The method of extraction of the $e/h$ ratio, the degree of non-compensation,
of the electromagnetic compartment of the combined calorimeter is suggested.
The $e/h$ ratio of $1.74\pm0.04$ has been determined on the basis of the 1996
combined calorimeter test beam data. This value agrees with the prediction that
$e/h > 1.7$ for this electromagnetic calorimeter.Comment: LATEX, 17 pages, 7 figure

Kulchitsky, Y. A.

Kuzmin, M. V.

Vinogradov, V. B.

English

arXiv

The method of extraction of the $e/h$ ratio, the degree of non-compensation, of the electromagnetic compartment of the combined calorimeter is suggested. The $e/h$ ratio of $1.74\pm0.04$ has been determined on the basis of the 1996 combined calorimeter test beam data. This value agrees with the prediction that $e/h > 1.7$ for this electromagnetic calorimeter.The method of extraction of the $e/h$ ratio, the degree of non-compensation, of the electromagnetic compartment of the combined calorimeter is suggested. The $e/h$ ratio of $1.74\pm0.04$ has been determined on the basis of the 1996 combined calorimeter test beam data. This value agrees with the prediction that $e/h > 1.7$ for this electromagnetic calorimeter

Kulchitsky, Y.A.

Kuzmin, M.V.

Vinogradov, V.B.

CERN Document Server

ATL-TILECAL-99-02115/11/99Non-compensation of an ElectromagneticCompartment of a Combined CalorimeterY.A. Kulchitsky, M.V. KuzminInstitute of Physics, National Academy of Sciences, Minsk, Belarus& JINR, Dubna, RussiaV.B. VinogradovJINR, Dubna, RussiaAbstractThe method of extraction of the e/h ratio, the degree of non-compensation, of the electromagnetic compartment of the ATLASbarrel combined prototype calorimeter is suggested. The e/h ratioof 1.740.04 has been determined on the basis of the 1996 combinedcalorimeter test beam data. This value agrees with the predictionthat e/h > 1.7 for this electromagnetic calorimeter.1 IntroductionThe existing calorimetric complexes (CDF, D0, H1 etc.) as well as thethe future huge ones (ATLAS [1], CMS etc.) at the CERN Large HadronCollider (LHC) are the combined calorimeters with the electromagneticand hadronic compartments. For the energy reconstruction and descriptionof the longitudinal development of a hadronic shower it is necessary to knowthe e/h ratios, the degree of non-compensation, of these calorimeters. Asto the ATLAS Tile barrel calorimeter there is the detailed informationabout the e/h ratio presented in [2], [3], [4], [5], [6]. But as to the liquidargon electromagnetic calorimeter such information practically absent.The aim of the present work is to develop the method and to determinethe value of the e/h ratio of the LAr electromagnetic compartment.This work has been performed on the basis of the 1996 combined testbeam data [7]. Data were taken on the H8 beam of the CERN SPS, withpion and electron beams of 10, 20, 40, 50, 80, 100, 150 and 300 GeV/c.2 The Combined Prototype CalorimeterThe future ATLAS experiment [1] will include in the central (“barrel”)region a calorimeter system composed of two separate units: the liquidargon electromagnetic calorimeter (LAr) [8] and the tile iron-scintillatinghadronic calorimeter (Tile) [5].For detailed understanding of performance of the future ATLAS com-bined calorimeter the combined calorimeter prototype setup has been madeconsisting of the LAr electromagnetic calorimeter prototype inside thecryostat and downstream the Tile calorimeter prototype as shown in Fig. 1.The dead material between the two calorimeters was about 2.2 X0or 0.28 λpiI . Early showers in the liquid argon were kept to a minimum byplacing the light foam material in the cryostat upstream of the calorimeter.The two calorimeters have been placed with their central axes at anangle to the beam of 12◦. At this angle the two calorimeters have an activethickness of 10.3 λI .Between the active part of the LAr and the Tile detectors a layer ofscintillator was installed, called the midsampler. The midsampler consistsof five scintillators, 20  100 cm2 each, fastened directly to the front faceof the Tile modules. The scintillator is 1 cm thick.2Beam quality and geometry were monitored with a set of beam wirechambers BC1, BC2, BC3 and trigger hodoscopes placed upstream of theLAr cryostat.To detect punchthrough particles and to measure the effect of longi-tudinal leakage a “muon wall” consisting of 10 scintillator counters (each2 cm thick) was located behind the calorimeters at a distance of about 1metre.2.1 The Electromagnetic Liquid Argon CalorimeterThe electromagnetic LAr calorimeter prototype consists of a stack ofthree azimuthal modules, each one spanning 9◦ in azimuth and extendingover 2 m along the Z direction. The calorimeter structure is defined by2.2 mm thick steel-plated lead absorbers, folded to an accordion shape andseparated by 3.8 mm gaps, filled with liquid argon. The signals are col-lected by Kapton electrodes located in the gaps. The calorimeter extendsfrom an inner radius of 131.5 cm to an outer radius of 182.6 cm, repre-senting (at η = 0) a total of 25 radiation lengths (X0), or 1.22 interactionlengths (λI) for protons. The calorimeter is longitudinally segmented intothree compartments of 9 X0, 9 X0 and 7 X0, respectively. More detailsabout this prototype can be found in [1], [9].In front of the EM calorimeter a presampler was mounted. The activedepth of liquid argon in the presampler is 10 mm and the strip spacing is3.9 mm.The cryostat has a cylindrical form with 2 m internal diameter, filledwith liquid argon, and is made out of a 8 mm thick inner stainless-steelvessel, isolated by 30 cm of low-density foam (Rohacell), itself protectedby a 1.2 mm thick aluminum outer wall.2.2 The Hadronic Tile CalorimeterThe hadronic Tile calorimeter is a sampling device using steel as theabsorber and scintillating tiles as the active material [5]. The innovativefeature of the design is the orientation of the tiles which are placed in planesperpendicular to the Z direction [10]. For a better sampling homogeneitythe 3 mm thick scintillators are staggered in the radial direction. The tilesare separated along Z by 14 mm of steel, giving a steel/scintillator volumeratio of 4.7. Wavelength shifting fibers (WLS) running radially collect3light from the tiles at both of their open edges. The hadron calorimeterprototype consists of an azimuthal stack of five modules. Each modulecovers 2pi/64 in azimuth and extends 1 m along the Z direction, such thatthe front face covers 100 20 cm2. The radial depth, from an inner radiusof 200 cm to an outer radius of 380 cm, accounts for 8.9 λ at η = 0 (80.5X0). Read-out cells are defined by grouping together a bundle of fibersinto one photomultiplier (PMT). Each of the 100 cells is read out by twoPMTs and is fully projective in azimuth (with ∆φ = 2pi/64  0.1), whilethe segmentation along the Z axis is made by grouping fibers into read-outcells spanning ∆Z = 20 cm (∆η  0.1) and is therefore not projectiveEach module is read out in four longitudinal segments (corresponding toabout 1.5, 2, 2.5 and 3 λI at η = 0). More details of this prototype can befound in [1], [2].3 Event SelectionWe applied some similar to [7] cuts to eliminate the non-single trackpion events, the beam halo, the events with an interaction before LArcalorimeter, the events with the longitudinal leakage, the electron andmuon events. The set of cuts is the following: the single-track pion events were selected by requiring the pulseheight of the beam scintillation counters and the energy released inthe presampler of the electromagnetic calorimeter to be compatiblewith that for a single particle; the beam halo events were removed with appropriate cuts on thehorizontal and vertical positions of the incoming track impact pointand the space angle with respect to the beam axis as measured withthe beam chambers; the electron events were removed by the requirement that the energydeposited in the LAr calorimeter is less than 90 % of the beam energy; a cut on the total energy rejects incoming muon; the events with the obvious longitudinal leakage were removed byrequiring of no signal from the punchthrough particles in the muonwalls;4 to select the events with the hadronic shower origins in the firstsampling of the LAr calorimeter; events with the energy depositionsin this sampling compatible with that of a single minimum ionizationparticle were rejected; to select the events with the well developed hadronic showers energydepositions were required to be more than 10 % of the beam energyin the electromagnetic calorimeter and less than 70 % in the hadroniccalorimeter.4 The e/h ratio of the LAr ElectromagneticCompartmentThe response, Rh, of a calorimeter to a hadronic shower is the sum ofthe contributions from the electromagnetic, Ee, and hadronic, Eh, parts ofthe incident energy [11]E = Ee + Eh , (1)Rh = e Ee + h  Eh = e  E  (fpio + (h/e)  (1− fpio)) , (2)where e (h) is the energy independent coefficient of transformation of theelectromagnetic (pure hadronic, low-energy hadronic activity) energy toresponse, fpio = Ee/E is the fraction of electromagnetic energy. From thisE =epi 1e Rh , (3)whereepi=e/h1 + (e/h− 1)fpio . (4)In the case of the combined calorimeter the incident beam energy,Ebeam, is deposited into the LAr compartment, ELAr, into Tilecal com-partment, ET ile, and into the dead material between the LAr and Tilecalorimeters, Edm,Ebeam = ELAr + ET ile + Edm . (5)Using relation (3) the following expression has been obtained:Ebeam = cLAr ( epi)LAr RLAr + cT ile ( epi)T ile RT ile + Edm , (6)5where cLAr = 1/eLAr and cT ile = 1/eT ile. From this expression the value ofthe (e/pi)LAr ratio can be obtained( epi)LAr=Ebeam − ET ile − EdmcLAr  RLAr , (7)whereET ile = cT ile ( epi)T ile RT ile (8)is the energy released in the Tile calorimeter.The (e/h)LAr ratio andfpio,LAr = kLAr  lnEbeam (9)can be inferred from the energy dependent (e/pi)LAr ratios:( epi)LAr=(e/h)LAr1 + ((e/h)LAr − 1)fpio,LAr . (10)We used the value (e/h)T ile = 1.3 [4] and the following expression forthe electromagnetic fraction of a hadronic shower in the Tilecal calorimeterfpio,T ile = kT ile  lnET ile. (11)with kT ile = 0.11 [12], [13].For the cLAr constant the value of 1.1, obtained in [14], [7], was used.The algorithm for finding the cT ile and cdm constants will be consideredin the next section.5 The cT ile ConstantFor the determining of the cT ile constant the following procedure wasapplied. We selected the events which start to shower only in the hadroniccalorimeter. To select these events the energies deposited in each samplingof the LAr calorimeter and in the midsampler are required to be compatiblewith that of a beam particle. We used the following expression for thenormalized hadronic response [11]RcT ileEbeam=cT ile(e/h)T ile(1 +(( eh)T ile− 1) (fpi0)T ile) , (12)6whereRcT ile = RT ile +cLArcT ile RLAr (13)is the Tile calorimeter response corrected on the energy loss in the LArcalorimeter, fpi0,T ile is determined by the formula (11).The values of RcT ile are shown in Fig. 2 together with the fitting line.The obtained value of cT ile is equal to 0.145 0.002.6 The Energy Loss in the Dead MaterialSpecial attention has been devoted to understanding of the energyloss in the dead material placed between the active part of the LAr andthe Tile detectors. The term, which accounts for the energy loss in thedead material between the LAr and Tile calorimeters, Edm, is taken tobe proportional to the geometrical mean of the energy released in the lastelectromagnetic compartment (ELAr,3) and the first hadronic compartment(ET ile,1)Edm = cdm √ELAr,3 ET ile,1 (14)similar to [7], [15]. The validity of this approximation has been tested bythe Monte Carlo simulation and by the study of the correlation between theenergy released in the midsampler and the cryostat energy deposition [7],[16], [17]. We used the value of cdm = 0.31. This value has been obtainedon the basis of the results of the Monte Carlo simulation performed byI. Efthymiopoulos [18]. These Monte Carlo (Fluka) results (solid circles)are shown in Fig. 3 together with the values (open circles) obtained byusing the expression (14). The reasonable agreement is observed. Theaverage energy loss in the dead material is equal to about 3.7%. Thetypical distribution of the energy losses in the dead material between theLAr and Tile calorimeters for the real events at the beam energy of 50GeV , obtained by using Eq. 14, is shown in Fig. 4.7 The (e/pi)LAr and (e/h)LAr Ratios.Figs. 5 and 6 show the distributions of the (e/pi)LAr ratio derived byformula (7) for different energies. The mean values of these distributionsare given in Table 1 and shown in Fig. 7 as a function of the beam energy.The fit of this distribution by the expression (10) yields (e/h)LAr = 1.7470.04 and kLAr = 0.1080.004 (χ2/NDF = 0.93). For the fixed value of theparameter kLAr = 0.11 [12] the result is (e/h)LAr = 1.770.02 (χ2/NDF =0.86). The quoted errors are the statistical ones obtained from the fit.The systematic error on the (e/h)LAr ratio, which is a consequence of theuncertainties in the input constants used in the equation (7), is estimatedto be 0.04.Wigmans showed [12] that the the e/h ratio for non-uranium calorime-ters with high-Z absorber material is satisfactorily described by the for-mula:eh=e/mip0.41 + 0.12 n/mip(15)in which e/mip and n/mip represent the calorimeter response to e.m. show-ers and to MeV-type neutrons, respectively. These responses are normal-ized to the one for minimum ionizing particles. The Monte Carlo calculatede/mip and n/mip values for the RD3 Pb-LAr electromagnetic calorime-ter are e/mip = 0.78 and n/mip < 0.5 leading to (e/h)LAr > 1.66. Ourmeasured value of the (e/h)LAr ratio agrees with this prediction.There is the estimation of the (e/h)LAr ratio of 3.7 1.7 for this elec-tromagnetic compartment obtained in [19] on the basis of data from thecombined lead-iron-LAr calorimeter [20]. This value agrees with our valuewithin errors. But we consider their method as the incorrect one since forthe determination of the (e/pi)LAr ratios the calibration constants are usedwhich have been obtained by minimizing the energy resolution that leadsto distortion of the true (e/pi)LAr ratios.8 ConclusionsThe method of extraction of the e/h ratio, the degree of non-compensa-tion, for the electromagnetic compartment of the ATLAS barrel combinedprototype calorimeter is suggested. On the basis of the 1996 combined testbeam data we have determined this value which turned out to be equal to1.74 0.04 and agrees with the Monte Carlo prediction of Wigmans thate/h > 1.7 for this LAr calorimeter.89 AcknowledgmentsThis work is the result of the efforts of many people from the ATLASCollaboration. The authors are greatly indebted to all Collaboration fortheir test beam setup and data taking. Authors are grateful Peter Jenniand Marzio Nessi for fruitful discussion and support of this work. Weare thankful Julian Budagov and Jemal Khubua for their attention andsupport of this work. We are also thankful Illias Efthymiopoulos for givingthe results of the Monte Carlo simulation, Irene Vichou and Marina Cobalfor constructive advices and fruitful discussion.References[1] ATLAS Collaboration, ATLAS Technical Proposal for a General Pur-pose pp Experiment at the Large Hadron Collider, CERN/LHCC/94-93, CERN, Geneva, Switzerland.[2] F. Ariztizabal et al., NIM A349 (1994) 384.[3] A. Juste, ATLAS Internal note, TILECAL-No-69, 1995, CERN,Geneva, Switzerland.[4] J.A. Budagov, Y.A. Kulchitsky, V.B. Vinogradov et al., JINR, E1-95-513, 1995, Dubna, Russia; ATLAS Internal note, TILECAL-No-72,1996, CERN, Geneva, Switzerland.[5] ATLAS Collaboration, ATLAS TILE Calorimeter Technical DesignReport, CERN/LHCC/96-42, ATLAS TDR 3, 1996, CERN, Geneva,Switzerland.[6] Y.A. Kulchitsky, V.B. Vinogradov, JINR, E1-99-12, 1999, Dubna,Russia; ATL-TILECAL-99-002, 1999, CERN, Geneva, Switzerland.[7] M. Cobal et al., ATL-TILECAL-98-168, 1998, CERN, Geneva,Switzerland.[8] ATLAS Collaboration, ATLAS Liquid Argon Calorimeter TechnicalDesign Report, CERN/LHCC/96-41, ATLAS TDR 2, 1996, CERN,Geneva, Switzerland.[9] D.M. Gingrich et al., (RD3 Collaboration), NIM A364 (1995) 290.9[10] O. Gildemeister, F. Nessi-Tedaldi and M. Nessi, Proc. 2nd Int. Conf.on Calorimetry in High Energy Physics, Capri, 1991.[11] D. Groom, Proceedings of the Workshop on Calorimetry for the Su-percollides, Tuscaloosa, Alabama, USA, 1989.[12] R. Wigmans, Proc. 2nd Int. Conf. on Calorimetry in High EnergyPhysics, Capri, 1991.[13] D. Acosta et al., NIM A316 (1992) 184.[14] Y.A. Kulchitsky, M.V. Kuzmin, JINR, E1-98-336, 1998, Dubna, Rus-sia.[15] Z. Ajaltouni et al., NIM A387 (1997) 333 – 351.[16] M. Bosman, Y.A. Kulchitsky, M. Nessi, ATL-COM-TILECAL-99-011,CERN, Geneva, Switzerland.[17] ATLAS Collaboration, ATLAS Physical Technical Design Report,Volume 1, CERN-LHCC-99-02, ATLAS-TDR-14, CERN, Geneva,Switzerland.[18] I. Efthymiopoulos, Private communication.[19] M. Stipcevic, RD3 Note 44, 1993, CERN, Geneva, Switzerland.[20] D.M. Gingrich et al., [RD3 Collaboration], NIM A355 (1995) 295.10Table 1: The mean (e/pi)LAr ratio as a function of the beam energy.Ebeam(GeV ) (e/pi)LAr10 1.471 0.02520 1.419 0.01540 1.331 0.01750 1.330 0.01980 1.276 0.010100 1.278 0.009150 1.255 0.009300 1.191 0.014EM AccordionTilecalMuon WallCryostatMidsamplerS3-4BC 3µ, e, pi  Θ = 12.00 1 2 m 10 GeV     300 GeVFigure 1: Test beam setup for the ATLAS combined prototype calorimeter.115.866.26.440 50 60 70 80 90 100EBeam (GeV)RTile/EBeam (pC/GeV)Figure 2: The corrected RT ile response as a function of the beam energy.12234510 102EBeam  (GeV)Edm/EBeam (%)Figure 3: The comparison between the Monte Carlo simulation (solid cir-cles) and the calculated values (open circles) for the average relative energylosses in the dead material, Edm/Ebeam, as a function of the beam energy.1311010 20 5 10 15 20Energy Loss in Gap (GeV)Number of EventsFigure 4: The distribution of energy loss in the dead material for 50 GeVpion beam.140204060800 1 2 3(e/pi)LArNumber of Events02550751000 1 2 3(e/pi)LArNumber of Events01002000 1 2 3(e/pi)LArNumber of Events0501001500 1 2 3(e/pi)LArNumber of EventsFigure 5: The distributions of the (e/pi)LAr ratio for Ebeam = 10, 40 GeV(left column, up to down) and Ebeam = 20, 50 GeV (right column, up todown).1501002003000 1 2 3(e/pi)LArNumber of Events01002000 1 2 3(e/pi)LArNumber of Events01002003000 1 2 3(e/pi)LArNumber of Events01002000 1 2 3(e/pi)LArNumber of EventsFigure 6: The distributions of the (e/pi)LAr ratio for Ebeam = 80, 150 GeV(left column, up to down) and Ebeam = 100, 300 GeV (right column, up todown).161.11.21.31.41.510 102EBeam (GeV)(e/pi) LArFigure 7: The mean values of the (e/pi)LAr ratios as a function of the beamenergy. The line is the result of a fit of eq. (10).17

Non-compensation of an Electromagnetic Compartment of a Combined Calorimeter

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