PEP-N: A 0.8 GeV X 3.1 GeV Collider at SLAC

The PEP-N project is a proposed new e+ecollider at SLAC to operate in the center of mass energy range of 1.0 GeV to 3.1 GeV. PEP-N consists of a new Very Low Energy electron Ring VLER (<800 MeV) to collide with the PEP-II e+ Low Energy Ring LER (3.1 GeV) parasitically to PEP-II operation for BaBar. Since the e+ ring has a fixed energy, the very low energy ring needs an energy range of 100 MeV to 800 MeV. This collider would likely be placed in Experimental Hall 12 of the PEP-II complex and have its own dedicated 800 MeV einjector. The peak luminosity should reach 2 x 10/cm/s. 1 PEP-N COLLIDER We discuss the parameters for an “e e --> N Nbar or multi-hadrons” collider based at PEP-II [1,2]. The plan is to collide the 3.1 GeV LER e+ beam against a 0.1 to 0.8 GeV electron beam stored in a new very low energy ring (VLER). The PEP-II LER is assumed to be operated for full BaBar operation with design parameters. The small electron storage ring has a circumference of 45.36 m and is located in straight section IR12 of PEP-II. The electrons are injected from a 40 m-long linac also located in IR12 of PEP-II. The luminosity of this collider, called PEP-N, is estimated to be above 10 /cm/s at a VLER energy of 500 MeV without affecting BaBar data collection. The location of PEP-N is shown in Figure 1. The collider straight section IR12 in PEP-II is relatively large, has good floor space both inside and outside the radiation enclosure, and has a large counting house. Both PEP-II rings are relatively simple in this straight section. The hall is 20 m along the beam line and about 12 m wide inside the radiation wall. A new 800 MeV linac would inject bunches of 3.6x10 9 electrons into every second ring RF bucket spaced 4.2 ns apart, as in PEP-II. The linac would be mounted on the accelerator floor of IR12 wrapped on itself to form four 12 m “girders”. Injection could be at 120 Hz if needed but 1 Hz is planned. At 1 Hz, the injection time is 36 seconds. The VLER circumference is about 45.3 m. The collision point is located in the center of the IR12 straight, but could be displaced a meter if the detector needs additional longitudinal space. A large bore dipole at the IP is used to separate the beams in the two rings and for detector momentum analysis. The vacuum system is relatively simple as the synchrotron radiation power is low. * Work support by US DOE Contract DE-AC03-76SF00515. The RF system is a single cavity (which exists as the prototype cavity for PEP-II). The VLER has two straights: one for the IP and one injection-RF-feedback straight. The LER ring would have to be slightly modified for this collider. The present LER quadrupole at the location of the collision point would be moved and reinstalled about 6.3 m upstream. A new symmetrical quadrupole would be added 6.3 m downstream. The IP beta functions in the LER are about a meter rather than about centimeters in traditional colliders. Thus, the chromaticity in the LER will not change very much and the present LER sextupoles are sufficient. The beam-beam tune shifts for the LER from PEP-N will be very low, about 0.004, which should not affect PEP-II operations. PEP-N will operate in a “parasitic mode” for about 9 months per year. If the average peak luminosity over different energies is about 3 x 10/cm/s over the year and the ratio of average to peak luminosity over long times including down times is about 0.5, then an integrated luminosity of about 35 pb is expected each year. The intent is to install the PEP-N accelerator and the detector in summer down times which are about two to three months per year. Approximately, two to three down times are needed.