Liquid argon calorimetry with LHC-performance specifications

Nuclear Instruments and Methods in Physics Research A315 (1992) 255-213North-Holland

Liquid argon calorimetry with LHC-performance specifications

Presented by F. Gianotti

B. Aubert, A. Bazan, B. Beaugiraud, F. Cavanna, J. Colas, M. Lebeau, T. Leflour,J.C. LeMarec, M. Maire, P. Petitpas, J. Thion, J.P . Vialle and I. Wingerter-SeezLAPP, Annecy, France

H.A. Gordon, V. Polychronakos, V. Radeka, D. Rahm and D. StephaniBrookhaven National Laboratory, Upton, USA

L. Baisirv, J.C . Berset, J.L. Chevalley, C.W. Fabjarv, A. Franz, P. Farthouat, O. Gildemeister,P. Jervni, M. Lefebvre, C.P. Marin, M. Nessi, F. Nessi-Tedaldi, M. Pepe, G. Polesello,W. Richter, A. Sigrist, G.R. Stevenson and W.J. WillisCERN, Genera, Switzerland

J.M. Baze, L. Gosset, P. Lavocat, B. Mansoulié, J.P . Meyer, J.F. Renardy, J. Teigerand H. ZacconeDPIiPe-CEN Saclay, Gif-sur-Yvette, France

G. Battistorvi, D. Camirv, D. Cavalli, G. Costa, A. Ferrari, F. Giarvotti, L. Marvdelli,M. Mazzarvti, L. Perini and G. PessinaDipartimento di Fisica dell'Università e Sezione INFN, Milano, Italy

E. Auge, R.L. Chase, J.C. Chollet, C. de la Taille, L. Fayard, D. Fournier, G. Guilhem,A. Hrisoho, L. Iconomidou-Fayard, P. Jean, B. Merkel, J.M. Noppe, G. Parrour, P. Petroff,J.P . Repellin, A. Schaffer, N. Seguin and J.J . VeilletLAL, Orsay; France

C. FuglesangManne Siegbahn Institute, Stockholm, Sweden

NUCLEARINSTRUMENTS8aIIIIETHODSIN PHYSICSRESEARCM

Section A

A novel geometry liquid argon calorimeter with accordion-shaped electrodes and converter plates has been recently ~:onceivcd.Such a design allows for a fast readout and for a high granularity over large volumes with minimal dead spaces, properties whichare considered essential for operation at the future hadron colliders.

The first electromagnetic prototype based on this scheme has been built and tested at the CERN SPS. For a response peakingtime of 140 ns an energy resolution of l0%/ E(GeV) and a space resolution of 4.4 mm/ E(GeVj with 2.7 cm cell size wereachieved for electrons. A few prehminary results from a test with fast readout (response peaking time of less than 40 ns) are alsopresented.

1. Introduction

performances of the electromagnetic and hadroniccalorimeters [1) .

Future high energy, high luminosity hadron collid-

Operation at an instantaneous luminosity of almosters like the LHC will be extremely demanding on the

2 x 1014/cm2 s requires radiation hardness and fast

0168-';-002/92/505 .00 O 1992 - Elsevier Science Publishers B.V. All rights reserved

V.ENERGY MEASUREMENTS

2

response of the device. In particular a barrel electro-magnetic calorimeter located at 1.5 m from the interac-tion region will have to stand an integrated dose of 10°Gy and a total fuence of 10 1 " n/cm2 over five years ofLHC operation, and its temporal response will have tocope with a rate of about 20, inelastic collisions perbunch crossing, i.e . every 15 ns.

Furthermore the calorimeter must be able to effi-ciently identify electrons. This is because the crosssection for production of high PT QCD jets is severalorders of magnitude higher than the signal expectedfrom "new" heavy particles, like the Higgs boson orthe top quark. There is no hope, therefore, to observetune particles through their hadronic decay and themore powerful signature produced by the less frequent(semi)leptonic channels must be exploited . It is alsoestimated [2] that a granularity of A# x Ail = 0.02 x0.02 will be needed in the electromagnetic compart-ment to achieve a rejection factor of at least 103against the huge hadronic background, through forinstance the application of suitable isolation cutsa

the electromagnetic shower.This fine granularity, which is also useful to reduce

the effect of overlapping consecutive interactions("pile-up"), has to combined with adequate cover-age and good hermeticity of the detector, to allow theobservation of weakly interacting neutral particlesthrough a reliable measurement of the event missingp-r. Furthermore, since several physics channels re-quire an electromagnetic energy resolution as low as1% and at the LHC energies the latter will be domi-nated by systematic effects, excellent uniformity ofresponse and precise control of the instrumental effects

r wide volumes and a large number of chan-nels (order of 105) will be mandatory. This last argu-ment also indicates that the calibration procedure must

easy and reliable .Finally the calorimeter response to leptons, hadrons

and jets must be linear over a large dynamic range.Considering these requirements, the liquid argon

MAO sampling calorimetey is one of the most attrac-tive options for several reasons. It is a mature tech-nique, extensively used over the last fifteen years, bothin fixed target and collider experiments . It is intrinsi-cally radiation resistant, expected to stand more than105 Gy with the only limitation coming from the hard-ness of the front-end electronics. It allows for a highgranularity and ensures good uniformity of response .Calibration is relatively easy and fast because, sincemechanical tolerances can be mantained at an ade-quate level, it is limited to the equalization of theelectronic channel responses . Finally it is a robusttechnique, stable in time and insensitive to the mag-netic field .

However, some weak points of the present LArcalorimeters need to be overcome if these detectors

B. Aubert et al. / Liquid argon calorimetry

are to be useful at the LHC. The temporal response,determined by the charge collection time over the LArgap and by the charge transfer time from the calorime-ter to the readout chain, is rather slow. The hadronicenergy resolution is generally modest (worse than 50%/E(GeV) ) due to lack of compensation . A cryostat

and cryogenic operations are needed.Investigation and improvements of these aspects is

the programme of an LHC Research and Developmentactivity recently started at Cern [3] . In this framework,a novel geometry detector in which the electrode andthe absorber plates are no longer planar but haveinstead an accordion shape has been conceived . Such ascheme allows for a fast readout over large volumeswhile keeping the non-instrumentable space at a negli-gible level, as will be explained in the next section . Thefirst electromagnetic prototype based on this concepthas been built and successfully tested at the CERNsuper proton synchrotron (SPS) with electron and muonbeams.

This paper illustrates the basic idea of this newdetector (section 2) and describes the test prototype(section 3) and the results of the first beam tests(section 4). A short outline of the present activities andfuture projects of this R&D effort is also presented(section 5).

2 . A fast liquid argon calorimeter. the Accordion

The current signal produced in an ion chambercalorimeter by a charged particle traversing the gaphas the characteristic triangular shape shown in fig. la.The electron drift time (t d ) is about 400 ns for a typical2 mm LAr gap, therefore a total charge measurementwill be excessively long at the LHC. A more rapidresponse is however possible by exploiting the very fastrise time of the ionization current (order of 1 ns) andby clipping the signal after a time t much smaller thant d (dashed area in fig . Ia).An advantageous way of doing that is to use equal

area bipolar shapers: in this case the pile-up of severalinteractions within the sensitive time of the detectorproduces no net shift in the energy measurement of ashower, contributing only to the calorimeter resolutionas additional noise . The response of a bipolar shaperto an input S-pulse, with peaking time tp(S), is shownin fig . lb . When convoluted with the triangular currentsignal from the detector, the shaper output has theform depicted in fig . lc, where tp = 2tp(b) is the result-ing peaking time of the calorimeter response.

The value of t p adequate to the LHC interactionrate has to be determined on the basis of a compro-mise . On the one hand it must be as small as possible,to reduce the number of bunch crossings overlapping

a)

b)

c)

O

a)

Fig. 1 . (a) Drift current and integrated charge vs time for anion chamber calorimeter. (b) Response of a bipolar shapingamplifier to a short current pulse (S). (c) Response of abipolar shaping amplifier to the current form shown in (a).The dots indicate where the beam crossings (every 15 ns)

would appear if tp(S) = 20 ns.

within the integration time of the detector (fig . lc). Forinstance if the maximum tolerable level of pile-upnoise within a calorimeter area large enough to contain

tParticle

B. Aubert et aL / Liquid argon calorirnetry

an electromagnetic shower (typically A,0 x A71 = 0.06x 0.06) is about 500 MeV, which corresponds to anenergy resolution of 10%/F at 20 GeV, then tpmust not exceed 50 ns [3]. On the other hand, theshorter tp the smaller the total charge seen by thedetector at the expenses of the signal to noise ratiowhich scales as tp(S)3/- [4] .

The further difficulty of this scheme is that fastshaping is impossible if the charge transfer time (7)from the calorimeter to the first readout element,usually the preamplifier (PA), is not as fast. The short-est r is achieved in critical damping conditions and isgiven by T= 2RC = 4 LC [4j, where L and C are thetotal inductance and capacitance of the detector ele-ments at the. PA entrance and R is the PA inputresistance .

In a conventional LAr calorimeter based on the ionchamber geometry the electrode and converter platesare perpendicular to the particle direction (fig. 2a). Toread out the detector in this configuration, the signalsmust be transferred from a given site inside thecalorimeter to the end of a module where the pream-plifiers are located and where consecutive electrodepads are usually grouped together to form longitudinaltowers. This operation requires long connections(several centimeters of cables in the best case) whichintroduce large capacitances and inductances, so that 'rbecomes long, and unacceptable dead spaces betweenmodules seriously limiting the achievable granularity.For these reasons such a geometry is not favoured atthe LHC.

However, if the converter and electrode plates weredisposed parallel to the particle direction, then linkingsuccessive pads to form a tower would become auto-matic and the signals could be extracted at the

b)

Particle

287

Fig . 2 . Conceptual view of (a) a traditional ion chamber calorimeter read out with parallel electrodes and (b) a calorimeter withaccordion geometry.

V. ENERGY MEASUREMENTS

288

calorimeter front and back faces, thus suppressing anyadditional transfer line . This is the basic idea of a newdetector, the Accordion calorimeter [3], in which, toavoid channeling of the incident particles through theLAr gaps, the absorber and the electrode plates arebent with an accordion shape (fig. 2b). The large re-duction of connections inherent to this geometry (theelectrodes themselves act as transmission lines) allowsachieving maximum speed of the response with mini-mal dead entice, noise and small cross-talk . How-ever to perform at the best of its capabilities such adetector requires a front-end electronics operating atthe LAr temperature (it must be installed on thecalorimeter faces), fast, with low input impedance(short 7), dissipating small power and very resistantbecause it will be located in a position fully exposed toradiation .

3. The prototype calorimeter

The first electromagnetic prototype based on theaccordion geometry has been built at CERN in 1990[5] . It has a transverse section of 40 cm x 40 cm, adepth of about 25 radiation lengths and consists of 1 .8mm cladded Pb plates alternated with 400 Wm copper-clad Kapton electrodes (fig. 3a). Both the lead and theKapton sheets, which are separated by 1 .9 mm of LAr,have an accordion shape with a pitch of 40.1 mm and abending angle of ±45° with respect to the nominaldirection of incidence (fig. 3b) . The converter platesare sticked in an horizontal support in which accor-dion-shaped grooves have been machined, while theelectrodes are held in place between two adjacent Pbsheets by verticai bands of a light honeycomb structure .

Each electrode consists of four conductive layersseparated by Kapton and glue . The two external layersare at high voltage and with the converter plates atground produce the electric field in the gap (- 10kV/cm) . The two inner layers, which are connectedtogether and do coupled to the preamplifier input,collect by capacitive coupling the fast signal from theelectrons drifting in the liquid argon .

The readout granularity is 2.7 cm along the horizon-tal (x) direction, achieved by grouping together threeconsecutive Kapton plates, and 2.5 cm in the vertical(y) view, obtained by chemically etching fifteen longi-tudinal strips on the electrodes . Longitudinally themodule is segmented into two samplings, 12.5 X� each,read out separately at the front and back faces throughpreamplifiers installed on the detector . The resultinginductance and capacitance of each calorimeter cell is10 nH and 400 pF respectively, giving a charge transfertime T of 8 ns .

To equip the prototype two types of charge sensitivepreamplifiers were chosen for their capability of work-

B. Aubert et al. / Liquid argon calorirnetry

a) 1.9 LAt

Fig. 3. (a) Artist's view of the Accordion prototype geometry.(b) Development of a 40 GeV electron shower in thecalorimeter (Monte Carlo simulation) . Only charged tracks

above 10 MeV are shown .

ing at low temperature, their fast rise time (- 20 ns),low input resistance (- 20 S2,), small power dissipation(- 70 mW) and low noise (equivalent noise charge(ENO of 2 x 104 electrons rms for tp(8) = 20 ns) : SiJ-Fees [6] and GaAs Mesfets [7] .

The electronic chain is completed by a bipolarshaper and a 12-bit ADC located outside the cryostat .

Precise and stable calibrations are indispensable forgood calorimeter performances (uniformity of re-sponse, energy resolution) and become a serious practi-cal problem when an accuracy of better than Âôneeded over a large number of cells .

The equalization of the prototype channels is car-ried out by injecting a sequence of known pulses at theentrance of each preamplifier through a set of preci-sion capacitors measured to an accuracy of 0.5% andby reading the output of the corresponding ADC at theend of the chain . Besides this fast electronic intercali-bration, only one number for the whole detector isneeded, the absolute energy scale, which was deter-mined locally with 122 GcV/c incident electrons by

requiring that the mean signal released in thecalorimeter was equal to the nominal beam energy .The sensitivity of the electronic chain turned out to beabout 18 MeV per ADC count.

4. Test beam results

The behaviour of the Accordion prototype has beenstudied in two beam tests at the CERN SPS . For thefirst one (July '90), only relatively slow bipolar shaperswith tp(S) = 100 ns were available to equip the 336channels of the module . During one week of parasiticrun, electron in the energy range 30 to 150 GeV andmuon data were taken . The relevant results are de-scribed in ref. [5].

For the spring '91 test, fast shapers with tp(8) = 20ns have been built, so that a calorimeter response fastenough ( - 40 ns) for operation at the LHC rate wasachieved . Data of energy, position and angular scanswith electrons and muons, were collected . Since mostof them are still being analyzed, only a few preliminaryoutcomes will be mentioned here (section 4.3), whilethe prototype performances with the "slow" electronicchain will be described in detail (section 4.1 and 4.2).

The H6 beam line of the CERN SPS, where themodule was installed for the tests, was equipped withfour scintillation counters used for triggering and witha set of proportional wire chambers needed to deter-mine the position of the incident beam. The resultingaccuracy on the particle impact point on the calorime-ter was about 500 Wm.

The beam spot size was typically 2 cm x 2 cm andthe momentum spread Ap/p = 0.2% . Above 90 GeV/celectrons were well recognized from pions by syn-chrotron radiation energy loss in traversing a set ofbending magnets, while below 90 GeV/c the beam wasunseparated with a 30% concentration of electrons .

4.1. Response to electrons

The energy spectrum measured in the Accordionfor 122 GeV/c incident electrons is shown in fig . 4 .The electromagnetic showers are reconstructed, in eachcompartment of the calorimeter, by summing the en-ergy deposited in a matrix of 5 x 5 cells around thechannel with the highest signal . The non-Gaussian tailon the left side of the distribution is due to electronslosing energy by Bremsstrahlung upstream of thecalorimeter in traversing about 2X0 of material dis-tributed over 40 m of beam line and belonging to otherexperiments running as main users. The energy resolu-tion at 122 GeV is 0.95%. A similar_ result is obtainedif the shower is reconstructed in a smaller size cluster(3 x 3 cells, i .e. 8 x 8 cm2), which still contains about


,13N

NCmW

Fig. 4. Energy reconstructed in the prototype for 122 GeV/cincident electrons . The solid line is a Gaussian fit.

93% of the electron energy and is more suitable to thehigh pile-up level of the LHC environment.

Fitting the resolutions measured at different beamenergies (fig. 5) with the linear formor kE FEwhere E is in GeV, gives k = (10.0 ± 0.6)%, and c =(0.0 ± 0.1)%. It can be seen that the constant term,

0.010

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t110

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130Experimental in 5x5 cells (GeV)

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29 GeV

0.10 0.15 0.20

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fit

289

Fig. 5. Energy resolution of the prototype at different electronenergies . The dashed line is a linear fit to the experimental

points .


150

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a (E) = 0.95%E

{-1ß . z ßl100

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290

which reflects the presence of systematic effects, iscompatible with zero over a calorimeter area of 2cm x 2 cm.

The dependence of the energy resolution on thehigh voltage applied to the detector was studied with122 GeVjc incident electrons by varying the operatingtension from 1200 V to 2400 V. At low voltage nodeterioration of the resolution is Observed (fig . 6),11-I'taua-'"v.aaa^ar "^aab that the calorimeter response is not affectedat least over this HV range; by the i_nhomogeneity ofthe electric field along the Accordion waves .

Accurate studies have been carried out, boththrough simulation of the detector design and through

L _o

idirect measurements during the beam tests, to ascer-tain whether and to what extent the unusual geometrydeteriorates the uniformity of the calorimeter re-sponse, which also affects the energy resolution. In theAccordion a potential source of non uniformity arisesfrom the fact that, to avoid too high values of theelectric field around the corners, the electrodes andthe converter plates are bent with rounded angles(radius of curvature 3 mm). As a consequence the ratioof the amount of LAr to the amount of passive mate-rial seen by an incident non showering particle varieswith the impact point along the x direction (top of fig-7). Before building the prototype this problem wasextensively investigated through Monte Carlo simula-tions [8] and the geometrical parameters of thecaloiüater, as the L.Ar gap and the Accordion foldpitch, were tuned to minimize the variation of thematerial density along x. For the set of parameterschosen for the present test module, fig . 7 shows thetotal_ 1A_r thickness as a function of the position alongthe horizontal view. The maximum variation, which isexperienced by a minimum ionizing particle incident at90° with respect to the calorimeter front face, stayswithin ±5%. A smoother response is expected for ahigh energy electromagnetic shower (see below).

0.020

0.015

w0.010

0

0.005

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1

1

i

11200 1600 2000 2400

High voltage (Volt)

Fig. 6 . Energy resolution for 122 GeV electrons as a functionof the high voltage applied to the test module .


2.2

- ------------

------

0

X impact point on cell

Fig . 7 . Total liquid argon thickness, in radiation lengths, as afunction of the position along the x view inside one calorime-ter cell (Monte Carlo simulation). The dotted lines delimit a

5% band around the mean value .

Good uniformity of response also relies on stricttolerances on the mechanics of the detector : thereforea special fabrication procedure and an expressly builtbending machine have been used for the preparation[3] of the plates of the test prototype .

Finally the signal uniformity improves with fastreadout because at small t p the charge seen by thedetector becomes almost independent of the gap sizeand therefore the calorimeter performances less sensi-tive to mechanical imperfections in the stacks .

Experimentally the local variation of the prototyperesponse as a function of the particle impact pointinside a cell was studied with 122 GeV incident elec-trons (fig . 8). A threefold periodical structure reflectingthe Accordion geometry (each readout channel groupstogether three electrodes and three converter plates) isvisible along x. Such a modulation, which stays within+ I%, is also predicted by a full shower Monte Carlosimulation [8] of the calorimeter, also shown in thefigure . Some discrepancies between Monte Carlo anddata can be attribu!ed to a possible tilting of the testmodule with respect to the plane perpendicular to thebeam, whereas in the simulation a 90° incidence anglewas assumed.

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Along y (fig . 8b) the Accordion behaves like astandard geometry pad detector and no structure inthe response is visible .An important merit of the Accordion calorimeter is

its excellent space resolution, direct consequence of itsgeometrical structure . Fig . 9 compares the electromag-netic shower position, reconstructed in the calorimeteras energy weighted barycentre of the 5 x 5 cell cluster,to the electron impact point determined by using thebeam chambers information. Along y discrepanciesare clearly visible between the true and the calorimeterreconstructed position which is systematically shiftedtoward the centre of the hit cell . This is a well knownbehaviour in a conventional pad detector. On the otherhand along x the calorimeter localizes correctly theincident particle position everywhere and with no bias .This is a quality inherent to the structure of the Accor-dion folds for which even a minimum ionizing particlealways releases its energy over at least two contiguouscells in x . It is this larger energy sharing which im-proves the accuracy in the reconstruction of the showerbarycentre .

The x space resolution has been measured withdifferent beam energies and the results (fig. 10) can befitted in the form

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i.e . o,,r ranges from 800 W to 300 pm when the beammomentum varies between 30 and 150 GeV/c. Theangular accuracy, measured by the shower barycentresin the two longitudinal sections, is about 6 mrad at 122G,-;-V/c.

Along the y view, after correction of the positionreconstructed in the calorimeter for the "S" shapeshown in fig. 9, a resolution of 570 pm is obtained at122 GeV/c.

4.2. Response to muons

The response of the Accordion prototype to mini-mum ionizing particles was studied with 100 GeV inci-dent muons: their spectrum in the calorimeter is shownin fig. 11 . To take into account the signal sharingbetween two x-adjacent channels due to the Accordiongeometry, the muon energy was reconstructed, in eachcompartment, by adding the signals from the mostenergetic pair of neighbouring cells along x .

The most probable energy loss (1 mip peak) is about350 MeV in the electron energy scale . Comparing it toa total electronic noise of about 7 MeV (less than 4MeV/channel) measured inside the four cell formingthe muon cluster gives a signal-to-noise ratio of about48 . This value is expected to reduce to about 4.5 when20 ns shapers are used.

-0.2 0 0.2Y impact point (cell units)

0.4

0.4

291

Fig. 8. Relative variation of the prototype response over a cell as a function of the electron x (a) and y (b) position. Black symbols:experimental points . Open circles: prediction of a Monte Carlo simulation of the Accordion. The dotted lines delimit the ±1%

deviation from the mean .


292

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0 .4 0 .6-0.6 -0.4 -0.2 0 0.2

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Fig. 9 . 122 GeV/c electron impact point as reconstructed bythe calorimeter versus the position determined by the beam

chamber system in the x (a) and y (b) view .

A space resolution o,x = 1 .75 ± 0.05 mm was mea-sured with muons. This is a substantially better resultthan usually obtained for minimum ionizing particleswith a conventional detector of comparable cell size.

146

122#' 89

~29 GeV

1/1/_E (GeV)Fig. 10. Space resolution of the prototype in the x view fordifferent electron beam energies . The dashed line is a linear

fit to the data points.

NOISEp

,

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50

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0.25

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Fig. 11 . Energy deposited in the prototype by 100 GeV/cincident muons. The distribution for the test beam data (fullline) is compared to the prediction of a Monte Carlo simula-tion of the calorimeter (points with error bars) and to thetotal electronic noise measured in the four cells of the muon

cluster (dashed area) .

The first important outcome from the test measure-ments with 20 ns shapers is that clean fast signals fromthe calorimeter were observed . As an example theshaper output of one calorimeter cell hit by a 60 GeVincident electron is shown in fig . 12 . The signal peaksat 40 ns and its tail extends over about 400 ns, the totalcharge drift time in the gap .

Fig . 12. Output signal from one calorimeter cell hit by anincident 60 GeV/c electron as seen at the oscilloscope (GaAspreamplifier, 20 ns shaper). The horizontal scale is 50 ns/div.,

the vertical one 50 mV/div .

100

120Energy in 3X3cells (GeV)

Fig . 13. Energy reconstructed in the prototype for 90 GeV/cincident electrons when 20 ns shaping amplifiers are used in

the read-out chain . The solid line is a Gaussian fit .

Preliminary studies indicate that the energy _resolu-tion for electrons is not significantly deteriorated withrespect to the "slow" readout conditions, as shown forinstance by the, clean spectrum obtained with 90 GeV/cincident electrons (fig . 13) . The electromagnetic show-ers are reconstructed in a 3 X 3 cell cluster and themeasurement was done over a calorimeter region of afew mm. It can be noticed that, due to the better beamquality in the '91 run, no asymmetric low energy tailappears in this case (compare fig . 13 to fig. 4) . Fittingthe spectrum within ± 3o, around the maximum gives a(preliminary) resolution of o/E = 1 .14% = 10.8%/VG

The analysis of these data is in progress .

5. Conclusions and future prospects

A dedicated research and development effort, re-cently started at CERN, aims at improving the liquidargon sampling calorimetry performances to meet thespecifications required for use in an experiment at theLHC. The starting point of this programme was thedevelopment of a novel geometry detector in which theelectrodes and the converter plates are no longer pla-nar but have an accordion shape. Such a design over-comes the two main weaknesses of the conventionalLAr calorimeters, the slow response and the poorhermeticity arising from the read-out scheme.

The first electromagnetic prototype based on thisconcept has been built and tested with electron andmuon beams . The results demonstrate that the unusual


geometry does not prevent good performances of thedetector . In particular an energy resolution of10%/ E(GeV) , with a constant term locally compat-ible with zero, and a space resolution parametrizableas 4.4 mm/ E(GeV) with a 2.7 cm cell size havebeen measured for electrons.

The first tests with a response peaking time of lessthan 40 ns, fast enough for operation at the LHC,indicate that the calorimeter behaves satisfactorily alsoat high speed.

Several aspects and projects are presently understudy and realization within this R&D activity [9J : abeam test in '91 of a small module with semi-projectivegeometry and threefold longitudinal segmentation ;studies of the mechanical and geometrical structure ofa full scale electromagnetic and hadronic calorimeter,based on the accordion scheme, for LHC; investigationof new solutions in the cryostat design to minimize theamount of dead space; construction of a whole electro-magnetic and hadronic calorimeter sector of dimen-sions 00 X 0q = 22.5° X 0.5 to be tested in '92; simu-lation studies to help in the detector design, to opti-mize the geometrical parameters, to inquire softwarecompensation methods able to improve the energyresolution of the hadronic compartment ; developmentof still better performing fast preamplifiers (see forinstance ref. [10]) and bipolar shapers and preparationof a test facility to measure the radiation hardness ofthe front-end electronics.

References

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[1] J. Colas et al ., Proc. Large Hadron Collider Workshop,Aachen 4-9 October 1990, eds . G. Jarlskog and D. Rein,ECFA 90-133 and CERN 90-10.

[2] J.P . Repellin, Proc . Large Hadron Collider Workshop,Aachen 4-9 October 1990, eds. G. Jarlskog and D. Rein,ECFA90 -133 and CERN 90-10 .

[3] B. Aubert et al., RD3 Collaboration, CERN/DRDC/90-31 (1990) .

[4] V. Radeka and S . Rescia, Nucl . Instr. and Meth. A265(1988) 228.

[5] B. Aubert et al ., RD3 Collaboration, Nucl . Instr. andMeth . A309 (1991) 438.

[6] SSC Detector R&D at BNL, eds . B. Yu and V. Radeka,BNL 52244, 1990.

[7] D.V. Camin et al ., IEEE Trans. Nucl . Sci . NS-38 (1991).[8] Geant 314, R . Brun et al ., Proc Large Hadron Collider

Workshop, Aachen 4-9 October 1990, eds . G . Jarlskogand D . Rein, ECFA 90-133 and CERN 90-10.

[9] B . Aubert et al ., RD3 Collaboration, CERN/DRDC/91-21, DRDC/P5-Add .1 .

[10] D.V. Camin, these Proceedings, Proc. 5th Pisa Meetingon Advanced Detectors : Frontier Detectors for FrontierPhysics, La Biodola, Isola d'Elba, Italy, May 26-31, 1991,eds. A . Baldini, A . Scribano and G. Tonelli, Nucl . Instr.and Meth. A315 (1992) 385.


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Liquid argon calorimetry with LHC-performance specifications