Scalar mesons at KLOE

Transcription

1 Salvatore Fiore QCD08 - July 9 th 2008 Montpellier 1 Scalar mesons at KLOE Salvatore Fiore (on behalf of the KLOE collaboration) Sapienza Università di Roma and INFN Roma

2 Talk outline DAFNE and KLOE Scalar Mesons at Φ-factory φ f 0 (980) π + π φ f 0 (980) π 0 π 0 φ a 0 (980) ηπ 0 5 photons final state 2 charged pions + 5 photons final state Conclusions Salvatore Fiore QCD08 - July 9 th 2008 Montpellier 2

3 Physics at a φ factory: a window on the lowest mass mesons φ decays give access to light mesons (scalar, pseudoscalar, vector) These processes allow us to study the structure of these mesons, in particular their s-quark content via couplings with φ (ss) and Kaons KK η ' (960) φ (1020) π a 0 (980) f 0 (980) Main decay channels K + K % K S K L 34.0 % ρπ + π + π π % η % Branching fraction η ρ(770) π % η π 0 Direct decay Radiative decay π-emission π 0 π 0 ~ 10-4 ηπ radiative return to π + π - #events in KLOE data = Br.F ~10 8 η; ~10 5 η, ππ, ηπ Salvatore Fiore QCD08 - July 9 th 2008 Montpellier 3

4 The DAΦNE e + e Φ-factory φ-factory : an e + e - collider with center of mass energy s=m( s=m(φ)=1019.4mev σ(e + e φ)~3 μb Separate e + e - rings to reduce beam-beam interactions crossing angle: 25 mrad Bunch crossing every 2.7 ns injection during acquisition integrated Luminosity : L dt = 2.4 fb -1 L peak = cm - 2 s cm Salvatore Fiore QCD08 - July 9 th 2008 Montpellier 4

5 The KLOE detector Drift chamber (4 m 3.75 m, CF frame) Gas mixture: 90% He + 10% iso-c 4 H stereo sense wires almost squared cells Superconducting coil (B = 0.52 T) Calorimeter lead/scintillating fibers (1 mm ), 15 X PMT s 98% solid angle coverage σ p /p = 0.4 % (tracks with θ > 45 ) σ hit x = 150 μm (xy), 2 mm (z) σ vertex x ~1 mm σ(m ππ ) ~1 MeV σ E /E = 5.7% / E(GeV) σ t = 54 ps / E(GeV) 50 ps σ vtx () ~ 1.5 cm (neutral vertex resolution) Salvatore Fiore QCD08 - July 9 th 2008 Montpellier 5

6 Scalar Mesons at a Φ-factory Mass (GeV/c 2 ) φ(1020) 1. f 0 (980) a 0 (980) κ(800) σ(500) 0. I=0 I=1/2 I=1 Scalar Mesons Spectroscopy: f 0 (980), σ(500) and a 0 (980) are accessible through φ S (κ not accessible) Questions: 1. Is σ(500) needed to describe the mass spectra? 2. couplings of f 0 (980) and a 0 (980) to φ ss> and to KK, ππ and ηπ. allows to investigate the inner structure: 4-quark vs. 2-quark vs. KK molecule Kaon-Loop model: (Achasov - Ivanchenko Nucl.Phys.B315(1989)465, Achasov - Gubin Phys.Rev.D63(2001)094007, Achasov - Kiselev Phys.Rev.D68(2003) ) Salvatore Fiore QCD08 - July 9 th 2008 Montpellier 6

7 The π 0 π 0 analysis 5 photons with θ >23 o and no tracks; Kinematic fit energy-momentum conservation; π 0 masses: choice of the photon pairing to π 0 s 2 main components Irreducible background fit in the amplitude (fixed parameters), also with interference terms e + ω π 0 e + ρ π 0 ρ φ,ω σ needed in the fit: P(χ 2 ) ~ 10-4 without σ σ completely fixed (no artificial improvement by enlarged parameter set) 0 0 BR( φ S π π ) = e - Salvatore Fiore QCD08 - July 9 th 2008 Montpellier 7 π 0 Fit parameters: M f0, g f0k+k, g f0π+π (= 2 g fπ0π0 ) f 0 (980) param. m f0 (MeV) g fπ+π (GeV) Systematic dominated by model-dependent fixed parameters. 10 sets of parameters available, 8 give P(χ 2 ) > 1% K-L results are the mean, and the errors are the RMS, of fit results e - π 0 NEW Kaon-Loop result ± ± 0.19 g fkk (GeV) 3.97 ± [ 1.07 (fit) (syst) (mod)] [EPJC49(2007)473]

8 Salvatore Fiore QCD08 - July 9 th 2008 Montpellier 8 The π + π analysis 2 tracks with θ t >45 o ; missing momentum θ ππ >45 o (large angle) pion identification through tracking, Time of Flight and Shower shape 1 photon matching the missing momentum events / 350 pb -1 Irreducible backgrounds fit in the amplitude - Kaon-Loop fit with σ contribution - no sensitivity to σ shown by the fit - systematic error to be evaluated f 0 (980) signal ISR: [Kühn-Santamaria ZPC48 (1990) 455] Free parameters: M ρ0, Γ ρ0, α, β FSR fixed [Achasov,Gubin,Solodov PRD55(1997)2672)] ρπ:(φ ρ ± π m ; ρ ± π ± ) VDM, a scale factor (a ρπ ) free scalar-fsr interference [Achasov-Gubin PRD57 (1998) 1987] B.R.(φ f 0 (980) π + π ) = (from integral of Amplitude 2 ) [PLB634(2006)148] NEW Fit result P(χ 2 ) = 2.5% M f0 = MeV g f0k+k- = 4.74 GeV g f0π+π- = GeV

9 Salvatore Fiore QCD08 - July 9 th 2008 Montpellier 9 The ηπ 0 analysis To extract the relevant a 0 (980) parameters we fit the M ηπ spectrum with the Kaon loop (5 parameters): M a0, g a0kk2 /(4π), g a0ηπ /g a0kk, η final state η 5 final state: pre-selection of 5- events + kinematic fit Background Process (after pre-selection) S/B (MC) φ f 0 (980) π 0 π 0 f e + e ωπ 0 π 0 π 0 ωπ φ η ; η π 0 η5 70 φ η ; η π 0 π 0 π 0 η7 0.2 φ η ; η η3 15 φ π 0 π 0 30 Total S/B 0.1 Br(φ ρπ 0 ηπ 0 ), δ (phase between scalar and vector amplitude) dominant scalar contribution from φ a0(980) with a0(980) ηπ0 (Br KLOE 00) vector contribution φ VP; V P' (V = ρ,ω P,P' = π 0,η) (Br VDM) Ldt = 424 pb -1 Events/(4 MeV) data ωπ 0 η7 f 0 η3 Events/(4 MeV) Background subtracted Br(φ ηπ 0 ) = (6.98 ± 0.10 stat ± 0.23 syst ) 10-5 obtained from event counting (model independent).

10 η π + π π 0 final state o Data Bckg (MC) η π + π π 0 π + π + 5 final state, Ldt = 380 pb -1 1 vertex close to I.P. with 2 tracks + 5 good photons No background process with the same final state of the signal: Br(φ ηπ 0 ) = (7.12 ± 0.13 stat ±0.24 syst ) 10-5 Salvatore Fiore M ηπ (MeV) M ηπ0 fit to ηπ 0 events Kaon-Loop model (see previous slides), both presented channels Fitted parameters: M a0, g a0k+k, g a0ηπ, strength and interference phase of ρπ background Fit result stat. syst. M a ± 1.3 ± 1.0 MeV g a0k+k- g a0ηπ 2.15 ± 0.05 ± 0.06 GeV 2.82 ± 0.04 ± 0.04 GeV g φa ± 0.09 ± 0.16 GeV -1 Br(VDM) (0.92 ± 0.40 ± 0.15) 10 6 δ(vdm) (222 ± 12 ± 3) VDM= φ ρπ ηπ M a0 g a0kk g a0ηπ Strong correlation between M a0 and KK coupling: pay attention in comparing with other experiments QCD08 - July 9 th 2008 Montpellier Correlation matrix 1.000

11 Comparison with scalar models and theoretical predictions qq: Achasov-Ivanchenko NPB315(1989) Close et al., NPB389(1993) 4q: Achasov-Ivanchenko NPB315(1989) KK molec.: Close et al., NPB389(1993) Achasov et al., PRD56(1997) KK molec.-2: Kalashnikova et al., EPJA24(2005) Palomar et al., NPA729(2003): UχPT Escribano, PRD74(2006): Linear σ model KLOE In the 2 quarks picture the f 0 prefers an ss structure 4q not able to accommodate small g a0kk coupling SU(3) 4q qqbar (g ak+k /g aηπ ) SND(2000): 1.8±2.5 (g f0k+k /g f0π+π ) CMD2(1999): 3.61±0.62 SND(2000): 4.6±0.8 BES(2005): 4.21± >>1 >>1 (f 0 =ssbar) 1/4 (f 0 =nnbar) (g f0k+k /g ak+κ ) (f 0 =ssbar) 1 (f 0 =nnbar) Salvatore Fiore QCD08 - July 9 th 2008 Montpellier

12 Salvatore Fiore QCD08 - July 9 th 2008 Montpellier 12 Conclusions Scalar Mesons: φ f 0 (980) π + π and φ f 0 (980) π 0 π 0 : update of published result, new improved fit and coupling evaluation φ a 0 (980) ηπ 0 with 5 photons final state and 2 charged pions + 5 photons final state: New result for Branching Ratio and couplings, to be published Next to come: Combined fit to the two f 0 (980) decay channels φ f 0 (980) K S K S decay channel