Development of an Aerogel Cherenkov Counter for the

Development of an Aerogel Cherenkov Counter for the J-PARC E 16 Upgrade 課題番号： 22105516（平成 22年度～ 23年度） 研究代表者：佐久間　史典（理化学研究所） F. Sakuma (RIKEN), M. Nakamura (TITECH), H. Kawai (Chiba-U), H. Ohnishi (RIKEN), M. Tabata (JAXA), M. Tokuda (TITECH) l Motivation l Aerogel Cherenkov Counter l Present Status l Summary 新学術領域「多彩なフレーバーで探る新しいハドロン存在形態の包括的研究」 領域研究会 @ 理研 2011/02/28 -03/01

Motivation l. J-PARC E 16 experiment measures in-medium f-meson modification in di-electron spectrum topics of the f-meson ü di-lepton spectrum ü Gll vs GKK (f-puzzle) l. K+K- measurement in the E 16 experiment is very important installation of Kaon detectors in the E 16 spectrometer is desired Do decay widths of f ll / KK change in nuclear matter caused by f / K spectral modification? PLB 262, 485(1991). Br*(f ll) /Br 0(f ll) Theory density (r. CR/r 0) NA 60 NPA 830, 753 c(2009). 2

Forward Kaon Spectrometer AC(n=1. 034) + TOF counter segmented STC +15 -15 +45 +15 -45 e+e- acceptance K+K- acceptance --- Requirements --1. threshold type AC for kaon trigger (veto counter) 2. work in magnetic field 3. small & compact 3

f e+e-/K+K- acceptance − e-accepted (double-arm) − e-accepted (single-arm) E 325 acceptance bg (LAB) p. T (LAB) y (LAB) − k-accepted (opposite-module pair) − k-accepted (same-module pair) − k-accepted (neighbor-module pair) bg (LAB) pt vs. y p. T (LAB) f e+ edouble-arm f K+ K- y (CM) pt vs. y neighbor-side Improvement of the acceptance overlap between e+e- and K+K- 4

AC design luse n=1. 034, as same as KEK-PS E 325 l 60 x 60 cm 2 divided by 6 (or 10) sectors 10 cm 60 cm X 4 modules index=1. 034 readout WLS + fiber + (FM)PMT index=1. 034 integration range : 300 -800 nm Goal : construct a prototype of ¼ size module 5

Some Hints in detector development in Russia? ar. Xiv: hep-ex/0106016 candidate for PEP-N detector @ SLAC barrel endcap ~8 p. e. Aerogel : t 74 mm, n=1. 05 WLS : BBQ p momentum 6

Minimum Goal : KEK-PS E 325 AC AC • n=1. 034 • 12. 5 cm Aerogel • 5 inch PMT (H 6527) M. Ishino et al. , NIM A 457, 581 8 p. e. 1. 1 p. e. p Rejection : 1 x 10 -2 @ 1. 4 Ge. V/c pion proton 7

Aerogel We have checked 3 -types of the aerogel (n~1. 034): l. Panasonic-denko l. KEK-PS E 325 l. Chiba-U 10 c m 10 cm Aerogel H 6410 (2”) Mirror Cosmic Ray 8

WLS l. Aerogel (t 2 cm) PMT lclear fiber x 100 (f 1 mm, single clad) cm l. WLS (ELJEN EJ-299 -27, t 1 mm) 10 Cosmic Ray fiber x 100 WLS m H 6410 (2”) 30 c m 10 c expected # of photon @ 1 Ge. V/c p & n=1. 034 x transmission length n=1. 034 (KEK) WLS(blue) PMT 9

WLS (Cont’d) 2 cm w/ Aerogel 1 mm 1 mm w/ Aerogel fitting is failed… w/o Aerogel 10

WLS (Cont’d) --- What we have learned --l. WLS (blue, t 1 mm) emits several photons with charged particles We cannot install a large amount of WLS in detector acceptance lpresent method of WLS+fiber readout cannot collect Cherenkov light from the Aerogel --- What we have to do --lreconsider the configuration of the Aerogel and WLS Øincrease the fibers? Øusage of blue and green WLS? 11

Other Ways … ldevelopment of a “normal type” Aerogel Cherenkov Counter with finemesh-PMTs such as BELLE AC. ldevelopment of a “reflection type” Aerogel Cherenkov Counter with optical mirrors such as E 325 AC NIM A 457, 581 R 5543 x 52 @ RIKEN (from KEK-PS E 325 GC) BELLE AC NIM A 453, 321 12

Summary l. We have been developing an Aerogel Cherenkov Counter for the E 16 upgrade in order to measure K+K- pair. l. Development of WLS+fiber readout has been started, but we have to adjust the configuration of AC+WLS+fiber. Further study is required… 13

14

Expected Photon Spectra expected # of photon @ 1 Ge. V/c p & n=1. 034 transmission length n=1. 034 (E 325) p 1 Ge. V/c Aerogel Detection p 1 Ge. V/c l x Aerogel Detection 15

WLS (Cont’d) Aerogel 6 cm H 6410 (2”) Aerogel 6 cm WLS 1 mm 16

WLS (Cont’d) WLS(blue) p 1 Ge. V/c Aerogel l PMT Detection PMT 300~600 nm WLS 300~400 nm 17

WLS (Cont’d) trigger Aerogel 9. 4 cm H 6410 (2”) trigger WLS 1 mm Aerogel 9. 4 cm trigger 18

Photon Fitting Poisson Gaussian C : normalized factor l : mean value of photoelectron p 0 : pedestal peak p 1 : distance of pedestal to single-photon s 1 : PMT resolution for single-photon parameter constant 19

Si. APD H 4083 S 8664 -55 S 8664 -1010 We purchased and tested Si. APDs. But we CANNOT see the signal of a few photons on Si. APD, because of read-out electronics noise! what we have learned is … “using low-gain devices for Cherenkov detection is awful difficult!” ~7500 photons (gain : x 50) 20

MPPC S 10362 -11 -100 C S 10362 -33 -050 C S 10362 -33 -025 C S 10362 -33 -100 C We purchased and tested MPPCs. The dark count signals of ~Mcps were confirmed as written in the product specification. It seems that usage of the MPPCs for a single-photon detector is too hard! Several tens of photons are required. 21

22

Vector Meson, f mfが変化 G*/G 0 J. D. Jackson, Nuovo Cimento 34, 1644 (1964). m. Kが変化 G*/G 0 f mass K mass 23

f Puzzle 核物質中でのfまたはKのスペクトラル関数の変化によって、 f ll/KKの崩壊幅が変化するのではないか? ltheoretical predictions PLB 262, 485(1991). − D. Lissauer and V. Shuryak, PLB 253, 15(1991). G*(f KK)/G*(f ll) の増加 − P. -Z. Bi and J. Rafelski, PLB 262, 485(1991). G*(f ll) /G 0(f ll) G*(f KK)/G*(f ll) の増加 − J. P. Blaziot and R. M. Galain, PLB 271, 32(1991). G*(f KK)/G*(f ll) の減少 l. NA 49/NA 50@CERN-SPS – PLB 491, 59(2000). ; PLB 555, 147(2003). ; J. Phys, G 27, 355(2001). – f K+K-/m+m-, 158 AGe. V Pb+Pb – production CS’s are inconsistent density (r. CR/r 0) d. N/mt. Dydmt − etc. J. Phys. G 27, 355(2001). f K+K- NA 49/ NA 50 f m+mmt-m 0 (Ge. V) 24

f Meson Measurements Hot Matter l. CERES(NA 45)@CERN-SPS – PRL 96, 152301(2006). – f e+e-/K+K-, 158 AGe. V Pb+Au – production CS’s are consistent CERES l. PHENIX@BNL-RHIC – EPJ, A 31, 836(2007). – f e+e-/K+K-, sqrt(s. NN)=200 Ge. V Au+Au – production CS’s are consistent PRL 96, 152301(2006). l. NA 60@CERN-SPS – NPA 830, 753 c(2009). – f m+m-/K+K-, 158 AGe. V In+In – production CS’s are consistent Cold Matter l. E 325@KEK-PS – PRL 98, 152302(2007). – f e+e-/K+K-, 12 Ge. V p+C/Cu NA 60 NPA 830, 753 c(2009). 25