Nuclear Instruments and Methods in Physics Research A 623 (2010) 399–401

Contents lists available at ScienceDirect

Nuclear Instruments and Methods inPhysics Research A

0168-90

doi:10.1

� Tel.

E-m

journal homepage: www.elsevier.com/locate/nima

Results from the EUDET telescope with high resolution planes

Antonio Bulgheroni �

I.N.F.N.—Sezione di Milano, via Celoria, 16 - 20133 Milano, Italy

For the EUDET-JRA1 Consortium

a r t i c l e i n f o

Available online 6 March 2010

Keywords:

Monolithic pixel detector

Detector R&D

ILC

02/$ - see front matter & 2010 Elsevier B.V. A

016/j.nima.2010.03.015

: +39 31 238 6141; fax: +39 31 238 6209.

ail address: antonio.bulgheroni@mi.infn.it

a b s t r a c t

A high resolution ðso3mmÞ beam telescope based on monolithic active pixel sensors is being

developed within the EUDET collaboration. EUDET is a coordinated detector R&D programme for the

future International Linear Collider providing test beam infrastructure to detector R&D groups. The

telescope consists of six sensor planes with a pixel pitch of either 30 or 10mm and can be operated

inside a solenoidal magnetic field of up to 1.2 T. A general purpose cooling, positioning, readout

infrastructure and data analysis tools are available. The telescope has been running for one and a half

years at test beams at CERN and DESY. In this paper the performances of the telescope with different

configurations of sensors are compared.

& 2010 Elsevier B.V. All rights reserved.

1. Introduction

The EUDET project, supported by the European Commission inthe 6th Framework programme, aims at providing infrastructuresfor research and development of novel detector technologies forthe future International Linear Collider. Within the EUDET project,the Joint Research Activity (JRA) 1 has the main task of developingand improving test beam infrastructures, in particular thecommissioning of a high resolution pixel telescope and thecharacterization of a large bore 1-Tesla magnet (not covered inthis paper).

The design goals of the pixel telescope include a hit positionresolution (so3mm), a readout rate at the kHz level and a verylimited material budget to allow an effective operation even withhigh multiple scattering. The construction was planned in twostages, to quickly offer an exploitable infrastructure in parallel tothe development of the final telescope. In the first stage(demonstrator telescope) a well established CMOS pixel technol-ogy was used to produce the detector planes with two differentpixel pitches: 30 and 10mm [1]. Thanks to the high flexibility ofthe mechanical support and of the readout electronics, thetelescope users can decide whether to use the sensor with highor moderate granularity according to their needs and the requiredprecision on the extrapolated position at the device under test.This paper compares the spatial resolution achieved using theEUDET telescope configured with high or moderate granularitysensors.

ll rights reserved.

In Section 2, a brief description of the overall setup is given,while in Section 3, the spatial resolutions obtained with thedifferent configurations are shown.

2. Experimental setup

The EUDET telescope is described in detail in [2]. The trackingplanes are divided into two arms along the beam direction to hostthe Device Under Test (DUT) in a space that ranges from 1.5 to 35centimeters. The inter-spacing in between the sensor planes canbe adjusted in order to take advantage of the lever arm in thetelescope resolution; on the other hand, in the case of a lowenergy beam, a close compact configuration with at least tworeference planes positioned as close as possible to the DUT shouldbe used to minimize the multiple scattering contribution to thespatial resolution.

2.1. The sensor planes

The properties of the sensors equipping the reference planesare summarized in the Table 1.

2.2. The readout electronics

The readout electronics is based on custom developed VMEboards called EUdet Data Reduction Board (EUDRB) equippedwith an FPGA generating the digital signals for the slow control ofthe sensors and steering the ADC for the analog signal sampling.The data of each sensor are then transmitted over the VME bus to

A. Bulgheroni / Nuclear Instruments and Methods in Physics Research A 623 (2010) 399–401400

a central computer running event building and data storage. A keyissue of this readout electronics is the possibility to operate in twomodes: the so-called RAW mode in which all the pixel signals aretransmitted to the PC and the Correlated Double Sampling (CDS)technique is applied off-line, and the Zero Suppressed (ZS) mode,in which just the signal and the position of the pixels above acertain threshold are transferred to the PC and the CDS is appliedby the hardware online. When working in ZS, the threshold can beadjusted on a pixel by pixel basis.

All the detector planes and the DUT are synchronized by theTrigger Logic Unit featuring a coincidence logic circuit anddistributing the trigger signal, the event number and the timestamp to all the hardware devices in the setup.

2.3. The analysis software

To analyze the collected data, the JRA1 consortium is using theexperience in pixel detector analysis and track reconstructionavailable among its partners. A new software package, EUTele-scope, within the standard ILC software framework has beendeveloped. This package executes all the analysis steps, from theconversion of the DAQ native data format to the track reconstruc-tion and extrapolation on the DUT. It is worth mentioning two keypoints of this software:

Alignment using Millepede 2: The EUTelescope alignmentprocedure of the tracker ad of the DUT is based on Millepede [3].Analytic track fitting: One of the most difficult task in track

Table 1Main properties of the two detector types.

Moderategranularity

Highgranularity

Sensor name MimoTel Mimosa18

Pixel pitch ðmmÞ 30 10

Sensitive area width (mm) � length

(mm)

7.68 �7.68 5.10 �5.12

Sensitive thickness ðmmÞ 14 14

Overall thickness ðmmÞ 700 700

In both cases the overall thickness can be reduced down to 50mm to minimize the

material budget.

Fig. 1. Residual distribution for a telescope plane used as a DUT. In a configuration (a)

found to be 3:0mm, corresponding to a single plane resolution of about 2:7mm. In a confi

is 0:9mm corresponding to a single plane resolution of 0:85mm.

fitting is the proper estimation of the multiple scatteringcontribution to the spatial resolution. Within EUTelescope, theso-called analytic approach [4] has been implemented in sucha way that the particle trajectory can vary after each materialcrossing. The w2 of the track fit then takes into account thisscattering angle properly weighted by the impinging particleenergy.

All the telescope components: mechanics, readout electronicsand analysis software have been designed to guarantee themaximum flexibility and the user can decide not only the positionof the reference planes, but also the granularity and the readoutmode.

3. Experimental results

The first step in the characterization of the telescope as atracking device was the measurement of the intrinsic resolutionof the reference planes and the ultimate spatial resolutionachievable combining all the hits into a track. The single planeresolution ðsDUTÞ can be obtained from the measured residualwidth ðsmeasÞ and the telescope resolution ðstelÞ using Eq. (1)

s2meas ¼ s

2DUTþs

2tel ð1Þ

The telescope resolution can be determined assuming that thereference planes all have the same intrinsic resolution usingEq. (2)

s2tel ¼ ks2

plane ð2aÞ

and

k¼

PNi z2

i

NPN

i z2i �ð

PNi ziÞ

2ð2bÞ

The formula for the geometrical scaling factor k defined in (2b) isbased on the assumption that the DUT is positioned at z¼0 and itreduces to 1/N if the reference planes are is symmetricallydistributed around the DUT and the beam and telescope axes areparallel.

In the limit case in which the device under test is of the sametype of the reference planes, combining Eqs. (1) and (2), theintrinsic resolution of the single telescope plane and of the overall

with all moderate granularity sensors, the measured residual distribution width is

guration (b) with all high granularity reference planes the measured residual width

Table 2Comparison between the two different configurations.

Moderate granularity High granularity

Measured width ðmmÞ 3.00 0.95

Scaling factor k 0.23 0.25

Single plane res. ðmmÞ 2.70 0.85

Telescope res. ðmmÞ 1.30 0.42

A. Bulgheroni / Nuclear Instruments and Methods in Physics Research A 623 (2010) 399–401 401

telescope can be derived directly from measured residualwidth (3)

s2plane ¼

s2meas

1þkð3aÞ

and

s2tel ¼

k

1þks2

meas ð3bÞ

During summer 2008, the pixel telescope was installed in the H6SPS beam line at CERN and several million 120 GeV pion trackswere collected. A small fraction of these data was acquired withthe main goal of measuring the intrinsic spatial resolution of bothtypes of reference planes.

Two main configurations were considered, the low resolution inwhich the six planes were all equipped with moderate granularitysensors and the high resolution with six high granularity planes.The two data samples were analyzed in the same way leaving oneplane out of the fit. The residual distributions measured on thisplane are shown in Fig. 1 for both cases. Applying Eq. (3) it waspossible to calculate the intrinsic resolution of all planes and thetelescope resolution. Results are shown in Table 2.

4. Conclusion

Within the EUDET project a pixel telescope has been designedand commissioned with the main goal of fostering the detectorR&D for the future International Linear Collider. The firstprototype of telescope with analog signals can be used with bothhigh and moderate granularity reference planes in order to betterfulfil user needs and requirements. The performance in terms ofspatial resolution of this telescope demonstrator has beenmeasured with a 120 GeV pion beam at CERN last year and theresults obtained for the single plane and telescope resolution arewell in agreement with the design specifications. The results willbe soon validated also on a low energy electron beam at DESYwhere the multiple scattering contribution is not negligible.

Acknowledgment

This work is supported by the Commission of the EuropeanCommunities under the 6th Framework Programme Structuringthe European Research Area, contract number RII3-026126.

References

[1] W. Dulinski, et al., Beam telescope for medium energy particles based on thin,submicron precision MAPS, in: Nuclear Science Symposium Conference Record2007, 26 October 2007, pp. 995.

[2] A. Bulgheroni, First test beam results from the EUDET pixel telescope, in:Nuclear Science Symposium Conference Record 2007, 26 October 2007,pp. 1878.

[3] V. Blobel, Nuclear Instruments and Methods in Physics Research.Section A Accelerators, Spectrometers Detectors and Associated Equipment566 (2006) 5.

[4] A.F. Zarnecki, P. Niezurawski, EUDET telescope geometry and resolutionstudies, EUDET-Report-2007-01, (arXiv:physics/0703058).