IP Measurements at PEP-II with BaBar

1. IP Measurements at PEP-IIwith BaBar M.Weaver, C.O’Grady, J.Thompson (SLAC), W.Kozanecki (Saclay), B.Viaud (Montreal) Super-B III Workshop June 15, 2006

2. IP Characterization • BaBar’s tracking resolution and prime venue allow measurement of important parameters at the IP • Use to measure production vertices and boost vector angles e- beam (resolution) Production vertices (x,y,z ~ 30mm) Boost trajectories (q ~ 0.6 mrad) e+ beam

3. Vertexing • <X>, <Y> provide steering information X (mm) 100mm Y (mm) 100mm

4. <Z> measures relative RF phase Z (mm) 2mm

5. 1mrad 1mrad • d<X>/dz, d<Y>/dz is one measure of the collision axis X’ (mrad) Y’ (mrad)

6. X-size of luminous region determined by emittances and IP-beta functions x-tune move towards half-integer (mm) dynamic b

7. Boost Trajectory • Technique • mmomenta poorly measured • trajectories well measured • reconstruct mm decay plane normal n n n l y n z m- f x P m+

8. Boost Trajectory tanl = - x’Bcosf – y’Bsinf ≈l x’(or y’)B = EH x’H – EL x’L EH - EL

9. 1mrad • <X’B>, <Y’B> is another measure of the collision axis X’B (mrad) 1mrad Y’B (mrad)

10. Crossing Angle • <X’B>-<X’L> = Run4 optimum from x-ing angle study <X’B>-<X’L> (mrad) <X’B>,<X’L> (mrad)

11. sX’B, sY’B dominant contribution from electron beam x-tune move towards half-integer (mrad) dynamic b

12. Studies on Luminosity Transient Track time resolution (~2ns) allows event association to RF bucket (476 MHz) Studied many IP parameters along bunch train z-centroid, size x,y-centroids, x-size x’,y’ means and spread mm Events 20% mini-train z-centroid x-size mm 66mm 63mm mini-train full-train

13. b*y Msmts I - Luminosity (Z) Z-resolution (~ 30mm) negligible compared to Sz,b*y Only acceptance/efficiency matter Neglecting complications from x-y coupling, dispersion,….

14. Luminosity (Z) Fits Run 62762-63049 Run 62101-62613 Chisq: 108, for 100-5 d.o.f. Prob: 17% Chisq: 132, for 100-5 d.o.f. Prob: 0.7% Norm 1.02125e+00 1.47665e-03 Zc 3.68052e-02 2.66972e-03 CapSigzSqrd 2.45044e+00 1.03738e-02 BetaY 1.33328e+00 1.96984e-02 Waist -8.00839e-02 1.26765e-02 Norm 1.02514e+00 1.63293e-03 Zc 2.64888e-02 2.62672e-03 CapSigzSqrd 2.21443e+00 9.75603e-03 BetaY 1.18414e+00 1.71040e-02 Waist -4.35208e-02 1.11199e-02

15. b*y Msmts II - Luminous Y-Size (Z) Assumes common by* Y-resolution (30mm) large compared to sYL (~4mm). Courageous analysis using track miss-distance to estimate per-event resolution. Some systematics not resolved. (cm)

16. Luminous Y-Size (Z) b*y (cm) Specific luminosity Nicely anti-correlated with Specific luminosity sLy,z=0 (cm) Specific luminosity

17. b*y Msmts III - Boost Y-Angular Spread (Z) collisions with very correlated trajectories collisions with very correlated trajectories collisions with uncorrelated trajectories y z (ebH+ebL)(f2e/bH + f2e/bL) + z2e/bHe/bL e b (1 + z2 / b2)H + e b (1 + z2 / b2)L s2Y’B(z) = (all bs are at IP) Depends upon vertical emittances and beta-stars

18. Boost Y-Angular Spread (Z) ey/by* by*

19. b*y Msmts Compared dL/dz Fit βy*(eff) from phase advance. Courtesy of Jerry Yocky. σy(z) method Boost method

20. b*y Msmts Compared BaBar results are significantly higher than PEP measurements. Possibilities: • Analysis errors • Optics different low current vs in-collision • X-Y coupling • promising; under investigation

21. Boost Angle-Position Correlation Negative x-x’B correlation here Positive x-x’B correlation here x (y) z (z-zH) fH – (z-zL) fL b2H+(z-zH)2b2L+(z-zL)2 x’B = x (all bs are at IP) Depends upon beta-stars and waist locations

22. Boost Angle-Position Correlation Z<0 Z>0 Adds an additional measured constraint upon vertical emittances and beta-function

23. Vertical Emittances sy’(z) + syy’(z) fit sy’(z) fit only Systematic shift not yet understood – coupling also possible explanation

24. IP Coupling Measurements • X-Y Coupling may explain systematic effects in our measurements and (more importantly) degrade luminosity. • Can we measure coupling parameters? • Measurements to explore • X-Y Tilt of Luminous Region Ellipsoid • X’-Y’ Tilt of Boost Vector Ellipse • X-Y’ Boost Vector Position-Angle Correlation • Y-X’ Boost Vector Position-Angle Correlation

25. BaBar IP measurements reported online • Luminous Region • centroids { x, y, z} • sizes { x, z } every 10 minutes • tilts { dx/dz, dy/dz } • dL/dz fit { Sz, b*y } every ~hour • Boost Trajectory • mean { x’, y’ } every 10 minutes • spread { x’HER, y’HER } every 30 minutes }

26. IP Measurements at Super-B • syL will be much smaller (20 nm) • sxL will be smaller than PEP-II syL • Z-resolution still ~< “effective” bunch lengths and by* • Boost angular spread similar • Boost angle-position correlation • larger intrinsic correlation (1/b2) • smaller x,y coordinates x-may be possible, y-not may lose due to systematic effects (alignment) • All online measurements still possible (except sxL) • Some offline analyses won’t work; replace with new ideas • Statistics will come much faster!

27. Summary • BaBar is trying to contribute to the understanding of the PEP-II collider • New ideas for measurements keep accumulating • Understanding of IP parameter analyses seems to be converging. • Hope that (this and) future experiment/accelerator combinations can benefit from our efforts

28. Spare Slides