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
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