The invariant double-differential cross section, E 1 E 2 d 6 σ / d p 3 1 d p 3 2 , and the double-spin asymmetry, A LL , for inclusive multi-γ pair production in which γ-rays came from neutral mesons were measured with a 200 GeV / c longitudinally-polarized proton beam and a longitudinally-polarized proton target. Most of the multi-γ pairs comes from two-jet type events which are sensitive to partonic interaction. The A LL values were found to be consistent with zero. The invariant double-differential cross section for inclusive π 0 π 0 production was also measured. These measured cross sections are consistent with LUND Monte Carlo simulations. Using the LUND Monte Carlo simulation package with the Carlitz-Kaur model of spin dependent distribution functions of valence quarks, the A LL values have been compared with theoretical predictions of gluon polarization, ΔG / G . The results put restrictions on the size of ΔG / G in the region of 0.05 ⪅ x ⪅ 0.35.
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We present a precise measurement of the neutron magnetic form factor G mn at low momentum transfer ( q = 1.69 fm −1 ). From a simultaneous measurement of D ( e , e ′ n ) and D ( e , e ′ p ) we obtain the ratio of neutron and proton cross sections. The neutron detection efficiency is obtained from a separate measurement using tagged neutrons produced by H ( n , p ) n scattering of a monochromatic neutron beam. In contrast to previous determinations of G mn , the present value is insensitive to the systematic uncertainties in the interpretation of the data in terms of G mn and represents a determination of G mn to ±1.7%.
Using kinematics I.
Using kinematics II.
Using kinematics I. SD is simple dipole model.
We study the polarization with respect to the normal to the production plane for a very clean sample of 27217 Λ 0 / Λ 0 hyperons produced in 230 GeV/ c π − Cu interactions. In general we find P(Λ 0 ) ≈ P( Λ 0 ap; 0 except for x F > 0, p T > 1GeV/ c where P ( Λ 0 ) = −0.28±0.09(stat.)±0.02(syst.).
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The production of neutral pions has been studied in the reactions 40 Ar + nat Ca , 86 Kr + nat Zr and 197 Au + 197 Au at 1 A GeV. For high energy pions emitted from the heavier systems a steeper than linear rise of the pion multiplicity with the centrality of the reaction is observed, indicating a pion production process other than binary nucleon-nucleon collisions. At low transverse momenta an enhancement of the π 0 -multiplicity increasing with the mass of the collision system is found. Systematic discrepancies between the experimental results and recent BUU, QMD and Cascade calculations are discussed.
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RESULTS OF AN EXTRAPOLATION TO THE FULL SOLID ANGLE TAKING THE EXPERIMENTALTEMPERATURES INTO ACCOUNT.
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Inclusive double differential multiplicities d2N/dy dpt and related quantities have been measured for protons and deuterons produced in 14.6A GeV/c Si+Al and Si+Pb collisions using the E814 forward spectrometer at the AGS at BNL. Collision ‘‘centrality’’ is determined by measuring Nc, the total charged particle multiplicity in the pseudorapidity range 0.85<η<3.8. For both systems Si + Al and Si + Pb, an increase in the proton rapidity distribution dN/dy at midrapidity and a corresponding decrease at higher rapidities are observed with increasing Nc. For Si+Pb, Boltzmann slope parameters TB increase significantly in the most central collisions. The measured distributions exhibit a centrality dependence even when σ/σgeo≲10%, where full overlap between the Si and Pb nuclei occurs in a simple geometric picture. The proton rapidity distribution dN/dy is presented for the symmetric system Si+Al over the entire rapididty interval. The total number of protons, which is the integral of this quantity over rapidity, varies with Nc. Results are compared with various model calculations, mostly using the hadronic cascade codes ARC and RQMD. No significant nuclear transparency is observed, indicating that large baryon and energy densities are produced in these collisions.
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Negative pion spectra emitted in the reactions of 775 MeV/nucleon La139+12C and La139+139La reactions have been measured in coincidence with the projectile fragments using the HISS spectrometer at the Bevalac. Prominent peaks near the beam velocity were observed in the pion spectra. Position and widths of the peaks were studied as a function of the ‘‘sum charge’’ of projectile fragments which is a good measure of impact parameter; the smaller the ‘‘sum charge,’’ the smaller the impact parameter. The peak position down shifts with the smaller ‘‘sum charge.’’ The pion peak is wider in the transverse than in the longitudinal direction, possibly mirroring the velocity dispersions of projectile fragments in the early stage of reactions.
THE CHARGE IN THE TABLE IS THE SUM CHARGE OF OBSERVED FRAGB. A TWO-DIMENSIONAL SPECTRUM WAS FITTED BY A SINGLE TWO-DIMENSIONAL GAUSSIAN FUNCTION ON A FLAT BACKGROUND.
THE CHARGE IN THE TABLE IS THE SUM CHARGE OF OBSERVED FRAGB. A TWO-DIMENSIONAL SPECTRUM WAS FITTED BY A SINGLE TWO-DIMENSIONAL GAUSSIAN FUNCTION ON A FLAT BACKGROUND.
We present a total of 191 and 203 data points of the elastic neutron-protonspin correlation parameters A ookk and A oosk , respectively. Both observables were measured in a large angular interval. The observable A ookk was measured from 0.312 to 1.10 GeV and A oosk from 0.80 to 1.10 GeV. The SATURNE II polarized beam of free neutrons obtained from the break-up of polarized deuterons was scattered on the polarized Saclay frozen-spin proton target. The beam polarization was oriented either along the beam direction or sideways, the target polarization was oriented longitudinally. Data are compared with phase-shift analyses predictions and with the PSI, LAMPF and SATURNE II results. Present results provide an important contribution to any future theoretical or phenomenological analysis.
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A new method to study the nuclear periphery using antiproton annihilation was applied to nine isotopes with mass numbers between 58 and 238. The method makes use of the detection of the radioactive annihilation products one unit lower in mass number than the target. A clear neutron halo effect, strongly correlated with the neutron binding energy, was observed in some nuclei. The experimental results are in qualitative agreement with calculations of proton and neutron densities at the nuclear periphery based on either a simple asymptotic density model or a more complex Hartree-Fock approach.
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A(FRAGT)=A(TARGET)-1.
Transverse momentum spectra of η mesons have been measured near the free nucleon-nucleon production threshold in the heavy ion reactions Ar40+ Canat, Kr86 + Zrnat, and Au197+ Au197 at 1.0A GeV and also in Ar40+ Canat at 1.5A GeV. The measured transverse momentum distributions are compared to model calculations. The relative abundance of Δ(1232) and N(1535) resonances excited in the collision is deduced. A comparison to pion data reveals scaling with the transverse mass of the emitted meson.
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Extrapolation to full solid angle.
We report on a measurement of the forward-backward charge asymmetry in e+e−→qq¯ at KEK TRISTAN, where the asymmetry is near maximum. We sum over all flavors and measure the asymmetry by determining the charge of the quark jets. In addition we exploit flavor dependencies in the jet charge determination to enhance the contributions of certain flavors. This provides a check on the asymmetries of individual flavors. The measurement agrees with the standard model expectations.
Forward--backward asymmetry summed over all flavours of quarks.
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