J. Bystricky

Analyzing power in inclusive π+ and π− production at high xF with a 200 GeV polarized proton beam☆

The analyzing power in inclusive charged pion production has been measured using the 200 GeV Fermilab polarized proton beam. A striking dependence in x(F) is observed in which A(N) increases from 0 to 0.42 with increasing x(F) for the pi+ data and decreases from 0 to -0.38 with increasing x(F) for pi- data. The kinematic range covered is 0.2 less-than-or-equal-to x(F) less-than-or-equal-to 0.9 and 0.2 less-than-or-equal-to p(T) 2.0 GeV/c. In a simple model our data indicate that at large x(F) the transverse spin of the proton is correlated with that of its quark constituents.

Large-xF spin asymmetry inπ0 production by 200-GeV polarized protons

The spin asymmetryAN for inclusive π0 production by 200-GeV transversely-polarized protons on a liquid hydrogen target has been measured at Fermilab over a wide range ofxF, with 0.5<pT<2 GeV/c. AtxF>0.3, the asymmetry rises with increasingxF and reaches a value ofAN=0.15±0.03 in the region 0.6<xF<0.8. This result provides new input regarding the question of the internal spin structure of transversely-polarized protons.

First results for the two-spin parameter ALL in π0 production by 200 GeV polarized protons and antiprotons

Abstract The two-spin parameter A LL in inclusive π 0 productionby longitudinally-polarized protons and antiprotons on a longitudinally-polarized proton target has been measured at the 200 GeV Fermilab spin physics facility, for π 0 s at x F =0 with 1⩽ p t ⩽3 GeV/ c . The results exclude, at the 95% confidence level, values of A LL (pp) > 0.1 and 0 s produced by protons, and values of A LL ( p p) > 0.1 and for incident antiprotons. The relevance of A LL (pp) for the gluon spin density is discussed. The data are in good agreement with “conventional”, small or zero, gluon polarization.

High-xT single-spin asymmetry in π0 and η production at xF=0 by 200 GeV polarized antiprotons and protons☆☆☆

A measurement of the single-spin asymmetry A(N) in P up + P --> pi-0 + X at 200 GeV with x(F) = O shows a transition in the production process from a low-x(T) regime with A(N) = 0, through an intermediate region of negative asymmetry, to a high-x(T) regime with A(N) > 0.3. This transition occurs at x(T) almost-equal-to 0.4 and is consistent with x(T)-scaling of A(N) in pion production using polarized beams or targets from square-root -s = 5.2 to 19.4 GeV. Results for A(N) in eta-production by polarized protons and in pi-0 production by polarized antiprotons are also presented.

Measurement of single spin asymmetry in η-meson production in p↑p and p̄↑p interactions in the beam fragmentation region at 200 GeV/c

We present experimental results on measuring a single spin asymmetry in η-meson production in the interaction of transversely polarized protons and antiprotons at plab = 200 GeV/c with a proton target in the region 0.2 < xF < 0.7 for p↑p, 0.3 < xF < 0.7 for p↑p and 0.7 < pT < 2.0 GeV/c. A comparison of single spin asymmetries in π- and η-meson production is made.

Measurement of the double-spin asymmetry ALL for inclusive multi-γ pair production with 200 GeV/c polarized proton beam and polarized proton target

The invariant double-differential cross section, E1E2d6 delta/dp(1)3dp(2)3, and the double-spin asymmetry, A(LL), for inclusive multi-gamma pair production in which gamma-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-gamma 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 pi0pi0 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, DELTAG/G. The results put restrictions on the size of DELTAG/G in the region of 0.05 less-than-or-similar-to x less-than-or-similar-to 0.35.

Single‐spin asymmetries and invariant cross sections of the high transverse‐momentum inclusive π0 production in 200 GeV/c pp and p̄p interactions

The π0 inclusive and semi‐inclusive, single‐spin asymmetries have been measured using transversely‐polarized, 200‐GeV/c proton and antiproton beams colliding with an unpolarized hydrogen target. The measured asymmetries are consistent with a value of zero within the error bars for the kinematic regions, −0.15<xF<+0.15 and 1<pT<4.5 GeV/c. These data indicate that the higher‐twist contribution in QCD to the single‐spin asymmetry in inclusive π0 production may not be as large as was previously expected. Additional evidence for such a conclusion comes from the measurement of a semi‐inclusive π0‐charged particle asymmetry, where the associated charged particles are detected opposite to the π0 azimuthal direction. This experiment also has a high‐statistics measurement of the inclusive π0 cross sections for pp and pp collisions at 200 GeV/c.

Measurement of single spin asymmetry for direct photon production in pp collisions at 200 GeV/c

The single spin asymmetry for inclusive direct photon production has been measured using a polarized proton beam of 200 GeV/c with an unpolarized proton target at −0.15<xF<0.15 and 2.5<pT<3.1 GeV/c at Fermilab. The measurement was done using lead glass calorimeters and the photon detectors which surround the fiducial area fo the calorimeters. Background rejection has been done using the surrounding photon detectors. The single spin asymmetry, AN, for the direct photon production is consistent with zero within experimental uncertainty.