Towards the edge measurement
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Towards the edge measurement. TOTEM Collaboration Meeting 15-16 Feb. 2005 Hubert Niewiadomski TOTEM, CERN Brunel University. X5 Data currently available for tracking. Available detectors:. Main available runs and corresponding events:. Run 3556 423k Run 3559 111k Run 3561 163k

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Towards the edge measurement

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Towards the edge measurement

Towards the edge measurement

TOTEM Collaboration Meeting

15-16 Feb. 2005

Hubert Niewiadomski

TOTEM, CERN

Brunel University


X5 data currently available for tracking

X5 Data currently available for tracking

Available detectors:

Main available runs and corresponding events:

  • Run 3556423k

  • Run 3559111k

  • Run 3561163k

  • Run 3565255k

  • Run 3611152k

  • Run 3668256k

    1.4 M


Detector overlappings

Top test RP

mm

Bottom reference RP

mm

mm

Top reference RP

Bottom test RP

Scintillator

mm

Detector overlappings

5.5 mm


The tracks

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) :


Example tracks run 3556

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


Software alignment 1

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.


Software alignment 2

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.


Aligning procedure

(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)


Aligning procedure1

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


Some alignment outcomes

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


Further steps

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


Jitterring problems

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)


Towards the edge measurement

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


Feasibilty and neccessity of jitterring correction

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


Statistical jitterring correction algorithm

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


Tests

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


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