TPOL Test Beam Telescope

Chris Collins-Tooth (ZEUS, IC-London)

Outline

Test Beam setup of the Telescope and TPOL What is the Telescope and what does it do? What data was gathered? Analysis of the data

Multiple Coulomb Scattering, Beam spread, and Telescope resolution Relative rotations

between parts of the Telescope between the Telescope and the TPOL silicon

What can be done about these factors? What does this tell us about the TPOL silicon?

TPOL silicon resolution TPOL silicon efficiency

Summary

Test Beam setup

6 GeV e- beam enters from left e- beam passes through Telescope then moves into the TPOL Telescope mounted as close to TPOL as possible on movable table Telescope has 3 position sensitive detectors T1,T2 and T3 (Td was

‘dead’ material being used for a second experiment)

Telescope TPOL

The Telescope

Previously, degree of polarisation estimated using energy asymmetry in calorimeter (Calorimeter resolution ~1000 m)

Now measure polarisation using 80 m pitch Si

Something more accurate needed to probe TPOL silicon resolution - the Telescope.

3 planes of 50 m pitch Si, with horizontal and vertical strips.

T1,T2,T3 detectors roughly 3cm × 3cm (TPOL silicon ~1 cm2)

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The data

T1,T2,T3 used to predict Si strip to fire.

As expected, fitted line has slope =1 0.01

Offset simply due to T1,2,3 being physically larger than TPOL Silicon

Width of data about fitted line gives indication of TPOL resolution

The width

Width =132.15 ± 2.93 m TPOL Silicon strip pitch =80 m Intrinsic resolution ~80/12 m

00 400-400 800-800

Analysis of the data

Observed width does not relate directly to the TPOL resolution

Multiple Coulomb Scattering (MCS) of e- beam at T1,Td,T2,T3 and TPOL Aluminium Box

Finite resolution of the Telescope e- beam not 100% collimated Misalignments of the Telescope detectors T1,T2,T3 Misalignments of the Telescope (as a whole) and the TPOL

Telescope internal misalignment

T1,T2 and T3 could all be misaligned with respect to each other. Rotations would produce systematic shifts of ‘predicted minus

actual’ strip firing from left-to-right Most important are rotations about beam-axis (pictured). A 0.08o

rotation would cause a shift of 1 strip across breadth of detector

‘Predicted minus Actual’ shifts for T3,T2 and T1 from LR

Using T1,T2 to predict T3 (left) we observe a shift from left to right of approximately 50 microns

T3 T2 T1

Correction of misalignment

Iterative process invoked Rotating T3 by 0.27o flattened off all the plots (to within

errors)

TPOL misalignment

The TPOL silicon had no vertical strips Track through T1,T2,T3 used to predict vertical strip to fire to

give indication of horizontal position of impact No discernable shift observed before or after T3 rotation applied Correction for rotations caused no discernable reduction in

observed ‘width’

MCS, Telescope resolution and beam collimation

Simple Monte-Carlo simulation using PDG formula for MCS with gaussian width: s=(13.6MeV/cp) (x/Xo) (1+0.038 n [x/ Xo])

Telescope resolution and beam collimation are small factors in comparison to MCS

Together, all these factors contribute ~102 m to the width

Subtracting in quadrature, the TPOL resolution obtained is (1322-1022) 83 m

But - MCS is not actually gaussian

Attempting to use GEANT to improve estimate

Error propagation

Alternative approach to Monte-Carlo Use errors introduced by MCS etc., and propagate them to the TPOL silicon T4=T3+Z4m3+Z43+(Z4-ZAl)Al

Var(T4)=Var(T3)+Z42Var(m3)+Z4

2Var(3)+(Z4-ZAl)2Var(Al)+Z4Cov(T3,m3)

T3=T1-Z1m3-Zdd-Z22

Var(m3)=(1/Z12)(T1-T3-Zdd-Z22)

Variances are calculated, (e.g. Var(T1,T2,T3)=2T1,T2,T3 =208 m)

T4=[Var(T4)]=120 m= Error on TPOL Si due to uncertainties in Telescope

Resolution of TPOL Si = [1322-1202]=55 m

T1 T2Td T3 Al T4 (TPOL)

+z

m3

m3

m3+3

TPOL Resolution

From Monte-Carlo Simulation we obtain RTPOL 83 m

From Error Propagation we obtain RTPOL 55 m

TPOL Silicon Efficiency

Telescope used to predict TPOL events Efficiency is the ratio of:

events with TPOL Silicon signalevents predicted by Telescope

TPOL Silicon edges found by looking at ratio of hits not registering in the TPOL as a function of position

Log plot reveals edges where Telescope predicts TPOL hits but TPOL does not register

Horizontal edges at 13000 & 20000 m

Vertical edges at 11000 & 18000 m Consistent with active area of Silicon

Horizontal Position (m)

Vertical Position (m)

Ratio of hits NOT registering in TPOL

Efficiency cuts

Using the edges from previous slide, we must remove predicted events from efficiency calculations where they miss the boundaries of the TPOL Si

Figures show events predicted by the Telescope and registered by the TPOL (black) For effect, events in red are added. They are predicted events which had no

TPOL response, but the event was inside the opposite direction boundary, and so should have registered.

Clearly, the boundaries look correct.

Final Efficiency

With the positional cuts made, the efficiency of the TPOL silicon can be calculated

This is the ratio of : events with a TPOL silicon response all predicted events inside the boundary

The efficiency is uniform across the detector, at ~97.8%

Summary

Misalignments, Coulomb Scattering and other factors contribute significantly to observed width of 132 m.

TPOL Silicon resolution TBA but preliminary studies suggest 55 and 83 m

TPOL Silicon efficiency uniform at 97.8%