Light Hadron Decays at

Transcription

1 Light Hadron Decays at Magnus Wolke Department of Physics and Astronomy

2 Light Hadron Decays at Focus in this talk: Decays of η Magnus Wolke Department of Physics and Astronomy

3 η and decays..are a perfect laboratory to explore the effective theory of QCD at low energies symmetry breaking mechanisms in low-energy QCD the η and η electromagnetic structure (TFF muon g-2) potential physics beyond the Standard Model mη = 548 MeV, Γη = 1.3 kev η π 0 π 0 π0 η π+ π- π 0 mη = 958 MeV, Γη = 200 kev hadronic decays 33 % 23 % π+ π- η π0 π0 η 43 % 23 % radiative decays η γγ η π+ π- γ 39 % 4% Σ 99 % ρ0 γ ωγ γγ 29 % 3% 2% Σ 99 %

4 η and decays at BESIII data J/Ψ events LINAC J / Ψ η(') γ η BESIII BEPCII J / Ψ η(') ϕ( K + K - ) η World s largest data sample of J/Ψ unique opportunity for large statistics data samples on η and η decays

5 Light Hadron Decays at ηππ γe+e πππ ωe+e γπ+π- γγπ0 Magnus Wolke Department of Physics and Astronomy

6 ηππ X= 3(T π1 T π 2) Q Y= (m η+2 m π ) T η 1 mπ Q Q=m m η 2m π T i =kinetic energies in rest frame 2 2 si =( P0 Pi ) =M jk x general representation of decay amplitude: linear representation of decay amplitude: M ( X,Y ) 2 1+aY +by 2 +cx +dx M ( X,Y ) 1+α Y +cx +dx +... representations equivalent if b > a2/4 > 0 isospin limit: identical parameters for ηπ0π0 and ηπ+π- a, b, c, d, real α complex

7 + - ηπ π at BESIII M.Ablikim et al., PRD 97 (2018) events 0.3% background

8 + - ηπ π at BESIII M.Ablikim et al., PRD 97 (2018) general parameterization a b c d = 0.056±0.004±0.003 = 0.049±0.006±0.006 = ±0.0024± = ±0.0004± a deviates from VES result by 3.8 σ b < 0: linear parameterization inadequate to describe data c consistent with zero most accurate data presently available!

9 0 0 ηπ π at BESIII M.Ablikim et al., PRD 97 (2018) events 0.9% background

10 0 0 ηπ π at BESIII M.Ablikim et al., PRD 97 (2018) general parameterization a b c d = 0.087±0.009±0.006 = 0.073±0.014±0.005 = = 0.074±0.009±0.004 a deviates from ηπ+π- result by 2.6 σ b < 0: linear parameterization inadequate to describe data similar precision from A2 at MAMI parameters agree within errors P.Adlarson et al., arxiv:

11 Comparison of ηπ π and ηπ π M.Ablikim et al., PRD 97 (2018) ηπ0π0 and ηπ+π- data and fit results normalized to phase space cusp effect expected in ηπ0π0 due to π+πthreshold as in K+ π+π-π0 Isken, Kubis, Schneider, Stoffer, EPJC 77 (2017) 489 present statistics not sufficient to identify cusp effect

12 πππ Motivation: decay potentially sensitive to light quark mass ratio Gross, Treiman, Wilczek, PRD 19 (1979) 2188 assumptions: decay proceeds entirely via π-η mixing decay amplitude constant over phase space But: both assumptions are found not to be valid in U(3) ChPT other tree diagrams important significant rescattering effects expected Borasoy, Nissler, EPJA 26 (2005) 383 Borasoy, Meissner, Nissler, PLB 643 (2006) 41

13 πππ at BESIII M.Ablikim et al., PRL 118 (2017) π+π-π events two clusters from ρ +- π -+ peaking bg from ρ γ π0π0π events low background peaking bg from ηπ 0 π 0

14 πππ at BESIII M.Ablikim et al., PRL 118 (2017) isobar model for Dalitz plot analysis Garcia-Martin, Kaminski, Pelaez, Ruiz de Elvira, Yndurain, PRD 83 (2011) i) P-wave ρπ ii) resonant S-wave σπ Iii) non-resonant Swave πππ s-wave interference sensitive only to sum of s-wave components Note: B( π0π0π0) twice as large as reported by GAMS! Alde et al., ZPC 36 (1987) 603

15 + - γπ π at BESIII dominated by γρ0 M.Ablikim et al., arxiv: model dependent fits to M(π+π-) evidence for box anomaly (4σ) reported by Crystal Barrel (7490±180 events), not confirmed by L3 (2123±53 events) Abele et al., PLB 402 (1997) 195 Acciarri et al., PLB 418 (1998) 399 BESIII preliminary BESIII: events, level of background < 1.5% p-wave dipion system BESIII preliminary BESIII preliminary

16 + - γπ π : model dependent fits M.Ablikim et al., arxiv: ρ0, ω, box anomaly and interference χ2/ndf = 207/107 Akhmetshin et al., PLB 527 (2002) 161 BESIII preliminary ρ0, ω, ρ(1450) and interference χ2/ndf = 303/106 only ρ0, ω not sufficient to describe data ω contribution observed tail of ρ(1450) similar line shape as box anomaly contribution refined model dependent amplitude necessary BESIII preliminary

17 + - γπ π : model independent fit M.Ablikim et al., arxiv: A=N P( s) F v (s) Stollenwerk, Hanhart, Kupsc, Meissner, Wirzba, PLB 707 (2012) 184 BESIII preliminary P (s)=1+ κ s+λ s2 + ξ BW ω +O(s 4 ) F v ( s)=π vector form factor ω and quadratic term significant κ = 0.992±0.039 GeV -2 λ = 0.523±0.039 GeV -4 ξ = 0.199±0.006 χ2/ndf = 145/109

18 + - γe e Dalitz decay Landsberg, PRP 128 (1985) 301 HLbL contribution to αμ contains two meson-photon-photon vertices, which can be related to the TFF point-like particle transition form factor + - related to η π π γ: knowledge of TFF can reduce uncertainty in SM prediction for αμ TFF can be predicted from M(π+π-) and B(η π+π-γ) in model independent way Hanhart, Kupsc, Meissner, Stollenwerk, Wirzba, EPJC 73 (2013) 2668 prior to BESIII result: only η μ+μ-γ measured at Serpukhov PS, slope b = (df(q2)/dq2) q2=0 = 1.7 ± 0.4 GeV-2 Dzelyadin et al., PLB 88 (1979) 379

19 + - γe e Dalitz decay at BESIII M.Ablikim et al., PRD 92 (2015) primary peaking background: η γγ, followed by γ conversion cut on δxy < 2.0cm: retains 80% of signal conversion events reduced to 5% of signal signal non-peaking bg peaking bg Γ( γ e + e - ) 2 =2.13±0.09± Γ( γ γ) B ( γ e + e - )=4.69±0.20± consistent with VMD prediction + Γ( γ e e ) 2 =2.06± Γ( γ γ) Petri, arxiv:

20 + - γe e Dalitz decay at BESIII bin-by-bin fit M.Ablikim et al., PRD 92 (2015) Exp QED VMD: single-pole theoretical predictions VMD b = 1.45 GeV 2 b = 1.60 GeV 2 ChPT b = GeV 2 dispersion Bramon, Masso, PLB 104 (1981) 311 Amettler, Bijnens, Bramon, Cornet, PRD 45 (1992) 986 Hanhart, Kupsc, Meissner, Stollenwerk, Wirzba, EPJC 73 (2013) 2668 fit result Λ = γ = b 0.79±0.04 ±0.02GeV 0.13±0.06±0.03 GeV = 1.60±0.17±0.08 GeV 2 TFF slope in agreement with theoretical predictions

21 + - ωe e at BESIII M.Ablikim et al., PRD 92 (2015) st ev e fi r beam pipe ro bs er va tio n major background: ωγ and γ e+e- in detector material inner MDC wall Γ( ω e + e - ) 3 =7.71±1.34± Γ( ω γ) in good agreement with theoretical prediction Faessler, Fuchs, Krivoruchenko, PRC 61 (2000)

22 0 π γγ at BESIII M.Ablikim et al., PRD 96 (2017) expected to be dominated by η γω γγπ0 can test QCD calculation on TFF signal: incoherent sum of ρ, ω and non-resonant component class I bg: η ηπ0π0, η 3π0 class II bg: J/Ψ γπ0π0, J/Ψ ωη B ( γ γ π 0 )incl=3.20±0.07± much lower than theoretical prediction (linear sigma model and VMD) Jora, NPB PS (2010) 224 Escribano, PoS QNP2012 (2012) 079

23 0 π γγ at BESIII M.Ablikim et al., PRD 96 (2017) fit of γπ0 invariant mass including η γω η γρ ρ-ω interference non-resonant η γγπ0 neglecting interference between non-resonant and resonant processes B ( γ γ π 0 )NR=6.16±0.64± agrees with upper limit by GAMS-2000 Alde et al, ZPC 36 (1987) 603 both inclusive and non-resonant BR measured for the first time!

24 decays at decay mode + - ηπ π 0 0 ηπ π π+ π- γ π π π (π π π )s π π π + e eγ + e eω 0 γγπ π π π π π π π π events B ( 10-4) remark ± ± ± ± 0.54± ± 0.77±2.22± ± 0.82±2.60 prev 20k evts prev 15k evts prev 10k evts prev 20 evts first data prev 235 evts 864 ± ± ± 68 4,69 ± 0.20± ± 0.34± ± 0.64±0.67 first data first data first data 199 ± ± ± 0.069± ± 0.35±0.18 first data first data present statistics: J/ψ η 1-2 orders of magnitude beyond world statistics low level of background data taking at BESIII continued near future goal: J/ψ

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