W. KozaneckiPEP-II MAC meeting, Dec 04Slide 1 Run-4 Beam-beam Performance Summary  Time evolution of beam currents, spot sizes, tunes & luminosity  Characterization of Beam-beam Performance  Comparison of measured luminosity with beam-beam simulations  Beam-current dependence of luminosity & beam sizes *  Scaling of luminosity with number of bunches *  “Pacman” effects  Crossing-angle Experiments  varying the horizontal crossing angle  varying the parasitic-crossing separation  varying the horizontal separation between the main IP * * These items were already presented to the MAC in April 04. They are mentioned here for completeness only. W. Kozanecki

PEP-II MAC meeting, Dec 04Slide 2 IP parameter Jun 03 Apr 04Jul 04 L (x /cm 2 /s) L sp (x /cm 2 /s) # bunches I LER (mA, e + ) I HER (mA, e - ) I LER / bunch (mA/b) I HER / bunch (mA/b) I LER / I HER ratio 1.3/1 1.6/1 1.6/1  y */  x * (cm) ‡ 1.2 / 40+, 1.2 / / 48+, 1.1 / / 32+, 1.05 / 32-  (nm) (y/x)™ 1.8 / 30+, 1.8 / / 30+, 1.3 / / 33+, 1.30 / 60- PEP- II Peak Collision Parameters ‡ from phase advance measurements ™ J. Seeman’s estimates

W. KozaneckiPEP-II MAC meeting, Dec 04Slide 3 Run 4 beam-current & bunch-number history LER total current HER total current # bunches L/H current ratio by-2

W. KozaneckiPEP-II MAC meeting, Dec 04Slide 4 Run 4 Luminosity History Specific luminosity Luminosity e + bunch current e - bunch current

W. KozaneckiPEP-II MAC meeting, Dec 04Slide 5 Luminosity vs. I + * I - 1 Oct Jul Oct-29 Jan29 Jan –30 Apr30 Apr – 31 Jul

W. KozaneckiPEP-II MAC meeting, Dec 04Slide 6 = in single-beam mode LER x-sizeLER y-size HER x-sizeHER y-size

W. KozaneckiPEP-II MAC meeting, Dec 04Slide 7 Comparison of measured luminosity with b-b simulations Simulations: Y. Cai / I. Narsky Luminosity in by-3 pattern (no parasitic Xings) 20 Oct 03 Beam-current dependence of L sp Absolute scale: % agreement Current-dependence steeper in data Uncertainties: assumed values of , ,  z lattice non-linearities (not incl’d)

W. KozaneckiPEP-II MAC meeting, Dec 04Slide 8 Beam-beam simulations: L sp & IP spot sizes Simulations: I. Narsky Parameter set: 2003 Dynamic  Vertical blowup (LER ??) BaBar lum. region

W. KozaneckiPEP-II MAC meeting, Dec 04Slide 9   =  ’ =   Simulation   ’   eff,  each current Beam-beam simulations: dynamic  x 2.3 x 1.3 Also see 13% (6%) dynamic  * y  in LER (HER)  dynamic-  growth strongest in the LER: sensitive to input simulation assumptions?

W. KozaneckiPEP-II MAC meeting, Dec 04Slide 10  The beam matrix at the SLM (  can be related to that at the IP (  *) by with, for instance with, for instance  The transformation matrix M can be obtained from  the design lattice (as done here)  MIA (does not work as well because coupling parameters not measured accurately enough)  This allows to predict the SLM/interferometer spot sizes if one “knows” the IP spot sizes (from simulation)  For the full formalism, see Yunhai’s presentation of 18 May 04: Beam-beam simulations: from the IP to the SLM Y. Cai

W. KozaneckiPEP-II MAC meeting, Dec 04Slide 11 Measured beam sizes: data vs. simulation Y. Cai / I. Narsky Parameter set: 2003 x 1.4 x 1.7 mainly  blowup + 17% (  tron) mainly dyn.  + 23% mainly  blowup x 2.3 dyn.  and   -beat

W. KozaneckiPEP-II MAC meeting, Dec 04Slide 12 Measured beam sizes: data vs. simulation Y. Cai / I. Narsky Parameter set: 2003 x % (  tron) mainly dyn.  + 23% mainly  blowup x 2.3 dyn.  and   -beat x 1.7 mainly  blowup The order of magnitude is right, and some of the qualitative features agree nicely (large horizontal LEB blowup finally explained, significant vertical HEB blowup). The fact that the simulation tends to overestimate the blowup in the LER may be due to differences between the actual tune and that in the simulation: dynamic-  effects are very sensitive to small tune changes near the ½ integer. Although large  -beats are present in both rings, they should not affect the magnification from the IP to the SLM. Therefore, it is unlikely that they are responsible for the large horizontal blowup predicted at the LER SLM.

W. KozaneckiPEP-II MAC meeting, Dec 04Slide 13  Goal: measure the luminosity degradation associated with  parasitic crossings  horizontal crossing angle  Principle  by-2 pattern: compare L sp at minimum, nominal & maximum parasitic-xing separation ( = e - x-angle) with full L optimization at each setting  sensitivity to Xing angle + parasitic crossings  by-4 pattern: compare L sp at minimum, 0, & maximum (achievable) Xing angles ( = e - x-angle) with full L optimization at each setting  sensitivity to Xing angle only  HEB only: measure impact (if any) of e - x-angle on e - beam properties Beam-beam sensitivity to parasitic crossings & Xing angle + x   parasitic crossings  XP(e-) more +ve   X (PC)   nominal:  X(PC) = 3.22 z = +/- 63 cm  XP max (e - ) = (+ 0.85) mrad   X  3.6 (2.7) mm

W. KozaneckiPEP-II MAC meeting, Dec 04Slide 14  At each XP setting  check orbit  Optimize LER+HER local & global skews, PR02 SEXT bumps, collision phase  Record tune spectra, gated camera data, L sp & I b +,- patterns along the train Xing angle / PC exp’t: scanning procedure  Even after  rad,L is higher at somewhat smaller crossing angle), and then drops again - until it is optimized again

W. KozaneckiPEP-II MAC meeting, Dec 04Slide 15 Xing angle / PC exp’t ==> small Xing angles preferred

W. KozaneckiPEP-II MAC meeting, Dec 04Slide 16  Without parasitic Xings (by-4) L sp exhibits a parabolic dependence on XP(e-)  With parasitic Xings (by-2)  the peak L sp is ~ 5% lower nominal PC separation) than in the by-4 pattern  the larger XP(e-), the steeper the L sp degradation  The optimum e - x angle is ~ 0.2 mrad more -ve in the by-2 pattern (  weaker PC effects)  This suggests that in the presence of parasitic Xings, the optimum e - angle is a compromise between Xing-angle & PC-induced luminosity degradation L sp dependence on Xing angle & PC separation: experimental summary

W. KozaneckiPEP-II MAC meeting, Dec 04Slide 17 L sp dependence on Xing angle &  X PC : data vs. simulations Simulations: Y. Cai Parm. set: 2003

W. KozaneckiPEP-II MAC meeting, Dec 04Slide 18  The simulation confirms that in the presence of parasitic crossings, introducing a small –ve Xing angle improves the luminosity  The optimum Xing angle is slightly larger in the simulation (-0.2 mrad) than in the data (-0.1 mrad) – consistent with the (previously) simulated Xing-angle dependence without PC’s  In the simulation, the best L sp achieved with parasitic Xings is 3% larger than without PC’s; in the data, it is 4% smaller with PC’s. Combined effect of Xing angle & parasitic crossings Y. Cai Parm. set: 2004

W. KozaneckiPEP-II MAC meeting, Dec 04Slide 19 Summary (I): luminosity performance  Luminosity parameters during Run 4  The LER/HER current ratio rose from ~ 1.3 in the by-3 pattern to ~ 1.6 in the by-2. The LER bunch current rose from ~ 1.3 mA/b to ~ 1.5 mA/b; the HER bunch current remained constant around mA/b. These should be compared to the target bunch currents at the end of Run 5: I + b = 1.92 mA/b, I - b = 1.05 mA/b, I + / I - = 1.83  The specific luminosity displays little global improvement over Run 4, and typically averages at high current. The peak in total luminosity ( > ) correlates with exeptionnally high L sp ( ).  Progress in peak luminosity during Run 4 is dominated by increased numbers of bunches (hence larger total I), and higher LER bunch current.  The history of the LER & HER beam sizes (SLM / interferometer) shows a progressive decrease in LER x size, and increase in HER y size. Some of the single-beam spot sizes also exhibit significant drifts; whether these are instrumental, or reflect actual optics changes, is unknown.  The total luminosity scales like the total # bunches constant I bunch )  Pacman effects  L sp at the edges of minitrains is ~ 10-20% lower than in the middle.  The L sp degradation is sensitive to the location along the train, the minitrain length, and the e - angle (or the Xing angle?), with patterns suggestive of wakefield effects. Gated-camera & gated-tune measurements suggest the same.

W. KozaneckiPEP-II MAC meeting, Dec 04Slide 20 Summary (II): beam-beam limits  Beam-beam simulations of luminosity performance  The absolute agreement on L sp is at the 15-20% level. The predicted blowup pattern is in qualitative agreement with the data; in particular, the large x-blowup at the LER SLM is now understood as the combination of dynamic  and dynamic .  But the current-dependence of L sp & individual e +- spot sizes (SLM/interferometer) is modelled qualitatively only.  Several improvements are needed more reliable measurement of colliding tunes & IP beam sizes ( IP  SLM model!) updated input parameters: tunes, ,  *,  z simulation of lattice non-linearities

W. KozaneckiPEP-II MAC meeting, Dec 04Slide 21 Summary (III): Crossing-angle experiments  crossing-angle scans [no parasitic crossings, full L reoptimization]  L sp exhibits a roughly parabolic dependence on the e - x-angle (after each angle).  The dependence of the luminosity on the Xing angle is steeper in the data (6-7 % for a half crossing angle  c = 0.3 mrad) than in the simulation (3%).  parasitic crossings [by-2 pattern, full L reoptimization]  The peak specific luminosity is ~ 5% lower nominal PC separation) than in the by-4 pattern, in agreement with the simulation; the more positive the e - x-angle, the steeper the additional luminosity degradation.  The optimum e - x-angle is ~ 200  rad more negative (i.e.  weaker PC effects) in the by-2 pattern, than in the by-4 pattern. Simulations confirm that in the presence of parasitic crossings, the optimum e - angle is a compromise between Xing-angle & PC-induced luminosity degradation.  Simulations predict a  c dependence of L sp similar to that observed; but they also suggest that the PC-induced L degradation can be fully compensated.

W. KozaneckiPEP-II MAC meeting, Dec 04Slide 22 Spare slides

W. KozaneckiPEP-II MAC meeting, Dec 04Slide 23 IP parameter Jun 03 Apr 04Jul 04 L (x /cm 2 /s) L sp (x /cm 2 /s) # bunches I LER (mA, e + ) I HER (mA, e - ) I LER / bunch (mA/b) I HER / bunch (mA/b) I LER / I HER ratio 1.3/1 1.6/11.6/1  y */  x * (cm/cm) 1.2 / 40+, 1.2 / / 48+, 1.1 / / 32+, 1.05 / 32-  (nm-rad) (y/x) 1.8 / 30+, 1.8 / / 30+, 1.3 / / 33+, 1.30 / 60- [ New sim. parms by YC/WK/JS, 11 Aug 04: 1.40 / 22+, 1.30 / 59-]  y (+/-).082/ / /  x (+/-).109/ / / PEP- II Peak Collision Parameters J. Seeman

W. KozaneckiPEP-II MAC meeting, Dec 04Slide 24 LER x-tune (msrd) LER y-tune (msrd) HER x-tune (msrd) HER y-tune (msrd)

W. KozaneckiPEP-II MAC meeting, Dec 04Slide 25 LER x-tune (msrd) HER x-tune (msrd) The LER & HER x-tunes track each other closely (as predicted by beam-beam simulations)

W. KozaneckiPEP-II MAC meeting, Dec 04Slide 26 Current dependence of L & beam sizes: HEB scan By-2 pattern 1320 bunches W.K. 31 Jul 04  27 Jan 04

W. KozaneckiPEP-II MAC meeting, Dec 04Slide 27  In single-beam mode, HER beam sizes are current-independent  When the HER current increases (with the LER nominal I + )  the specific luminosity first rises, then turns over.  L sp reaches a broad maximum around 0.5 mA/b  specific luminosity comparable at the highest & lowest HER bunch currents  as a function of the beam-current product, the total luminosity (in Jan 04) exhibits only moderate saturation is mostly limited by transverse losses (lifetime, beam-beam bgds) [Jul 04: ??]  the LEB blows up transversely with rising HER current  65% [40%] increase in x, 23% [10%] in the SLM/interf. (wrt single beam)  evolution of the transverse e + loss rate is consistent with blowup in both x & y, and confirms a significant Touschek contribution to the LEB lifetime  the HEB experiences both ‘LEB-induced’ & ‘self’ blowup  up to 0.8 mA/b, the x-size remains constant (4 % > single beam), then blows up by an additional ~ 4-7% (8-11% total blowup)  the y-size first decreases (50%  25% blowup, then back up to 40%). Its HER-current dependence largely mirrors that of the specific luminosity  evolution of transverse e - loss rate consistent with blowup pattern above  Jul 04: smooth extrapolation from above, except LER x,y blowup  HER-current dependence of L & beam sizes in Jan 04: observations

W. KozaneckiPEP-II MAC meeting, Dec 04Slide 28 HEB scan (continued)

W. KozaneckiPEP-II MAC meeting, Dec 04Slide 29 Current dependence of L & beam sizes: LEB scan By-2 pattern 1320 bunches 27 Jan Jul 04

W. KozaneckiPEP-II MAC meeting, Dec 04Slide 30  In single-beam mode, the LER beam sizes are current-independent  When the LER current increases (with I - nominal )  L sp remains roughly constant, except at the highest LER current  5 % decrease in L sp observed for i b + > 1.0 mA/b [Jul 04: 10-15% for i b + ~ 1.5]  the dependence of the total luminosity on the beam-current product exhibits only moderate saturation; however, raising the LEB current gains little L is limited by transverse losses (lifetime, beam-beam backgrounds) [Jul 04: ??]  the transverse LEB size  in x: remains constant in the horizontal plane, but 60-70% larger than in LEB-only mode [Jul 04: 40-50% larger than single beam]  in y: varies from 1.2 to 1.3 times its single-beam value as I + increases [Jul 04: ]  the evolution of the transverse e + loss rate suggests moderate or no variation of the blowup level with increasing positron current  the transverse HEB size  in x: varies from 1.04 to 1.08 times its single-beam value as I + increases [Jul 04: ]  in y: rises rapidly with LEB current, up to 1.4 times its single-beam value [Jul 04: 1.6 times]  both horizontal & vertical loss rates rise sharply for i b + > 1.2 mA/b LEB-current dependence of L & beam sizes in Jan 04: observations

W. KozaneckiPEP-II MAC meeting, Dec 04Slide 31 LEB scan (continued) Main features in Jul 04 (vs. Jan 04): less LER x,y blowup, more HER y blowup

W. KozaneckiPEP-II MAC meeting, Dec 04Slide 32 LEB scan (continued)

W. KozaneckiPEP-II MAC meeting, Dec 04Slide 33 Beam blowup: beam-beam (both) + Touschek (LER) Data: 27 Jan 04

W. KozaneckiPEP-II MAC meeting, Dec 04Slide 34 Bunch-number dependence of specific luminosity  Motivation: is L/bunch independent of the number of bunches ?  Principle: measure L, L sp, beam sizes, tunes,...  varying only the # of bunches (not the bunch separation within a train)  at constant bunch currents  Procedure  bunch currents representative of stable trickle running: LER/HER ~ 1.4/1.0 mA/b  start with a sparsified pattern, then progressively ‘fill it up’.  by-2, 94 trains, 6 bunches filled, 12 empty bunches (total bunches = 584) ....  by-2, 94 trains, 13 bunches filled, 5 empty bunches (total bunches = 1228)  for each pattern  top-off both rings  optimize tunes on Luminosity W.K. Dec 03 data

W. KozaneckiPEP-II MAC meeting, Dec 04Slide 35

W. KozaneckiPEP-II MAC meeting, Dec 04Slide 36  The specific luminosity remains independent of the bunch pattern, with an accuracy of a few %. Experimental conditions:  by-2 pattern  the number of buckets varies from 584 to 1228  the bunch currents are the same in the various patterns  Data taken on 31 Jul 04 remain to be analyzed Bunch-number dependence of specific luminosity: conclusions I b + = mA/b 0.96 < I b - < 1.00 mA/b

W. KozaneckiPEP-II MAC meeting, Dec 04Slide 37 “Pacman” effects (I): bunch pattern A. Novokhatski Apr 04 3 Apr bunches 3 Apr bunches

W. KozaneckiPEP-II MAC meeting, Dec 04Slide 38  How do the Pacman bunches fare?  What is happening in the long minitrain? “Pacman” effects (II): e - x angle experiments Data: 1 Jul 04

W. KozaneckiPEP-II MAC meeting, Dec 04Slide 39 Pacman bunches: phase transient ? Sparsified by-2 pattern, crossing-angle MD of 1 Jul 04

W. KozaneckiPEP-II MAC meeting, Dec 04Slide 40 Parasitic crossings: how do the Pacman bunches fare? Sparsified by-2 pattern, crossing angle MD of 1 Jul 04 Plot L sp / L sp XP=0 bins of XP(e-) (0 = opt) regular minitrains only nominal currents L sp optimized at each e - angle Bucket # W. Colocho Data: 1 Jul 04 Collision phase jumps Long train suppressed L sp = f(Xing Ang)

W. KozaneckiPEP-II MAC meeting, Dec 04Slide 41 Pacman & regular bunches: sensitivity to e - x-angle Bucket # (modulo 72) Pacman & regular bunches show a different sensitivity to x angle  the e - -angle dependence of L sp is not primarily due to the Pacman bunches W. Colocho Data: 1 Jul 04 Plot: minitr / L sp XP=0 Superpose regular minitrains on each other (excuding the long minitrain  average L sp (+/- stat)

W. KozaneckiPEP-II MAC meeting, Dec 04Slide 42 Pacman bunches: parasitic crossings or phase transient ? Bucket # 1 st 1 st, 8 th & 9 th bunch react differently to e - x angle. Could this be because the impact of phase transients (z coll offset) increases w/ Xing angle? could there be orbit-dependent wakefields (& hence tune shifts) ?? W. Colocho Data: 1 Jul 04 Plot L sp /L sp XP=0 green = 1 stgreen = 1 st bunch blue = last bunch (8 bunches/minitrain) red = last bunch (9 bunches/minitrain)

W. KozaneckiPEP-II MAC meeting, Dec 04Slide 43 Pacman bunches in the HER: gated-camera results D. Dujmic Data: 1 Jul 04

W. KozaneckiPEP-II MAC meeting, Dec 04Slide 44 Pacman bunches in the HER: gated-camera results D. Dujmic Data: 1 Jul 04

W. KozaneckiPEP-II MAC meeting, Dec 04Slide 45 Parasitic crossings: the dro o o o ping minitrain

W. KozaneckiPEP-II MAC meeting, Dec 04Slide 46 From : “Pacman” effects (III): tune variation long the train R. Holtzapple + A. Fisher Jul 04

W. KozaneckiPEP-II MAC meeting, Dec 04Slide 47 “Pacman” effects (details) A. Novokhatski 21 Mar bunches 3 Apr bunches

W. KozaneckiPEP-II MAC meeting, Dec 04Slide 48 Crossing-angle experiments  Goal: measure impact on beam-beam performance, of  horizontal crossing angle  XP  horizontal IP separation  X  Principle  scan horizontal IP angle (XP) or position (X) of e - beam  in the HER, no sextupoles within closed orbit bump  variation in XP-induced coupling should be small: scan range~ +- 1 mrad  separate optical & beam-beam effects by comparing scans at low, intermediate & high bunch currents using patterns without & with parasitic crossings (  XP   PC)  at each beam current setting  keep collisions well-centered, other angles fixed (XP +, YP +, YP - )  optimize luminosity before scanning  record L sp, LEB & HEB beam sizes, tranverse loss rates... x z Y. Cai, W.K., I. Narsky, J. Seeman, M. Sullivan March - July 04 data  XP = 1 mrad x  =10 mm x 2    X = 20 

W. KozaneckiPEP-II MAC meeting, Dec 04Slide 49  x eff = 21  1.54 x 0.92 mA/b by-2 (minitrains)  x = 152 .06 x.06 mA/b by-4 Crossing-angle experiments (II): X offset scan No tune nor optical adjustments during X-scans.

W. KozaneckiPEP-II MAC meeting, Dec 04Slide 50 X-dependence of luminosity & beam sizes LowLow current: excellent agreement between data & simulation High current: qualitative agreement between data & simulation  on L sp out to  X ~ 40 . At higher  X, simulation underestimates L sp drop.   on the HER y blowup   but not on the other beam sizes! Specific luminosity and vertical HEB size vs. horizontal beam separation, at various e + e - bunch currents, for data and simulation. At each current, the luminosity and spot size are normalized to their value at zero separation. The data are from a bunch pattern without parasitic crossings. No tune or other optical adjustments are carried out during the scan. Simulations: I. Narsky Parameter set: 2003

W. KozaneckiPEP-II MAC meeting, Dec 04Slide 51 X-dependence of specific luminosity Low current Excellent agreement between data & simulation Medium / high current Qualitative agreement betw. data & simulation on L sp out to  X ~ 40  (but: beam sizes!). Simulation underestimates L sp drop

W. KozaneckiPEP-II MAC meeting, Dec 04Slide 52 X-dependence of beam sizes at high current

W. KozaneckiPEP-II MAC meeting, Dec 04Slide 53 Summary (I): luminosity performance  Luminosity parameters during Run 4  The LER/HER current ratio rose from ~ 1.3 in the by-3 pattern to ~ 1.6 in the by-2. The LER bunch current rose from ~ 1.3 mA/b to ~ 1.5 mA/b; the HER bunch current remained constant around mA/b. These should be compared to the target bunch currents at the end of Run 5: I + b = 1.92 mA/b, I - b = 1.05 mA/b, I + / I - = 1.83  The specific luminosity displays little global improvement over Run 4, and typically averages at high current. The peak in total luminosity ( > ) correlates with exeptionnally high L sp ( ).  Progress in peak luminosity during Run 4 is dominated by increased numbers of bunches (hence larger total I), and higher LER bunch current.  The history of the LER & HER beam sizes (SLM / interferometer) shows a progressive decrease in LER x size, and increase in HER y size. Some of the single-beam spot sizes also exhibit significant drifts; whether these are instrumental, or reflect actual optics changes, is unknown.  The total luminosity scales like the total # bunches constant I bunch )  Pacman effects  L sp at the edges of minitrains is ~ 10-20% lower than in the middle.  The L sp degradation is sensitive to the location along the train, the minitrain length, and the e - angle (or the Xing angle?), with patterns suggestive of wakefield effects. Gated-camera & gated-tune measurements suggest the same.

W. KozaneckiPEP-II MAC meeting, Dec 04Slide 54 Summary (II): beam-beam limits  Experimental charaterization  the luminosity/bunch exhibits moderate –albeit growing - saturation at the highest operational currents. The bunch currents appear mainly limited by transverse losses (  lifetime, beam-beam backgrounds) [+ RF, heating !]  the performance at run end is a smooth extrapolation from the Jan 04 scans, except for a reduction in LEB x/y blowup, and an increase in HEB y-blowup  the specific luminosity appears limited by horizontal LEB blowup (40-45% wrt single e + beam), and vertical HEB blowup (60% wrt single e - beam). This is the controllling factor at the upper edge of the beam-current range. Vertical LEB blowup is noticeable (10-15%), as is horizontal HEB blowupe (10-15%).  Beam-beam simulations of luminosity performance  The absolute agreement on L sp is at the 15-20% level. The predicted blowup pattern is in qualitative agreement with the data; in particular, the large x-blowup at the LER SLM is now understood as the combination of dynamic  and dynamic .  But the current-dependence of L sp &  ’s is modelled qualitatively only.  Several improvements are needed more reliable measurement of colliding tunes & IP beam sizes ( IP  SLM model!) updated input parameters: tunes, ,  *,  z simulation of lattice non-linearities

W. KozaneckiPEP-II MAC meeting, Dec 04Slide 55 Summary (III): Crossing-angle experiments  x-offset scans (  X) [no parasitic crossings, no L reoptimization]  The dependence of the specific luminosity L sp on horizontal e + - e - separation has been measured in a pattern without parasitic Xings. The  X fall-off of L sp becomes steeper with increasing currents.  Beam-beam simulations are in qualitative agreement with the measurements. In particular, they highlight HEB vertical blowup as the primary cause of luminosity degradation for horizontally offset beams.  crossing-angle scans [no parasitic crossings, full L reoptimization]  L sp exhibits a roughly parabolic dependence on the e - x-angle (after each angle).  The dependence of the luminosity on the Xing angle is steeper in the data (6-7 % for a half crossing angle  c = 0.3 mrad) than in the simulation (3%).  parasitic crossings [by-2 pattern, full L reoptimization]  The peak specific luminosity is ~ 5% lower nominal PC separation) than in the by-4 pattern, in agreement with the simulation; the more positive the e - x-angle, the steeper the additional luminosity degradation.  The optimum e - x-angle is ~ 200  rad more negative (i.e.  weaker PC effects) in the by-2 pattern, than in the by-4 pattern. Simulations confirm that in the presence of parasitic crossings, the optimum e - angle is a compromise between Xing-angle & PC-induced luminosity degradation.  Simulations predict a  c dependence of L sp similar to that observed; but they also suggest that the PC-induced L degradation can be fully compensated.