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Register a new userMeasurement of Inclusive Spin Structure Functions of the Deuteron
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J. Yun
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We report the results of a new measurement of spin structure functions of the deuteron in the region of moderate momentum transfer ($Q^2$ = 0.27 -- 1.3 (GeV/c)$^2$) and final hadronic state mass in the nucleon resonance region ($W$ = 1.08 -- 2.0 GeV). We scattered a 2.5 GeV polarized continuous electron beam at Jefferson Lab off a dynamically polarized cryogenic solid state target ($^{15}$ND$_3$) and detected the scattered electrons with the CEBAF Large Acceptance Spectrometer (CLAS). From our data, we extract the longitudinal double spin asymmetry $A_{||}$ and the spin structure function $g_1^d$. Our data are generally in reasonable agreement with existing data from SLAC where they overlap, and they represent a substantial improvement in statistical precision. We compare our results with expectations for resonance asymmetries and extrapolated deep inelastic scaling results. Finally, we evaluate the first moment of the structure function $g_1^d$ and study its approach to both the deep inelastic limit at large $Q^2$ and to the Gerasimov-Drell-Hearn sum rule at the real photon limit ($Q^2 to 0$). We find that the first moment varies rapidly in the $Q^2$ range of our experiment and crosses zero at $Q^2$ between 0.5 and 0.8 (GeV/c)$^2$, indicating the importance of the $Delta$ resonance at these momentum transfers.
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The Ayy data for deuteron inclusive breakup off hydrogen and carbon at a deuteron momentum of 9.0 GeV/c and large Pt of emitted protons are presented. The large values of Ayy independent of the target mass reflect the sensitivity of the data to the deuteron spin structure. The data obtained at fixed $x$ and plotted versus Pt clearly demonstrate the dependence of the deuteron spin structure at short internucleonic distances on two variables. The data are compared with the calculations using Paris, CD-Bonn and Karmanovs deuteron wave functions.
Precise measurements of the spin structure functions of the proton $g_1^p(x,Q^2)$ and deuteron $g_1^d(x,Q^2)$ are presented over the kinematic range $0.0041 leq x leq 0.9$ and $0.18 $ GeV$^2$ $leq Q^2 leq 20$ GeV$^2$. The data were collected at the HERMES experiment at DESY, in deep-inelastic scattering of 27.6 GeV longitudinally polarized positrons off longitudinally polarized hydrogen and deuterium gas targets internal to the HERA storage ring. The neutron spin structure function $g_1^n$ is extracted by combining proton and deuteron data. The integrals of $g_1^{p,d}$ at $Q^2=5$ GeV$^2$ are evaluated over the measured $x$ range. Neglecting any possible contribution to the $g_1^d$ integral from the region $x leq 0.021$, a value of $0.330 pm 0.011mathrm{(theo.)}pm0.025mathrm{(exp.)}pm 0.028$(evol.) is obtained for the flavor-singlet axial charge $a_0$ in a leading-twist NNLO analysis.
We report on measurements of the neutron spin asymmetries $A_{1,2}^n$ and polarized structure functions $g_{1,2}^n$ at three kinematics in the deep inelastic region, with $x=0.33$, 0.47 and 0.60 and $Q^2=2.7$, 3.5 and 4.8 (GeV/c)$^2$, respectively. These measurements were performed using a 5.7 GeV longitudinally-polarized electron beam and a polarized $^3$He target. The results for $A_1^n$ and $g_1^n$ at $x=0.33$ are consistent with previous world data and, at the two higher $x$ points, have improved the precision of the world data by about an order of magnitude. The new $A_1^n$ data show a zero crossing around $x=0.47$ and the value at $x=0.60$ is significantly positive. These results agree with a next-to-leading order QCD analysis of previous world data. The trend of data at high $x$ agrees with constituent quark model predictions but disagrees with that from leading-order perturbative QCD (pQCD) assuming hadron helicity conservation. Results for $A_2^n$ and $g_2^n$ have a precision comparable to the best world data in this kinematic region. Combined with previous world data, the moment $d_2^n$ was evaluated and the new result has improved the precision of this quantity by about a factor of two. When combined with the world proton data, polarized quark distribution functions were extracted from the new $g_1^n/F_1^n$ values based on the quark parton model. While results for $Delta u/u$ agree well with predictions from various models, results for $Delta d/d$ disagree with the leading-order pQCD prediction when hadron helicity conservation is imposed.
We establish the relationship between distribution and fragmentation functions and the structure functions appearing in the cross section of polarized 1-particle inclusive deep-inelastic scattering. We present spectator model evaluations of these structure functions focusing on the case of an outgoing spin-1/2 baryon. Distribution functions obtained in the spectator model are known to fairly agree at low energy scales with global parameterizations extracted, for instance, from totally inclusive DIS data. Therefore, we expect it to give good hints on the functional dependence of the structure functions on the scaling variables x(Bjorken), z and on the transverse momentum of the observed outgoing hadron, P_{hperp}. Presently, this dependence is not very well known, but experiments are planned in the near future.
New measurements of the reduced cross section $sigma_r^{D(3)}$ for the diffractive process $ep to eXY$ in the kinematic domain $12 leq Q^2 leq 90$ GeV$^2$, $0.01 leq beta leq 0.65$ and $xpom<0.1$ are presented. Data events recorded by the H1 detector during the years 1999--2000 and 2004 have been used, corresponding to a total integrated luminosity of 68 pb$^{-1}$. The measurements are derived in the same range as previous H1 data, namely $M_Y < 1.6$ GeV and $|t| < 1.0$ GeV$^2$. Two different analysis methods, rapidity gap and $M_X$, are used and similar results are obtained in the kinematic domain of overlap. Finally, together with previous data, the diffractive structure function measurements are analysed with a model based on the dipole formulation of diffractive scattering. It is found to give a very good description of the data over the whole kinematic range.
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