Studies of the NSY Model

These are a set of studies of the NSY predictions for the azimuthal asymmetries in DIS.

Model predictions at the parton level

Fig. 1 shows the model prediction at the parton level compared with data. The agreement is poor.

Lepto predictions

Fig. 2 shows the LEPTO predictions at the hadron and parton levels. LEPTO has been run ( for both parton and hadron levels) with LST(8) =1 . The objective was to produce a final state without initial and final state radiation similar to that of the NSY model. The LEPTO hadronic final state produces mean values that are broadly consistent with the data. The LEPTO parton level predictions are inconsistent with the predictions of the NSY model; Thus correction factors from LEPTO ( correction from parton to hadron) cannot be expected to produce hadronisation corrected NSY predictions that agree with the data.

Fig. 2a These plots, similar to Fig 2, are made to show the influence of the Pt and theta cuts on the LEPTO hadronic final state. In these plots the cuts are removed. As expected, the hadronic level of LEPTO no longer agrees with the data. The plot does show, however, the naively expected reduction in asymmetry from parton to hadron level consequent upon hadronisation.

Correction of NSY model from parton to hadron level

As stated above, in view of the discrepancy between the NSY and LEPTO parton levels, this correction is not expected to be meaningful. However it has been attempted, as described below.

LEPTO has been used ( see paragraph for Fig 2 ) to produce 100 bin plots of cos(phi), cos(2phi) for the parton and hadron levels, Fig. 3. The plots 1,2 (3,4) show cos(phi), cos(2phi) for the hadron (parton) levels of LEPTO. The division of these plots give correction factors from parton to hadron, see plots 5,6 ( the factor 0.5 results from 5*10**6 generated events for the hadron level vs 10**7 events for parton level). The NSY code calculates mean cos(phi), mean cos(2phi) rather than distributions. Consequently these values have been used to calculate the distributions at a given eta. The calculated distributions, parton level, are shown in plots 7,8. These distributions are then corrected to the hadron level (plots 9,10) by multiplication by the correction factors (plots 5,6). From plots 9, 10, the mean values of cos(phi), cos(2phi), corresponding to NSY corrected to the hadron level, can be read off.

Fig. 4 shows ( green curve) the NSY predictions corrected to hadron level. As expected, the agreement between model and data is poor.

Correction of NSY model from parton to hadron level - standard LEPTO

The above analysis has been repeated with LEPTO run with default LST(8).

Fig. 5 shows the LEPTO predictions at the hadron and parton levels ( equivalent to Fig 2 above).

Fig. 6 shows the correction plots (equivalent to Fig 3).

Fig. 7 shows ( green curve) the NSY predictions corrected to hadron level. As for Fig 4, the agreement between model and data is poor.

Fig. 8 Revised Fig. 7 as requested by Matthew.






















































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IOS 2/6/2006