More luminosity
During the present accelerator shutdown, the main activity will be the installation of the aforementioned superconducting quadrupole magnets close to the interaction point. While the previous permanent-magnet quadrupoles had helped greatly in improving the CESR luminosity by squeezing the colliding beams, their fixed magnetic field limited the accelerator's collision energy range.
The new superconducting quadrupoles will provide stronger focusing of the beams, with a possible corresponding 2.5 times increase in luminosity. They will also permit much more flexibility in the accelerator operation, with running now being possible down to a collision energy of 3 GeV.
After the shutdown, the CLEO experiment will begin a programme of running on the three resonances Y(1S), Y(2S) and Y(3S). They anticipate accumulating an integrated luminosity of more than 4 fb-1 during this run - an order of magnitude more than the present world's total for these resonances.
With this data available, the collaboration will be able to carry out a large number of measurements, including much-improved determinations of the leptonic and hadronic widths of several of the resonances, new searches for and possible discoveries of more b quark-antiquark bound states and a family of D (charmed) states, and precise studies of the various pion-pion transitions between the three Y resonances.
New objectives
For the longer term, the CESR and CLEO physicists are considering converting the accelerator into a lower-energy machine, running in the 3-5 GeV collision energy range. This is the region of the J/Y and Y charm quark-antiquark bound-state resonances, as well as several /Y' resonances above the threshold for the production of D particle pairs and the threshold for the production of the tau lepton.
The physics potential for a high-luminosity electron-positron collider in this energy range is large and includes 1 to 2% measurements of vital quark transitions (cs and cd), precise determinations of crucial charm meson decay constants and branching ratios, much more sensitive searches for neutral D mixing and non-Standard Model charm and tau lepton decays, and greatly increased statistics with much improved systematic errors on the production of glueballs and quark-gluon hybrid states.
These measurements would provide powerful new contraints on predictions from lattice quantum chromodynamics (QCD). To inform the community of this programme, the CLEO group sponsored a three-day workshop at Cornell in May. More than 120 physicists attended, over a third of whom were not CLEO members.
The plan for the high-luminosity operation of CESR in this lower collision energy range envisages a set of superconducting wiggler magnets to be inserted into the accelerator to decrease the damping time of the beams and increase their horizontal emittance.
The preliminary design calls for 14 superferric wigglers with a total length of 18 m and a peak magnetic field of 2.1 T. Two recently wound, prototype superconducting wiggler coils reached their short-sample current limit, and the first full-length prototype wiggler is scheduled for completion in December. Simulations predict that, with the insertion of the wigglers, the peak luminosity of the lower-energy accelerator, designated CESR-c, should range from about 1 to 5 ¥ 1032cm-2s-1 as the collision energy changes from 3 to 5 GeV.
The CESR-c design and the potential CLEO physics programme, correspondingly referred to as CLEO-c, were presented at two recent US HEPAP subpanel meetings and at the 2001 Snowmass Summer Study. A "yellow book" containing both the CESR-c and the CLEO-c project descriptions (CLNS 01/1742) is available via http://www.lns.cornell.edu/public/CLEO/spoke/CLEOc/ProjDesc.html.
If the CESR-c project is approved by early 2002, the first low-energy collisions could occur by December 2002.