We report a high precision measurement of the transverse single spin asymmetry $A_N$ at the center of mass energy $\sqrt{s}=200$ GeV in elastic proton-proton scattering by the STAR experiment at RHIC. The $A_N$ was measured in the four-momentum transfer squared $t$ range $0.003 \leqslant |t| \leqslant 0.035$ $\GeVcSq$, the region of a significant interference between the electromagnetic and hadronic scattering amplitudes. The measured values of $A_N$ and its $t$-dependence are consistent with a vanishing hadronic spin-flip amplitude, thus providing strong constraints on the ratio of the single spin-flip to the non-flip amplitudes. Since the hadronic amplitude is dominated by the Pomeron amplitude at this $\sqrt{s}$, we conclude that this measurement addresses the question about the presence of a hadronic spin flip due to the Pomeron exchange in polarized proton-proton elastic scattering.
The asymmetry $\varepsilon(\varphi)/(P_B + P_Y)$ for various $t$-intervals.
The measured single spin asymmetry $A_N$ for five $-t$ intervals.
Fitted value of $r_5$.
Antiproton-proton elastic scattering was measured at c.m.s. energies √s =546 and 1800 GeV in the range of four-momentum transfer squared 0.025<-t<0.29 GeV2. The data are well described by the exponential form ebt with a slope b=15.28±0.58 (16.98±0.25) GeV−2 at √s =546 (1800) GeV. The elastic scattering cross sections are, respectively, σel=12.87±0.30 and 19.70±0.85 mb.
Final results (systematic errors included).
Final results (systematic errors included).
Statistical errors only. Data supplied by S. Belforte.
Proton Compton scattering has been measured in a coincidence experiment at photon energies between 2.2 and 7 GeV and four-momentum transfers t between −0.06 and −0.85(GeV/ c ) 2 . For ∣ t ∣ ⩽ 0.4 (GeV/ c ) 2 fits of the form d σ /d t = ( A · exp( Bt )) yield forward cross sections A in good agreement with the values calculated from the total hadronic γ p cross section via the optical theorem and the forward dispersion relation. The slopes B do not show a significant energy dependence, the mean value being 5.7 ± 0.4 (GeV/ c ) −2 . The cross section is substantially larger than predicted by the vector-meson dominance model.
No description provided.
No description provided.
No description provided.
Compton scattering on protons has been measured at a mean photon energy of 6 GeV and four-momentum transfers − t between 0.06 and 0.60 (GeV/ c ) 2 . The differential cross section shows a diffraction-like behaviour. The cross section extrapolated to t =0 is in fair agreement with the optical point. Discrepancies with the vector meson dominance model are pointed out.
No description provided.
Cross-section values for Compton scattering on the proton were measured at 25 kinematic settings over the range s = 5-11 and -t = 2-7 GeV2 with statistical accuracy of a few percent. The scaling power for the s-dependence of the cross section at fixed center of mass angle was found to be 8.0 +/ 0.2, strongly inconsistent with the prediction of perturbative QCD. The observed cross-section values are in fair agreement with the calculations using the handbag mechanism, in which the external photons couple to a single quark.
Cross section of proton Compton Scattering at centre of mass energy squared of 4.82 GeV.
Cross section of proton Compton Scattering at centre of mass energy squared of 6.79 GeV.
Cross section of proton Compton Scattering at centre of mass energy squared of 8.90 GeV.
Compton scattering from protons has been measured between 650 MeV and 1350 MeV for angles between 60° and 140° CM.
No description provided.
We have measured elastic scattering of 5 and 6 GeV photons on hydrogen and deuterium in the angular range 10–50 mrad. On hydrogen we observe a forward diffraction peak with a slope of 8.5 (GeV/ c ) −2 . The extrapolated forward cross sections in units μ b/(GeV/ c ) 2 are 0.82 ± 0.04 at 5 GeV and 0.79 ± 0.04 at 6 GeV. They are consistent with the calculated amplitudes obtained from total cross section measurements via the optical theorem and dispersion relations assuming negligible contributions of spin-dependent amplitudes. Deuterium cross sections show a transition from coherent scattering at low | t | to incoherent scattering at higher | t |. They indicate that the isovector exchange amplitude a 1 is very small compared to the isoscalar a 0 . We obtain |a 1 | 2 /|a 0 +a 1 | 2 =0.13±0.09 , Re (a 0 a ∗ 1 )/|a 0 +a 1 | 2 =0.0±0.03, at 5 GeV , |a 1 | 2 /|a 0 +a 1 | 2 =−0.12±0.15 , Re (a 0 a ∗ 1 )/|a 0 +a 1 | 2 =0.10±0.04, at 6 GeV .
No description provided.
No description provided.
Results are presented on the elastic scattering of photons by protons. The incident photon energy ranged from 0.55 GeV to 4.5 GeV, and the four-momentum transfer t ranged from 0.12 to 1.0 (GeV/c)2. The data at large angles, 60°<θ*<115°, are characterized by a pronounced excitation of the D13(1518) resonance, a shoulder in the 1688-MeV mass region, and a precipitous drop thereafter in the cross section as a function of incident energy. The low-t data are characterized by a diffraction slope of 5 (GeV/c)−2. The data are inconsistent with the predictions of the vector-dominance model if the latter is restricted to ρ0, ω, and φ vector mesons.
No description provided.
Deep inelastic scattering and its diffractive component, $ep \to e^{\prime}\gamma^* p \to e^{\prime}XN$, have been studied at HERA with the ZEUS detector using an integrated luminosity of 52.4 pb$^{-1}$. The $M_X$ method has been used to extract the diffractive contribution. A wide range in the centre-of-mass energy $W$ (37 -- 245 GeV), photon virtuality $Q^2$ (20 -- 450 GeV$^2$) and mass $M_X$ (0.28 -- 35 GeV) is covered. The diffractive cross section for $2 < M_X < 15$ GeV rises strongly with $W$, the rise becoming steeper as $Q^2$ increases. The data are also presented in terms of the diffractive structure function, $F^{\rm D(3)}_2$, of the proton. For fixed $Q^2$ and fixed $M_X$, $\xpom F^{\rm D(3)}_2$ shows a strong rise as $\xpom \to 0$, where $\xpom$ is the fraction of the proton momentum carried by the Pomeron. For Bjorken-$x < 1 \cdot 10^{-3}$, $\xpom F^{\rm D(3)}_2$ shows positive $\log Q^2$ scaling violations, while for $x \ge 5 \cdot 10^{-3}$ negative scaling violations are observed. The diffractive structure function is compatible with being leading twist. The data show that Regge factorisation is broken.
Cross section for diffractive scattering GAMMA* P --> DD X where M(DD) < 2.3 GeV and M(X) = 1.2 GeV for Q**2 = 25 GeV**2.
Cross section for diffractive scattering GAMMA* P --> DD X where M(DD) < 2.3 GeV and M(X) = 1.2 GeV for Q**2 = 35 GeV**2.
Cross section for diffractive scattering GAMMA* P --> DD X where M(DD) < 2.3 GeV and M(X) = 1.2 GeV for Q**2 = 45 GeV**2.
We measured the differential cross section for p̄p and pp elastic scattering in the momentum-transfer range 0.01 <| t | < 1.0 GeV 2 at the CERN Intersecting Storage Rings with center-of-mass energy s = 52.8 GeV . Fitting the differential cross section with an exponential [ A exp ( bt )], we found b p p = 13.92 ± 0.59 GeV −2 for | t | < 0.05 GeV 2 , whilst for | t | > 0.09 GeV 2 , b p p = 10.68 ± 0.26 GeV −2 . Using the optical theorem, we obtained for the total cross section σ tot ( p p)= 44.86 ± 0.78 mb and, by integrating the differential cross section, we obtained for the total elastic cross section σ el ( p p) = 7.89 ± 0.28 mb . Calculations of σ tot combining elastic-rate and total-rate measurements are also given. All of these measurements were also performed for pp scattering at the same energy, and the results for both reactions are compared.
NUMERICAL VALUES OF DATA IN FIGURE TAKEN FROM PREPRINT CERN-EP/82-65.
NUMERICAL VALUES OF DATA ON FIGURES TAKEN FROM PREPRINT CERN-EP/82-65.
No description provided.
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