Preshower detector for π+π− hadronic atom studies
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- 作者：M. Pentia ; C. Ciocarlan ; S. Constantinescu ; M. Gugiu ; Gh. Caragheorgheopol
- 关键词：Preshower detector ; Hadron/electron separation ; Hadronic atoms
- 刊名：Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
- 出版年：2009
- 出版时间：21 May 2009
- 年：2009
- 卷：603
- 期：3
- 页码：309-318
- 全文大小：1418 K
文摘
A preshower (PSh) detector has been prepared, tested and used at the CERN-DIRAC experiment [B. Adeva, et al., DIRAC proposal, CERN/SPSLC 95-1, SPSLC/P 284, 1995]. The aim of this experiment was to test some nonperturbative QCD predictions [J. Gasser, H. Leutwyler, Phys. Lett. B 125 (1983) 325; J. Gasser, H. Leutwyler, Ann. Phys. 158 (1984) 142; J. Gasser, H. Leutwyler, Nucl. Phys. B 250 (1985) 465; J. Bijnens, G. Colangelo, G. Ecker, J. Gasser, M.E. Sainio, Phys. Lett. B 374 (1996) 210] by measuring pionium (π+π− hadronic atom) lifetime. In this context the PSh detector, together with the Cherenkov detector, pursued to reject the background electron pairs in the region 1–4 GeV where the pion pairs from atom breakup were present.
The technique used for pion/electron separation was to probe the electron shower development in the early formation stage in Pb converter. We have studied the dependence of the amplitude spectra on particle momentum and converter and scintillator thickness. The estimated electron rejection efficiency was better than 85 % with a pion loss less than 5 % for a preshower detector with Pb converter thickness wPb=2.5 cm and scintillator slab wSc=1 cm.
The PSh track efficiency within the DIRAC setup has been measured with a global efficiency per arm better than 99 % , slab efficiency per arm better than 96 % and corresponding pair events efficiency per arm 99 % and per slab 93 % .