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Hadrons: color singlets “white states”
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antisymmetric in color
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Quantum Field Theory: Finestructure constant becomes function of energy or scale due to quantum fluctuations of electron-positron pairs => partial screening of bare charge of the electron at distances less than the compton wavelength of the electron
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OPAL ALEPH L3 DELPHI 35
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as as
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3 Quarks: u,d,s
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Effective potential between quark and antiquark:
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Large distance: linear term
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bound states: simplest color singlets bound states: simplest color singlets
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Nuclear Forces indirect consequences …….of color force……. nuclear force : gluonic force nuclear force : gluonic force ~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~ Van-der-Waals force : electromagnetic force Van-der-Waals force : electromagnetic force
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nucleon mass in limit of vanishing quark masses: const. calculable, error about 10 %. Exp: 938.272 MeV Exp: 938.272 MeV
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:about 250 MeV Mass: confined field energy
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Nuleon mass: QCD mass and mass contributions from the quark masses QCD u d s QED QCD u d s QED
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m(quark)=0 axialvector currents also conserved
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chiral symmetry: very light pions, but no SU(2) singlet with small mass
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deep inelastic scattering electron proton variables Q 2 = 4 E E ’ sin 2 /2 x = Q 2 /2M p (E ’ – E) Q 2 measures resolution modern experiments measure Q 2 < 10 5 GeV 2 > 10 -18 m = r p /1000 x measures inelasticity x = 1 → elastic 0 < x < 1 → inelastic E E’ photon
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probability that a quark carries fraction of parent proton ’ s momentum is q( ) ( 0< < 1 ), then
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‘ Fermilab
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e +, e (28 GeV) p (920 GeV)
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electron proton quark a deep inelastic scattering event at HERA
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where the logarithm comes from (‘collinear singularity’) and then convolute with a ‘bare’ quark distribution in the proton: pxp q 0 (x) + … + + 2 + 2
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scaling violations and QCD quarks emit gluons! Q1Q1 Q 2 > Q 1 The structure function data exhibit systematic violations of Bjorken scaling:
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bound states of QCD
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114 dibaryons thus far not observed
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120 experiment: quark – gluon states and gluonia not observed.
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Quark-Gluon-PlasmaQuark-Gluon-PlasmaQuark-Gluon-PlasmaQuark-Gluon-Plasma atomsnucleusplasma
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quark – gluon plasma: inside neutron stars ?
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