quark structure of the pentaquark(?) jo dudek, jefferson lab
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Quark structure of Quark structure of the Pentaquark(?)the Pentaquark(?)
Jo Dudek, Jefferson LabJo Dudek, Jefferson Lab
Jo Dudek, Jefferson LabJo Dudek, Jefferson Lab 22
““Pentaquark” ? Pentaquark” ? baryon seen in
must have strangeness = +1
isospin = 0,1 - unless decay is I-violating
minimal quark structure then is
naïve application of constituent quark model
??
“fall-apart decay mechanism”
“fall-apart decay mechanism”
Jo Dudek, Jefferson LabJo Dudek, Jefferson Lab 33
in expt ?in expt ?experimental candidate is doubly mysterious
why so light?
why so narrow?
in addition we don’t know the
low spins usually lightest
S -wave decay is unlikely
small width makes production mechanism mysterious
if is small then why produced by kaon exchange?
would require an internal P -wave in quark picture
Jo Dudek, Jefferson LabJo Dudek, Jefferson Lab 44
multitude of states is problem common to all multiquark models
Jo Dudek, Jefferson LabJo Dudek, Jefferson Lab 55
Jo Dudek, Jefferson LabJo Dudek, Jefferson Lab 66
achieved prominance through prediction of Diakonov, Polyakov & Petrov in Chiral Soliton Model
degrees of freedom are pion & kaon fields
baryons are solitons in the pion & kaon fields
predicts a with
why so light?
chiral properties of the model make it reasonable though, since rather than adding constituent quarks to the nucleon mass, we add a pseudo-Goldstone
not obvious – scale set by assuming is in the ,
splitting depends upon (unsettled) nucleon sigma term value
why so narrow?relies upon a cancellation between two couplings in the model. accidental? – no obvious physical origin
Jo Dudek, Jefferson LabJo Dudek, Jefferson Lab 77
flavour sym
colour antisymspin sym
diquarks are identical bosonsspace
Jaffe & WilczekJaffe & WilczekJaffe & WilczekJaffe & Wilczekdegree-of-freedom
SCALAR DIQUARK
Jo Dudek, Jefferson LabJo Dudek, Jefferson Lab 88
no axials/tensors
ad-hoc?ad-hoc?ad-hoc?ad-hoc?scalar diquarks solve(?) another hadronic puzzle - LIGHT SCALAR
MESONS
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Light Scalar Mesons a la Light Scalar Mesons a la JaffeJaffe
Light Scalar Mesons a la Light Scalar Mesons a la JaffeJaffe
diquarks are light
Jo Dudek, Jefferson LabJo Dudek, Jefferson Lab 1010
Width in “Fall-Apart” Width in “Fall-Apart” DynamicsDynamics
Width in “Fall-Apart” Width in “Fall-Apart” DynamicsDynamics 1 fm square well
nK P-wave @ 1540 MeV
1 fm square well nK P-wave @ 1540 MeV
CG(F) x CG(C) x CG(LS)
“fall-apart decay mechanism”
“fall-apart decay mechanism”
Jo Dudek, Jefferson LabJo Dudek, Jefferson Lab 1111
Light Scalar Mesons a la Light Scalar Mesons a la JaffeJaffe
Light Scalar Mesons a la Light Scalar Mesons a la JaffeJaffe
a multitude of multiquarks
the width problem
Jo Dudek, Jefferson LabJo Dudek, Jefferson Lab 1212
Lattice QCDLattice QCDLattice QCDLattice QCDlattice field theory on a computer has been used to look at a theory similar to QCD with light quarks
- “quenched” lattice QCD with “fairly light quarks”
no quark loops
pion masses down to 500 MeV
at these heavier quark masses, our familiar lightest hadron resonances become bound states
Jo Dudek, Jefferson LabJo Dudek, Jefferson Lab 1313
Lattice QCDLattice QCDLattice QCDLattice QCDwhat is the lattice method extracting?
hopefully – the lightest asymptotic state with the quantum numbers of a chosen “interpolating operator”
not seennot seen
Jo Dudek, Jefferson LabJo Dudek, Jefferson Lab 1414
Lattice QCD for the Lattice QCD for the Lattice QCD for the Lattice QCD for the Lasscock et al
Jo Dudek, Jefferson LabJo Dudek, Jefferson Lab 1515
Lattice QCD for the Lattice QCD for the Lattice QCD for the Lattice QCD for the Lasscock et al
no bound state observed
Jo Dudek, Jefferson LabJo Dudek, Jefferson Lab 1616
SummarySummarySummarySummaryexistence of the light and narrow pentaquark presents a challenge to many theoretical ideas
existence is an issue to be decided by experiment, not theories or models