Machine Design Goal
The nuclear physics programs outlined in the previous chapter provide a set of high-level requirements for MEIC at Jefferson Lab as follows: 1. Energy The center-of-mass (CM) energy of this collider should be between 15 and 65 GeV. (The value of s=(4EeEu)1⁄2 is from a few hundred to a few thousand GeV2, where Ee and Eu are kinetic energies of electron and nucleon) Thus energies of the colliding beams should range - from 3 to 11 GeV for electrons, - from 20 to 100 GeV for protons, and - up to 40 GeV per nucleon for ions. Protons or ions with energies below 20 GeV per nucleon are also interesting to investigate certain potentially important physics processes. 2. Ion species Ion species of interest include polarized protons, deuterons, and helium-3. Other polarized light ions are also desirable. Heavy ions up to lead do not have to be polarized. All ions are fully stripped at collision. 3. Multiple detectors The facility should be able to accommodate up to three detectors with at least two of them available for collisions of electrons with medium energy ions. A third detector is desirable for collisions of electrons with ions whose energies are lower than 20 GeV/u. 4. Luminosity 33 34 -2 -1 The luminosity should be in the range of mid 10 to above 10 cm s per interaction point over a broad energy range. Further, optimization of luminosity should be centered around 45 to 50 GeV CM energy (the value of s is around 2000 to 2500 GeV2). 22 5. Polarization Longitudinal polarization for both electron and light-ion beams at the collision points should be achieved with greater than 70% polarization. Transverse polarization of the ions at the collision points and spin-flip of both beams are extremely desirable. High- precision (1–2%) ion polarimetry is required. 6. Positrons Polarized positron beams colliding with ions are desirable, with a high luminosity similar to that of the electron-ion collisions. In addition, an MEIC accelerator design should be flexible to allow an option of a future energy upgrade for reaching electron energy up to 20 GeV, proton energy up to 250 GeV, and ion energy up to 100 GeV per nucleon.