Presentation on theme: "Fast BCT in vdM fill 1653 V.Balagura, BCNWG,18 Apr 2011 Raw data, averages per bunch over LHCb vdM scan (27 Mar 14:25:39 – 15:05:00). 76 bunches per beam."— Presentation transcript:
Fast BCT in vdM fill 1653 V.Balagura, BCNWG,18 Apr 2011 Raw data, averages per bunch over LHCb vdM scan (27 Mar 14:25:39 – 15:05:00). 76 bunches per beam
2 Pilots and part of 1 st trainEmpty bunches in beam2 (oscillation) Afterpulsing patterns in beam1, 2 are similar in all bunches except pilots.
For vdM analysis sum over [bx-4…bx+11] is taken (contains all pre-spill-over) If one takes bx or [bx..bx+1] and renormalizes to DC: systematics 0.3, 0.2% May be not a problem (?) during vdM with isolated bunches. Problem for future LHCb beam-gas analysis with bunch trains. Does afterpulsing depends on filling pattern, why it is different for beam1,2?
For nominal bunches Best(bx) = Raw(bx) + Raw(bx+1) up to a small ((1.4-1.6)e6) offset correction Fast BCT correction in timber, best now data (Raw(bx) + Raw(bx+1)) - Best(bb) All BX Two trains of nominal BX
LHCb vdM scan on 27 Mar at 1.38 TeV 5 RMS spread between cross sections in different bunches: 1.6% =50.7 mb =50.2 mb May be explained by Fast BCT offsets (P1,P2), but for beam2 it is too big: (0.87 +/- 0.15) e10 (i.e. true value = measured – 0.87e10). In two Oct. scans: P1= 0.41+/-0.10, 0.28 +/ 0.15 P2 = -0.02 +/- 0.10, 0.24 +/- 0.13
Cross section variations correlate not only with Fast BCT 6 ln(X/average X), where X= (dashed), N1xN2 (solid), X (blue), Y (red) integrals, ln( average ) shifted to 0.5 for illustration There is also a correlation with e.g. vdM shape width (approx. proportional to integral / 0, ln width = ln integral – ln 0 + const)