Dynamics of the near threshold η meson production in proton-proton collisions N * (2007), Bonn, R. Czyżykiewicz for the COSY-11 collaboration: IKP, Forschungszentrum Jülich, Germany INP, Jagiellonian University, Cracow, Poland IKP, Westfälische Wilhelms-Universität, Münster, Germany Institute of Nuclear Physics, Cracow, Poland Institute of Physics, University of Silesia, Katowice, Poland ZEL, Forschungszentrum Jülich, Jülich, Germany

Motivation: unknown production mechanism of the η meson Tools - measurements of: σ, dσ/dθ, A y, C ij

K. Nakayama et al., Phys. Rev. C65 (2002) Dane eksperymentalne: E. Chiavasa et al., Phys. Lett. B322 (1994) 270 H. Calen et al., Phys. Rev. Lett. 79 (1997) 2642 F. Hibou et al., Phys. Lett. B438 (1998) 41 J. Smyrski et al., Phys. Lett. B474 (2000) 180 B. Tatisheff et al., Phys. Rev. C62 (2000) H. Calen et al., Phys. Rev. C58 (1998) 2667 P. Moskal et al., Phys. Rev. C69 (2004) Experi,mental data: E. Chiavasa et al., Phys. Lett. B322 (1994) 270 H. Calen et al., Phys. Rev. Lett. 79 (1997) 2642 F. Hibou et al., Phys. Lett. B438 (1998) 41 J. Smyrski et al., Phys. Lett. B474 (2000) 180 B. Tatisheff et al., Phys. Rev. C62 (2000) H. Calen et al., Phys. Rev. C58 (1998) 2667 P. Moskal et al., Phys. Rev. C69 (2004) Total cross sections for the pp ppη reaction

Differential cross sections for the pp ppη reaction model: K. Nakayama et al., Phys. Rev. C65 (2002) data: M. Abdel-Bary et al., Eur. Phys. J. A16 (2003) 127

σ(pp ppη) = σ 1 σ(pn pnη) = ½ (σ 0 + σ 1 ) R η = σ(pn pnη) / σ(pp ppη) σ 0 = (2R η -1) σ 1 =12 σ 1 Isovector meson exchange H. Calén et al., Phys. Rev. C58 (1998) 2667 Isospin dependence of the η meson production

G. Fäldt, C. Wilkin – Phys. Scripta 64 (2001) 427 K. Nakayama et al., Phys. Rev. C68 (2003) Theoretical predictions for A y at Q=10 and 36 MeV G. Fäldt, C. Wilkin: A y ( ) = A y max sin(2 )

where: A y max = A y max (Q ) G. Fäldt, C. Wilkin: A y ( ) = A y max sin(2 )

Detection setup Beam: p(pol) COSY: ~7·10 9 x 10 6 /s Cluster target H 2 : ~10 13 atoms/cm 2 Momentum separation due to magnetic field Momentum reconstruction: DC+ magnetic field Velocity measurement – scintillator hodoscope Particle identification by means of the missing mass technique

σ(m η ) = 1.50 MeV/c 2 m 2 inv = [p 2 (1 - β 2 )] / β 2 m 2 X = ( E b + E t – E 1 – E 2 ) 2 - ( p b + p t – p 1 – p 2 ) 2

Madison convention ζ = {m pp, m p η, θ η, φ η, ψ} σ(ζ, P) = σ 0 (ζ) * (1 + PA y cos(φ η )) cos(φ η ) 1 N up + (θ η ) = σ 0 (θ η ) * (1 + P up A y (θ η ) ) * E(φ η, 0) * L up dt N dn - (θ η ) = σ 0 (θ η ) * (1 - P dn A y (θ η ) ) * E(φ η, 0) *L dn dt L rel = L up dt / L dn dt, P up P dn = P A y (θ η ) = 1 P N up + (θ η ) - L rel N dn - (θ η ) N up + (θ η ) + L rel N dn - (θ η )

Luminosity L rel L rel = L up dt / L dn dt = n up /n dn L rel (Q=10 MeV)= ± (stat) ± (sys) L rel (Q=36 MeV)= ± (stat) ± (sys)

Polarisation measurement

Polarisation

P(Q=10 MeV)= ± 0.007(stat) ± 0.054(sys) -- COSY-11 P(Q=36 MeV)= ± 0.003(stat) ± 0.008(sys) -- EDDA Polarisation

Asymmetries – Q = 36 MeV cos θ η N up + (cos θ η ) N dn - (cos θ η ) A y (cos θ η ) [-1 ; -0.5) [-0.5 ; 0) 103 ± 16(stat) ± 2(sys) 100 ± 18(stat) ± 2(sys) ± 0.179(stat) ± 0.012(sys) [0 ; 0.5) 144 ± 16(stat) ± 2(sys) 153 ± 18(stat) ± 2(sys) ± 0.122(stat) ± 0.010(sys) [0.5 ; 1] 259 ± 24(stat) ± 4(sys) 296 ± 28(stat) ± 4(sys) ± 0.100(stat) ± 0.011(sys) R. Czyżykiewicz, P. Moskal et al., Phys. Rev. Lett. 98 (2007) ; R. Czyżykiewicz, P. Moskal et al., Int. J. Mod. Phys. 22 (2007) 518.

Asymmetries – Q = 10 MeV cos θ η N up + (cos θ η ) N dn - (cos θ η ) A y (cos θ η ) [-1 ; -0.5) 306 ± 27(stat) ± 5(sys) 250 ± 26(stat) ± 4(sys) ± 0.099(stat) ± 0.022(sys) [-0.5 ; 0) 267 ± 22(stat) ± 4(sys) 260 ± 24(stat) ± 4(sys) ± 0.091(stat) ± 0.012(sys) [0 ; 0.5) 198 ± 18(stat) ± 3(sys) 208 ± 19(stat) ± 3(sys) ± 0.095(stat) ± 0.011(sys) [0.5 ; 1] 279 ± 23(stat) ± 4(sys) 286 ± 25(stat) ± 4(sys) ± 0.088(stat) ± 0.009(sys ) R. Czyżykiewicz, P. Moskal et al., Phys. Rev. Lett. 98 (2007) ; R. Czyżykiewicz, P. Moskal et al., Int. J. Mod. Phys. 22 (2007) 518.

χ 2 pseudoscalar /DOF = 0.54 Prob(pseudoscalar) 81 % χ 2 vector /DOF = 2.76 Prob(vector) 0.6 % Results for Q = 10, and 36 MeV A y 0 s-wave production ( 2S+1 L J 2S'+1 L' J' s ) R. Czyżykiewicz, P. Moskal et al., Phys. Rev. Lett. 98 (2007) ; R. Czyżykiewicz, P. Moskal et al., Int. J. Mod. Phys. 22 (2007) 518.

where: A y max = A y max (Q ) G. Fäldt, C. Wilkin: A y ( ) = A y max sin(2 )

A y max (Q=10 MeV) = ± A y max (Q=36 MeV) = ± Results

A y max (Q=10 MeV) = ± A y max (Q=36 MeV) = ± Results

A y max (Q = 10 MeV) = ± A y max (Q = 36 MeV) = ± Results A y max (Q = 10 MeV) = ± A y max (Q = 36 MeV) = ± σ 4.3 σ R. Czyżykiewicz, P. Moskal et al., Phys. Rev. Lett. 98 (2007) ; R. Czyżykiewicz, P. Moskal et al., Int. J. Mod. Phys. 22 (2007) 518.

Predictions of the pseudoscalar meson dominance model are in line with the experimental data at the significance level of α = 0.81 indication of the π meson exchange Predictions of the vector meson exchange model, based on the η meson photoproduction aymmetries, disagree with the experimental data at a significance level of α = Analysis of the A y max shown that the pseudoscalar meson exchange model agrees with the experimental data at the level of 1 σ, while the predictions of the vector meson exchange model lie within 4.3 σ from exp. data A y for Q = 10 and 36 MeV consistent with zero – possible production of the η meson in the s-wave Conclusions

Measurements with WASA-at-COSY

K. Nakayama, private communication (2007). S 11 (1535) D 13 (1520) + S 11 (1535) + S 11 (1650) + D 13 (1700)

Results

Kraków, Średnie geometryczne N ± : str : N + = N + N + N - = N - N - N ( ) = s 0 (q ) * (1 + P A y (q ) ) * E(q, 0) * L dt N ( ) = s 0 (q ) * (1 + P A y (q ) ) * E(q, ) * L dt N ( ) = s 0 (q ) * (1 - P A y (q ) ) * E(q, ) * L dt N ( ) = s 0 (q ) * (1 - P A y (q ) ) * E(q, 0) * L dt

Produkcja rezonansowa Kraków,

Wykresy Dalitz'a – Q=10 MeV PRELIMINARY Zgodne z wynikami dla Q=15.5 MeV P. Moskal et al., Phys. Rev. C69 (2004) ; K. Nakayama et al., Phys. Rev. C68 (2003) ) Kraków,

Wykresy Dalitz'a c.d. PRELIMINARY Dopasowanie kinematyczne i poprawki na akceptancję Brakuje odcięcia tła Kraków,

dane: P. Moskal et al., Phys. Rev. C69 (2004) M. Abdel-Bary et al., Eur. Phys. J. A16 (2003) 127 Róż niczkowe przekroje czynne dla pp pp Q = 15 i 15.5 MeV Q = 41 MeV Kraków,

(pp pph) = 1 (pn pnh) = ½ ( ) R h = (pn pnh) / (pp pph) 0 = (2R h – 1) 1 =12 1 (pp pph) = C|t p + t h + t r + t w | 2 |y I=1 (0)| 2 (pn pnh) = C|-3t p + t h + 3t r - t w | 2 |y I=0 (0)| 2 |y I=0 (0)| 2 / |y I=1 (0)| 2 = 0.8 |t p + t h + t r + t w | 2 |-3t p + t h + 3t r - t w | 2 =15 wymiana mezonów izowektorowych H. Calen et al., Phys. Rev. C58 (1998) 2667 C. Wilkin, Report No. TSL/ISV (1996) Kraków,

Zasada zachowania parzystości a świetlność Kraków,

2 pseudoscalar /DOF = 0.54 Prob(pseudoscalar) 81 % 2 vector /DOF = 2.76 Prob(vector) 0.6 % Wyniki analizy dla Q=10 oraz 36 MeV A y 0 prawdopod. fali s ( notacja: 2S+1 L J 2S'+1 L' J' s ) Kraków,

A y max (Q=10 MeV) = A y max (Q=36 MeV) = Wyniki analizy Kraków,

A y for the pp COSY-11 Q = 40 MeV P. Winter et al., Phys. Lett. B 544 (2002) 251; 553 (2003) 339 (E) G. Fäldt, C. Wilkin, Phys. Scripta 64 (2001) 427 K. Nakayama et al., Phys. Rev. C68 (2003) Kraków,