Strong Interactions and QCD

Strong Interactions and QCD Sourendu Gupta DTP: TIFR DIM 2009 TIFR, Mumbai November 4, 2009 SG (DTP: TIFR) Strong Interactions DIM 09 1 / 14

The experimental context of strong interactions 1 Thomson and Rutherford: splitting the atom and the discovery of the atomic nucleus (1895 1909) 2 Cosmic rays and particle accelerators: discovery of hadron families and the quark-model classification (c1950 1964) 3 Deep-inelastic scattering (SLAC): discovery of quarks and QCD (c1960 1969) 4 CERN, SLAC, DESY: testing and refining the QCD Lagrangian, probing the limits of perturbation theory (c1970 c1995) SG (DTP: TIFR) Strong Interactions DIM 09 2 / 14

The experimental context of strong interactions 1 Thomson and Rutherford: splitting the atom and the discovery of the atomic nucleus (1895 1909) 2 Cosmic rays and particle accelerators: discovery of hadron families and the quark-model classification (c1950 1964) 3 Deep-inelastic scattering (SLAC): discovery of quarks and QCD (c1960 1969) 4 CERN, SLAC, DESY: testing and refining the QCD Lagrangian, probing the limits of perturbation theory (c1970 c1995) 5 Heavy-ion collisions (RHIC, LHC, FAIR, NICA): probe T, µ 0 (2000??) 6 Supernovae and neutron stars: probe T 0, µ 0 (c1925??) 7 Hadron machines (JLAB, KEK, BES, SLAC): glueballs, non quark-model physics, string tension (c1990??) 8 Very low-energy light nuclei: nuclear physics from QCD, fine-tuning in stellar thermonuclear reactions. (c1930??) 9 B-factories, LHC, erhic: semi-perturbative QCD (c2000??) SG (DTP: TIFR) Strong Interactions DIM 09 2 / 14

QCD today Nuclear physics few body problem exotic nuclei hadron superfluids nuclear forces nuclear matter thermonuclear reactions plasmas freezeout neutrino diffusion supernovae neutron stars phase transitions Astrophysics Particle physics hadronic molecules, exotic hadrons, glueballs QCD hydrodynamics transport theory nanomaterials colour superconductivity Condensed matter strong coupling Higgs multi jet phenomena large rapidity gaps hadronization flavour physics simulations and algorithms large scale computing network and switching data sharing grid Computer science SG (DTP: TIFR) Strong Interactions DIM 09 3 / 14

The QCD phase diagram T Quark gluon plasma Hadron gas Colour superconductor Nuclear gas Nuclear liquid µ SG (DTP: TIFR) Strong Interactions DIM 09 4 / 14

Phase diagram of QCD matter Fermion sign-problem, evaded by Taylor expansion around µ = 0. Need to control: N f (now 2), m π (now 230 MeV), V (finite size scaling), a (now 0.19 fm), order of expansion (now 8). (Gavai and SG) SG (DTP: TIFR) Strong Interactions DIM 09 5 / 14

Heavy-ion collisions SG (DTP: TIFR) Strong Interactions DIM 09 6 / 14

Screening masses: is the fireball large? 8 7 6 5 ρ π ρ π g g g g g m(t)/t 4 3 2 1 g g SU(3), T=2Tc a=1/(8tc) a=1/(16tc) 0 A 1 ++ A 2 -+ A 1 -+ A 2 -- B 1 ++ B 1 -+ B 2 ++ Mesons heavier than glueballs: reversal of T = 0 physics; dimensional reduction works (roughly). Near T c? Below T c? (Banerjee, Dutta, Gavai, SG, Lacaze, Maiti, Mathur) SG (DTP: TIFR) Strong Interactions DIM 09 7 / 14

Hydrodynamics and diffusion: is the fireball long lived? Diffusion: x t, outside the lightcone at small t. Use kinetic theory instead? Numerically complicated. KT implies improved diffusion eqn: f 2f + + D 2 f = 0. 2 t t Transport coefficients: D and τ. No change as t. Observable differences for t/τ O(1). Easy to spot in event to event fluctuations in heavy-ion collisions. Preliminary analysis by STAR collaboration positive. τ 6 ΤnHJ,ΗL 4 2 0 0.0 10 5 Η 0.5 1.0 J 1.5 ΤnHJ,ΗL5 0 10 0.0 5 0.5 1.0 J 2.0 0 1.5 Η 2.0 0 Similarly for Navier-Stokes. However, signals of causal corrections to NS harder to observe. (Bhalerao, SG) SG (DTP: TIFR) Strong Interactions DIM 09 8 / 14

Equations of state 1 0.8 SU(3) p/p SB 0.6 0.4 SU(4) SU(6) 0.2 0 0 0.2 0.4 0.6 0.8 1 ε/ε SB (Datta, Gavai, SG, Mukherjee) SG (DTP: TIFR) Strong Interactions DIM 09 9 / 14

New directions Nuclear physics few body problem exotic nuclei hadron superfluids nuclear forces nuclear matter thermonuclear reactions plasmas freezeout neutrino diffusion supernovae neutron stars phase transitions Astrophysics Particle physics hadronic molecules, exotic hadrons, glueballs QCD hydrodynamics transport theory nanomaterials colour superconductivity Condensed matter strong coupling Higgs multi jet phenomena large rapidity gaps hadronization flavour physics simulations and algorithms large scale computing network and switching data sharing grid Computer science SG (DTP: TIFR) Strong Interactions DIM 09 10 / 14

Electrical conductivity 75 10 σ /T 5 50 25 2 3 C EM T d p ω =p=0 3 8π ω d Ω 0 1 1.5 2 2.5 3 0 3.5 T/T c Finite volume effects? Is the analytic continuation stable? SG (DTP: TIFR) Strong Interactions DIM 09 11 / 14

The hadron spectrum SG (DTP: TIFR) Strong Interactions DIM 09 12 / 14

String tension 1000 Mesons: nonstrange 100 ρ c (m) 10 1 0.1 0 500 1000 1500 2000 m (MeV) Fits to string tension: σ 150 400 MeV, depending on pre-exponential factor to Hagedorn exponential! Which is the correct string model? SG (DTP: TIFR) Strong Interactions DIM 09 13 / 14

Nucleon-nucleon scattering lengths 4 m a( 3 S 1 ) π 2 0-2 -4-20 -15-10 -5 0 5 m a( 1 S 0) π Scattering lengths are not natural. Fine-tuned quark masses? SG (DTP: TIFR) Strong Interactions DIM 09 14 / 14