Two Important Long Range Programs for RHIC

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Transcript Two Important Long Range Programs for RHIC

Two Important Long Range
Programs for RHIC
In addition to the many important RHIC
research programs that are currently
underway or projected. There are two
programs which are not so well known but
are of high significance and which are not
likely to be done at the LHC and, in any
case, need to be done at the RHIC
January 12, 2007
J. Sandweiss
A. Photon-Photon HBT
• Only direct photons and weakly interacting
leptons can be emitted from the quark gluon
phase of the collision prior to hadronization.
• A unique property of the HBT is that only direct
photons will display an HBT correlation (due to
the “long” life of the π0 meson).
• The - HBT can be studied as a function of pt,
yielding unique information on space time
evolution of the early, deconfined, phase.
January 12, 2007
J. Sandweiss
Feasibility of - HBT
• Our group has studied this, including many
increasingly sophisticated simulations, (for the
past 3 years).
• We have concluded that the measurement is
both feasible and very informative.
• It is necessary to use a thin (~.1 rl) converter
together with the calorimeter so each detector
observes one , and s that have vanishing
momentum difference can be reliably detected.
January 12, 2007
J. Sandweiss
Challenges of the - HBT
• The π0 photon flux, while not making an
HBT correlation, does lower the size of the
signal observed by a large factor (of order
• Very careful analysis, which we believe
can certainly be done is needed. And
• Large event samples are needed, event
numbers of 1-2 billion. With DAQ1000 this
is, however “just” a few weeks of running.
January 12, 2007
J. Sandweiss
• To carry out the - HBT measurement, long, dedicated
runs will be needed along with the commitment of the
serious analysis efforts.
• This is a long range program for RHIC, for example one
can anticipate different collision energies, etc.
• It provides information which cannot be obtained by
other means and is one of the strong arguments for a
strong continuing RHIC deployment.
• Some more detailed discussion of the experiment can be
found at <>, a
proposal to STAR (not yet acted upon).
January 12, 2007
J. Sandweiss
B. Violation of P,T by the Strong
• There is a good possibility that parity (P)
and time reversal symmetry (T) are
violated in collisions that produce a “QGP
• This violation is a spontaneous effect and
the P,T effects will be randomly different in
each event. This greatly complicates the
experimental study of the effect.
January 12, 2007
J. Sandweiss
• It is not possible here to explain the underlying
theory. However this effect deals with the most
fundamental aspects of the basic field theory of
QCD. Some references are:
• D. Kharzeev,R.D. Pisarski,& M.H.G.Tytgat Phys.
Rev. Lett. 81, 512 (1998)
• D. Kharzeev, Phys. Lett.B663, 260-264 (2006)
• Lattice calculations support the existence of the
effect (show a distribution of topological winding
January 12, 2007
J. Sandweiss
Experimental Aspects
• Since the effect (spontaneous symmetry
breaking) varies randomly in each event, any P
(T) odd observable will average to zero over
many events.
• Thus the effect must be seen in correlations.
We have made some estimates (with the help of
D. Karzeev) and the effects, e.g. in the
observable helicity correlations of Λ pairs (via
the parity violating decay of the Λ).
January 12, 2007
J. Sandweiss
What is needed?
• Large samples. The Λ-Λ correlation would take
several billion STAR events. Other correlations
will be similar.
• Further theoretical as well as experimental work
because these correlations do not by
themselves prove the effect. They could be
caused by “ordinary” strong interactions.
• The behaviour of the effects must be compared
with theoretical estimates of that predicted by
the P,T effect and by the “usual” strong
January 12, 2007
J. Sandweiss
• These two programs offer unique qand
fundamental information about the new
state of matter produced in high energy
heavy ion colissions.
• They are difficult, but clearly possible.
• It is my hope that the long range plan will
recognize the importance and
requirements of these studies.
January 12, 2007
J. Sandweiss