1. Thoughts on using the Spin Flipper Stephen Pate New Mexico State University (opinions are mine, not that of PHENIX)

2. Assumptions For the purposes of this presentation, I’ll assume that the spin flipper will not decrease the beam polarization or luminosity; neither will it cause any background in the experiments.

3. Objectives Automated Spin Flip – no phone calls, no TV announcements; the spin flip should be a regular component of RHIC polarized proton operation Frequent Spin Flip – to maximize the benefit of the Spin Flipper, we should flip the spin as often as possible; if we can flip the spin in 5-10 seconds, then we should flip about every 10 minutes; then the “deadtime” associated with flipping is kept to ~2% Continuous Spin Information – the experiments always know the spin state Continuous Data Acquisition – we should not stop runs to flip the spin; instead we should simply record the spin state as part of the data stream

4. Spin Bits In the V124 system, there are three spin bits for each blue beam bunch: Spin Invalid (V124_B_ZERO) – we will use this to mean that the beam spin is not in a stable, valid state Spin Up (V124_B_UP) – spin orientation is up Spin Down (V124_B_DOWN) – spin down These are recorded in every event in PHENIX.

5. Use of Spin Bits Before flipping the spin, the "Spin Invalid" bit would go to 1. This will indicate to the experiments that a spin flip is imminent. This needs to be done before any actual change occurs in the spin, so that the data acquisition systems have time to do anything that they need to do in response. (In practice we should arrange things so that the DAQ doesn't do anything special at all during the spin flip.) The "Spin Up" and "Spin Down" bits should go to their new states during the spin flip. After the spin flipping is completely finished, then the "Spin Invalid" bit goes back to 0.

6. PHENIX and the Spin Bits We should not stop and start runs when the beam spin is flipped. We should simply record the spin bits as part of the event stream. I'll break this down into three areas of concern. Event data – We record the Spin Bits in every event, then during analysis we throw out the events with Spin Invalid = 1. GL1P -- This board is read with every event, so these spin-sorted scalers are tagged with the spin bit state. In analysis, remove increments that occur during Spin Invalid = 1. STAR Scalers -- The Spin Bits are in the addressing word, so these scalers already have the complete spin bit state.

7. Spin Quartets Initially we may just flip the spin every time, generating a +-+-+-… spin time sequence, but since the luminosity is decreasing with time then eventually we will want to use each of these “quartets” of spin states. +-+- +--+ -++- -+-+ A program will randomly select one of these, implement it over four spin flips, and then select another one, etc…