Mitglied der Helmholtz-Gemeinschaft The η-meson Decay Program at WASA-at-COSY 15.09.2015 Daniel Lersch for the WASA-at-COSY collaboration XVI International Conference on Hadron Spectroscopy
The η-meson! " " " # #, (" + " - ) l + Hadronic Radiative l - (Semi-)Leptonic #, (" + " - ), (l + l - ) m η = 0.5478 GeV/c 2, τ 5 10 19 s (Γ η = (1.31 ± 0.05) kev) J PC = 0 + η-meson is: C-, P-, G- and CP- eigenstate All strong and electromagnetic decays are forbidden to first order Access to rare decay processes: Explore anomalous sector of QCD Determine electromagnetic transition form factors Study of symmetry-breaking-phenomena η-meson production at WASA-at-COSY: 1 pd 3 Heη[η...] σ(η) = (0.412 ± 0.016) µb at T beam = 1 GeV 2 pp ppη[η...] σ(η) = (9.8 ± 1) µb at T beam = 1.4 GeV 15.09.2015 Daniel Lersch for the WASA-at-COSY collaboration Slide 2
2 The data sets Events per 0.65 MeV/c 450 400 350 300 250 200 150 100 50 3 10 N(+q,-q) 1 and N(γ) 2 GeV c 2 = 0.5478 m η 0 0.35 0.4 0.45 0.5 0.55 0.6 0.65 Missing mass (p, p, p, p ) GeV beam target 1 2 c 2 Reconstruct η-meson via missing mass: P in P out Background contributions from direct pion production reactions: pd 3 HeX, pp ppx X = π + π, X = π 0 π 0 and X = π + π π 0 pd 3 Heη pp ppη Data taken in 2008 2009 2008 2010 2012 Duration of beam time 4 weeks 8 weeks 2 weeks 7 weeks 8 weeks η-mesons detected / produced 1 10 7 2 10 7 1 10 8 4 10 8 5 10 8 15.09.2015 Daniel Lersch for the WASA-at-COSY collaboration Slide 3
Wide Angle Shower Apparatus - WASA Example: pp ppη[η π + π γ] 15.09.2015 Daniel Lersch for the WASA-at-COSY collaboration Slide 4
η π + π π 0 Dalitz plot analysis Dalitz plot variables: X = 3 Y = T π + T π T π + +T π +T π 0 3T π 0 T π + +T π +T π 0 (a) KLOE coll., JHEP, 05, (2008) Decay via strong isospin violation: Γ meas = ( QD Q ) 4 Γ Q 2 = m2 s ˆm2, ˆm = 1 m d 2 m2 2 (mu + m d) u Γ calculated with ChPT at Dashen limit, Q D = 24.2 dγ Dalitz plot analysis: (1 + ay + by 2 + dx 2 + fy 3 + gx 2 Y +...) dxdy c, e and h would imply C-violation 15.09.2015 Daniel Lersch for the WASA-at-COSY collaboration Slide 5
η π + π π 0 Results from pd 3 Heη Parameter: a b d f Theo. 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) Exp. KLOE (a) 1.090(5)( +8 19 ) 0.124(6)(10) 0.057(6)(+7 16 ) 0.14(1)(2) WASA (d) 1.144(18) 0.219(19)(47) 0.086(18)(15) 0.115(37) (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 1.2 10 5 η π + π π 0 events selected via a kinematic fit for the final event sample Dalitz plot analysis for pp ppη[η π + π π 0 ] in progress 15.09.2015 Daniel Lersch for the WASA-at-COSY collaboration Slide 6
η π + π γ The box anomaly and π + π FSI Beyond chiral limit: ρ π + π + Γ Theory (η π + π γ) = 35.7 ev (b) Γ Exp. (η π + π γ) = (55.3 ± 2.4) ev (c) - π (b) B.R. Holstein, Phys. Scripta, T99:55-67, 2002 π 0,η,η' L WZW = + +... γ η,η' Include π + π Final State Interactions - π Modification of decay amplitude: (a) (a) F.Stollenwerk et al., Phys. Lett., B707:184-190, 2012 A η π + π γ [F PV (s ππ) (1 + αs ππ)] Description of FSI: *Input from theory { by F PV α = 0 reaction specific α 0 γ (c) PDG, Chin. Phys., 090001, 2014 Photon energy distribution E γ: (d) (d) WASA-at-COSY coll. Phys. Lett., B707:243-249, 2012 [a.u.] de d Γ γ 9000 8000 7000 6000 5000 4000 3000 2000 1000-2 α = 1.89 GeV α = 0 WASA-at-COSY: + - pd 3 Heη[η π π γ] A η π + - π γ 0 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 E γ in η-rest frame [GeV] = Determine Γ(η π+ π γ) Γ(η π + π π 0 ) and α via Eγ-distribution in pp ppη[η π+ π γ] 15.09.2015 Daniel Lersch for the WASA-at-COSY collaboration Slide 7
η π + π γ Status in pp ppη 2 Events per 0.65 MeV/c 22000 Analysis of η π + π - γ 20000 Data 18000 MC cocktail - 16000 η π + π γ 14000 η π + π - π 0 12000 pp ppπ + π - π 0 - pp ppπ + π 10000 8000 Preliminary [a.u.] de d Γ γ 14000 Preliminary 12000 10000 8000 6000 6000 4000 4000 2000 2000 0 0.35 0.4 0.45 0.5 0.55 0.6 0.65 GeV Missing mass (p,p,p,p ) c 2 beam target 1 2 0 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 E γ in η-rest frame [GeV] 209 k η π + π γ events reconstructed i) Rejection of wrongly reconstructed photons Reduce background from pp ppπ + π ii) Kinematic fit Further reduction of multi pion background and improvement of E γ resolution E γ distribution after background correction from direct pion production Next steps (ongoing): 1.) Include efficiency corrections for different assumptions on α 2.) Calculate Γ(η π+ π γ) and determine α Γ(η π + π π 0 ) 15.09.2015 Daniel Lersch for the WASA-at-COSY collaboration Slide 8
η π + π e + e η π + π γ CP-conserving for M 1 and E 2 transitions Access to CP-violation: Measure E 1 transition Need information about polarisation of single photon CP-Violation η π + π γ [γ e + e ] Look at asymmetry A Φ (a) of angle Φ between decay planes of electrons and pions: A Φ = N(sin[Φ] cos[φ]>0) N(sin[Φ] cos[φ]<0) N(sin[Φ] cos[φ]>0)+n(sin[φ] cos[φ]<0) Upper limit predicted by theory (a) : 1% Results found by KLOE: (b) 1.) A Φ = ( 0.6 ± 2.5 stat ± 1.8 sys) 10 2 2.) Γ(η π + π e + e ) Γ η = (2.68 ± 0.09 stat ± 0.07 sys) 10 4 (a) D. Gao. Mod. Phys. Lett., A17:1583-1588, 2002 (b) KLOE coll. Phys. Lett., B675:283-288-914, 2009 15.09.2015 Daniel Lersch for the WASA-at-COSY collaboration Slide 9
η π + π e + e Results from pd 3 Heη Preliminary Entries / (0.04) 45 40 35 30 - - η π + π e + e events (includes background) Flat reference distribution Prelimiary 25 20 15 10 5 0.5 0.4 0.3 0.2 0.1 0 0.1 0.2 0.3 0.4 0.5 sin φ cos φ 251 ± 17 η π + π e + e events in the final sample i) Rejection of photon conversion events Reduce contributions from η π + π γ / η π + π π 0 ii) Identification of π ± and e ± in the mixed final state Crucial for the determination of A Φ iii) Kinematic fit Reduction of η π + π π 0 [π 0 e + e γ] Preliminary: 1.) A Φ = ( 1.1 ± 6.6 stat ± 0.2 sys) 10 2 Γ(η π + π e + e ) Γ η 2.) = (2.7 ± 0.2 stat ± 0.2 sys) 10 4 Need more statistics ppη data set 15.09.2015 Daniel Lersch for the WASA-at-COSY collaboration Slide 10
η π + π e + e Status in pp ppη Analysis procedure shown above done for a fraction of 2010 pp ppη data set: (c) 220 η π + π e + e events reconstructed 1, 000 events expected for full pp ppη data sample Analysis in pp ppη needs to be continued (c) D. Coderre,PhD Thesis, 2012 15.09.2015 Daniel Lersch for the WASA-at-COSY collaboration Slide 11
η e + e γ and η e + e e + e Dalitz decays Single off-shell transition form factor F (q 2 ) [ ] dγ dq = dγ 2 dq F 2 QED (q2 ) 2 Observables to test: Γ(η e+ e γ) Γ η and Dilepton mass Recent result: Γ(η e+ e γ) = (6.9 ± 0.4) 10 Γ 3(a) η (a) K. Olive et al. Chin. Phys., C38, 090001, 2014 Double off-shell transition form factor F (q 2 1, q2 2 ) Different approaches for calculation of F (b) Observable to test: Γ(η e+ e e + e ) Γ η Current result measured by KLOE: (c) Γ(η e + e e + e ) =(2.4±0.2 Γη stat ±0.1 sys) 10 5 (b) J. Bijnens et al. arxiv:hep-ph/0106130v1, 2001 (c) KLOE coll. Phys. Lett., B702:324-328, 2011 15.09.2015 Daniel Lersch for the WASA-at-COSY collaboration Slide 12
η e + e γ and η e + e e + e Results from pd 3 Heη Preliminary Preliminary 14, 040 ± 120 events η e + e γ events reconstructed Preliminary: Γ(η e+ e γ) Γ η = (6.72 ± 0.07 stat ± 0.31 sys) 10 3 18 ± 5 η e + e e + e events reconstructed Preliminary: Γ(η e+ e e + e ) Γ η = (3.2 ± 0.9 stat ± 0.5 sys) 10 5 Need more statistics ppη data set Challenges in analysis: i) Dilepton pairs from conversion events at the beam pipe ii) Handling of large pion background 15.09.2015 Daniel Lersch for the WASA-at-COSY collaboration Slide 13
η e + e γ Status in pp ppη Preliminary Reduce uncertainty of F(q 2 ) at high q 2 : Increase statistics ppη data set 29 k η e + e γ events reconstructed in current pp ppη[η e + e γ] analysis i) PID Reduction of pions ii) Rejection of conversion events Suppression of η γγ iii) Check for energy and momentum conservation In preparation: 1.) Calculation of Γ(η e+ e γ) Γ η 2.) Dilepton invariant mass distribution F(q 2 ) Analysis of pp ppη[η e + e e + e ] in preparation 15.09.2015 Daniel Lersch for the WASA-at-COSY collaboration Slide 14
η π 0 e + e Different decay models: C-Violation?! Forbidden by SM: BR(η π 0 e + e 5 (a) ) < 4 10 Investigate existing upper limit BR with hight statistics pp ppη data set entries / bin 15 10 5 p r e l i m i n a r y (a) K. Olive et al. Chin. Phys., C38, 090001, 2014 0 0 0.1 2 invariant 0.2 mass 0.3 of lepton 0.4 pair 0.5 / GeV/c 0.6 15.09.2015 Daniel Lersch for the WASA-at-COSY collaboration Slide 15
Summary and Outlook Decay mode Γ(η...)/Γ η (a) Issue η π 0 π 0 π 0(b) (32.68 ± 0.23)% Dalitz plot analysis η π + π π 0(c) (22.92 ± 0.28)% Dalitz plot analysis η π + π γ (d) (4.22 ± 0.08)% Box anomaly, π + π -FSI η e + e γ (e) (0.69 ± 0.11)% Single-off-shell transition form factor η π 0 γγ (2.7 ± 0.5) 10 4 Test of ChPT η π + π e + e (e) (2.68 ± 0.11) 10 4 CP-Violation η e + e e + e (e) (2.40 ± 0.22) 10 5 Double-off-shell transition form factor η π 0 e + e < 4 10 5 C-Violation η e + e < 5.6 10 6 Physics beyond the SM 1 pd 3 Heη[η...] 2 pp ppη[η...] Analysis ongoing (a): PDG, Chin. Phys., 090001, 2014 (b): WASA-at-COSY coll., Phys. Lett., B677:24-29, 2009 (c): WASA-at-COSY coll., Phys. Rev., C90(045207), 2014 (d): WASA-at-COSY coll., Phys. Lett., B707:243-249, 2012 (e): Publication in preparation More fun with η-decays: See talk by M. Kunkel (1F1) 15.09.2015 Daniel Lersch for the WASA-at-COSY collaboration Slide 16
Contents (2) The η-meson (3) The data set (4) WASA η π + π π 0 (5) Dalitz plot analysis (6) Results from pd 3 Heη η π + π γ (7) The box anomaly and π + π FSI (8) Status in pp ppη η π + π e + e (9) CP-Violation (10) Results from pd 3 Heη (11) Status in pp ppη η e + e γ and η e + e e + e (12) Dalitz decays (13) Results from pd 3 Heη (14) Status in pp ppη η π 0 e + e (15) C-Violation (16) Summary and Outlook 15.09.2015 Daniel Lersch for the WASA-at-COSY collaboration Slide 17
Backup η π + π γ Theoretical Models Theoretical Predictions and Recent Measurements Analysis (Split-off rejection) Analysis (Kinematic fit) Determining the E γ -distribution η e + e γ and η e + e e + e Form factor F (q 2 ) Theoretical predictions for Γ(η e + e e + e )/Γ(η) Conversion events η Production mechanisms Preselection of the pp ppη data set PID at WASA 15.09.2015 Daniel Lersch for the WASA-at-COSY collaboration Slide 18
η π + π γ Theoretical Models N/D-Model: a) One-loop chiral corrections and VMD [ 1+0.5m 2 ] Modify A η π + π γ with: ρ sππ D 1 (sππ ) a) B.R. Holstein, Phys. Scripta, T99:55-67, 2002 [a.u.] de d Γ γ 50000 40000 30000 20000 10000 0 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 E γ in η-rest frame [GeV] 15.09.2015 Daniel Lersch for the WASA-at-COSY collaboration Slide 19
η π + π γ Theoretical Models N/D-Model: a) One-loop chiral corrections and VMD [ 1+0.5m 2 ] Modify A η π + π γ with: ρ sππ D 1 (sππ ) HLS (Hidden Local Symmetries)-Model: b) γ V Transitions Modify A η π + π γ with: [ 1 + 3m2 ] ρ Dρ(sππ ) [a.u.] de d Γ γ a) B.R. Holstein, Phys. Scripta, T99:55-67, 2002 b) M.Benayoun et al., Europ. Phys. Journal, C31:525-547, 2003 50000 40000 30000 20000 10000 0 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 E γ in η-rest frame [GeV] 15.09.2015 Daniel Lersch for the WASA-at-COSY collaboration Slide 19
η π + π γ Theoretical Models N/D-Model: a) One-loop chiral corrections and VMD [ 1+0.5m 2 ] Modify A η π + π γ with: ρ sππ D 1 (sππ ) HLS (Hidden Local Symmetries)-Model: b) γ V Transitions Modify A η π + π γ with: O(p 6 ) + 1 loop-modell: c) [ 1 + 3m2 ] ρ Dρ(sππ ) Higher momentum orders O(p 6 ) and one loop chiral corrections Modify A η π + π γ with: [ 1 + C loops + 3 2mρ 2 (p π + + p π ) 2] [a.u.] de d Γ γ a) B.R. Holstein, Phys. Scripta, T99:55-67, 2002 b) M.Benayoun et al., Europ. Phys. Journal, C31:525-547, 2003 c) J.Bijnens et al., Phys. Lett., B237:488-494, 1990 50000 40000 30000 20000 10000 0 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 E γ in η-rest frame [GeV] 15.09.2015 Daniel Lersch for the WASA-at-COSY collaboration Slide 19
η π + π γ Theoretical Models N/D-Model: a) One-loop chiral corrections and VMD [ 1+0.5m 2 ] Modify A η π + π γ with: ρ sππ D 1 (sππ ) HLS (Hidden Local Symmetries)-Model: b) γ V Transitions Modify A η π + π γ with: O(p 6 ) + 1 loop-modell: c) [ 1 + 3m2 ] ρ Dρ(sππ ) Higher momentum orders O(p 6 ) and one loop chiral corrections Modify A η π + π γ with: [ 1 + C loops + 3 2mρ 2 (p π + + p π ) 2] Pion-Vektor-Formfactor: d) π + π -interactions (universal) Modify A η π + π γ with: F PV (s ππ) a s 3 ππ + b s2 ππ + c sππ + d [a.u.] de d Γ γ a) B.R. Holstein, Phys. Scripta, T99:55-67, 2002 b) M.Benayoun et al., Europ. Phys. Journal, C31:525-547, 2003 c) J.Bijnens et al., Phys. Lett., B237:488-494, 1990 d) F.Stollenwerk et al., Phys. Lett., B707:184-190, 2012 50000 40000 30000 20000 10000 0 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 E γ in η-rest frame [GeV] 15.09.2015 Daniel Lersch for the WASA-at-COSY collaboration Slide 19
η π + π γ Theoretical Predictions and Recent Measurements Experiment Theory 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 - 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 KLOE 0.1856 ± 0.003 1.32 ± 0.2 CLAS Analysis ongoing - N/D 0.2188 ± 0.0088 0.64 ± 0.02 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 15.09.2015 Daniel Lersch for the WASA-at-COSY collaboration Slide 20
η π + π γ Theoretical Predictions and Recent Measurements Experiment Theory Γ(η π + π γ)/γ(η π + π π 0 ) α [GeV 2 ] Phys. Rev.,D2:501-505, 1970 0.202 ± 0.006 1.8 ± 0.4 Phys. Rev.,D7:2569-2571, 1973 0.209 ± 0.004 - Phys. Rev.,D7:2565-2568, 1973-0.9 ± 0.1 Phys.,C50:451-454, 1991-2.7 ± 0.1 Phys. Lett.,B402:195, 1997-1.8 ± 0.53 Phys. Rev. Lett.,99(122001), 2007 0.175 ± 0.013 - Phys. Rev. Lett.,B707:243-249, 2013-1.89 ± 0.86 Phys. Lett.,B718:910-914, 2013 0.1856 ± 0.003 1.32 ± 0.2 Chin. Phys., 090001, 2014 0.1847 ± 0.003 - Phys. Scripta, T99:55-67, 2002 0.2188 ± 0.0088 0.64 ± 0.02 Europ. Phys. Journal, C31:525-547, 2003 0.1875 ± 0.0094 0.23 ± 0.01 Phys. Lett., B237:488-494, 1990 0.1565 ± 0.0063 0.7 ± 0.1 Phys. Scripta, T99:55-67, 2002 0.119 ± 0.0048 1.7 ± 0.02 Measured η π + π γ 15.09.2015 Daniel Lersch for the WASA-at-COSY collaboration Slide 20
η π + π γ Analysis i) Rejection of split-offs One (charged) particle in the calorimeter No split-off split-off Edep = 0 Edep! 0 (charged) particle (charged) particle Hit in calorimeter is assigned to a cluster Split-off: Satellite cluster with close distance to primary cluster low energy fake photon Predominant background: pp ppπ + π (γ) Reject low energy fake photons with close distance to primary cluster 15.09.2015 Daniel Lersch for the WASA-at-COSY collaboration Slide 21
ii) Kinematic fit η π + π γ Analysis Counts per bin 10 7 6 10 5 10 10 4 3 10 10 2 10 reject + - Fit hypothesis: pp ppπ π γ Data accept MC cocktail + - η π π γ η π + π - π 0 + - η e e γ pp ppπ + π - π 0 + - pp ppπ π 1 0 0.2 0.4 0.6 0.8 1 Probability P(χ 2 pp ppπ,4) + π - γ Least squares fit: χ 2 Np Nv ( v fit v ij meas ) ij 2 = +2 σ i=1 j=1 ij meas λ µf µ(v11 fit,..., vfit µ Np Nv ) F µ: energy and momentum conservation 4 constraints P(χ 2 1, N) = e t 2 t 1 2 N Γ( 1 2 N 1 dt 2 N) χ 2 Use kinematic fit to: a) Improve resolution b) Suppress background 15.09.2015 Daniel Lersch for the WASA-at-COSY collaboration Slide 22
η π + π γ Determining the E γ -distribution Scan two proton missing mass distribution in E γ-intervals Subtract background for each E γ-interval Obtain number of η π + π γ events 15.09.2015 Daniel Lersch for the WASA-at-COSY collaboration Slide 23
η e + e γ Form factor F (q 2 ) a) Result of the CB/TAPS b) Results of the Lepton-G (open circles) Single-pole measurement formula: of thef η e + e P (q 2 ) = (1 γ bpq 2 and 2 ) 1 the, b P NA60 1 (triangles) measurements of the η µ + µ γ decay. The Λ P decay [28] solid and dashed-dotted lines are fits to 15.09.2015 Daniel Lersch for the WASA-at-COSY collaboration Slide 24
η e + e e + e Theoretical predictions for Γ(η e + e e + e )/Γ(η) Double transition form factor F(q 2 1, q 2 2) Different approaches for calculation of F (a) : F (q 2 1, q 2 2) Γ(η e + e e + e )/Γ(η) [10 5 ] 1 2.52 ± 0.02 m 4 ρ (m 2 ρ q2 1 )(m2 ρ q2 2 ) 2.65 ± 0.02 m 2 ρ (m 2 ρ q2 1 q2 2 ) 2.64 ± 0.02 m 4 ρ 4π2 F 2 π N C (q 2 1 +q2 2 ) (m 2 ρ q2 1 )(m2 ρ q2 2 ) 2.61 ± 0.02 (a) J. Bijnens et al. arxiv:hep-ph/0106130v1, 2001 15.09.2015 Daniel Lersch for the WASA-at-COSY collaboration Slide 25
Conversion events! "# $%%$! "&! "# $%%$! "&!"#"$!"#"$ '()*$ '()*$ +,+( +,+( %&'()*+,-./*+0.1*232, 4+,5'*-2+,.%5',) Radius of closest approach (xy-plane) [mm] 90 80 70 60 50 40 30 20 10 conversion events non-conversion events 0 0 0.02 0.04 0.06 0.08 0.1 + - Invariant mass (e e ) at beam pipe GeV c 2 2 10 10 1 Conversion events: small opening angle and origin at beam pipe Non-Conversion events: large opening angle and origin at reaction vertex 15.09.2015 Daniel Lersch for the WASA-at-COSY collaboration Slide 26
η Production mechanisms pd 3 Heη pp ppη T beam 1 GeV 1.4 GeV σ(η) a),b) (0.412 ± 0.016) µb (9.8 ± 1) µb Suited for study of not-so-rare η decays study of (not-so-) rare η decays Background low multi-pion background high multi-pion background Reaction T beam [GeV] σ[µb] b),c) pd 3 Heπ 0 π 0 0.893 2.8 ± 0.3 pd 3 Heπ + π 0.893 5.1 ± 0.5 pp ppπ + π π 0 1.36 4.6 ± 1.5 pp ppπ 0 π 0 1.36 200 ± 30 pp ppπ + π 1.36 660 ± 100 a) R. Bilger et al., Phys. Rev., C65(044608), 2002 b) CELSIUS/WASA coll.., Phys. Lett., B649:122-127, 2007 c) M. Bashkanov et al.., Phys. Lett., B637:223-228, 2006 15.09.2015 Daniel Lersch for the WASA-at-COSY collaboration Slide 27
2 Preselection of the pp ppη data set Counts per 0.01 GeV/c 6 700 10 600 500 400 300 Before cut on missing mass After cut on missing mass MC: pp ppη Cut on missing mass accept event Counts per bin 6 10 6000 accept event 5000 4000 3000 200 2000 100 1000 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 Missing mass (p,p,p,p ) GeV beam target 1 2 c 2 0 0 1 2 3 4 5 Number of charged particle pairs in CD with Q Q = -1 1 2 Preselection done in two steps: i) Condition on missing mass Rejection of multi-pion background ii) Condition on charged tracks in the Central Detector Selection of charged η decay modes 15.09.2015 Daniel Lersch for the WASA-at-COSY collaboration Slide 28
E FRH(Layer1) [GeV] PID at WASA 0.14 0.12 0.1 0.08 0.06 0.04 0.02 0.02 0.04 0.06 0.08 Counts per 10-3 GeV/c2 0 0 0.1 0.12 0.14 E FRH(Layer2) [GeV] 16000 Data 14000 MC: η π+π- π0 12000 10000 8000 6000 4000 2000 0 0 15.09.2015 0.05 0.1 0.15 0.2 0.25 0.3 Invariant mass (γ 1,γ 2) GeV c2 Daniel Lersch for the WASA-at-COSY collaboration Slide 29