Eta Meson Production in Proton-Deuteron Collisions MESON 2014: 13 th - PowerPoint PPT Presentation

Eta Meson Production in Proton-Deuteron Collisions MESON 2014: 13 th International Workshop on Meson Production, Properties and Interaction 29 th May - 3 rd June 2014 Institut für Kernphysik Alfons Khoukaz

Erzeugung von h -Mesonen Why h -Meson Production Close to Threshold? h • Attractive S -wave h N interaction R.S. Bhalerao and L.C. Liu, Phys. Rev. Lett. 54 (1985) 685 • Possible formation of h -nucleus bound states Q. Haider and L.C. Liu, Phys. Lett. B172 (1986) 257 C. Wilkin, Phys. Rev. C47 (1993) 938 • Broad h -mesic nuclei program at COSY GEM ( h 7 Be) • A>4: • h 4 He: ANKE, GEM, WASA-at-COSY • h 3 He: ANKE, COSY11, GEM, WASA-at-COSY • h d: ANKE • New data from proton-deuteron collisions Alfons Khoukaz

Erzeugung von h -Mesonen Why h -Meson Production Close to Threshold? • Do bound meson-nucleus systems exist? h 3 He ( → ) d+p → 3 He+ h • Experimental access e.g. via g + 3 He → 3 He+ h • Excitation function close to threshold → FSI • Polarized beam → Test of FSI hypothesis, role of spins Alfons Khoukaz

Erzeugung von h -Mesonen Results for the Reaction d+p → 3 He+ h • A good candidate for a bound state is the h 3 He-system • High precision data from ANKE and COSY-11 Data: ANKE Collaboration • Observation of strong FSI • Strong indication for a pole   2   f p d   prod at |Q 0 | ≈ 0.37 MeV f  2 d p 1       i 2 1 i a p a r p • Further evidence for pole f 0 f 2 2 f p hypothesis by angular   prod f 2 p       p p i  dependence of dp→ h 3 He     f f 1 1 p p     1 2 T. Mersmann et al. , Phys. Rev. Lett. 98 (2007) 242301 Alfons Khoukaz

Erzeugung von h -Mesonen The d+p → 3 He+ h Scattering Amplitude Extracted scattering amplitude (Q > 0 MeV) • Scattering amplitude   2   f p d   prod decreases rapidly f  2 d p       p p i  with increasing final     1 f 1 f p p     1 2 state momentum p f • Scattering amplitude almost constant at high energies T. Mersmann, A.K., et al., PRL 98 (2007) 242301 → strong FSI in h 3 He system Alfons Khoukaz

Erzeugung von h -Mesonen Consideration of Higher Partial Waves: P -Waves • Close to threshold: d  /d  ( q ) = const. → s -wave • Q > ~ 4 MeV: Contributions ~cos( q ) visible → p -wave • Asymmetry in the angular distribution ( h -meson): Slope at cos( q )=0:        d d d            q   ln tot 1 cos q      CM (cos )   d d 4 d h q  cos 0 h CM Alfons Khoukaz

Erzeugung von h -Mesonen Consideration of Higher Partial Waves: P -Waves • Slope might arises from the dp→ h 3 He interference between the s - and p -waves in the h 3 He system • Indication of a strong phase variation of the s-wave at low Q • Data (  total and d  /d  ) can be described well by assumption    d d     ln of a pole close to threshold q    (cos ) d d h q  cos 0 h     d        q   tot 1 cos   CM   4 d CM T. Mersmann et al. , Phys. Rev. Lett. 98 (2007) 242301 C. Wilkin et al., Phys. Rev. B 649 (2007) 92 Alfons Khoukaz

Erzeugung von h -Mesonen Consideration of Higher Partial Waves: P -Waves • Assumption: Only s - and p -waves Production operator: C. Wilkin et al., PLB 654 (2007) 92             ˆ  e   e     e   e    ˆ ˆ f A p iB p C p iD p h h p p  A, B : s -wave amplitudes p p d h h 2   f I C, D : p -wave amplitudes  3 d p p e : polarisation vector of the deuteron p p   2 2 2 2         q 2 2 2 2 2 Re 2 cos I A B p C p D p A C B D h h h h Alfons Khoukaz

Erzeugung von h -Mesonen Consideration of Higher Partial Waves: P -Waves • Resulting asymmetry factor:      Re 2 A C B D   2 p h 2 2 2 2    2 2 2 2 A B p C p D h h Assumption: • Same s -wave amplitudes: A = B = f s energy dependence due to FSI • Same p -wave amplitudes: C = D = const.     * p Re f C h 2 2     2   S 4 f p C 2 p h h s 2  2 2 p f p C h p S Alfons Khoukaz

Erzeugung von h -Mesonen Compare: dp- and g 3 He-Scattering Photon + 3 He 3 He + h Deuteron + Proton • Different initial states and production mechanism, but same final state Alfons Khoukaz

Erzeugung von h -Mesonen Compare: dp- and g 3 He-Scattering • Scattering amplitudes show similar energy dependence • Strong hint for a strong FSI between He-nuclei and h - mesons F. Pheron et al., PLB 709 (2012) 21-27 Alfons Khoukaz

Erzeugung von h -Mesonen Compare: dp- and g 3 He-Scattering • Scattering amplitudes show similar energy dependence • Strong hint for a strong FSI between He-nuclei and h - mesons Alfons Khoukaz

Erzeugung von h -Mesonen Compare: dp- and g 3 He-Scattering C. Wilkin et al., PLB 654 (2007) 92 d+p → 3 He+ h g + 3 He → 3 He+ h        d   d d        q     tot ln 1 cos   F. Pheron, PhD thesis, University Basel, 2012 q    CM   4 (cos ) d d d h q  CM cos 0 h Alfons Khoukaz

Erzeugung von h -Mesonen Need of Further Data • Excitation function(s) and differential cross sections for the h 3 He final state are compatible with the presence of a pole close to threshold • Further input is needed to investigate e.g. the role of the spin of the entrance channel • Very close to threshold the d+p → 3 He+ h reaction is dominated by an s -wave 3 He+ h system • ANKE: Studies with tensor polarised deuterons dp→ 3 He+ h Possible spins: S dp = 1/2 or 3/2 Alfons Khoukaz

Erzeugung von h -Mesonen Polarized Measurements Production amplitude for dp→ 3 He+ h  0 :   e  e   ( ) f u p A iB u  B p d d p    2 2 p  1 d   B A h 2 2   2  A B   Determination of the   2 T  3 20 d p 2 2    2  A B  p energy dependence   p p 1 d d of the amplitudes A     p 2 2 p | | (1 2 ) | | (1 ) A T B T  20  20 p d p 2 d and B by measurement h h of:         / ( ) / ( ) d d d d 2 2    0   T 0 0 0 180 or 20    / ( ) p d d 0 zz Alfons Khoukaz

Erzeugung von h -Mesonen Polarized Measurements Assumption for dp→ 3 He+ h: • Negligible effect of ISI • Energy dependence of |f | 2 only given by FSI → Shape of excitation function independent of spins → Same energy dependence of amplitudes |A| 2 and |B| 2       2 2 2 2  | | | | ( ) A A FSI p FSI p B A h h 0       0 0 2 const. T   20   2  2 2 2   | | | | ( ) 2 FSI p B B FSI p A B   h h 0 0 0 • Measure T 20 as function of the excess energy Alfons Khoukaz

Erzeugung von h -Mesonen Recent results from ANKE: d+p → 3 He+ h • Data close to threshold M. Papenbrock, nucl-ex/1404.5425, accepted by PLB consistent with T 20 =const. 𝑈 20 = −0.21 ± 0.02 ± 0.05 • |T 20 |<< 1 → |A| 2 / |B| 2 = O( 1 ) • S -Wave amplitudes |A| 2 and |B| 2 are of similar size Alfons Khoukaz

Erzeugung von h -Mesonen Recent Results: d+p → 3 He+ h • Energy dependence of |f | 2 known from „ old “ unpolarized measurements → |A| 2 (p f ) and |B| 2 (p f ) can be calculated 𝑔 2 = 𝐵 2 + 2 𝐶 2  p 1 d   h  2  2 2 A B 𝐵 2    3 d p p  p d   2 p | | (1 2 ) A T  20 p d h  p 1 d   2 p | | (1 ) B T 𝐶 2 20  p 2 d h M. Papenbrock, nucl-ex/1404.5425, accepted by PLB Alfons Khoukaz

Erzeugung von h -Mesonen Recent Results: d+p → 3 He+ h • Allow for a linear energy dependence of T 20 and |A| 2 /|B| 2 : 𝐶 2 𝑈 20 = −0.14 ± 0.04 + −0.02 ± 0.01 𝑅 𝐵 2 = 0.75 ± 0.06 − 0.014 ± 0.014 𝑅 M. Papenbrock, nucl-ex/1404.5425, accepted by PLB → Possible energy variation of |A| 2 (p f ) and |B| 2 (p f ) on the scale of 0.75/0.014 MeV ≈ 50 MeV Alfons Khoukaz

Erzeugung von h -Mesonen Recent Results: d+p → 3 He+ h • No significant different energy dependence of |A| 2 and |B| 2 • Remarkable excitation function of d+p→ 3 He+ h still an indication for very strong FSI effect M. Papenbrock, nucl-ex/1404.5425, accepted by PLB Alfons Khoukaz

Angular Dependence of T 20 𝑒𝑈 20 𝛽 = 𝑒 cos 𝜘 • Asymmetry parameter: cos 𝜘=0 • sensitive to interferences between even and odd h partial waves • odd function of p h with  ( Q =0)=0 • No sign for any s-p interference here But: • Unpolarized data show already at Q = 4 MeV a 𝛽 = 0.0002 ± 0.0005 𝑞 𝜃 𝑞 𝜃 in MeV/c non-isotropy d  /d  M. Papenbrock, nucl-ex/1404.5425, accepted by PLB Alfons Khoukaz