Stability of the collision diamond at STAR during pp510 data taking this year.

Based on private BFC production using official TPC calibration form DB the beam line params were determined runby-run for 3 fills from pp510 data.

For the same fills Angelika reported beam position (and ~angle) measured by BPMs. Below you will find both data for each fill, with quoted comments from Angelika and myself.

FYI: the DX BPMs in STAR are slightly asymmetric. On the 5 o'clock side it's 8.3 m and on the 6 o'clock side its 8.0 m (from the center of the IR). They are mounted on the inside (i.e. towards the experiment) of the DX magnets, in the common beam pipe

Fill 16582 

Fig 1 , Beam line X0,Y0 (in cm) from STAR TPC from consecutive runs[R13077064,R13078014] from this one fill

Angelika: "The top plot shows the blue and yellow DX BPM readbacks (unit is micron), the bottom the STAR ZDC coincidence rate and (if applicable) the optimizations that were run in that store (units in mm).

16582: no automatic orbit corrections (don't know why). About +/- 0.5 mm drift, mostly yellow vertical. Drift appears as an angle in the vertical plane since it is not parallel but opposite direction on either side of STAR. There is a small angle in blue as well and both together result in a total of 35 micro rad angle between the beams before it is corrected (only angles between the beams are reflected as a drop in luminosity). At the same time the angle is corrected, the transverse position is corrected as well (by 60 micron in Y and 30 micron in X). The combination of both (angle and position drift) caused the drop in collision rate which is then corrected.

just want to correct one thing: yes, there is a drift of about 0.5 mm in 16582 -- but in the opposite direction on the two sides of the IP, i.e. what is 'visible' at the IP is simply a change of beam angle, not position! The total drift in transverse position seems to be only about 60 micron, that's what is corrected by our opimization program (aka "lisa")."

Fig 2 , BMPs from Angelika

Fig 2B,C , BMPs from Angelika , Hor and Vert position, separate for the two rings, extrapolated to the IP (from the DX BPMs). Units are in microns. My 1st statement still holds though, there is only < 100 micron transverse drift in the vertical plane and less in the horizontal.

Fill 16668

Fig 3 Beam line X0,Y0 (in cm) from STAR TPC from consecutive runs[R13093044,R13094021]

Angelika: "only one optimization at the very beginning. no significant correction needed. Automatic store orbit correction is ON and you can see the regular small position changes. There is no significant total drift, certainly not 200 microns.'

Fig 4  BPMs from Angelika

Fill 16693

Fig 5 Beam line X0,Y0 (in cm) from STAR TPC from consecutive runs[R13099025,R13099046]

Angelika: same a s above but 3 optimizations with very small corrections. don't know why there were more than one. I don't see a change of up to 300 micron as indicated in your plot? Note that drifts in the opposite directions in the two DX BPMs of one plane (and ring of course ;)) that are labeled g5 and g6 respectively indicate an angle change while drifts in the same direction are a transverse position change

Fig 6 BPMs from Angelika