The MVD is the only device in Phenix with a rapidity coverage large enough
to deliver a measurement of the event multiplicity. There are three
important aspects to the multiplicity:
Total multiplicity:
this is an accurate measure of event centrality.
Therefore the MVD plays an important role in the selection of events
most likely to contain the new physics we're after. An estimate of
total multiplicity is available at the LVL-1 trigger.
dn/deta:
this addresses questions of stopping, directional flow and the like.
Fluctuations:
this is where we can look for signatures of DCC.
Measure the vertex position
The MVD can measure the vertex position in x, y and z to a few hundred
microns.
An accurate vertex will help in event
selection (e.g. away from the poles).
An accurate vertex will improve the momentum
resolution of the central tracking system.
The MVD can track the mean beam position
.
Do all this with no mass
The MVD sits in front of the electron arms. Ideally of course the device
has no mass. Everything possible has been done to reduce the mass seen by
electrons streaming towards the electron arms:
The support structure and enclosures
of the central part of the MVD are fabricated out of lightweight
foam and thin foils.
The relatively heavier components (FEE, power and communication
cables) are moved to the bottom, out of
the direct electron arm acceptance.
Cooling in the central section is done with
air rather than water.
The outer silicon panels facing the electron arm acceptance are
removed.
(supporting slide)
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