The high-resolution hypernuclear spectroscopy experiment at Jefferson Lab, Hall A (E94-107), needs unambiguous kaon identification. Due to the huge pion and proton background, the standard Hall A hadron particle identification, based on a time of flight and two aerogel threshold Cherenkov detectors, is not sufficient. For this task a proximity focusing C6F14/CsI RICH has been built. Recently, after some improvements to the mechanical structure of its wire chamber and to its electronics rate capability, the RICH has been tested with cosmic rays. This paper represents a status report of the RICH detector

B. Reitz

E. Cisbani

F. Cusanno

F. Garibaldi

Fabio Santavenere

Fausto Giuliani

G. de Cataldo

G. M. Urciuoli

L. Lagamba

M. Gricia

Maurizio Lucentini

R. De Leo

S. Colilli

English

Open Access Repository

ARTICLE IN PRESSNuclear Instruments and Methods in Physics Research A 525 (2004) 163–167*CorrespE-mail a(F. Cusann0168-9002/$doi:10.1016A RICH detector for strangeness physics in Hall Aat Jefferson LabF. Cusannoa,*, F. Garibaldia, E. Cisbania, S. Colillia, G. De Cataldob,R. De Leob, F. Giuliania, M. Griciaa, L. Lagambab, M. Lucentinia, B. Reitzc,F. Santavenerea, G.M. UrciuolidaLaboratory of Physics, Viale Regina Elena 299, ISS, 00161 Rome, Italyb INFN, Sezione di Bari, ItalycJefferson Lab, Newport News, VA, USAd INFN, Sezione di Roma I, ItalyAbstractThe high-resolution hypernuclear spectroscopy experiment at Jefferson Lab, Hall A (E94-107), needs unambiguouskaon identification. Due to the huge pion and proton background, the standard Hall A hadron particle identification,based on a time of flight and two aerogel threshold Cherenkov detectors, is not sufficient. For this task a proximityfocusing C6F14/CsI RICH has been built. Recently, after some improvements to the mechanical structure of its wirechamber and to its electronics rate capability, the RICH has been tested with cosmic rays. This paper represents a statusreport of the RICH detector.r 2004 Elsevier B.V. All rights reserved.PACS: 29.40 Ka; 85.60 GzKeywords: RICH; StrangenessTable 1The expected counting rates for the E94-107 experiment atJefferson Lab, for the excited levels of 16NLProcess Rate (Hz)Signal (e,e0K) 104–102Accidentals (e,e0)(e,p) 100(e,e0)(e,p) 1001. IntroductionA high-resolution hypernuclear spectroscopyexperiment (E94-107) is scheduled at JeffersonLab, Hall A, beginning at the end of the year 2003.The expected signal ðSÞ and accidental ðBÞ ratesfor the 16O(e,e0k+)16NL experiment, reported in(e,e0)(e,K) 0.1The background is mainly due to pions and protons. The lastline is due to accidentals from a strangeness exchange reactionwith no production of bound state (hypernucleus).onding author. Fax: +390649387075.ddress: francesco.cusanno@iss.infn.ito).- see front matter r 2004 Elsevier B.V. All rights reserved./j.nima.2004.03.041ARTICLE IN PRESSF. Cusanno et al. / Nuclear Instruments and Methods in Physics Research A 525 (2004) 163–167164Table 1, show that the kaon missing massspectrum will be highly contaminated by pionsand protons. A contamination ðC ¼ B=SÞ ofFig. 1. The contamination C in different hypotheses of the HallA PID apparatus. White bars are for an S signal of the order of104Hz, dark bars for S=102Hz.Fig. 2. Simulated 9Be(e,e0K+)9LiL (top panels) and12C(e,e0K+)12BL(left panels) and with the same implemented with the RICH (right pathe order of 104–106 is expected from the data inTable 1.Assuming that a peak in the kaon missing massspectrum could be disentangled from the back-ground, and thus considered a real hypernuclearexcited level, only if its counts ðSÞ are at leastfour times the background fluctuation ðffiffiffiBpÞ; itresults the need of minimizing the contamination.This cannot be achieved by decreasing the time-coincidence interval, but only by decreasing thenumber of misidentified particles [1,2]. Therefore abetter particle identification (PID) system has beendesigned [3], built and tested: a RICH detectorwith a proximity focusing geometry, a liquid C6F14radiator and a CsI film as photoconverter. TheRICH detector has been successfully tested atCERN (November 2000) and commissioned dur-ing the E00-102 experiment (December 2002) atJefferson Lab.The superior performance of this RICH isoutlined in Fig. 1, where it is compared with thestandard Hall A PID system based on a time offlight (TOF) and two aerogel Cherenkov detectors.(bottom panels) spectra obtained with the standard Hall A PIDnels).ARTICLE IN PRESSFig. 3. Comparison between old and new (present) MWPCconfigurations. The gain is measured in term of C-RAM ADCchannel, corresponding to 0.13 fC. The dark area show the zonewhere the signal/noise ratio is optimized: at lower gain the lostphotoelectrons affect the performance of the particle identifica-tion, at higher gain the photon feedback affects it.F. Cusanno et al. / Nuclear Instruments and Methods in Physics Research A 525 (2004) 163–167 165Fig. 2 shows the 9Be(e,e0K+)9LiL (top panels)and 12C(e,e0K+)12BL (bottom panels) spectrasimulated by assuming the standard Hall A PID(right panels), and the same PID implemented bythe RICH detector (right panels). The improve-ment of the spectra quality produced by theintroduction of the RICH is evident, particularlyfor the 9Be(e,e0K+)9LiL reaction.2. The RICH detectorThe Hall A RICH is conceptually identical toone module of the ALICE–HMPID [4]. TheRICH [5] has a proximity focusing geometry (nomirror involved), which makes the detector com-pact (less than 50 cm), thin (nearly 18% of X0),and relatively unexpensive. The hadron momen-tum in the E94-107 experiment is 2GeV/c, for thisreason a liquid radiator (refractive index around1.3) has to be used. The C6F14 liquid radiator,15mm thick, is housed in a NEOCERAM(a glass–ceramic material with thermal and me-chanical properties nearly identical to those ofquartz) vessel with a pure quartz (5mm thick) exitwindow. After travelling in a 100mm methaneproximity gap, Cherenkov photons are convertedinto photoelectrons [6] into a 300 nm thick CsI filmdeposited on a padded plane (11 520 pads,8 8mm2 each). The photoelectrons are acceler-ated by a tension of 2100V in a Multi WireProportional Chamber (MWPC), 2mm gap. Eachpad is connected to the input channel of amultiplexed sample-and-hold Front End Electro-nics (FEE). The read-out electronics consists oftwo CAEN VME modules, the V551 sequencerand the V550 C-RAM (fast ADC, two channelsper module).3. ResultsIn the commissioning E00-102 experiment,whose results have been partially presented in aprevious paper [5], the need of a better matching ofthe anode–cathode distances over the wholedetector was evidenced. Then a new wire chamber(and photocathodes) has been mounted recently.The improvement in the MWPC performance isshown in Fig. 3.Furthermore, in order to increase the RICHdata acquisition rate to the need of the experi-ment (nearly 2 kHz), the FEE row length hasbeen divided by two. The electronics is nowsubdivided in 48 rows with 240 daisy chainedchannels (instead of 24 rows and 480 channels). Toread out these 48 FEE rows, two VME crates arefully equipped with 12 CRAMs each. In this newconfiguration, the electronics allows to reach adata acquisition rate of 1.5 kHz with 25% of deadtime.A new cosmic ray test has been performed afterthe modifications. The results in Figs. 4 and 5,compared to the commissioning experiment onesand to a previous cosmic rays test, show betterperformance. The MWPC RICH is now operatedat HV=2100V. This tension brought to 2150V ifneeded.ARTICLE IN PRESSFig. 5. Performance of the RICH with the MWPC operating at 2150V. Respect to Fig. 4, the gain is increased by a factor of nearly1.5, but the number of photoelectron in the fiducial zone is increased by 20%. The probability that a photon feedback photoelectron isin the fiducial zone is nearly 10%, so the real increasing of signal is 10%.Fig. 4. Performance of the RICH with the MWPC operating at 2100V. The plots show the pulse height for Minimum IonizingParticles (MIP), the MIP pad size, the number of photoelectrons and the charge for photoelectron cluster.F. Cusanno et al. / Nuclear Instruments and Methods in Physics Research A 525 (2004) 163–167166ARTICLE IN PRESSF. Cusanno et al. / Nuclear Instruments and Methods in Physics Research A 525 (2004) 163–167 1674. ConclusionA proximity focusing C6F14 RICH detector hasbeen built for the high-resolution hypernuclearspectroscopy experiment in Hall A at JeffersonLab. During the last months the RICH mechanicsand electronics have been improved to increase thestability of the MWPC and the data acquisitionrate. Cosmic rays tests have been performed afterthe last changes, showing that the performanceachieved so far is within the estimations.References[1] F. Garibaldi, S. Frullani, J. LeRose, P. Markowitz, T. Saito,CEBAF experiment E94-107 Proposal.[2] G.M. Urciuoli, et al., Nucl. Phys. A 691 (1–2) (2001) 43.[3] F. Garibaldi, Future hypernuclear program in Hall A,Presentation at Hyp2003 Conference.[4] ALICE Collaboration, Technical design report of the highmomentum particle identification detector, CERNLHCC98-19, ALICE TDR1, 1998.[5] F. Garibaldi, et al., Nucl. Instr. and Meth. A 502 (2003)117.[6] F. Cusanno, et al., Nucl. Instr. and Meth. A 502 (2003) 251.

A RICH detector for strangeness physics in Hall A at Jefferson Lab

https://www.openaccessrepository.it/record/136105/files/fulltext.pdf

A RICH detector for strangeness physics in Hall A at Jefferson Lab

Abstract

Similar works

Full text

Available Versions

Open Access Repository