Investigation o the 3 He-η system with olarized beams at ANKE II International Symosium on Mesic Nuclei Setember -5, 013 Institut ür Kernhysik Alons Khoukaz
Why η-meson Production Close to Threshold? Do bound meson-nucleus systems exist? 3 He η ( ) ANKE: d+ 3 He+η Excitation unction close to threshold FSI Polarized beam Test o FSI hyothesis, role o sins Alons Khoukaz
The COSY-Accelerator at Jülich Energy range 0.045.8 GeV () 0.03.3 GeV (d) (momentum 3.7 GeV/c) Beam cooling Electron cooling Stochastic cooling Polarisation, d beams & targets Beams internal, external Exeriments, Detectors ANKE, TOF, WASA, COSY (Cooler Synchrotron) Alons Khoukaz
The ANKE-Facility WASA COSY (Cooler Synchrotron) ANKE TOF PISA Alons Khoukaz JULIC (Injector Cyclotron)
Identiication o 3 He Nuclei at ANKE Erzeugung von η-mesonen Diole Q 10 MeV d-beam -target Multi-wire chambers Scintillation walls 3 He Geometric accetance: ~ 100% (u to Q ~ 0 MeV) Alons Khoukaz
Identiication o the Reactions: d+ 3 He+X Momentum rabbit Alons Khoukaz
Identiication o the Reactions: d+ 3 He+X Energies and momenta o the incoming articles (d,) known Deuteron (mass m d ): energy + momentum: Adjustable by the accelerator Proton (mass m ): target article at rest, momentum 0 Energy o the 3 He nucleus measurable by detectors η-meson: Not directly detectable at ANKE Identiication o the reaction via the missing mass analysis Alons Khoukaz
Two-Particle Final State: Phase Sace Assumtion: Two-article reaction a+b c+d without initial and inal state interactions ( ISI and FSI ): Scattering (and roduction) amlitude const. Increase o the cross section according to hase sace exectations dσ ( ϑ) s Q dω i / : Momenta o in- and outgoing articles in the CMS Q: Q-value Sum o kinetic energies im CMS i Alons Khoukaz
Results or the Reaction d+ 3 He+η ~Q 1/ But: Strong deviation rom hase sace exectation! Most robably not caused by higher artial waves Alons Khoukaz
The Reaction d+ 3 He+η Erzeugung von η-mesonen Extreme increase o the total cross section close to the roduction threshold Increase o the cross sections within Q < 1 MeV strong energy deendence at threshold Ater that total cross sections remain almost constant Additional eect beside ure hase sace Exlanation: Strong inal state interaction (FSI) between 3 He nucleus and η-meson Alons Khoukaz
Scattering Theory and Final State Interaction Descrition o the cross section including FSI: ( ϑ) dσ dω i s i rod + 1 1 i a a r0 Assumtion: Energy deendence o the roduction amlitude Prod is negligible close to threshold: Prod ~ const. Initial State Interaction (ISI) also: ISI const. Alons Khoukaz
Scattering Theory and Final State Interaction The scattering length can deliver inormationen about ossible bound states Conditions or bound η 3 He state: Existence o a ole in the comlex lane s rod i 1 1 i a + a r a a r + ia r r r + ir i As well as a r < ai 0, ai > 0, R < 1 a r Alons Khoukaz
The Reaction d+ 3 He+η Erzeugung von η-mesonen Fit to data very close to threshold: Only s-wave Data: ANKE Collaboration ( ϑ) dσ dω i rod 1 1 i a + a r0 Fit arameter: Comlex scattering length aa r +ia i Comlex eective range rr r +ir i Finite momentum width δ beam o the accelerator beam Alons Khoukaz
The Reaction d+ 3 He+η Erzeugung von η-mesonen Excitation unction without accelerator beam smearing δ beam : Blue line: Deolded shae, extracted rom data (no accelerator beam smearing) Total cross section reaches maximum already Q<0.5 MeV above threshold Alons Khoukaz
The d+ 3 He+η Scattering Amlitude Extracted scattering amlitude (Q > 0 MeV) scatt ( ϑ) dσ dω i rod 1 1 i a + a r0 Scattering amlitude decreases raidly with increasing inal state momentum Scattering amlitude almost constant at high energies strong FSI in η 3 He system Alons Khoukaz
η 3 He Scattering Length Fit to data delivers inormation about the comlex η 3 He scattering length: dσ dω ( ϑ) i scat rod FSI rod FSI Result: [ ( + 0.1 ) ( + 1.0 ± 10.7 ± 0.8 + 1.5.6 )]m a i 0.5 ± Notice: Determination o a r! 0.9 FSI 1 1 1 i a + a r0 Alons Khoukaz
η 3 He-Interaction: Determination o Pols dσ dω ( ϑ) i scatt rod FSI rod FSI FSI 1 1 1 i a + a r0 FSI 1 1 1 1 a i + 1 1 r 0 + i + 1 ( + ) i ( ) 5 7 19 1 ± ± ± ± MeV/c 1 1 ( ) ( + 1 i ) 106 5 76 13 ± ± ± MeV/c Alons Khoukaz
η 3 He-Interaction: Determination o Pols Pole close to the reaction threshold Q 1 0 m red Position o the near-threshold ole (and scattering length) stable, i.e. nearly indeendend o it range Large real art o scattering length and a r >a i indication or the existence o a bound state 3 He η 0.37 MeV (strong interaction!) Alons Khoukaz
Polarized Measurements Production amlitude or d 3 He+η (π 0 ): uτ ( Aε + ibε σ ) u B d d Determination o the energy deendence o the amlitudes A and B by measurement o: T dσ 1 η A + B dω 3 A (1 T0 ) η 0 dσ 0 / dω( ϑ) dσ / dω( ϑ) dσ / dω( ϑ) zz dσ dω 0 B A T0 A + B 1 dσ B (1 + T0 ) dω η 0 0 ϑ 0 or180 Alons Khoukaz
Polarized Measurements Assumtion: d 3 He+η Negligible eect o ISI Energy deendence o only given by FSI Shae o excitation unction indeendent o sins Same energy deendence o amlitudes A and B A A FSI ( ) 0 B B FSI ( ) 0 η η Measure T 0 as unction o the excess energy ( η ) ( η ) B0 A FSI 0 T0 const. A0 + B0 FSI Alons Khoukaz
The Reaction d+ 3 He+η at ANKE Erzeugung von η-mesonen Alternating injection o unolarized and tensor olarized deuterons in COSY Ramed COSY beam: Q -5 MeV... +10 MeV (300 s) Full geometrical accetance o ANKE or d+ 3 He+η Determination o zz by, e.g., d+ ()+n (analyzing owers known) dσ dσ 0 ( q, ϕ ) ( q, ϕ ) T d 1. GeV dt dt 1+ 1 3zit cos 3 zzt ( ϑ) ( ϕ ) t ( ϑ) 11 zz 0 ( ϑ ) cos( ϕ ) Alons Khoukaz
Preliminary Results: d+ 3 He+η Erzeugung von η-mesonen T 0 dσ 0 / dω( ϑ) dσ / dω( ϑ) dσ / dω( ϑ) zz 0 Data are consistent with T 0 const. close to threshold Extraction o A / B : T B A A + B 0 A B 1 T 0 1 + T / 0 Alons Khoukaz
Preliminary Results: d+ 3 He+η Erzeugung von η-mesonen Assumtion: T 0 const. A / B const. Alons Khoukaz
Preliminary Results: d+ 3 He+η Energy deendence o known rom old unolarized measurements A ( ) and B ( ) can be calculated Erzeugung von η-mesonen dσ 1 η A + B dω 3 A (1 T0 ) η 1 B (1 + T0 ) η dσ dω dσ dω Alons Khoukaz
Preliminary Results: d+ 3 He+η Erzeugung von η-mesonen Allow or an energy deendence o A / B : Test: Dierent energy deendence o A ( ) and B ( )? dσ 1 η A + B dω 3 A m Q + n B Alons Khoukaz
Preliminary Results: d+ 3 He+η Erzeugung von η-mesonen No signiicant dierent energy deendence o A and B Remarkable excitation unction o d+ 3 He+η still an indication or very strong FSI eect Alons Khoukaz
Next Stes: Quantiication o uer limits or non-fsi eect Evaluation o eect on ole osition or scattering length In arallel: Analysis o new data on +n d+η via +d d+η+ sec Comarison o results rom +n d+η d+ 3 He+η d+d 4 He+η Alons Khoukaz
Summary Alons Khoukaz