Towards the edge measurement

1. Towards the edge measurement TOTEM Collaboration Meeting 15-16 Feb. 2005 Hubert Niewiadomski TOTEM, CERN Brunel University

2. X5 Data currently available for tracking Available detectors: Main available runs and corresponding events: • Run 3556 423k • Run 3559 111k • Run 3561 163k • Run 3565 255k • Run 3611 152k • Run 3668 256k 1.4 M

3. Top test RP mm Bottom reference RP mm mm Top reference RP Bottom test RP Scintillator mm Detector overlappings 5.5 mm

4. The tracks • 80 % events suitable for tracking • Tracks are fitted separately in U and V direction with clusters from references detectors • 15 % - 18 % of tracks (depending on run and cut) go through the overlapping region of test detectors • Frequencies of hits for tracking (always at least 3 hits for U and V directions of reference pots required) :

5. U direction, [strips] V direction, [strips] Z position, [mm] Z position, [mm] Track U projection Track V projection Track 1, run 3556 Example tracks, run 3556 U direction, [strips] V direction, [strips] Z position, [mm] Z position, [mm] Track U projection Track V projection Track 2, run 3556

6. α 2,1 v2 v1 v1 v2 u1 beam beam Software alignment (1) • Rotations: • Shifts: • In alignment procedures instead of dets. u1 and v1 the corresponding values from tracking are used. • Shifts and rotations are then calculated with respect to the tracking reference system.

7. Δvtop ref 6 [strips] Δvtop ref 6 [strips] u fitted, top_ref_6 [strips] u fitted, top_ref_6 [strips] Software alignment (2) • Example residual distribution and profile of top ref. 6 det.

8. (positions inside RP with accuracy of 0.1mm, distances between assemblies will be measured more precisely), In fact better because of charge sharing – multiple strip cluster position weighted by signal Aligning procedure • Input data resolutions: • Aligning is an iterative process, still in progress • Steps of aligning procedure: • Transformations of signs axes of coordinate systems (bottom pots were upsite down) • Application of rough u and v shifts (from detector correlations) • Tracking, calculation of residual and Chi-Squared distributions • Calculation of improvements to the shifts and rotations • Application of shifts and rotation corrections(rotations are performed around the center of overlapping area of reference detectors, one coordinate is taken from the detector and the other form a fitted track) • Go to c)

9. Residual [strip] Residual [strip] Residual [strip] Residual [strip] Residual [strip] Residual [strip] Residual [strip] Residual [strip] Perpendicular direction [strip] Perpendicular direction [strip] Perpendicular direction [strip] Perpendicular direction [strip] Perpendicular direction [strip] Perpendicular direction [strip] Perpendicular direction [strip] Perpendicular direction [strip] Aligning procedure Behaviour of residuals Shifts and rotations correction

10. Some alignment outcomes • Relative u and v shifts • Relative rotations between detector planes of strips in the same direction • Improvenemt of Chi-Squared distributions • Beam angular spread

11. Further steps • Some further tuning interations of software alignment • Studies on ortogonality of u and v coordinates • Analysis of errorsand expected residual distributions • Investigating the influence of charge sharing on detectors resolution (currently the positon of a multistrip cluster is weighted by signal of the strips) • Measurements of the vacuum pipe assembly

12. Serial data stream from detectors shouid be synchronized up to one clock at FED’s entry Some problems with hybrids’ PLLs caused sometimes shifts of several clock cycles in the serial data stream The problem appeared both in SPS and in X5 test beams Correction of data is complex since data stream headers are not available in new FEDs Jitterring detectors (without correction) are useless for analysis Jitterring problems • Each fiber stream containes 2 interleaved streams from APVs • APV channels are read out in a nonsequential way (several levels of multiplexers in readout)

13. The 2 fibers of a jitterring hybrid generally jitter in parallel, but not always Stream values Stream values Correct start of data stream Stream byte no Stream byte no Expected start of data stream Data transmision delayed by 1 clock Stream byte no Run 3037, bottom RP, 2nd card

14. X5: Jitterring correction would increase the precision of detector edge studies (up to 4 more detectors in tracking, depending on the run) Correction of several clock shifts is probably possible with statistical methods (tests in progress), but complex We don’t know what kind of data the jitterring detectors can provide us with (without good pedestals clusters are not visible) SPS data: Jitterring correction is needed for tracking on SPS runs Correction possible basing on available headers of data streams, quite complex Strips of det. 2 Correlation of 2 paralell jit. dets. Strips of det. 6 Feasibilty and neccessity of jitterring correction

15. Statistical jitterring correction algorithm • Periodic structure of fiber data stream, can be used for resynchronization of the order of several clock cycles • Application of discrete highpass filter to data buffers in order to emphasize the periodic structure of the signal: • Distributions of differences between corresponding bytes of such signals become narrowest if no shift is present, which allows to determine the shift RMS = 8.23 Buffers not shifted RMS = 33.18 Buffers shifted by 1 clock

16. Tests • Tests on not jitterring detectors (runs 3556, 3668) shown that error rate of shift determination of the order of 10-4 is probably achievable • Tests with jitterring detectors revealed jitterring shifts of up to ±2 clocks • Tests of event correlations between jitterring and nonjitterring detectors are needed