Dear collaborator I attach and include an update on the pp running discussing changes in setup, and run plans. ------------------------------------------------------ Flemming Videbaek Physics Department Brookhaven National Laboratory tlf: 631-344-4106 fax 631-344-1334 e-mail: videbaek@bnl.gov Update on pp running / Dec. 7 The machine commissioning is continuing with machine development so far mainly at injection energy, and some colliding beam also injection p=24 GeV/c. The major problem so far seem to be a lack of high polarization out of AGS ~30%. This could mean that the polarized measurements may in fact not be as feasible as it was forecast. On the other hand this is not a stumbling block for the pp comparison part of the run. The physics running of the pp program is still planned to run for 5 weeks from December 20 to January 24. During the run the pp2pp will have dedicated runs for possible 2 days with a low number of bunches. Actual machine and run plans are developed at the weekly coordinations meeting. Even though it is still not known how to deal with triggering, background (see more later) we have to take planning for this period seriously if we want to collect data, this means setting up a plausible program and having the manpower at RHIC for running the experiment. - Experimental setup Several modification additions have been made to the setup. a) A 3- slat trigger counter was put in front of D1. This counter in connection with H1 and the RC will hopefully give us a good spectrometer trigger i.e. select with high efficiency events with tracks through D1, D2 and not have too many false triggers. This is a must because the particle densities are down by about a factor 170, while the luminosities up by a factor hundred, but our DAQ rate probably only goes to maybe 150-200 /sec up from ~80-90/sec. b) The pp2pp experiment has installed a set of inelasticity detectors that will also help BRAHMS in identifying collisions. The detectors consist of 8 modules each with 4 quadrants and positioned around the beam pipe on each side of the IR. They were designed to have a high efficiency for inelastic pp events (double, and single diffractive events). More details on the geometry can be found on http://www.sdcc.bnl.gov/brahms/private/detectors/pp/index.html . Signals are split at the PMT level using transformers and fed to our FE-hut. At present each signal is connected to a discriminator, and logic setup to select pp collision events. We want to feed all signals to TDC. At present there are not enough delay cables for all 32 channels, so only a single tdc channel is instrumented from each module (total of 8). c) A large slat with two PMT has been build and put in front of the MRS. This will prevent the MRS to go much more forward than about 60 deg, unless the D5 platform is moved back as done in part of the Au running. Ideal though you would want TPM1 to be as close as possible to the IR for the pp running (increase solid angle). A set of large slat will also be installed behind the TOFW ( so a trigger can be formed (we cannot setup a trigger based on the 125 slats due to lack of space, and electronics). - Run plans There are two basic goals we want to achieve. (see RBUP and presentations of this) One: comparison /reference spectra for pi, K and p at several rapidities. Two: investigation of feasibility of transverse polarization measurements. The expected pp luminosity will result in an interaction rate of about ~50-200K/sec, while at the same time the yield compare with Au-Au is down by approximately 175. If the trigger rejection factor can be brought up to above 50 we will get a trigger-rate of about 1K/sec still high so the utilization of the beam luminosity is not optimal. I am hopeful that the FS trigger can be brought to work, but it is by now mean assured. So in laying out the program we should be careful not over evaluating how much useful data can be collected at a given luminosity It would be very good in addition to spectra at a few angle setting to get a reference spectrum to the 12 deg setting. The second goal is one that will help establish if in up-coming run we will be able to perform an asymmetry measurement at high Xf i.e. at small angle and high field. This involves trigger studies and learning how to record polarization information. - shifts For the second item first I will like to gather from each institution the effort that is available in the above mention period for running the experiment. I will request to have this in hand by Monday, and will then see how (bad) the situation turns out to be. Looking forward to hear from you. Flemming
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