The LHCb Calorimeter System

The LHCb Calorimeter System

Nuclear Physics B (Proc. Suppl.) 177–178 (2008) 310–311 www.elsevierphysics.com The LHCb Calorimeter System Machikhiliyan Irinaa ∗ for the LHCb Cal...

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Nuclear Physics B (Proc. Suppl.) 177–178 (2008) 310–311 www.elsevierphysics.com

The LHCb Calorimeter System Machikhiliyan Irinaa



for the LHCb Calorimeter group

a

Institute for Theoretical and Experimental Physics, SSC RF ITEP, Bolshaya Cheremushkinskaya, 25 117218 Moscow Russia The Calorimeter System for the LHCb experiment is described.

1. GENERAL DESIGN DESCRIPTION The Calorimeter System of the LHCb detector[1] comprises four components (subsystems): Scintillator Pad Detector (SP D), Preshower Detector (P S), Electromagnetic (ECAL) and Hadron (HCAL) Calorimeters (see Fig. 1). Their combined information is used to seed LHCb trigger system with high transverse energy (ET ) electron/photon (ECAL) and hadron (HCAL) candidates. SP D is responsible for early e/γ discrimination, while P S is essential in e/π separation and improvement of ECAL energy measurement. At the stage of data analysis Calorimeter System provides precise parameters of γ’s, thus giving an opportunity to reconstruct B-decay channels containing prompt photon or π 0 . All four subsystems employ similar design of projective rectangular wall-like structures (solid angle coverage 300×250 mrad except central 30 mrad cut-out for beam pipe) divided in square cells with variable size following the steep hit density dependence on the distance from the beam pipe. Similar technologies of sampling scintillator/absorber structure are employed in all components. Light collection system is made of wavelength-shifting (W LS) fibers; photomultipliers (P M T ) are used as photo-detectors. P M T signals are digitized and processed by Front-End electronics, which shapes and integrates P M T signal at 40 MHz rate without any dead time as well as subtracts pileup from previous bunchcrossings. Stability of P M T s is traced by LEDbased Monitoring System. For SP D/P S each cell is illuminated with an individual LED embedded ∗ Present address: European Organization for Nuclear Research CERN CH-1211 Geneve 23 Switzerland

0920-5632/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.nuclphysbps.2007.11.138

SPD Preshower ECAL

Outer section

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Inner section

Middle section

particle stream

beam pipe cut−out

Lead absorber

HCAL

Figure 1. LHCb Calorimeter System: schematic view

directly in the scintillator tile body. As concerns ECAL/HCAL, LEDs are located outside detector area, each of them monitors large group of cells. LED light transportation and distribution is performed via long-distance clear fibers. Additional PIN-diodes system is foreseen to correct for the LEDs instability themselves. Basic subsystems parameters are summarized in Table 1. SP D and Preshower are organized as two layers of 15 mm thick scintillator tiles interleaved with 14 mm thick lead wall. W LS fiber loop is embedded into each tile, its output is coupled with long clear fiber transporting light outside the detector area to multi-anode photomultiplier (M aP M T ). Each tile is read out by one M aP M T pixel. ECAL employs ’shashlik’ technology. Basic con-

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Table 1 LHCb Calorimeter System: general parameters Lateral size, m×m Z-position, m Longitudinal size Number of channels Max radiation dose, kGy/year Basic requirements Dynamic range

SP D/P S 6.2 × 7.6 12.3 2.5X0 6016/6016 ∼ 1.2

ECAL 6.3 × 7.8 12.5 25X0 , 1.1λI 6016 2.5

HCAL 6.8 × 8.4 13.3 5.6λI 1488 0.5

20 ÷ 30p.e./M IP 100 M IP s 1/10 bits

√  10%/ E 1.5% 10 GeV ET 12 bits

√  80% E 10% 10GeV ET 12 bits

struction unit is a module, implemented as a rectangular stack of alternating lead/scintillator layers perpendicular to the beam direction. Required lateral segmentation is achieved by different number of readout cells per module. Minimal cell size is compatible with the Moliere radius of the ECAL media (3.5 cm). W LS fibers running parallel to the beam axis penetrate entire module length. All fibers serving given cells are bundled together at the rear side of the module and coupled with P M T window via prism light mixer. In each cell an additional clear fiber penetrating through the stack delivers monitoring LED light from the optical connector in the front of module to the P M T window. HCAL consists of interleaving scintillator tiles and iron plates, running parallel to the beam axis. W LS fibers follow the same direction along the edges of the tiles. Each fiber penetrates the entire depth of the HCAL wall. To compensate light extinction effects the length of fiber optical contact with tile progressively increases as relative tile position with respect to HCAL rear side. Readout cell is formed by grouping together a set of W LS fibers which is readout by an individual P M T located at the rear side of the detector wall. Unlike SP D/P S and ECAL, which will be calibrated with physical signals only, HCAL is equipped with an embedded calibration system on the basis of movable radioactive source 137 Cs, which allows to measure the response of each individual scintillator tile.

2. CURRENT STATUS Currently LHCb Calorimeter System undergoes commissioning stage. All subsystem walls are installed, cabling and installation of FrontEnd electronics are almost finished. All detector cells are precalibrated with precision better than 10% with a help of test beam or cosmic rays facilities. Extensive studies of components performance, conducted for last three years in parallel, had shown that basic detectors parameters comfortably meet project demands[2]. In particular, measured average light yield is equal to 20÷30 photoelectrons (p.e.)/M IP for SP D/P S, 2500÷3500 p.e./GeV for ECAL and 105 p.e./GeV for √ HCAL. √  are  Energy resolutions found to be 8%/ E 0.8% and 67% E 9% for ECAL and HCAL correspondingly. 3. ACKNOWLEDGMENTS Author is mostly grateful to S. Barsuk, I. Belyaev, V. Egorychev, Yu. Gilitsky, A. Golutvin, Yu. Guz and A. Schopper for useful comments and valuable discussion. REFERENCES 1. LHCb Technical Proposal, CERN-LHCC-984, 1998. 2. LHCb Calorimeters: Technical Design Report, CERN-LHCC-2000-036, 2000.