Arteaga, J

Cerna, A

Fernandez, A

Gamez, E

García, J

Herrera, G

Lopez, R

Martínez, M I

Ortiz, A

Paic, G

Pelayo, R

Roman, S

Tejeda, G

Vargas, M A

Vergara, S

Villasenor, L

Zepeda, A

CERN Document Server

29th International Cosmic Ray Conference Pune (2005) 9, 5760ACORDE, a cosmic ray detector for ALICEJ. Arteaga , A. Cerna , A. Ferna´ndez, E. Ga´mez, J. Garcı´a , G. Herrera , M. I. Martı´nez,R. Lo´pez, , A. Ortiz, G. Paic, R. Pelayo , S. Roma´n, G. Tejeda , M. A. Vargas,S. Vergara, L. Villasen˜orand A. Zepeda (a) Centro de Investigacion y de Estudios Avanzados, Mexico, Mexico(b) Benem·erita Universidad Autonoma de Puebla, Puebla, Mexico(c) Inst. Ciencias Nucleares, Universidad Nacional Autonoma de Mexico, Mexico, Mexico(d) Inst. Fisica y Matematicas, Universidad Michoacana de San Nicolas de Hidalgo, Morelia, MexicoPresenter: A. Zepeda (zepeda@fis.cinvestav.mx), mex-zepeda-A-abs1-he21-posterALICE is an experiment devoted to heavy ion physics at LHC. The underground location of the apparatus with30 m of overburden can be exploited for studying cosmic rays through the muons reaching the experiment. TheALICE setup includes a cosmic ray trigger system (ACORDE), a big TPC designed to track large densitiesof charged particles, a TRD and a TOF all of which can be used for the detection of atmospheric muons.These instruments open new possibilities on the study of cosmic ray physics, mainly in the range of primaryenergies around 	 eV. Here we discuss the design of ACORDE, including the performance of the plasticscintillator material available to build the ACORDE counter array, the simulated response of this array toatmospheric muons arriving at the ALICE hall, as well as the proposed electronics design for this cosmic raytrigger. We also discuss the integration of the ACORDE scintillator array into the ALICE detector.1. IntroductionALICE is an experiment designed to detect the products of heavy nuclei collisions at the LHC at CERN in orderto study the physics of strongly interacting matter and the possible formation of quark-gluon plasma [1]. It willbe located in the same place in which the L3 experiment was installed. The underground site of the ALICEapparatus with 30 m of overburden composed of subalpine molasse is ideal for muon based experiments.The ALICE cosmic ray trigger, shown in Figure 1, is based on the ACORDE sub-detector, an array of 60plastic scintillator modules placed on the top sides of the central magnet. The central part of the ALICEapparatus consists of an Inner Tracking System (ITS), unuseful for our purposes due to its small size, a largevolume Time Projection Chamber (TPC), a high granularity Transition Radiation Detector (TRD) and a TimeOf Flight (TOF) detector with a high resolution array (Particle Identification Detector). Additional detectors donot cover the whole azimuth angle. The ACORDE array and the TPC are the main detectors for atmosphericmuons, while the TRD and TOF can improve the tracking performance. The molasse above imposes an averageenergy threshold for atmospheric muons reaching the experiment of  GeV cutting all the hadronicand electromagnetic components, while the upper energy limit for reconstructed muons will be less than 2 TeV,depending of the magnetic field intensity (up to 0.5 T).ACORDE will provide a fast L0 trigger signal, to the central trigger processor, when atmospheric muonsimpinge upon the ALICE detector. The signal will be useful for calibration, alignment and performance ofseveral ALICE tracking detectors, mainly the TPC and the ITS. The cosmic ray trigger will be capable todeliver signals before and during the operation of the LHC beam. The typical rate for single atmosphericmuons crossing the ALICE cavern will be less than 3-4 Hz/m ﬀ [2]. The rate for multi-muon events will belower (less than 0.04 Hz/m ﬀ [3]) but sufficient for the study of these events provided that one can trigger andstore tracking information from cosmic muons in parallel to ALICE normal collider data taking.58 J. Arteaga et alFigure 1. Left: General view of the ALICE setup. Right: ACORDE array, TPC, TOF and TRD detectors, used to detectatmospheric muons.2. Performance of the ACORDE scintillator countersAn ACORDE module consists of two plastic scintillator paddles with ﬂﬁﬃﬁ! ﬃ cm ﬀ effective area, arranged ina doublet configuration. Each doublet consists of two superimposed scintillator counters with their correspond-ing photomultipliers active faces looking back to back, see Figure 2. A coincidence signal (in a time windowof 40 ns) from this two scintillator paddles will be the useful information from each module. We developed aPCI BUS electronics card to measure the plateau and efficiency of the ACORDE counters. The PMT signalswere discriminated with a threshold of 15 mV. In average, a plateau voltage is reached at 1450-1550 V with ameasured rate of 73.4 Hz (at 2,200 m above the sea level). In order to measure the efficiency of the moduleswe took data at three positions along the doublet. We triggered on vertical muons by using a scintillation ho-doscope consisting of two plastic scintillation paddles with an active area of  "#$ " cm ﬀ , one placed above themodule and the other below it; the vertical separation between these paddles was 30 cm. In order to harden themuon spectrum and to get rid of low energy muons, we used a 1” steel slab just above the lower paddle. Thetrigger was given by the coincidence between the PMT signals from the two scintillation paddles within a timewindow of 100 ns. The trigger signal was obtained at a rate of around 0.17 Hz using the same NIM electronicsdescribed above for the plateau measurement. As mentioned above, the longitudinal overlap between the twoplastics, named A and B respectively, is 188 cm. The first position where we positioned our scintillation ho-doscope was 15 cm away from the start of the overlap, at the end closest to PMT A, the second position was atthe center of the overlap (i.e. 79 cm away from the first position) and the third at 15 cm away from the start ofthe overlap at the end closest to PMT B (i.e. 158 cm away from the first position). From now on we call thesepositions 15 cm from A, central and 15 cm from B, respectively. These data were saved in a PC and analizedoff-line. We measured the distributions for the voltage amplitude, integrated charge, rise times from 10% to50% and from 10% to 90%, as well as the arrival time of the pulses form PMT A and PMT B at a threshold of10% of their amplitudes for a number of modules chosen arbitraryly. In order to get the efficiencies we dividedthe number of events with amplitudes VA and VB above 15 mV and VA and VB below 350 mV by the numberof events with amplitudes VA and VB below 350 mV, for each of the three positions of each module tested.The efficiencies calculated this way for a typical module were 93.1%, 97.7% and 92.6% for each of the threepositions, respectively.ACORDE, a cosmic ray detector ... 59Figure 2. ACORDE module. This scintillatorcounter module consists of two superimposed scin-tillator counters with their corresponding photomulti-pliers active faces looking back to back. The activearea is %'&&(*)ﬂ+ cm , .In order to gain further understanding of the operational stateof the scintillation plastics we are using, we made a roughestimate of the attenuation length of light along the analyzedplastics. Given that we measured the amplitude and chargedistribution of PMT A and B for three test positions, we ob-tained the ratio of the charge collected by PMT A in theposition 15 cm from A to the charge collected in the centralposition. The most probable value (MPV) of the charge dis-tribution, for PMT A at first position is 33 pC and the MPVfor the same PMT A at the central position is 13 pC. Thisgives a charge ratio of 2.54 for plastic A. Likewise, the MPVfor PMT B at last position is 41 pC, whereas the MPV forPMT B at the central position is 17 pC. This gives a chargeratio of 2.41 pC for plastic B. Given that the distance be-tween the extreme positions and the central one is 79 cm,and assuming and exponential attenuation of light along theplastics, we get attenuation lengths of 84.7 cm and 89.8 cmfor plastic scintillator A and B of module 1, respectively. Werepeated these measurements for a number of modules ob-taining similar values for the efficiencies and the attenuationlengths.3. Electronics and Detector Control SystemThe signal of each ACORDE scintillator channel will be applied to a leading edge discriminator. The discrim-inators should convert the negative low signal coming from each PMT to a digital signal. These signals willbe analyzed to generate the single muon and the multi-coincidence trigger signals. In both cases we will usea tracking system to identify which ACORDE modules were hit. This information will be stored in a FIFOmemory before being sent to the DAQ system through the Detectors Data Link (DDL). The proposed systemwill contain a TTCrx chip in order to receive and decode the LHC clock signal and the trigger messages com-ing from the ALICE trigger system through the TTC partition. This TTCrx chip will be connected to a Dataheader generator. This generator will produce the data header using the trigger messages. This will supply thedata header and the hit information to the DAQ system. This interface will be used to receive and supply thedata to the Source Interface Unit (SIU). The SIU is part of the DAQ system and has two optical links, one canbe used to send data from the DAQ to ACORDE and the other can be used to send data from ACORDE to theDAQ system. One requirement is to set the multi-coincidence number remotely. The ACORDE electronicscan receive data from the DAQ system through one of the optical links of the DDL. We can use this opticallink to transmit the calibration signal and the multi-coincidence data from the DAQ system to the ACORDEelectronics. See Figure 3.We have developed a Detector control System (DCS) for ACORDE. The main tasks of this system are the mon-itoring and control of the necessary electrical and physical parameters to operate our detector. These includethe high voltage (HV) and low voltage (LV) power supplies, the front-end electronics (FEE) configuration pa-rameters, alarm handling, and parameter archiving. A general view of our DCS is shown in Figure 3. We planto use the SY1527 and the EASY [4] (Embedded Assembly SYstem) power supply systems from CAEN asthe HV and LV supplies respectively. The latter is a radiation- and high-magnetic-field tolerant power supply60 J. Arteaga et alsystem to be installed in the cavern racks to supply the LV for ACORDE. The SY1527 crate can hold up to 16boards. Ten of its slots will be filled with 12-channel HV boards (A1733N) to feed the 120 PMTs. We will alsoinstall the EASY Branch Controller (A1676A) board that can control up to 6 EASY crates. We will need twofull EASY 3000 crates each with five 12-channel 2–8 V boards (A3009) for the discriminators. The remainingfour channels for the ACORDE Electronics Card and the shoebox producing the TRD wake up signal will behosted by a third EASY 3000 crate with an additional A3009 board. The intrinsic grouping of the scintillatorsinto modules (each with a couple of scintillators and PMTs) and the fact that the FEE cards will be mounted onthe modules make it natural to select a detector-oriented hierarchy for our DCS. This hierarchy will allow usto independently control a single module in a simple way which can be useful for purposes of isolating, testingor calibrating it. There will be a total of 183 Control Units (CU) in the DCS; the parent ACORDE DCS with61 module CUs (M0 through M60). M1 to M60 will control each one of the modules respectively, includingits associated FEE card. Module 0 will take care of the LV supply to the electronics and TRD shoebox cards.clientOPCPVSSIICAEN OPC ServerOPC clientPVSSII120312013CAENEASYFEE4CAENSY1527PVSSIIHigh VoltageUser interfaceDatabaseACORDEControl roomEthernetHVLVLVFEECounting roomCavernEthernetMario I. MartinezPwr and ctrlDetector Electronics CardWake−up shoeboxFigure 3. Left: Scheme of the ACORDE electronics. Right: General view of the ACORDE-DCS.4. Physics topics of interestAn accurate measurement of the energy spectrum and charge ratio of atmospheric muons in the energy range20–2000 GeV can be performed in one year of data taking by ALICE, provided that a dedicated scintillatortrigger system (ACORDE) is added to the apparatus. ALICE will be also able to measure the atmosphericmuon flux and charge ratio at different zenith angles, giving information on hadrons created in the air showerand constraining the hadronic interaction models. Given the high spatial resolution of the ALICE TPC, wewill be able to resolve muon bundles with densities higher than 20 muons/m ﬀ , and analyze the momentum andthe charge of each muon of the bundle. This will bring the opportunity to study cosmic ray composition in therange of primary energies around the knee of the spectrum.References[1] ALICE Collaboration: J. Physics G. Nucl. Part. Phys. 30 (2004) 1517.[2] B. Alessandro, et. al., Proceedings of the 28th ICRC 2003, Tokyo, Japan, pp. 1203,Universal AcademicPress.[3] O. Adriani, et. al. (L3 + C Collaboration), NIMA, 488, (2002) pp. 209-225.[4] CAEN S.p.A., http://www.caen.it/nuclear/easy info.html

ACORDE, a cosmic ray detector for ALICE

ACORDE, a cosmic ray detector for ALICE

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