Measurement of the Spin Structure of the Deuteron in the DIS Region

Abstract

We present a new measurement of the longitudinal spin asymmetry A_1^d and the spin-dependent structure function g_1^d of the deuteron in the range 1 GeV^2 < Q^2 < 100 GeV^2 and 0.004< x <0.7. The data were obtained by the COMPASS experiment at CERN using a 160 GeV polarised muon beam and a large polarised 6-LiD target. The results are in agreement with those from previous experiments and improve considerably the statistical accuracy in the region 0.004 < x < 0.03.

Figures (6)

• Figure 1: Layout of the COMPASS spectrometer used in 2003. The configuration was identical in 2002 except for Electromagnetic Calorimeter 2 which was not included in the read-out. The thin vertical lines represent the tracking detectors.
• Figure 2: Fraction of inclusive, semi-inclusive, and calorimetric triggers in the final data sample (2002 and 2003) as a function of $x$ (left) and $Q^2$ (right). Events are counted with the weight they carry in the asymmetry calculation [Eq. (7)].
• Figure 3: The dilution factor $f$ of the $^6$LiD polarised target as a function of $x$ for inclusive and hadronic events. The dilution due to radiative effects on the deuteron is included. The values quoted for each $x$ bin are averaged over the kinematic range of the corresponding triggers.
• Figure 4: The asymmetry $A_1^d(x)$ as measured in COMPASS and previous results from SMC smc, HERMES semiinc4, SLAC E143 e143 and E155 e155 at $Q^2>1~\hbox{GeV}^2$. The SLAC values of $g_1/F_1$ have been converted to $A_1$ and the E155 data corresponding to the same $x$ have been averaged over $Q^2$. Only statistical errors are shown with the data points. The shaded areas show the size of the COMPASS systematic errors.
• Figure 5: Values of $A_1^d$ as a function of $Q^2$ in intervals of $x$. The solid lines are the results of fits to a constant; the dashed lines show the $Q^2$ dependence predicted by perturbative QCD.