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Low energy kaon scattering, an experimental overview

Low energy kaon scattering, an experimental overview. Alessandra Filippi INFN Torino. Low energy kaon scattering, a proposal for a new experiment at DA Φ NE. Workshop “Strangeness in Nuclei” – ECT* Trento, Oct 7th, 2010. Overview. Slow kaons at DA Φ NE: unique features

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Low energy kaon scattering, an experimental overview

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  1. Low energy kaon scattering, an experimental overview Alessandra Filippi INFN Torino Low energy kaon scattering, a proposal for a new experiment at DAΦNE Workshop “Strangeness in Nuclei” – ECT* Trento, Oct 7th, 2010

  2. Overview • Slow kaons at DAΦNE: unique features • The physics of charged kaon scattering: • Kaons • Antikaons • Open issues • Reasons of interest • IKON: an experiment at DAΦNE to perform precision cross-section measurements of in-flight low momentum kaons • VDET+KLOE: high precision general purpose detector • Feasibility studies (VDET simulations, kinematics, yields) • Synergy between IKON and AMADEUS • Summary

  3. K+p total K-p total K+p elastic K-p elastic K+d total K-d total K-n total K+n total K-n elastic DAΦNE DAΦNE Kaon-Nucleon scattering database • at low energy POOR WORLD DATABASE and LARGE ERROR BARS • DAФNE is the only world facility for near-threshold KN measurements

  4. K- K+ Φ 25 mrad e- e+ Experimental challenge: • Track kaonsand measure their momentum before their interaction • Track final state productsof K± scattering K±’s at DAΦNE: experimental conditions • Crab Waist Crossing: 25 mrad • (1020) produced with boost: ~12 MeV/c • Kaons from  decay: (1020) → K+K-, B.R. 48% • 115-141 MeV/c decay kaons • ~103 (1020) / s

  5. KLOE + VDET = IKON KLOE VDET: KLOE can host a vertex detector with a gas target (H2/D2), available room r=20 cm Same approach as AMADEUS

  6. K+N K+ = (us) • Existence of I=0,1 resonances, even below threshold • Strong coupling to many channels • Perturbative methods cannot be applied • Approximated models with coupled channels K-N K- = (us) The physics issues: K+N and K-N Different features of the K±N interaction call for different theoretical approaches • Small cross sections • Absence of resonances • Only elastic and CEX reactions possible • Studied with perturbative approaches or meson exchange models

  7. Jülich OBEP + Coulomb int. K+p, σtotal K+p, σelastic IKON pK(GeV/c) K+n, σelastic Jülich OBEP model IKON pK(GeV/c) K+N: present experimental situation I • TOTAL σ(K+p) on Hydrogen (I=1) • Dominant: elastic channel • No measurements pK< 150 MeV/c • TOTAL σ(K+n) on Deuterium (I=0,1) • Elastic + CEX reactions • Only source of I=0 KN interaction

  8. cosθCM cosθCM K+d → K+n ps K+p→K+p K+d → K+p ns cosθCM K+N: present experimental situation II • DIFFERENTIAL dσ/dΩ • K+p data: different trend between interactions in H2 and D2 • K+d: disagreement with theoretical predictions, both on p and n • General lack of low momentum measurements • K+d: no data < 342 MeV/c

  9. Precision measurement of KN Σ-term • More sensitive to the nucleon strangeness content than πN σ-term • Existing measurements very old and with large errors • Precision improvement: factor >5 with σ evaluations @ 10% Why new K+N measurements needed? • Low energy data crucial totune Chiral SU(3) theories • Better understanding of SU(3) at low energy • Fix low energy parameters • I=0 K+N scattering lengths • Known at 10%, based on data > 130 MeV/c • Nuclear phase shift sign (+/-) • Make “educated guess” of higher energy behaviour (Θ+)

  10. Scattering cross sections for elastic & inelastic processes Hadronic branching ratios close to threshold Data for below threshold resonance excitations: Σπ spectra Energy shift & width of kaonic atoms K-N interaction: overview IKON • NO ChPT • Baryonic resonances, I=0,1:Λ(1115), Σ(1190), Σ(1385), Λ(1405)… • Non-perturbative coupled-channel approach to describe all aspects of the K-N interaction • Low-energy data crucial input to enhance the predicting power of the KN models • Lack of experimental constraints close to threshold • scarcely selective models • poor below-threshold predictivepower • Exp.data with inconsistencies • No model able to account for them IKON IKON SIDDARTHA

  11. K-p → K-p K-p → K0n ~80 mb ~30 mb K0n threshold, 89 MeV/c 89 K-p →Σ+π- K-p →Σ-π+ >100 mb ~50 mb CC Model by Borasoy, Meißner, Nißler (2006), 1σ C.L.bands K-p →Λπ0 K-p →Σ0π0 ~40 mb ? ~50 mb ? ? ? K-N cross sections: available data & best fit Experimental data with 20% precision at most

  12. Produced below the K- N thr. • γp → Λ(1405) K* • K-p → Λ(1405) γ • K-p → Λ(1405) π0 • K-d → Λ(1405) n Small σ K-d Bauer 1977 KLOE KLOE Λ (1405) observed via its Σπ decay Σ±π∓decay: topology of secondary vertex • Σ0π0decay forbidden to Σ*(1385) IKON IKON ANKE 2008 M(Σ0π0) (GeV) Excitation of resonances below threshold: the Λ(1405) case - • Σπ measured lineshapes not reproduced satisfactorily by models yet • Old experiments measured Σ±π∓channels only, at high momentum • New results by ANKE & CLAS, also on Σ0π0 • More data still needed

  13. Direct scattering double scattering (2 steps) pK = 130 MeV/c Resonant contribution π+Σ- Quasi elastic π0Σ0 K-d scattering : a tool to observe Λ(1405)? At low momentum forward emitted neutrons help separating the elastic peak from the Λ(1405)→Σπ signal D. Jido et al. arXiv:1008.4423v1 [nucl-th]

  14. K±elastic scatteringon protons: K± p→K± p • K± quasi-elastic scattering on neutrons: K± d → K± np • K± elastic scattering on deuterons: K± d→ K± d • InelasticK- reactions on protons close to threshold (Y prod.) • K- p → Λπ0 • K- p → Σ±π∓,Σ0π0 • InelasticK- reactions on protons close to threshold (Y prod.) • K- p → Σ±π∓,Σ0π0 • Inelastic K- interactions on deuterons close to thr. (Y prod.) • K- d → YN π (Y = Λ, Σ) • Charge-exchange reactions (threshold: 89 MeV/c) • K- p →K0 n, K+ n → K0 p • K0L p → K+ n • Λ(1405) production in D2: K-d → Λ(1405)n → Σ±π∓n,Σ0π0n • Regeneration reaction: K0L p → K0Sp Summary: possible Kp(d) measurements All of them will be collected at the same time

  15. VDET TRACKING • Finesegmentation • Resolution below 50 μm • secondary vertex reconstruction • Very low mass • minimize ΔE & multiple scattering • Capable of operating in magnetic field (B=0.6 T) • TARGETS • Solid targets (CH/CD) • Active (trigger) • Very thin ( ~500 μm) • Background from C • Gaseous (H2/D2) • Large dimension (~2 cm) • High pressure (~2-3 bar) • Mylar walled (beware! Material budget) • Clean vertex identification IKON IKON • PARTICLE ID. • Charged Particles: mass identification (dE/dx) • Highly ionizing kaons • Outgoing protons • Outgoing pions (MIPs) • Neutral particles • γ’s & Neutrons • TRIGGER • Fast trigger required on incoming K+K- pairs • Thin segmented scintillator (500 μm) – mat. budget! • Self-triggering Si modules IKON IKON KLOE KLOE Experimental setup: general requirements

  16. Proposed VDET architecture I • Sensor type: double sided micro-strip based on Silicon technology • 200 μm x (~6 x 5 cm2) modules • state-of-the-art: 300 μm thickness • Spatial resolution: < 50 μm • Wide dynamic range for mass discrimination (1-20 MIPs) • Cylindrical symmetry around beam axis • large angular coverage • 100 equal modules arranged in prisms

  17. Proposed VDET architecture II tgt F(1020) K+ K- Si Si Si Si Si • 2 Inner layers • discrimination and reconstruction of K-K+ tracks coming from Φ’s (primary vertex) • 3 Outer layers • discrimination and reconstruction of K-,K+,π-,π+,p tracks coming from the interaction of K-K+ pairs in the target (interaction vertex)

  18. 3 Outer layers: 12.4 cm long 200 μm thick H2 gas target 2.5 cm thick 13 cm Y 2 Mylar foils 100 μm thick 13 cm X 2 Inner layers: 6.2 cm long 200 μm thick Beam pipe (Be) 350 μm thick Simulations and feasibility studies Igeometry

  19. Simulations and feasibility studies IIbeam and primary kaons Z • Φ generation with the present phase space configuration (Crab Waist) • Φ → K+K- decay • Beam spread: σz ~ 1.5 cm • Magnetic field: 0.6 T • Realistic VDET geometry • Simulations with Virtual MonteCarlo Tools (Geant3 + Geant4 engines) 1st Si layer 3rd Si layer Beam spread along z: ± 3.25 cm inner layers ± 6.5 cm outer layers

  20. 10000 generated K- (K+) at rest sin2θ @ the target Material Budget: Be Pipe 500 μm Si 2×200 μm pkrange accessible to measurements @ the outmost layer Generated @ Φ vertex Material Budget: Be Pipe 500 μm Si 4×200 μm H2 2.5 cm K- (K+) momentum distribution (MeV/c) • Measurements @ • 2-3 momenta: • 122 ± 10 MeV/c • 102 ± 10 MeV/c • < 95 MeV/c • (possibly) Simulations and feasibility studies III 75%: K+K- acceptance 46%: generated kaons reaching the outmost layer (decay)

  21. Simulations and feasibility studies IVspecific energy loss Energy lost in Si layers • Simulation of energy loss in 200 μm sensors: • Every layer can easily mass discriminate kaons from MIPs • Same technique as applied in FINUDA

  22. Simulations and feasibility studies Vkaon multiple scattering (picture not to scale) Z coord Si Si Si Si Si tgt 2σ ~0.7cm ~3° K± Θ 13 cm Y coord cm angular uncertainty due to Coulomb scattering: Θ~ 3 - 4° FWHM cm VDET with 100 μm pitch OK

  23. Simulations and feasibility studies VIK±N→K±N elastic scattering, kinematics and yields Coulomb dominance p Lab frame MeV/c β K- K- α low σ 127 MeV/c K- p Differential xsections measurable in the angular range 4o -75o 75o Cos α 3 fb-1 enough to perform precision measure-ments

  24. Simulations and feasibility studies VIIK-d→ Σπn @ Λ(1405) peak 4 fb-1 necessary to collect a statistically significant bulk of data (8 months data taking) With 4 fb-1: differential cross section for K±d scattering feasible in 9 momentum bins with a 6% stat. err./bin

  25. IKON for AMADEUS • Tracking of both K+ andK- is vital to determine cleanly the K- vertex, get rid of background from K+ decay particles and to get a correct beam normalization • With the proposed setup targets can be easily changed • Adding thin degrader foils: K-stop physics at hand

  26. Summary and Conclusions • DAΦNE is at present the only world facility where low momentum kaon scattering studies can be performed • Missing data • Needed inputs for low energy strong interaction theories • First feasibility studies performed: geometry, detector requirements, reaction kinematics, multiple scattering and energy loss effects, expected yields • Si Vertex-Detector + KLOE spectrometer & calorimeter • Full know-how on Silicon Detectors, reduced R&D phase needed • IKON only possible integrating with AMADEUS • Time scale fitting to KLOE/DAΦNE schedule for the next 3-4 years

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