A strong dependence of the p ̄ p→φπ 0 yield on the quantum numbers of the initial state is observed. The branching ratio of the φπ 0 channel from the 3 S 1 initial state is more than 15 times larger than the one from the 1 P 1 state. A large apparent violation of the OZI rule for tensor meson production from p ̄ p -annihilations from the P -waves (1 ++ +2 ++ ) is observed: R exp ( f ′ 2 π 0 / f 2 π 0 )=(149±20)·10 −3 , significantly exceeding the OZI-rule prediction R =16·10 −3 .
Three densities (LH2, NTP, and LP) of the hydrogen target.
S- and P-wave in the initial PBAR P system.
S- and P-wave in the initial PBAR P system.
We have searched for first generation scalar leptoquark (LQ) pairs in the enu+jets channel using ppbar collider data (integrated luminosity= 115 pb^-1) collected by the DZero experiment at the Fermilab Tevatron during 1992-96. The analysis yields no candidate events. We combine the results with those from the ee+jets and nunu+jets channels to obtain 95% confidence level (CL) upper limits on the LQ pair production cross section as a function of mass and of beta, the branching fraction to a charged lepton. Comparing with the next-to-leading order theory, we set 95% CL lower limits on the LQ mass of 225, 204, and 79 GeV/c^2 for beta=1, 1/2, and 0, respectively.
The cross section values are extracted with the assumption that BR(LQ --> EQUARK) = 1/2.
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PI+ PI+ correlations. The correlation function is parametrized as follows R = 1 + CONST(NAME=BEC-LAM)*EXP(-CONST(NAME=BEC-R)**2*MQ**2), where MQ**2 = M(pi1 + pi2)**2 - 4*M(pi)**2.
PI- PI- correlations. The correlation function is parametrized as follows R = 1 + CONST(NAME=BEC-LAM)*EXP(-CONST(NAME=BEC-R)**2*MQ**2), where MQ**2 = M(pi1 + pi2)**2 - 4*M(pi)**N = RE.
We present an analysis of dilepton events originating from top-antitop production in proton-antiproton collisions at sqrt{s}=1.8 TeV at the Fermilab Tevatron Collider. The sample corresponds to an integrated luminosity of 109+-7 pb^{-1}. We observe 9 candidate events, with an estimated background of 2.4+-0.5 events. We determine the mass of the top quark to be M_top = 161+-17(stat.)+-10(syst.) GeV/c^2. In addition we measure a top-antitop production cross section of 8.2+4.4-3.4 pb (where M_top = 175 GeV/c^2 has been assumed for the acceptance estimate).
No description provided.
We present limits on anomalous WWZ and WW-gamma couplings from a search for WW and WZ production in p-bar p collisions at sqrt(s)=1.8 TeV. We use p-bar p -> e-nu jjX events recorded with the D0 detector at the Fermilab Tevatron Collider during the 1992-1995 run. The data sample corresponds to an integrated luminosity of 96.0+-5.1 pb~(-1). Assuming identical WWZ and WW-gamma coupling parameters, the 95% CL limits on the CP-conserving couplings are -0.33<lambda<0.36 (Delta-kappa=0) and -0.43<Delta-kappa<0.59 (lambda=0), for a form factor scale Lambda = 2.0 TeV. Limits based on other assumptions are also presented.
CONST(NAME=SCALE) is the model parameter, used in the modification of the couplings as follows: g = g0/(1 + M(gamma Z)**2/CONT(NAME=SCALE)**2)**n.
We report the first measurement of the parity-violating asymmetry in elastic electron scattering from the proton. The asymmetry depends on the neutral weak magnetic form factor of the proton which contains new information on the contribution of strange quark-antiquark pairs to the magnetic moment of the proton. We obtain the value $G_M~Z= 0.34 \pm 0.09 \pm 0.04 \pm 0.05$ n.m. at $Q~2=0.1$ (GeV/c)${}~2$.
Polarized beam. FORMFACTOR(NAME=GZM) = (1/4)*(GM_P-GM_N) - SIN2TW*GM_P - (1/4)*GM_S, whereFORMFACTOR(NAME=GM_S) is the strange quark contribution. FORMFACTOR(NAME=GZM) and FORMFACTOR(NAME=GM_S) are in nucleon magnetic FF.
Differential cross sections for Compton scattering by the proton have been measured in the energy interval between 200 and 500 MeV at scattering angles of θ cms = 75° and θ cms = 90° using the CATS, the CATS/TRAJAN, and the COPP setups with the Glasgow Tagger at MAMI (Mainz). The data are compared with predictions from dispersion theory using photo-meson amplitudes from the recent VPI solution SM95. The experiment and the theoretical procedure are described in detail. It is found that the experiment and predictions are in agreement as far as the energy dependence of the differential cross sections in the Δ-range is concerned. However, there is evidence that a scaling down of the resonance part of the M 1+ 3 2 photo-meson amplitude by (2.8 ± 0.9)% is required in comparison with the VPI analysis. The deduced value of the M 1+ 3 2 - photoproduction amplitude at the resonance energy of 320 MeV is: |M 1+ 3 2 | = (39.6 ± 0.4) × 10 −3 m π + −1 .
No description provided.
No description provided.
The total cross section for the γn→pπ−π0 reaction has been measured over the photon energy range 450–800 MeV at the 855 MeV MAMI Microtron in Mainz with the large acceptance detector DAPHNE and using a deuterium target. As expected, this reaction has a very similar cross section to the γp→nπ+π0 channel and its amplitude is strongly underestimated by the existing double pion photoproduction models.
No description provided.
We measured the in flight annihilation frequencies and cross sections of reactions n p → π + π 0 ,π + η and K + K S in the antineutron momentum range between 50 and 400 MeV/c. The annihilation frequencies of these channels from the different allowed initial states were calculated and some information about the n p annihilation dynamics were obtained. The first determination of the D-wave contribution in this momentum range was also obtained.
No description provided.
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