Working group report: Neutrino and astroparticle physics

This is the report of neutrino and astroparticle physics working group at WHEPP-7. Discussions and work on CP violation in long baseline neutrino experiments, ultra high energy neutrinos, supernova neutrinos and water Cerenkov detectors are discussed.     

The quark gluon plasma: Lattice computations put to experimental test

I describe how lattice computations are being used to extract experimentally relevant features of the quark gluon plasma. I deal specifically with relaxation times, photon emissivity, strangeness yields, event-by-event fluctuations of conserved quantities and hydrodynamic flow. Finally I give evidence that the plasma is rather liquid-like in some ways.     

Lattice QCD with chemical potential: Evading the fermion-sign problem

Since the turn of the millennium there has been tremendous progress in understanding QCD at finite chemical potential, μ. Apart from qualitative results obtained using models, and exact results at very large μ obtained in weak coupling theory, there has been tremendous progress in getting exact and quantitative results from lattice simulations. I summarize the status of lattice QCD at finite chemical potential —locating the critical end-point in the QCD phase diagram, predicting event-to-event fluctuation rates of conserved quantities, and finding the rate of strangeness production.     

Partial deconfinement of quarks in nuclei and the EMC effect

We investigate the possibility that in a heavy nucleus a few nucleons exist in a state of total deconfinement. The constituents of these deconfined nucleons are regarded as a mixture of quark-and gluon-gases in thermal equilibrium at a fixed temperatureT. This approach reproduces the observed softening of the valence quarks in heavy nuclei and predicts fewer gluons atx<1 and an exponential decrease of the structure functions atx>1.     

Spin dependent gluon densities from largeP T photon and dimuon production

We investigate spin asymmetries in highp _T photon and dimuon production and show that the spin dependent gluon density can be extracted reliably frompp collisions with these final states. The statement remains true even when the balancing jet is not observed. Hence fixed target experiments can be used to measure the spin dependent gluon density. We also compute the asymmetries in \(p\bar p\) collisions, and show that the EMC measurement of the spin structure function can be verified and the spin dependent gluon density can be extracted from these experiments.     

Spin dependent parton densities

We propose a set of polarised-beam polarisedtarget experiments to determine the complete set of spin dependent parton densities. The polarised valence quark densities are determined through semi-inclusive hadroproduction in polarised muon-proton collisions. This, together with present data then fixes the polarised sea quark densities. Polarised gluon densities are measurable through asymmetries in large,p _T direct photon production in polarisedp-p collisions. An independent measurement of polarised sea quark densities comes from direct double photon production in polarisedp-p collisions at rapidities close to zero. We illustrate these results with numerical estimates.     

Spatial and temporal hadron correlators below and above the chiral phase transition

Hadronic correlation functions at finite temperature in QCD, with four flavours of dynamical quarks, have been analyzed both above and below the chiral symmetry restoration temperature. We have used both point and extended sources for spatial as well as temporal correlators. The effect of periodic temporal boundary conditions for the valence quarks on the spatial meson correlators has also been investigated. All our results are consistent with the existence of individual quarks at high temperatures. A measurement of the residual interaction between the quarks is presented.     

Heavy-ion collisions

This is a short summary of the systematics observed in various heavy-ion experiments at CERN SPS energies.     

Finite size scaling on the phase diagram of QCD

In the last few years there has been remarkable progress in the comparison of experimental data on the shape of event-by-event distributions of conserved quantities and lattice thermodynamic predictions based on the grand canonical ensemble. In this talk we discuss how the QCD crossover temperature and the freezeout curve are extracted from the analysis of fluctuations. We report that one can also go further and locate the QCD critical point at ?? }~ 2T _c . We also list the systematics which must be brought under control in future.