Study - PowerPoint Presentation

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Study of Large-area GEM Detectorsfor a Forward Tracker at a Future Electron-Ion Collider Experiment

Aiwu Zhang, Vallary Bhopatkar, Marcus HohlmannFlorida Institute of Technology (FIT)Kondo Gnanvo, Nilanga LiyanageUniversity of Virginia (U.Va)for the EIC RD6-FLYSUB Consortium

Electron Ion Collider Users Meeting

June 24-27, 2014 at Stony Brook University, NYSlide2

ContentsMotivations (will skip)FIT 1-m size zigzag GEM detectorU.Va 1-m size u-v strip GEM detectorBeam test configuration at FermilabBeam test results of the zigzag GEM detectorBeam test results of U.Va’s GEM detector

SummaryA. Zhang et al., Study of Large-area GEM Detectors as a Forward Tracker at an EIC6/27/20142Slide3

Zigzag-strip GEM @ FIT

Zigzag strips, 1.37mrad pitch

0.1mm

1

2

3

4

5

6

7

8

-sectors

1.37

mrad

The zigzag strips run in radial direction and can measure the azimuthal direction. Opening angle is 10 degrees,

angle pitch 1.37mrad

.

The readout board is designed to fit a 1-m long trapezoidal GEM

prototype (originally for CMS

muon

upgrade).

It is divided to 8

η

-sectors with radial length of each sector ~12cm, and

128 strips/sector

.

For the same GEM prototype with straight strips, 24 APV chips are needed to fully read out the chamber. In the zigzag case, only 8 APV chips can fully read out the entire chamber. This means 2/3 electronic channels can be saved.We use self-stretch technique so that GEM foils can be changed easily.

0.5mm

A. Zhang et al., Study of Large-area GEM Detectors as a Forward Tracker at an EIC

6/27/2014

3Slide4

Pitch

= 550 mm,

T

op

strips = 140

m

m,

Bottom strips = 490

m

m

12°

2D u/v readout strips

Entrance window

Drift region

Transfer region

Transfer region

Induction region

spacers

Gas inlet

Gas

outlet

2D readout board on Honeycomb support

Cross section of low mass triple GEM

6/27/2014

A. Zhang et al., Study of Large-area GEM Detectors as a Forward Tracker at an EIC

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2D u/v strip GEM @

U.Va

100 cm

22 cm

44 cm

Key characteristics:

Largest GEM detector with 2D readout ever build

Low mass (narrow edge and honey comb support) and small dead area

Fine strips 2-dimensional flexible small stereo angle u/v

readout so that good spatial resolution can be achieved, and with low capacitance noise

Gluing technique is used so that GEM foils can not be changedSlide5

Beam test setup @ FNAL

zigzag GEM and

U.Va

GEM

Trackers

Trackers

The RD6-FLYSUB consortium conducted a three-week beam test at

Fermilab

(Meson Test area 6, MT6) in Oct 2013,

operated

20

GEM detectors

.

The FIT group and

U.Va

group tested

10 GEMs as a tracking system

.

4 reference detectors (3/2/2/2mm gaps); the

zigzag GEM gaps: 3/1/2/1

mm;

Ar

/CO

2

(70:30) was used to operate all the detectors.

DAQ: RD51 SRS with SRU to read out 4FECs/64APVs simultaneously.

A. Zhang et al., Study of Large-area GEM Detectors as a Forward Tracker at an EIC

6/27/2014

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Beam test results of the zigzag GEM– basic performances

Cluster charge distribution in sector 5 at 3200V

MPV value of charge distribution vs. HV

Stat.

e

rrors smaller than marker size

peak pos.

Cluster

charge distribution

fits well to a Landau function.

Mean

cluster size

(number of fired strips in one event) from each cluster size distribution shows approximately exponential dependence on HV.

Mean cluster size vs. HV on sector 5

(number of hits in a cluster)

Stat.

e

rrors smaller than marker size

A. Zhang et al., Study of Large-area GEM Detectors as a Forward Tracker at an EIC

6/27/2014

6Slide7

Beam test results of the zigzag GEM– basic performances (cont.)Detection efficiency in middle-sector 5. Fitted with a sigmoid function, plateau efficiency ~98.4%.Different thresholds (N=3,4,5,6 times of pedestal

width σ) were tested, the efficiency plateau is not affected by thresholds.

On each sector, two points were measured. The response from sector to sector varies by ~20%.

The

non-uniformity

could be caused by bending of the drift board. The CMS-GEM group is

investigating this aspect to avoid bending after chambers are assembled.

A. Zhang et al., Study of Large-area GEM Detectors as a Forward Tracker at an EIC

6/27/2014

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Beam test results of the zigzag GEM – spatial resolution studiesThe zigzag strips measure the azimuthal coordinate φ.

Angle pitch between two strips is 1.73mrad. So we study its spatial resolution in polar coordinates.Spatial resolution is calculated from the geometric mean of exclusive and inclusive residual widths:

. Exclusive (Inclusive) means the probed detector is excluded (included) when fitting the tracks.

The trackers are aligned first and their spatial resolutions in (x, y) are found to be around 70

μ

m, which is the typical resolution of a standard triple-GEM. Their resolutions in

φ

coordinate are then calculated to be 30-40

μ

rad.

X offset

Eta5

vertex

10°

Y offset

Aligning trackers to zigzag GEM det.

σ

=21

μ

rad

Inclusive residual for 1

st

tracker

Resolution in

φ

for trackers

Errors smaller than marker size

tracker

A. Zhang et al., Study of Large-area GEM Detectors as a Forward Tracker at an EIC

6/27/2014

8Slide9

Beam test results of the zigzag GEM– spatial resolution studies (cont.)A. Zhang et al., Study of Large-area GEM Detectors as a Forward Tracker at an EIC6/27/20149

Exclusive residual

σ

=281

μ

rad

Inclusive residual

σ

=223

μ

rad

Residual distributions of the zigzag GEM in middle-sector 5 at 3350V

Hit positions are calculated with

Center of Gravity (COG)

method, and all

cluster size >0 events

are used.

Resolution is

for this case.

Note that the resolution in number of strips is about ~18%

 Slide10

Beam test results of the zigzag GEM– spatial resolution studies (cont.)

Resolution of the zigzag-GEM vs. HV in middle-sector 5.At highest tested voltage, resolution is ~240μrad.If only use 2-strip events, resolution is smaller (especially at lower voltages).

Resolution of the zigzag-GEM on different sectors at 3200V

(without cluster size cut).

A. Zhang et al., Study of Large-area GEM Detectors as a Forward Tracker at an EIC

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Beam test results of the zigzag GEM– cluster position correctionBy further checking the centroid position distributions of fixed cluster size events, we observe that these distributions have apparent bumps around each strip.

This brings us to study the non-linear strip response of charge distribution on position reconstruction, and hence make these distributions flat.A. Zhang et al., Study of Large-area GEM Detectors as a Forward Tracker at an EIC6/27/2014

11

Centroid position distribution from COG method (in middle-sector 5).

2-strip events

3-strip eventsSlide12

Beam test results of the zigzag GEM– cluster position correction (cont)

The idea is to build strip response functions for different cluster sizes (

η

-algorithm

).

, is defined as the centroid position (in strip units) minus the center of strip with maximum charge.

The

position correction functions

can be calculated:

.

h(

η

2

)

distribution

h(

η

3

)

distribution

Correction function

for 2-strip events

Correction function

for 3-strip events

A. Zhang et al., Study of Large-area GEM Detectors as a Forward Tracker at an EIC

6/27/2014

12Slide13

Beam test results of the zigzag GEM– cluster position correction (cont.)

After correction functions are figured out, the centroid position of an event can be corrected. Only clusters with 2,3 and 4 strips are because of better statistics (they make up ~90% of all clusters on the efficiency plateau).

2-strip before correction

2-strip after

correction

3

-strip before correction

3

-strip after correction

A. Zhang et al., Study of Large-area GEM Detectors as a Forward Tracker at an EIC

6/27/2014

13Slide14

Beam test results of the zigzag GEM– spatial resolution after correction

After position correction, we observe that resolution gets improved at higher voltages (to ~170μrad).Resolution vs. HV in middle-sector 5 after positions are corrected (with 2, 3, 4-strip events)

The results give us a clue that strip response correction is affected by

gas gain

and

incident angle of particles

.

A. Zhang et al., Study of Large-area GEM Detectors as a Forward Tracker at an EIC

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ADC Charges distribution

Efficiency vs. HV

Nb

of strips /cluster vs. HV

P1

P3

P2

P4

P5

Position scan with 32 GeV hadron

beam

Spatial resolution in (r,

) at different location in the chamber

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A. Zhang et al., Study of Large-area GEM Detectors as a Forward Tracker at an EIC

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Performances of the

U.Va

GEMSlide16

Gas input

Gas out

Top Entrance window

Bottom gas window

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A. Zhang et al., Study of Large-area GEM Detectors as a Forward Tracker at an EIC

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4 new ideas from

U.Va

towards a lighter, better resolution GEM detector

Ultra low mass chamber to minimize multiple scattering and background

“Re-

openable

” chamber – without gluing GEM foils

“mini-drift” GEM tracker to improve spatial resolution at large angle tracks

All readout electronics arranged at the outer edge of the chamber, to further reduce dead area and get better radiation hardness.Slide17

Summary on the zigzag GEMThe zigzag-GEM detector worked well in the beam test at FNAL.The 98% detection efficiency is good. The gain uniformity needs to be further investigated.Corrections for non-linear strip responses bring the resolution from ~240

μrad down to ~ 170μrad on the eff. Plateau, which could be transferred to 170μm at R=1m. The zigzag

structures

can probably still be optimized by interleaving

zigs

and

zags

more to improve resolution performance even further.

We conclude that a readout with zigzag strips is a viable option for

cost efficient

construction for a forward tracker

with GEMs

.

The

U.Va

u/v strip GEM detector also performance well in the beam test.

A. Zhang et al., Study of Large-area GEM Detectors as a Forward Tracker at an EIC

6/27/2014

17Slide18

Summary on the dedicated EIC forward tracker with GEMsBoth FIT and U.Va groups have experience on building and operating large-area GEM detectors.

U.Va group has experience on low-materials for drift and readout; FIT group constructs GEMs without gluing foils, and are pursuing a optimized cost effective zigzag readout structure.We are joining forces with Temple U.

in

designing and constructing

a

dedicated GEM

prototype for the EIC forward

tracker

, which goes to even higher eta regions in the forward region.

We plane to work

out e

ntirely

domestically sourced

GEM

foils

(see

the next talk from Temple U. group

).6/27/2014

A. Zhang et al., Study of Large-area GEM Detectors as a Forward Tracker at an EIC18Slide19

We would like to acknowledge BNL for the support of this work through the EIC RD-6 collaboration and the staff of the FNAL test beam facility for all their help.

Thanks!

The FLYSUB consortium

A. Zhang et al., Study of Large-area GEM Detectors as a Forward Tracker at an EIC

6/27/2014

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Back up – align the zigzag detector

X offset

Eta5

vertex

10°

Y offset

Aligning trackers to zigzag GEM det.

tracker

At a fixed Y offset, check residual sigma and chi-2

Residual sigma vs. X offset

Chi2 vs. X offset

At a fixed X offset, check residual mean and chi-2

Residual mean

vs. Y offset

Chi2 vs. Y offset

After checked (X,Y) groups in reasonable ranges, an intersecting point can be found from the scattering plot.

A. Zhang et al., Study of Large-area GEM Detectors as a Forward Tracker at an EIC

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Back up - referencesReferences on the strip response correction:CERN-Thesis-2013-284 by Marco Villa.G. Landi, NIMA 485 (2002) 698; NIMA 497 (2003) 511Reference about inclusive and exclusive residual studyR. K. Carnegie, NIMA 538 (2005) 327

6/27/2014A. Zhang et al., Study of Large-area GEM Detectors as a Forward Tracker at an EIC21Slide22

Motivation

Conceptual design of EIC detectorForward/backward GEM trackers

The

RD6-FLYSUB consortium

is jointly working on

tracking and particle ID

,

based on the

Gaseous Electron Multiplier (GEM)

technique,

for a future EIC.

The

zigzag-strip readout

structure is proposed and under study by Florida Tech to make the forward tracker much

less costly

.

Each zigzag strip occupies more space than a straight strip so that the total readout channels can be reduced and hence reduce the cost significantly, while

good spatial resolution can be conserved because of charge sharing on these

zigs and zags.

A. Zhang et al., Study of Large-area GEM Detectors as a Forward Tracker at an EIC

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Example of zigzag strips

2.5mm