Results of KEK-PS E325 experiment F. F.Saku kuma, , RIKEN - PowerPoint PPT Presentation

Results of KEK-PS E325 experiment F. F.Saku kuma, , RIKEN • Introduction • E325 Experiment • Results of data analysis  ρ/ω  e + e - spectra  φ  e + e - spectra  φ  K + K - spectra  nuclear mass-number dependences of φ  e + e - & φ  K + K - • Summary

Phys ysics cs Motiva vation Quark Mass chiral symmetry restoration effective mass bare mass in QCD vacuum m u ≒ m d ≒ 5MeV/c 2 m u ≒ m d ≒ 300MeV/c 2 m s ≒ 150MeV/c 2 m s ≒ 500MeV/c 2 chiral symmetry breaking How we can detect such a quark mass change? at very high temperature or W.Weise NPA553,59 (1993) density , the chiral symmetry is expected to restore even at normal nuclear density , the chiral symmetry is expected to restore partially 2

Vec ector Mes eson on M Mod odifi fication dropping mass  Brown & Rho (’91) m*/m=0.8 ( ρ = ρ 0 )  Hatsuda & Lee (’92) m*/m=1-0.16 ρ/ρ 0 for ρ/ω m*/m=1-0.03 ρ/ρ 0 for φ  Muroya, Nakamura & Nonaka (’03) Lattice Calc. width broadening  Klingl, Kaiser & Weise (’97&98) 1GeV> for ρ , 45MeV for φ ( ρ = ρ 0 )  Oset & Ramos (’01) 22MeV for φ ( ρ = ρ 0 )  Cabrera & Vicente (’03) 33MeV for φ ( ρ = ρ 0 ) 3

Vec ector Mes eson on, ρ/ω/φ ρ/ω meson  mass decreases 16%  130MeV/c 2  large production cross-section  cannot distinguish ρ & ω φ meson  mass decreases 2~4%  20-40MeV/c 2  small production cross-section  narrow decay width ( Γ =4.3MeV/c 2 ), no other resonance nearby T.Hatsuda, S.H.Lee, ⇒ sensitive to the mass Phys. Rev. C46 46(1992)R34. spectrum change 4

Expec ected ed Modified Mass ass Sp Spectra ra in e + e -  small FSI in e + e - decay channel ρ+ω  double peak (or tail-like) structure m*/m=1-0.16 ρ/ρ 0  second peak is caused by ω φ inside-nucleus decay m*/m=1-0.02 ρ/ρ 0 ρ e e βγ lab ~1 e p p ρ/ω/φ ρ/ω/φ e outside decay inside decay  depends on the nuclear size & meson velocity  enhanced for larger nuclei & slower meson 5

Ex Experim imental Re l Result lts o on the In-mediu ium m the ρ , , ω an and φ me Mass ass an and W Width th o of th meso son R.S.Hayano and T.Hatsuda, arXiv:0812.1702 [nucl-ex] Invariant In nt mass Atte ttenuati tion KEK EK-PS S Jlab Jl Jl Jlab Spring ng8 8 CBEL ELSA/TAP APS E325 325 CLAS AS g7 g7 CLAS AS g7 g7 LEP EPS γ A 0.6 - 3.8 γ A 0.6 - 3.8 γ A 1.5 - 2.5 Reactio ion γ A 0.7 - 2.5 GeV pA 12 GeV GeV GeV GeV 0 > 0.5 p > 0.8 p < 0.5 0.4 < p < 1.7 p > 0.8 1.1 < p < 2.2 Moment ntum um GeV/c GeV/c GeV/c GeV/c GeV/c GeV/c ∆ m ∼ 0 ρ ∆ m( ρ 0 )/m = - broadening 9% confirmation Γ ω ( ρ 0 ) = 130- our report is no broadening 150MeV/c 2 ω @ J-PARC E16 minority report!? ∆ m ∼ 0? → σ ω N ∼ 70mb ∆ m( ρ 0 )/m = - σ φ N ∼ 20mb σ φ N ∼ 35mb 3.4% φ → Γ φ ( ρ 0 ) ∼ Γ φ ( ρ 0 )/ Γ ∼ → Γ φ ( ρ 0 ) ∼ 15MeV/c 2 45 MeV/c 2 80 MeV/c 2 6

KEK-PS E325 Experiment 7

KEK EK-PS E325 325 Experiment Measurements History of E325 Invariant Mass of e + e - , K + K - ’93 proposed in 12GeV p+A  ρ , ω , φ +X reactions ’96 construction start  NIM, A457 581(’01). slowly moving vector mesons  NIM, A516 390(’04). (p lab ~2GeV/c) ’97 first K + K - data large probability ’98 first e + e - data to decay inside a nucleus  ρ/ ω : PRL, 86 5019(’01). ’99~’02 Beam x100 statistics in e + e - Primary proton beam  ρ/ω : PRL, 96 092301('06). (~10 9 /spill/1.8s)  φ  ee: PRL, 98 042501(’07).  α : PR, C75 025201(’06). Target x6 statistics in K + K - Very thin targets  φ  KK: PRL, 98 152302(’07). (X/ λ I =0.2/0.05%, ’02 completed X/X 0 =0.4/0.5% for C/Cu) 8

Detect ctor Se r Setup M.Sekimoto et al. , NIM, A516, 390 (2004). Hodo doscope pe Start rt Timing Forw orward LG Calori orimeter Count unter Ae Aerogel el Cher erenk enkov Rear r LG Calori orimeter Forw orward TOF Sid ide LG Calo Calorim imeter Barre rrel Dri rift Chamber B 0.81Tm Cylindrical D Cyli l DC 1m Rear r Gas Chere renkov ov Ver ertex ex DC Front nt Gas Cher heren enkov 9

E325 325 Spectr tromete ter front view top view beam 10

Spectrom omet eter er Perfor ormance s  π + π - Λ  p π - K 0 [counts / 2MeV/c 2 ] [counts / 0.5MeV/c 2 ] － Data － Data － MC － MC M = 496.8 ± 0.2 (MC 496.9) MeV/c 2 M = 1115.71 ± 0.02 (MC 1115.52) MeV/c 2 σ = 3.9 ± 0.4 (MC 3.5) MeV/c 2 σ = 1.73 ± 0.04 (MC 1.63) MeV/c 2 mass resolution for φ -meson decays φ  e + e - : 10.7 MeV/c 2 φ  K + K - : 2.1 MeV/c 2 11

Observe rved Invari riant Mass Sp Spectra ra counts/10MeV/c 2 counts/10MeV/c 2 C ω(783) ω(783) Cu e + e - φ(1020) φ(1020) counts/4MeV/c 2 counts/4MeV/c 2 C Cu φ(1020) φ(1020) K + K - K + K - threshold 12

Result of ρ/ω  e + e - M.Naruki et al., PRL, 96 092301 (2006). 13

e + e - Invar ariant Mass ass Spectr tra counts/10MeV/c 2  from 2002 run data C ω(783) (~70% of total data)  C & Cu targets  acceptance uncorrected φ(1020)  M<0.2GeV/c 2 is suppressed by the detector acceptance  fit the spectra with known sources 14

Fitting g with known source rces  resonance – ρ/ω/φ  e + e - , ω  π 0 e + e - , η  γ e + e - – relativistic Breit-Wigner shape (with internal radiative corrections) – nuclear cascade code JAM gives momentum distributions – experimental effects are estimated through the Geant4 simulation (multiple scattering, energy loss, external bremsstrahlung, estima mate ted s spectrum m chamber resolution, using G g GEANT4 T4 detector acceptance, etc.) φ  e + e -  background experim imental al – combinatorial background obtained effects relat ativ ivis istic ic by the event mixing method + Breit it-Wi Wigner internal al  fit parameter radia iativ ive – relative abundance of these correc ection on components is determined by the fitting

Fitti tting Resu sults ts Cu C χ 2 /dof=159/140 χ 2 /dof=150/140 the excess over the known hadronic sources on the low mass side of ω peak has been observed. the region 0.60-0.76GeV/c 2 is excluded from the fit, because the fit including this region results in failure at 99.9% C.L.. 16

Fitti tting Resu sults ts ( (BG su subtr btracte ted) events[/10MeV/c 2 ] events[/10MeV/c 2 ] Cu C ρ/ω ratios are consistent with zero ! ρ/ω = 0.0 ± 0.03(stat.) ± 0.09(sys.) 0.0 ± 0.04(stat.) ± 0.21(sys.) ρ/ω =1.0 ± 0.2 in former experiment (p+p, 1974)  the origin of the excess is modified ρ mesons

Sim imple le Model Ca l Calc lculation • pole mass: m*/m = 1-k ρ/ρ 0 (Hatsuda-Lee formula) e • generated at surface of incident p ρ/ω e hemisphere of target nucleus – α ω ~2/3 [PR, C75 025201 (2006).] – decay inside a nucleus: Cu C C Cu r=4.1fm r=2.3fm ρ 52% 66% ω 5% 10% • nuclear density distribution : Woods-Saxon • mass spectrum: relativistic Breit-Wigner Shape • no width modification 18

Fitti tting Resu sults ts by by th the Sim imple le Mod odel el m*/m = 1 - 0.092 ρ/ρ 0 ρ/ω = 0.7 ± 0.1 ρ/ω = 0.9 ± 0.2 Cu C the excesses for C and Cu are well reproduced by the model including the mass modification. 19

Con ontours for for ρ/ω an and k k  C and Cu data are simultaneously fitted.  free parameters – production ratio ρ/ω – shift parameter k  Best-Fit values are k = 0.092 ± 0.002 ρ/ω = 0.7 ± 0.1 (C) 0.9 ± 0.2 (Cu) mass of ρ/ω meson decreases by 9% at normal nuclear density. 20

Result of φ  e + e - R.Muto et al., PRL, 98 042501 (2007). 21

φ  e + e - Invar ariant Mass ass Spectr tra  from 2001 & 2002 run data φ(1020)  C & Cu targets  acceptance uncorrected  fit with – simulated mass shape of φ (evaluated as same as ρ/ω ) – polynomial curve background  examine the mass shape as a function of βγ (=p/m) (anomaly could be enhanced for slowly moving mesons) 22

Fitti tting Resu sults ts 1.75< βγ (Fast) βγ <1.25 (Slow) 1.25< βγ <1.75 Small Nucleus Large Nucleus Rejected at 99% confidence level 23

Amou ount of of Excess A significant enhancement is seen in the Cu data, in βγ <1.25  the excess is attributed to the φ mesons which decay inside a nucleus and are modified To evaluate the amount the excess N excess , fit again excluding the excess region (0.95~1.01GeV/c 2 ) and integrate the excess area. excluded from the fitting 24

Sim imple le Model Ca l Calc lculation Simple model like ρ/ω case, except for • pole mass: m*/m = 1-k 1 ρ/ρ 0 (Hatsuda-Lee formula) • width broadening: Γ */ Γ = 1+k 2 ρ/ρ 0 to increase the (no theoretical basis) decay probability in a nucleus – e+e- branching ratio is not changed Γ * e+e- / Γ * tot = Γ e+e- / Γ tot • uniformly generated in target nucleus p – α φ ~1 [PR, C75 025201 (2006).] φ – decay inside a nucleus (for βγ <1.25): C Cu φ 3% 6% 25

Fitti tting Resu sults ts by by th the Simple e Mod odel el m*/m = 1 - 0.034 ρ/ρ 0 , Γ */ Γ = 1 + 2.6 ρ/ρ 0 1.75< βγ (Fast) βγ <1.25 (Slow) 1.25< βγ <1.75 Large Nucleus Small Nucleus well reproduce the data, even slow/Cu 26