Vector Meson predictions of vector meson modification in

Vector Meson predictions of vector meson modification in medium Brown, Rho(1991), Hatsuda, Lee(1992), Klingle, Keiser, Weise(1997), etc. mass 2 x. Mq+(small interaction term) クォークの有効質量の変化をとらえやすい Di-electron decay Final state interaction の影響を あまり受けない ρ/ω l真空中に比べて通常原子核密度内での 質量変化は　　 ～ 150 Me. V/c 2 φ ・・・しかし、ρ/ωの区別は難しい & ρの幅は広くて分かりにくい l真空中に比べて通常原子核密度内での 質量変化は　　 ～ 20 -40 Me. V/c 2 l～ 4. 3 Me. V/c 2の狭い崩壊幅 　　⇒mass spectrum の変化に敏感 ρ0: : normal nuclear density T. Hatsuda, S. H. Lee, Phys. Rev. C 46, R 34 (1992). 3

ρ/ω expected Shape e In vacuum C nuclear density: Woods-Saxon mass shape: Breit-Wigner + mass modification. (m*/m=1 -0. 16ρ/ρ0) generate : 原子核前半球 I. JAMより得たmomentumで飛 ばし、寿命に従ってe+e-に decayさせる decay pointの密度により massを求める II. e p Cu inside decay outside decay e e ρ/ω outside decay p ρ/ω e inside decay *detector effectは含まない Pb 4

KEK-PS E 325 Related Experiments Measurements invariant mass 12 Ge. V p+A→ρ, ω, φ+X e+e-, K+K- invariant mass 核内で崩壊する～ 2 Ge. V/cの 遅いベクターメソンを測定する Beam Primary proton beam (~109/spill/1. 8 s)を用いる Target γconversionを減らすために 薄いターゲットを用いる (0. 4% radiation length & 0. 2% interaction length @C) • CERES@CERN – 158 A Ge. V Pb – Au collisions – e+e-　spectrum modification • RHIC@BNL – 200 A Ge. V Au – Au collisions – e+e-, K+K- channels • TAGX@INS – A(γπ+π-)X ; A=2 H, 3 He, 12 C – ρ→π+π- spectrum modification bound state • Deeply bound pionic atom@GSI – Sn(d, 3 He) – πN interaction in pion-nucleus potential JPS 2004/03/27 5

Setup Hodoscope Forward LG Calorimeter Aerogel Cherenkov Rear LG Calorimeter Forward TOF Side LG Calorimeter Barrel Drift Chamber B Cylindrical DC m ea b n 1 V e 2 G o t o pr Rear Gas Cherenkov Vertex DC Front Gas Cherenkov JPS 2004/03/27 6

Observed e+e- invariant mass spectra 2002 run data (~70% of total data) ω→e+e- C φ→e+e- Fitting with known sources l. Hadronic source of e+e • ρ/ω/φ→e+e-, ω→π0 e+e-, η→γe+e • Breit-Wigner shape (no modification) • Detector simulation by Geant 4 (energy loss, acceptance, etc. ) l. Background • combinatorial background obtained by mixed events l. Relative abundance of mesons and background • determined by fitting JPS 2004/03/27 7

Detector Simulation by Geant 4 ω→e+eradiative tail utracking region の物質を全て再現 • chamber wire も1本 1本全て入っている ~20, 000本 u考えているPhysics • Energy loss (Ionization, Bremsstrahlung) • Multiple Scattering uacceptance の再現 uchamber resolution, efficiency の再現 Breit. Wigner 8

Detector Simulation Study Ks→π+π- ω→e+e- φ→e+e- resolution data: 9. 2± 0. 4(stat. ) ± 0. 4(sys. ) MC : 5. 9± 0. 1(stat. ) ± 0. 3(sys. ) C peakの左側合わない! C resolution data: 3. 5± 0. 2(stat. ) ± 0. 1(sys. ) MC : 3. 1± 0. 1(stat. ) ± 0. 1(sys. ) dataを再現する resolution data: 8. 8± 1. 3(stat. ) ± 1. 4(sys. ) MC : 7. 5± 0. 2(stat. ) ± 0. 2(sys. ) いずれもpeakの右側は良く合うが、左側は… 9

Fitting results C Cu excess ωのpeakの左側に既知のhadronic sourceからは 説明不可能なexcessが見られる excess JPS 2004/03/27 10

Fitting results ( background subtracted ) C Cu r / w ratio is consistent with zero 0. 0 A 0. 01(stat. )A 0. 2(sys. ) 0. 0 A 0. 05(stat. )A 0. 5(sys. ) Excess は modified ρ(ω) mesons によるものと理解できる JPS 2004/03/27 11

Model Calculation m*/m=1 -0. 16 r/r 0 • generate : 原子核前半球表面 • mass shape : Breit-Wigner + mass modification. • ρ/ω ratio = 1 [過去の実験(pp)より] • decay width は変えていない C Cu 12

JPS 2004/03/27 14

w Measured Kinematical Distribution ycm(1. 66) JPS 2004/03/27 15

Target @’ 02 comment total material Interaction length radiation length C 0. 21% 0. 4% Cu 0. 05% 0. 6% C, Cux 4 0. 41% 2. 8% Vertex Distribution Cu beam Cu 2 C m m 3 Cu Cu m m 0 9 mm JPS 2004/03/27 16

History φ→K+K − 1997 June First Physics Run　with K+K− ω→e+e− φ→e+e− 99 95 12 1998 May Already Published (P. R. L. vol. 86　22(2001) ) 1999 July Hawaii JPS/QM 2002/PANIC 02 178 ～ 700 ～ 125 2000 June Production Run with newly installed Dec. Vertex Chamber & Lead Glass Calorimeter Drift. Chamber pre. Amp Upgrade 2001 Nov. Production Run ～ 350 2002 Feb. LAST Production Run JPS 2004/03/27 ～ 6500 ～ 1300 17

Trigger 18

Electron ID JPS 2004/03/27 19

Spectrometer Performance JPS 2004/03/27 20

Mass Acceptance acceptance mass acceptance for ρ→e+e- C target invariant mass [Ge. V/c 2] 21