Hard Scattering at RHIC

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Hard Scattering at RHIC
John Lajoie Iowa State University lajoie_at_iastate.e
du
A disjointed, random collection of general
musings...
1. How did I get interested in this? 2. Hard
Scattering at RHIC 4. Jet Quenching 5. Jet Flavor
Tagging 6. A program of study for RHIC? 7. Where
do I go from here?
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semi-leptonic D decays
NA44
single particle distributions
NA50
heavy flavor decay
strangeness production
Nch, dNch/dh, fluctuations
spin program W,W-
WA80
E859
jet quenching
ET, dET/dh, fluctuations
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QGP Signatures
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Hard Scattering and Jets
Low momentum particles arise from soft (large
distance scale) interactions. High transverse
momentum particles arise from parton (qq, qg and
gg) scattering.
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PQCD at RHIC
Relativistic Heavy Ion collisions have been
extremely difficult to study due to the lack of a
well-established, generally accepted theoretical
framework for calculating experimental
observables. However Theoretical estimates
predict that approximately half of the energy
transfer from the projectile frame to midrapidity
may be calculable using Perturbative Quantum
Chromodynamics (PQCD).
Input to Theoretical Models
Low Energy (AGS, SPS) flux and energy of nucleons
High Energy (RHIC) flux and energy of
quarks/gluons
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Structure Functions
Quark distributions determined in DIS
experiments. Gluon distributions poorly
determined experimentally - note the soft gluon
distribution.
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Shadowing
Parton distributions modified when nucleons bound
in a nucleus - depletion at low x. Similar for
gluons? Complicates things for RHIC...
XN Wang an M. Guylassy, Phys. Rev. D 44 (1991)
3501
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Leading Particles in Jets
Leading particles arise from the originally
scattered partons and have a large fraction of
the jets transverse momentum. Consider trying
to sum the jet energy at RHIC
(Jet cone)
Typical pedestal energy
Need to use high-pT leading particles at RHIC.
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Jets and the QGP
How does a QGP affect the evolution of jets?
Energy loss and rescattering in the QGP
dE/dl increased (or reduced) in the plasma?
pT20GeV/c reduced by a factor of 10
Guylassy and Plümer, Phys Lett B243 (1990) 432
Dramatic effects at the phase transition?
Energy imbalance in back-to-back jets? Jet
acoplanarity? (Difficult?) Rammerstorfer and
Heinz, Phys Rev D41 (1990) 306
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Jet Scattering in pA
FNAL E609 pPb at 400GeV/c
E609 Collaboration, Phys. Lett. B259 (1991) 209
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HIJING
Includes hard scattering and minijet
production. Also includes a model for parton
energy loss.
XN Wang an M. Guylassy, Phys. Rev. Lett. 68
(1992) 1480
Jets, shadowing and quenching will all be
important at RHIC!
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Jet Flavor Tagging
q
Select quark-quark and quark-gluon jets
(average gluon at smaller xB). High-pT
particles reflect scattered partons (string
fragmentation).
q
g
q
In addition, the leading particle indicates the
flavor of the scattered parton

• Leading p selects mainly u-quark jets
• Leading p- selects mainly d-quark jets
• Leading K- selects mainly gluon jets

Use this to extract structure functions for AA?
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Selecting Jets by Leading Particles
G. Bordes and A. Nicolaidis, Phys. Rev. D22
(1980) 2152 and Phys. Lett B114 (1982) 175
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A program of study for RHIC?
Observables inclusive high-pT, dijets, g-jet
coincidence
Too naive!
Requires systematic study - real results will
take time!
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Where do I go from here?
Lots more literature to read - study up on
predictions as well as results from the ISR and
Fermilab. Start to think about the first year -
how far out in pT might we expect to look with a
limited data sample. How do we trigger
effectively on qq, qg and gg jets? What can we
learn from looking at AuAu data alone (without
the benefit of g(x))? HIJING/PISA simulations
of jet triggered events.