Studying -Meson Decays with WASA-at-COSY 03.06.2016 Daniel Lersch - PowerPoint PPT Presentation

Mitglied der Helmholtz-Gemeinschaft Studying η -Meson Decays with WASA-at-COSY 03.06.2016 Daniel Lersch for the WASA-at-COSY collaboration Institute for Nuclear Physics - J¨ ulich Research Center

From Quarks to Mesons q f ( i γ µ D µ − m f ) q f − 1 L QCD (¯ � ¯ 4 G a q , q , g ) = µν G a µν f = u , d , s , c , b , t General Chiral Limit Energy � MeV ∼ GeV Quark mass m u , m d , m s , ..., � = 0 ( m u , m d , m s ) → 0 L- and R-Quarks coupled via m f decoupled chiral symmetry ∗ Symmetry SU ( 3 ) colour Theory Full QCD Full QCD → ChPT L QCD (¯ Lagrangian q , q , g ) L eff ( π, K , η ) = L 2 N + L WZW + ... K ∗ spontaneously broken in ground state Goldstone Theorem = ⇒ massless bosons ⇔ , 3 8 pseudoscalar ⋆ mesons: π, K , η ⋆ J = ℓ = s = 0 03.06.2016 Daniel Lersch for the WASA-at-COSY collaboration Slide 2

One Meson, many Opportunities m η = 0 . 5478 GeV / c 2 η Γ η = ( 1 . 31 ± 0 . 05 ) keV (Semi-)Leptonic τ ≈ 5 · 10 − 19 s c R n i ¯ o a r d d a H i a J PC = 0 − + = t i ⇒ η -meson is: v e C -, P -, G - and CP - eigenstate All strong and electromagnetic π π π γ γ γ l + l - γ decays are forbidden to first order (π + π - ) (π + π - ) (π + π - ) ( l + l - ) ⇒ Access to rare decay processes →Quark mass ratio →QCD anomalies →Transition Form Factor →Isospin violation →FSI →CP-violation η -Meson production at WASA-at-COSY: pd → 3 He η [ η → ... ] � σ ( η ) = ( 0 . 412 ± 0 . 016 ) µ b at T beam = 1 GeV 1 2 pp → pp η [ η → ... ] � σ ( η ) = ( 9 . 8 ± 1 ) µ b at T beam = 1 . 4 GeV 03.06.2016 Daniel Lersch for the WASA-at-COSY collaboration Slide 3

Wide Angle Shower Apparatus - WASA 03.06.2016 Daniel Lersch for the WASA-at-COSY collaboration Slide 4

Wide Angle Shower Apparatus - WASA E FRH(Layer1) [GeV] 0.14 0.12 0.1 0.08 ∆ 0.06 0.04 0.02 0 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 ∆ E FRH(Layer2) [GeV] 03.06.2016 Daniel Lersch for the WASA-at-COSY collaboration Slide 5

Wide Angle Shower Apparatus - WASA 03.06.2016 Daniel Lersch for the WASA-at-COSY collaboration Slide 5

The Data Sets × 3 10 2 Events per 0.65 MeV/c ≥ γ ≥ N(+q,-q) 1 and N( ) 2 450 400 350 300 250 GeV 2 c 200 = 0.5478 150 100 η m 50 0 0.35 0.4 0.45 0.5 0.55 0.6 0.65 GeV Missing mass (p , p , p , p ) 2 beam target 1 2 c Reconstruct η -meson via missing mass: | P in − P out | Background contributions from direct pion production reactions: pd → 3 HeX , pp → ppX with: X = π + π − , X = π 0 π 0 and X = π + π − π 0 pd → 3 He η pp → pp η Data taken in 2008 2009 2008 2010 2012 Duration of beam time 4 weeks 8 weeks 2 weeks 7 weeks 8 weeks ∼ 1 · 10 7 ∼ 2 · 10 7 ∼ 1 · 10 8 ∼ 4 · 10 8 ∼ 5 · 10 8 # η detected (pd) / produced (pp) 03.06.2016 Daniel Lersch for the WASA-at-COSY collaboration Slide 6

✞ ☎ η → π + π − π 0 The Dalitz Plot ✝ ✆ Dimensionless Dalitz plot variables: √ T π + − T π − X = 3 T π + + T π − + T π 0 3 T π 0 Y = T π + + T π − + T π 0 (a) KLOE coll., JHEP , 05, (2008) � 4 ¯ � Q D Decay via strong isospin violation: Γ meas = Γ Q Q 2 = m 2 m 2 s − ˆ u , ˆ m = 1 2 ( m u + m d ) m 2 d − m 2 ¯ Γ calculated with ChPT at Dashen limit, Q D = 24 . 2 dXdY ∝ ( 1 + aY + bY 2 + dX 2 + fY 3 + gX 2 Y + ... ) d 2 Γ Dalitz plot analysis: → c , e and h would imply C-violation 03.06.2016 Daniel Lersch for the WASA-at-COSY collaboration Slide 7

✞ ☎ η → π + π − π 0 Results from pd → 3 He η ✝ ✆ Parameter: − a b d f Theor. ChPT (NNLO) ( b ) 1 . 271 ( 75 ) 0 . 394 ( 102 ) 0 . 055 ( 57 ) 0 . 025 ( 160 ) NREFT ( c ) 1 . 213 ( 14 ) 0 . 308 ( 23 ) 0 . 050 ( 3 ) 0 . 083 ( 19 ) PWA ( e ) 1 . 116 ( 32 ) 0 . 188 ( 12 ) 0 . 063 ( 4 ) 0 . 091 ( 3 ) KLOE (08) ( a ) 1 . 090 ( 5 )( + 8 0 . 057 ( 6 )( + 7 Exp. − 19 ) 0 . 124 ( 6 )( 10 ) − 16 ) 0 . 14 ( 1 )( 2 ) WASA ( d ) 1 . 144 ( 18 ) 0 . 219 ( 19 )( 47 ) 0 . 086 ( 18 )( 15 ) 0 . 115 ( 37 ) KLOE (16) ( f ) 0 . 142 ( 3 )( 5 0 . 073 ( 3 )( + 4 0 . 154 ( 6 )( + 4 1 . 104 ( 3 )( 2 ) − 4 ) − 3 ) − 5 ) (a) KLOE coll., JHEP , 05, (2008) (b) J. Bijnens and K. Ghorbani., JHEP , 11, (2007) (c) S- P . Schneider et al., JHEP , 028, (2011) (d) WASA-at-COSY coll., Phys. Rev. , C90(045207), 2014 (e) Peng Guo et al., Phys. Rev. , D92(05016), (2015) (f) KLOE coll., JHEP , 019, (2016) ∼ 120 k η → π + π − π 0 events in the final 45000 2 + - 0 Analysis of η → π π π GeV/c Preliminary Data event sample 40000 MC cocktail -3 + - η → π π γ (0.5%) 10 35000 + - 0 Calculation from JPAC ⋆ group: η → π π π (99.5%) × Events per 0.65 + - 0 pp → pp π π π 30000 + - pp → pp π π Q = 21 . 4 ± 0 . 4 ( e ) 25000 20000 ⋆ Interactive web page: http://www.indiana.edu/ jpac/index.html 15000 (e) Peng Guo et al., Phys. Rev. , D92(05016), (2015) 10000 Dalitz plot analysis for 5000 pp → pp η [ η → π + π − π 0 ] in progress 0 0.35 0.4 0.45 0.5 0.55 0.6 0.65 GeV Missing mass (p ,p ,p ,p ) 2 beam target 1 2 c 03.06.2016 Daniel Lersch for the WASA-at-COSY collaboration Slide 8

✞ ☎ η → π + π − γ The box anomaly and π + π − FSI ✝ ✆ Γ Theory ( η → π + π − γ ) = 35 . 7 eV ( c ) Chiral limit: ( a ) , ( b ) Γ Exp. ( η → π + π − γ ) = ( 55 . 3 ± 2 . 4 ) eV ( d ) π + triangle anomaly box anomaly γ (c) B.R. Holstein, Phys. Scripta , T99:55-67, 2002 (d) PDG, Chin. Phys. , 090001, 2014 π η η η η 0 , , ' , ' γ L = + + ... Photon energy distribution E γ : ( e ) WZW (e) WASA-at-COSY coll. Phys. Lett. , B707:243-249, 2012 γ π - 9000 [a.u.] A η → π + π - γ 8000 Wess-Zumino-Witten Lagrangian γ Γ dE WASA-at-COSY: d → 3 η η → π + π - γ 7000 pd He [ ] (a) Wess, Zumino, Phys. Lett , B37(95), 1971 6000 (b) Witten, Nucl. Phys. , B223:422-432, 1983 5000 Decay amplitude A η → π + π − γ is sensitive to 4000 box anomaly ( c ) : 3000 � √ � e F π 2 F π 2000 A η → π + π − γ ∝ F 8 cos θ − F 0 sin θ √ 3 π 2 F 3 4 π 1000 0 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 η E in -rest frame [GeV] γ E γ ( s ππ ) = 1 � m η − s ππ � 2 · m η 03.06.2016 Daniel Lersch for the WASA-at-COSY collaboration Slide 9

✞ ☎ η → π + π − γ The box anomaly and π + π − FSI ✝ ✆ Γ Theory ( η → π + π − γ ) = 35 . 7 eV ( b ) Beyond chiral limit: Γ Exp. ( η → π + π − γ ) = ( 55 . 3 ± 2 . 4 ) eV ( c ) π + π + ρ π - (b) B.R. Holstein, Phys. Scripta , T99:55-67, 2002 (c) PDG, Chin. Phys. , 090001, 2014 π η η η η 0 , , ' , ' γ L = + + ... Photon energy distribution E γ : ( d ) WZW (d) WASA-at-COSY coll. Phys. Lett. , B707:243-249, 2012 γ π - 9000 [a.u.] α -2 A = 1.89 GeV η → π + π - γ α 8000 = 0 Wess-Zumino-Witten Lagrangian γ Γ dE WASA-at-COSY: d → 3 η η → π + π - γ & π + π − Final State Interactions 7000 pd He [ ] 6000 Modification of decay amplitude: ( a ) 5000 (a) F .Stollenwerk et al., Phys. Lett. , B707:184-190, 2012 4000 A η → π + π − γ × [ F PV ( s ππ ) × ( 1 + α s ππ )] 3000 2000 � by F PV α = 0 ⇒ Description of FSI: 1000 reaction specific ∗ α � = 0 0 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 *Input from theory η E in -rest frame [GeV] γ E γ ( s ππ ) = 1 � m η − s ππ � 2 · m η 03.06.2016 Daniel Lersch for the WASA-at-COSY collaboration Slide 9

✞ ☎ η → π + π − γ Theoretical Predictions and ✝ ✆ Recent Measurements Γ( η → π + π − γ ) / Γ( η → π + π − π 0 ) α [ GeV − 2 ] Gormley et al. 0 . 202 ± 0 . 006 1 . 8 ± 0 . 4 Thaler et al. 0 . 209 ± 0 . 004 - Experiment Layter et al. - − 0 . 9 ± 0 . 1 GAMS-200 ∗ - 2 . 7 ± 0 . 1 CRYSTAL BARREL ∗ - 1 . 8 ± 0 . 53 CLEO 0 . 175 ± 0 . 013 - WASA-at-COSY Preliminary: 0 . 206 ± 0 . 011 1 . 89 ± 0 . 86 1 . 32 ⋆ ± 0 . 2 KLOE 0 . 1856 ± 0 . 003 CLAS See talk by M.C. Kunkel (Session B) - Analysis ongoing for η and η ′ BESIII - N/D 0 . 2188 ± 0 . 0088 0 . 64 ± 0 . 02 Theory HLS 0 . 1875 ± 0 . 0094 0 . 23 ± 0 . 01 ( O ( p 6 ) + 1 − loop ) 0 . 1565 ± 0 . 0063 − 0 . 7 ± 0 . 1 Box anomaly 0 . 119 ± 0 . 0048 − 1 . 7 ± 0 . 02 ∗ Measured η ′ → π + π − γ / ⋆ Include effects of a 2 : Kubis and Plenter, Eur. Phys. J., C75: 283, 2015 Γ( η → π + π − γ ) Γ( η → π + π − π 0 ) and α via E γ -distribution in pp → pp η [ η → π + π − γ ] = ⇒ Determine 03.06.2016 Daniel Lersch for the WASA-at-COSY collaboration Slide 10