Citation: M. Tanabashi et al. (Particle Data Group), Phys. Rev. D 98, 030001 (2018) and 2019 update LIGHT UNFLAVORED MESONS (S = C = B = 0) For I =1(π, b, ρ, a): ud, (uu dd)/√2, du; − for I =0(η, η′, h, h′, ω, φ, f , f ′): c1(u u + d d) + c2(s s) ± G P π I (J )=1−(0−) Mass m = 139.57061 0.00024 MeV (S = 1.6) ± 8 Mean life τ = (2.6033 0.0005) 10− s (S=1.2) cτ = 7.8045 m ± × [a] π± ℓ± ν γ form factors ± → ± FV = 0.0254 0.0017 F = 0.0119 ± 0.0001 A ± FV slope parameter a = 0.10 0.06 +0.009 ± R = 0.059 0.008 − π− modes are charge conjugates of the modes below. For decay limits to particles which are not established, see the section on Searches for Axions and Other Very Light Bosons. p + π DECAY MODES Fraction (Γi /Γ) Confidence level (MeV/c) µ+ ν [b] (99.98770 0.00004) % 30 µ ± µ+ ν γ [c] ( 2.00 0.25 ) 10 4 30 µ ± × − e+ ν [b] ( 1.230 0.004 ) 10 4 70 e ± × − e+ ν γ [c] ( 7.39 0.05 ) 10 7 70 e ± × − e+ ν π0 ( 1.036 0.006 ) 10 8 4 e ± × − e+ ν e+ e ( 3.2 0.5 ) 10 9 70 e − ± × − e+ ν ν ν < 5 10 6 90% 70 e × − Lepton Family number (LF) or Lepton number (L) violating modes µ+ ν L [d] < 1.5 10 3 90% 30 e × − µ+ ν LF [d] < 8.0 10 3 90% 30 e × − µ e+ e+ ν LF < 1.6 10 6 90% 30 − × − 0 G PC + π I (J )=1−(0 − ) Mass m = 134.9770 0.0005 MeV (S = 1.1) ± mπ mπ0 = 4.5936 0.0005 MeV ± − ± 17 Mean life τ = (8.52 0.18) 10− s (S=1.2) cτ = 25.5 nm ± × HTTP://PDG.LBL.GOV Page1 Created: 5/22/2019 10:04 Citation: M. Tanabashi et al. (Particle Data Group), Phys. Rev. D 98, 030001 (2018) and 2019 update For decay limits to particles which are not established, see the appropriate Search sections (A0 (axion) and Other Light Boson (X 0) Searches, etc.). Scale factor/ p 0 π DECAY MODES Fraction (Γi /Γ) Confidence level (MeV/c) 2γ (98.823 0.034) % S=1.5 67 ± e+ e γ ( 1.174 0.035) % S=1.5 67 − ± γ positronium ( 1.82 0.29 ) 10 9 67 ± × − e+ e+ e e ( 3.34 0.16 ) 10 5 67 − − ± × − e+ e ( 6.46 0.33 ) 10 8 67 − ± × − 4γ < 2 10 8 CL=90% 67 × − ν ν [e] < 2.7 10 7 CL=90% 67 × − ν ν < 1.7 10 6 CL=90% 67 e e × − ν ν < 1.6 10 6 CL=90% 67 µ µ × − ν ν < 2.1 10 6 CL=90% 67 τ τ × − γ ν ν < 6 10 4 CL=90% 67 × − Charge conjugation (C) or Lepton Family number (LF ) violating modes 3γ C < 3.1 10 8 CL=90% 67 × − µ+ e LF < 3.8 10 10CL=90% 26 − × − µ e+ LF < 3.4 10 9 CL=90% 26 − × − µ+ e + µ e+ LF < 3.6 10 10CL=90% 26 − − × − G PC + + η I (J )=0 (0 − ) Mass m = 547.862 0.017 MeV ± Full width Γ = 1.31 0.05 keV ± C-nonconserving decay parameters + 0 +0.11 2 π π− π left-right asymmetry = (0.09 0.12) 10− − × π+ π π0 sextant asymmetry = (0.12+0.10) 10 2 − 0.11 × − π+ π π0 quadrant asymmetry = ( 0−.09 0.09) 10 2 − − ± × − π+ π γ left-right asymmetry = (0.9 0.4) 10 2 − ± × − π+ π γ β (D-wave) = 0.02 0.07 (S=1.3) − − ± CP-nonconserving decay parameters π+ π e+ e decay-plane asymmetry A = ( 0.6 3.1) 10 2 − − φ − ± × − Dalitz plot parameter π0 π0 π0 α = 0.0288 0.0012 (S = 1.1) − ± Parameter Λ in η ℓ+ ℓ γ decay = 0.716 0.011 GeV/c2 → − ± HTTP://PDG.LBL.GOV Page2 Created: 5/22/2019 10:04 Citation: M. Tanabashi et al. (Particle Data Group), Phys. Rev. D 98, 030001 (2018) and 2019 update Scale factor/ p η DECAY MODES Fraction (Γi /Γ) Confidence level (MeV/c) Neutral modes neutral modes (72.12 0.34) % S=1.2 – ± 2γ (39.41 0.20) % S=1.1 274 ± 3π0 (32.68 0.23) % S=1.1 179 ± π0 2γ ( 2.56 0.22) 10 4 257 ± × − 2π0 2γ < 1.2 10 3 CL=90% 238 × − 4γ < 2.8 10 4 CL=90% 274 × − invisible < 1.0 10 4 CL=90% – × − Charged modes charged modes (28.10 0.34) % S=1.2 – ± π+ π π0 (22.92 0.28) % S=1.2 174 − ± π+ π γ ( 4.22 0.08) % S=1.1 236 − ± e+ e γ ( 6.9 0.4 ) 10 3 S=1.3 274 − ± × − µ+ µ γ ( 3.1 0.4 ) 10 4 253 − ± × − e+ e < 7 10 7 CL=90% 274 − × − µ+ µ ( 5.8 0.8 ) 10 6 253 − ± × − 2e+ 2e ( 2.40 0.22) 10 5 274 − ± × − π+ π e+ e (γ) ( 2.68 0.11) 10 4 235 − − ± × − e+ e µ+ µ < 1.6 10 4 CL=90% 253 − − × − 2µ+ 2µ < 3.6 10 4 CL=90% 161 − × − µ+ µ π+ π < 3.6 10 4 CL=90% 113 − − × − π+ e ν + c.c. < 1.7 10 4 CL=90% 256 − e × − π+ π 2γ < 2.1 10 3 236 − × − π+ π π0 γ < 5 10 4 CL=90% 174 − × − π0 µ+ µ γ < 3 10 6 CL=90% 210 − × − Charge conjugation (C), Parity (P), Charge conjugation Parity (CP), or × Lepton Family number (×LF ) violating modes π0 γ C < 9 10 5 CL=90% 257 × − π+ π P,CP < 1.3 10 5 CL=90% 236 − × − 2π0 P,CP < 3.5 10 4 CL=90% 238 × − 2π0 γ C < 5 10 4 CL=90% 238 × − 3π0 γ C < 6 10 5 CL=90% 179 × − 3γ C < 1.6 10 5 CL=90% 274 × − 4π0 P,CP < 6.9 10 7 CL=90% 40 × − π0 e+ e C [f ] < 8 10 6 CL=90% 257 − × − π0 µ+ µ C [f ] < 5 10 6 CL=90% 210 − × − µ+ e + µ e+ LF < 6 10 6 CL=90% 264 − − × − HTTP://PDG.LBL.GOV Page3 Created: 5/22/2019 10:04 Citation: M. Tanabashi et al. (Particle Data Group), Phys. Rev. D 98, 030001 (2018) and 2019 update [g] G PC + + + f0(500) I (J )=0 (0 ) Mass (T-Matrix Pole √s) = (400–550) i(200–350) MeV − Mass (Breit-Wigner) = (400–550) MeV Full width (Breit-Wigner) = (400–700) MeV f0(500) DECAY MODES Fraction (Γi /Γ) p (MeV/c) π π seen – γ γ seen – [h] G PC + ρ(770) I (J )=1 (1 − −) Mass m = 775.26 0.25 MeV ± Full width Γ = 149.1 0.8 MeV ± Γ = 7.04 0.06 keV ee ± Scale factor/ p ρ(770) DECAY MODES Fraction (Γi /Γ) Confidence level (MeV/c) π π 100 % 363 ∼ ρ(770)± decays π γ ( 4.5 0.5 ) 10 4 S=2.2 375 ± ± × − π η < 6 10 3 CL=84% 152 ± × − π π+ π π0 < 2.0 10 3 CL=84% 254 ± − × − ρ(770)0 decays π+ π γ ( 9.9 1.6 ) 10 3 362 − ± × − π0 γ ( 4.7 0.6 ) 10 4 S=1.4 376 ± × − η γ ( 3.00 0.21 ) 10 4 194 ± × − π0 π0 γ ( 4.5 0.8 ) 10 5 363 ± × − µ+ µ [i] ( 4.55 0.28 ) 10 5 373 − ± × − e+ e [i] ( 4.72 0.05 ) 10 5 388 − ± × − + 0 +0.54 4 π π− π ( 1.01 0.36 0.34) 10− 323 − ± × π+ π π+ π ( 1.8 0.9 ) 10 5 251 − − ± × − π+ π π0 π0 ( 1.6 0.8 ) 10 5 257 − ± × − π0 e+ e < 1.2 10 5 CL=90% 376 − × − G PC ω(782) I (J )=0−(1 − −) Mass m = 782.65 0.12MeV (S =1.9) ± Full width Γ = 8.49 0.08 MeV ± Γ = 0.60 0.02 keV ee ± HTTP://PDG.LBL.GOV Page4 Created: 5/22/2019 10:04 Citation: M. Tanabashi et al. (Particle Data Group), Phys. Rev. D 98, 030001 (2018) and 2019 update Scale factor/ p ω(782) DECAY MODES Fraction (Γi /Γ) Confidence level (MeV/c) π+ π π0 (89.3 0.6 ) % 327 − ± π0 γ ( 8.40 0.22) % S=1.8 380 ± π+ π ( 1.53 0.06) % 366 − ± 0 +7 3 neutrals (excludingπ γ ) ( 7 4 ) 10− S=1.1 – − × η γ ( 4.5 0.4 ) 10 4 S=1.1 200 ± × − π0 e+ e ( 7.7 0.6 ) 10 4 380 − ± × − π0 µ+ µ ( 1.34 0.18) 10 4 S=1.5 349 − ± × − e+ e ( 7.36 0.15) 10 5 S=1.5 391 − ± × − π+ π π0 π0 < 2 10 4 CL=90% 262 − × − π+ π γ < 3.6 10 3 CL=95% 366 − × − π+ π π+ π < 1 10 3 CL=90% 256 − − × − π0 π0 γ ( 6.7 1.1 ) 10 5 367 ± × − η π0 γ < 3.3 10 5 CL=90% 162 × − µ+ µ ( 7.4 1.8 ) 10 5 377 − ± × − 3γ < 1.9 10 4 CL=95% 391 × − Charge conjugation (C) violating modes η π0 C < 2.2 10 4 CL=90% 162 × − 2π0 C < 2.2 10 4 CL=90% 367 × − 3π0 C < 2.3 10 4 CL=90% 330 × − invisible < 7 10 5 CL=90% – × − ′ G PC + + η (958) I (J )=0 (0 − ) Mass m = 957.78 0.06 MeV ± Full width Γ = 0.196 0.009 MeV ± p η′′(958) DECAY MODES Fraction (Γi /Γ) Confidence level (MeV/c) π+ π η (42.6 0.7 ) % 232 − ± ρ0 γ (including non-resonant (28.9 0.5 ) % 165 + ± π π− γ) π0 π0 η (22.8 0.8 ) % 239 ± ω γ ( 2.62 0.13) % 159 ± ω e+ e ( 2.0 0.4 ) 10 4 159 − ± × − γ γ ( 2.22 0.08) % 479 ± 3π0 ( 2.54 0.18) 10 3 430 ± × − µ+ µ γ ( 1.09 0.27) 10 4 467 − ± × − π+ π µ+ µ < 2.9 10 5 90% 401 − − × − π+ π π0 ( 3.61 0.17) 10 3 428 − ± × − (π+ π π0) S-wave ( 3.8 0.5 ) 10 3 428 − ± × − HTTP://PDG.LBL.GOV Page5 Created: 5/22/2019 10:04 Citation: M.