In this coming week RHIC will work to achieve high intensity beams wioth 56 bunches, but no rebunching, in order to re-establish routine (?) operations for the machine and get data running for the experiments. The re-bunching will be commisioning later (following week).
Our near term goals will be to accomplish the first goal outlined a few weeks ago i.e. several million trig s. a/b triggers for 90 a/b and 6 deg setting. The plan is to discuss a longer term run-plan at this coming Thursday BNL meeting.
As you may have gleamed from the shift reports as well as the RHIC reports the DX magnets in the Brahms IR is now run at ~90 % max field, with compensating using D0. This results in a non-zero degree crossing angle of 1.8 mrad (2*0.9). We have looked today what this implies for the experiment. The neutron will impinge on the ZDCs offset by ~ 1.7 cm; the energy resolution (as thus the shower containment) is good enough to maintain energy resolution. There was a concern about the effeciency due to
Fermi smearing of the neutron distributions (angular and energy) , but at the 1.7 cm shoift is is likely ok.
The finite crossing angle also implies a change in pt-acceptance of the spectrometer. This effect is not complertly negliable, but finite. The cm system will move with a beta of about .9*10-3 and an pt change of approximately p*beta (you can work out the detailed formulae your self) i.e 10MeV/c for 10GeV/c acceptance up to 20 MeV/c as the maximum correction (towards higher pt for the FS). Hopefully as the RHIC op progresses the DX will behave better and the correction become smaller.
A benifit from this is that the effective vertex distribuiton will be truncated, as e.g. seen from the lowered int. rate seen by our exp compared to others (the far end of the vertex will not overlap).
regards
Flemming
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Flemming Videbaek
Physics Department
Brookhaven National Laboratory
tlf: 631-344-4106
fax 631-344-1334
e-mail: videbaek@bnl.gov
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