Summary of the PEP-N meetings held at SLAC on January 29-30, 2001 Attendees: R.Baldini, D.Bettoni, M.Biagini, M.Mandelkern, C.Munger, P.Patteri, J.Seeman, S.Serednyakov, M.Sullivan + member of the workshop LOC 1. Magnet Diego shows calculations of the magnetic field, carried out in Ferrara using the program TOSCA. The magnet is a dipole, with the following geometry: distance between poles: 1.0 m pole diameter : 1.2 m distance between yokes: 2.0 m magnetic field : 3.0 Kgauss The resulting magnetic field is homogeneous only over a central region 0.8 m in diameter; furthermore it has a sizeable component in the horizontal plane. The field produced by TOSCA can be input to the program by M.Posocco which studies the behaviour of a TPC with such a field. Modelling of the magnet can be done fairly easily with TOSCA, and a new configuration can be implemented in a short time. This will allow to find the optimal field. Some interaction with the accelerator group is necessary. 2. Tracking detector studies Using the magnetic field maps produced by TOSCA Mario has produced plot which show the displacement of the drift electrons from the electric field lines of force due to the B field nonuniformity and to the non parallelism between E and B. Displacements as large as 5 cm are calculated even for the smallest values of omega*tau (0.5) which would make the operation of a TPC problematic. However the NA49 experiment at CERN operated a TPC under similar conditions (i.e. with similar displacements). Since they report good values for the spatial resolution (around 250 microns) these effects can probably be corrected for. Further investigation will be carried out in this field. NA49 used a Ne/CO2 mixture for their TPC, which could be for us a viable alternative to a He based mixture. 3. Monte Carlo simulation The development of the Monte Carlo simulation of the detector has been going on in Padova (M.Posocco) and Ferrara (M. Negrini). The program now works well with 4 pi, 6 pi and 2pi2K events. The acceptance for 4pi events is above 90 percent, well within expectations. Further work will be done to refine the detector geometry and to include further generators for multihadronic events provided by our friends in Novosibirsk. The tools described in points 1-3 now make up a working package which will allow to study the main aspects of the tracking system. 4. Interaction region and energy range of the machine The highest attainable c.m. energy is Ecm = 3.52 GeV, which is just above the tau+tau- threshold. This corresponds to a VLER energy of 1 GeV. Since it has been suggested (by M. Perl) that it might be interesting to reach such an energy John, Mike and Marica are working on a configuration of the interaction region that would enable us to go to 3.52 GeV. The dipole magnet would be 1.2 m in diameter, its center 0.4 m downstream of the interaction point Two additional small magnets are foreseen in this scenario: - a permanent magnet located on the horizontal plane, on the edge of the main dipole and 0.4 m from the beam pipe (quadrupole); - a 2 KG dipole magnet immediately behind the main dipole magnet. The values of the required magnetic field are calculated for three energy intervals which cover the overall energy range. They are given in the following table: VLER Energy range B field 1 GeV - 500 MeV 4 KG - 2 KG 500 - 250 MeV 3 KG - 1.5 KG 250 - 125 MeV 2 KG - 1 KG There was some discussion about the energy range of the machine: - maximum energy: while it is certainly worthwhile to go up to the J/Psi, in order to fully exploit the physics potentials of the region up to 3.52 GeV (and be competitive with dedicated facilities) would require a completely different experiment from the one we are designing. - minimum energy: a VLER energy of 125 MeV corresponds to Ecm = 1245 MeV, which would give us a good overlap with existing measurements by VEPP-2M. To go down to the phi mass would bring us down to the energy range of Daphne. In conclusion: the minimal energy range required by the experiment is 1.5 to 2.5 GeV, and extensions to reach the J/Psi on one end and the Phi on the other would certainly be welcome and would add considerably to the physics potential of the experiment. 5. Workshop organization The program of the workshop is now almost completely defined. The first day will be dedicated to R, the second day to form factors and all other physics topics, the third day to a few contributed papers and to the details of the PEP-N detector. There will be PEP-N talks also at the end of the first day (detector design for the measurement of R) and of the second day (detector design for the nucleon form factor measurement). In addition to that the PEP-N project will be presented by John Seeman in the first day after the introductory talk.