We present a description of the CMS central hadron calorimeter. We describe
the production of the 1996 CMS hadron testbeam module. We show the results of
the quality control tests of the testbeam module. We present some results of
the 1995 CMS hadron testbeam.Comment: 7 pages, 11 Figures, corresponding author: H. Budd, hbudd@fnal.go

Albrow

de Barbaro

Foster

Freeman

Howard S. Budd

Kryshkín

Swenberg

English

arXiv

Crossref

CMS Central Hadron Calorimeter

We present a description of the CMS central hadron calorimeter. We describe the production of the 1996 CMS hadron testbeam module. We show the results of the quality control tests of the testbeam module. We present some results of the 1995 CMS hadron testbeam

Budd, Howard S.

CERN Document Server

1CMS Central Hadron CalorimeterHoward S. BuddaaDepartment of Physics and Astronomy, University of Rochester, Rochester, NY 14627We present a description of the CMS central hadron calorimeter. We describe the production of the 1996 CMShadron testbeam module. We show the results of the quality control tests of the testbeam module. We presentsome results of the 1995 CMS hadron testbeam.1. CMS Central Hadron CalorimeterThe design of the CMS detector starts with the4 T solenoidal magnet of length 13 m and innerdiameter 5.9 m. The magnet determines many ofthe features of the CMS calorimeters, since theCMS calorimeter is located inside the magnet.Figure 1 shows a quarter slice of the CMS upto the coil. The EM calorimeter, ECAL, consistsof lead tungstate, PbW04, crystals. The hadroncalorimeter, HCAL, surrounds ECAL. The mostimportant requirement of HCAL is to minimizethe non-gaussian tails of the energy resolutionfunction. Hence, HCAL design maximizes asmuch interaction length of material inside themagnetic coil as possible. Copper absorber sat-ises this requirement, as well as being nonmag-netic. In addition, copper is fairly low Z, so itdoes not degrade the muon momentum measure-ment. Maximizing the amount of absorber beforethe magnet requires minimizing the amount ofspace devoted to active medium. The tile/bertechnology is an ideal choice. It consists of plas-tic scintillator tiles read out with embedded wavelength shifting (WLS) bers. This technology wasrst developed by the UA1 collaboration and atProtvino [1]. The system is being used in theupgrade of the CDF endcap calorimeter [2]. Itenables HCAL to be easily built with a tower ge-ometry readout. The entire HCAL area can beinstrumented with no uninstrumented cracks.HCAL covers the pseudorapidity range || <3.0with a barrel (central) and endcap hadroncalorimeter. The barrel calorimeter covers0< || <1.4, while the endcap calorimeter cov-ers down to ||=3.0. The region to ||=5.0 iscovered by a very forward calorimeter. HCALis segmented into towers of granularity  ×=0.087×0.087. This granularity is sucientfor good dijet mass resolution. The rest of this ar-ticle will only discuss the barrel hadron calorime-ter.HCAL is built as 20o wedges inside the magnet.Figure 2 shows a 20o wedge, with ECAL on theright side and HCAL on the left side. The bodyof wedges are copper, but the inner and outerplates are stainless steel for structural strength.The wedges are bolted together. This enables thewedges to be assembled cheaply and minimizesthe crack between the wedges to ≤ 2 mm. Thewedges contain 15 active layers segmented into 2readouts. A space of 9 mm is left for active layers.The HCAL is about 1 meter thick inside the mag-net, 6.2  at =0. This is not enough materialto contain a high energy hadron shower. Hence,2 layers are instrumented outside the magnet. Alayer of scintillator is put after the coil and afterthe innermost muon steel. This adds an addi-tional 4  at =0.The active medium uses the tile/ber conceptas used by the CDF plug upgrade. The hadroncalorimeter consists of about 70,000 individualtiles. In order to limit the number of individualelements, the tiles of a given layer are put intoa single mechanical unit called a megatile. Fig-ure 3 displays a typical megatile. The megatilewith segmentation of 16()×2() goes into the center of a wedge while the megatile with seg-mentation 16()×1() goes into the edge slots ina wedge. Each layer has 108 megatiles. Figure 4shows a cross section of the megatile. The scintil-lator is surrounded by Tyvek 1073D for reflectiv-2Figure 1. CMS electromagnetic detector, hadronic detector, and solenoidal magnet.Figure 2. Drawing of 20o wedge.3Figure 3. CMS electromagnetic detector, hadronic detector, and solenoidal magnet.ity. The scintillator and Tyvek are surrounded bytedlar for light tightness. The top plastic routesthe bers and source tubes.The baseline scintillator is 4 mm KuraraySCSN81. The scintillator is read out by a WLSber, Kuraray multiclad Y-11 (Fluor K27), em-bedded in the tile in a  pattern. Outside thescintillator, the WLS ber is spliced to Kuraraymulticlad clear ber. Next, the clear ber goesto an optical connector at the end of the pan.An optical cable takes the light to an optical de-scrambler. The descrambler arranges the bersinto readout towers and brings the light to a hy-brid photomultiplier tube (HPMT). Since the de-scrambler will be operating in the 4 T magneticeld, conventional phototubes will not work.The HPMT consists of a photocathode and aPIN diode separated by ∼ 1 mm. The photoelec-trons from the photocathode are accelerated tothe PIN diode by high voltage, ∼ 10,000 volts.The HPMT has a gain of 1000 to 2000. If theelectric eld is aligned with the magnetic eld,they can operate in a magnetic eld of 4 T. Thismakes them suitable for CMS HCAL.Figure 4. Cross section view of a megatile.4Figure 5. Megatile for 1996 CMS HCAL test-beam.2. CMS hadron calorimeter test beamWe have built modules for a 1995 and 1996 test-beam at CERN. The purpose of the testbeam isto determine the response of the calorimeter ina magnetic eld and to determine the resolutionof the combined ECAL and HCAL calorimeter.To determine the response in a magnetic eld,the calorimeter was put inside the EPS magnetin the H2 beam line at CERN. We describe thecalorimeter and its production to illustrate theproduction of the real device and show some ofthe quality control tests we will use for the realdevice. All numbers we quote for the quality con-trol are for the 1996 testbeam module.2.1. 1996 HCAL Testbeam MegatileFigure 5 shows the megatile for the 1996 test-beam. The active area is 64 cm by 64 cm andconsists of 9 separate towers. The transverse sizeof the testbeam megatile is determined by size ofthe center of the EPS magnet. Embedded in eachtile is a WLS ber in the  pattern. Outside thetile, the WLS bers are spliced to multiclad clearbers. The clear bers are routed out to a con-nector at the end of the megatile. The ber on theleft going into the middle tile is a light injectionber. For calibration purposes light is injectedinto the tile through this ber. The megatile has3 thin stainless steel tubes, diameter=1 mm, thatwill route Cs137 radioactive sources through thecenter of each tile. A picoammeter measures thecurrent generated by the source to simultaneouslycalibrate the tile, bers, and photodetector.The elements for the megatile are drawn on aCAD system. The drawings are converted to ma-chine code which can be run on a computer con-trolled router, a Thermwood machine.We describe the production and quality controlof the device. First the WLS bers are cut, pol-ished, and mirrored. The reflectivity of the mirroris checked by measuring test bers which are mir-rored along with the bers used in the calorime-ter. Measuring the reflectivity of the mirror giveslightwith mirror=lightwith mirror cut off = 1:85This measurement is done with a computer con-trolled UV scanner with the bers read out by pindiodes. Clear bers are spliced onto WLS berswith a fusion splicer. The transmission acrossthe splice is checked by splicing a sample of WLSbers onto WLS bers. The splice region is mea-sured with the UV scanner. The transmissionacross the splice is 92.6% with an RMS of 1.8%.Next, the optical bers are glued into a 10 berconnector. This conguration is called a pigtail.In order to get the ber lengths correct, the pig-tail is assembled in a templet. The connector isdiamond polished. The bers are measured withthe UV scanner. The scanner checks the greenber, clear ber, splice, and mirror. The RMS ofthe light from the bers is 1.9%.The pigtail is inserted into the megatile. Thecompleted megatile is checked with an automatedsource scanner. A Cs137 source is in a lead colli-mator. This yields a 4 cm diameter source spoton the megatile. The collimator is moved with acomputer controlled x-y motor. From the scannerwe determine the relative light yield of each tileand the uniformity of the each megatile. The gain5of the individual tiles has an RMS of 4.6%, whilethe transverse uniformity of the megatile is 4.5%.A Cs137 wire source is run through the 3 sourcetubes and the light yield is measured. The RMSof the ratio of collimated source to wire sourceis 1.3%. This means the line sources, which canbe used when the calorimeter is completely as-sembled, can calibrate the tiles to better than1.3%. Fiber cables are constructed separately andtested with the UV scanner.The testbeam module has several methods tomaintain the calibration. As just described, it hassmall steel tubes to run a wire source. It has alaser and LED light injection system. The pho-tomultiplier tube that reads out the calorimeterhas an addition ber going to it. Either a laseror an LED can inject light into this ber. Dur-ing the testbeam we injected light with both thelaser and LED. As shown on the drawing of themegatile, there is a ber which can inject lightinto a tile. A more complete description of thecalibration, including procedures for calibratingthe full calorimeter, is given in ref [4].2.2. 1995 HCAL Testbeam ResultsWe present results from the 1995 testbeam. Re-sults for the 1996 testbeam are not yet nal. Fig-ure 6 shows the testbeam congurations. For thePb/scin ECAL module, ECAL is the 10 layerlead/scintillator sandwich sampling calorimeter,positioned directly upstream of the HCAL. TheHCAL corresponds to the end cap conguration(5 cm and 10 cm copper absorber plates in HAC1and HAC2 respectively). For the PbWO4 crystalECAL module, the ECAL detector (7 × 7 matrixof 2 cm by 2 cm by 23 cm PbWO4 crystals) isfollowed by the HCAL in the barrel conguration(3 cm and 5 cm copper absorber plates in HAC1and HAC2 respectively). There is approximately46 cm air gap between the end of ECAL and thefront face of HCAL. Each layer for both congu-rations is readout by a phototube connected to a10 m optical cable.Figure 7 shows the average pion and electronresponse of the calorimeter, as a function of theB eld, relative to the 0 T setting. The dataindicates an approximate 6% increase in the re-sponse of the calorimeter to pions and electronsNO B FIELDB FIELDFigure 6. Schematic drawing of the calorimetermodules used during the 1995 test beam.for B eld at 1 T, 2 T, and 3 T. The measurementis consistent with the increased light yield of thescintillator tiles, as measured by the calibrationsystem using the radioactive γ source. The 1996test beam run had the magnetic eld transverseto the beam direction. The result is dierent ifthe magnetic eld is transverse to the beam di-rection. A discussion is in ref [4] and will be infuture presentations of the 1996 test beam.The overall calibration constant of the hadroncalorimeter is determined by using 50 GeVhadrons, and the overall calibration constant ofEM calorimeter is determined using 150 GeV elec-trons. The total energy of pions is dened asEpionstot = × Eem + Ehadwhere  is a parameter we vary to study linearityand resolution. Figure 8 shows the linearity of thePb/scin ECAL conguration for pions which areminimum ionizing (mip) in ECAL and all pions(=1). The energy resolutions for the 2 cases arecomparable. The t of this data to the relative6Figure 7. H2 Test Beam results: average pion,average electron, and Cs137 source response of thecalorimeter, as a function of the B eld.0.750.80.850.90.9511.051.10 50 100 150 200 250 300 350 400Figure 8. Linearity of Pb/scin ECAL module.0.750.80.850.90.9511.051.10 50 100 150 200 250 300 350 400Figure 9. Linearity of PbWO4 crystal module forhadrons.energy resolution function isE=E = (stoch: term)=√E ⊕ (const: term)where stochastic and constant terms are com-bined in quadrature. For pions which are mipin ECAL we havepi mip in ECALE =E =(90± 0:1)%=√E ⊕ (4:8± 0:1)%:For the case of all pions we haveall piE =E =(77± 0:1)%=√E ⊕ (5:5± 0:1)%:At low energies the energy resolution of all pionsis narrower than pions which are mip in ECALdue to the ne sampling of the ECAL calorimeter.Figure 9 and Figure 10 show the linearityand resolution of the PbWO4 crystal congura-tion for hadrons mip in ECAL and all hadrons.Hadrons mip in ECAL have the same linearity7and resolution in both congurations. However,the PbWO4 crystal data for all pions (=1) isnon-linear. The average response of the com-bined ECAL+HCAL calorimeter to pions is alsoapproximately 10% lower than the HCAL onlycalorimeter. The resolution is much worse for allpions than pions mip in ECAL. The linearity andresolution is shown for =1.4. Although both thelinearity and resolution are improved, this type ofenergy sum cannot be used for jets.Figure 11 shows the scatter plot of the to-tal energy response of the calorimeter nor-malized the beam momentum, ETOT =pbeam =(EEM + EHAD)=pbeam as a function of the frac-tion of energy deposited in the ECAL, fEM =EEM=(EEM +EHAD). Data points with fEM ≈ 0correspond to pions that interacted in the HCAL.Data with fEM ≈ 1 correspond to pions fullycontained in the ECAL. A t of the data binnedas a function of fEM to a second degree polyno-mial is shown on the gure. The tted functioncorr(fEM ) is used to correct the total energy.EcorTOT = (EEM + EHAD)=corr(fEM )The linearity and resolution are shown on Fig-ure 9 and 10 for the fEM corrected data. Thecorrection improves the linearity and resolution.REFERENCES1. V.I. Kryshkin and A.I. Ronzhin, Nucl. In-strum. Methods, A247 (1986) 583.; M.G. Al-brow et al., Nucl. Instrum. Methods, A256(1987) 232. G.W. Foster, J.Freeman, and R.Hagstrom,Nucl. Phys. B, A23 (1991) 93; P. de Barbaroet al., Nucl. Instrum. Methods, A315 (1992)317; P. de Barbaro and A. Bodek, A Compi-lation of Tile/Fiber R&D Results, Universityof Rochester Preprint UR-1389 (1994)3. C. Swenberg and N.E. Geacintov, OrganicMolecular Photophysics, Vol I, J. Birks, ed.,J. Wiley and sons, New York, 19734. J. Freeman, The CMS Central HadronCalorimeter, Proc. VI International Confer-ence on Calorimetry in High-Energy Physics,Frascati, Italy, June 8-14, 199600.050.10.150.20.250.30.350 50 100 150 200 250 300 350 400Figure 10. Resolution of of PbWO4 crystal ECALmodule for hadrons.0.50.60.70.80.911.11.21.31.41.50 0.2 0.4 0.6 0.8 1Figure 11. Energy response to pions, as a functionof ECAL fraction for the PbWO4 crystal ECALmodule.

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CMS Central Hadron Calorimeter

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