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Doubly Strange Systems at Panda F. Iazzi – Politecnico di Torino and INFN Sez. Di Torino

Doubly Strange Systems at Panda F. Iazzi – Politecnico di Torino and INFN Sez. Di Torino. Beam-target interaction Expected X - rates. Physics of Double Strangeness. X - hyper-atoms X - hypernuclei LL hypernuclei. Production of Doubly Strange Systems. Overview.

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Doubly Strange Systems at Panda F. Iazzi – Politecnico di Torino and INFN Sez. Di Torino

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  1. Doubly Strange Systems at PandaF. Iazzi – Politecnico di Torino and INFN Sez. Di Torino Beam-target interaction Expected X- rates Physics of Double Strangeness • X- hyper-atoms • X- hypernuclei • LL hypernuclei Production of Doubly Strange Systems Overview • Direct and indirect production with kaons, ions and antiprotons • Two-target technique in PANDA Antiproton beam and internal target STRANGENESS IN NUCLEI F. Iazzi INFN-Torino&Politecnico

  2. n p X- p n e- n p p n X- Doubly strange systems (S=±2) hyperon –antihyperon systems are fully accessible in HESR energy range Exotic hyperatom: Doubly Strange Hypernucleus: (X- occupies an atomic level) X-occupies a nuclear level Double Hypernucleus: 2 L‘s replace 2 nucleons in a nucleus STRANGENESS IN NUCLEI F. Iazzi INFN-Torino&Politecnico n L p L p n

  3. e- n p p n X- Exotic X- atoms Exotic hyperatom: • Physics:X - -nucleus interaction • Atomic orbits overlap nucleus • Strong interaction and Coulomb force interplay • Lowest atomic levels are shifted and broadened • Potential: Coulomb + optical • Measurements: • X ray emission during cascade • Level shift ( high precision g detector required ) • Level width ( high statistics required ) Fitting optical potential parameters STRANGENESS IN NUCLEI F. Iazzi INFN-Torino&Politecnico

  4. e- n p p n X- Exotic X- atoms: status of art Exotic hyperatom: • Strong interaction in hadronic atoms: • Absorption from an atomic level into nucleus ends the atomic cascade • shift and width of only 1 (last) level • can be measured in an atom • Absorption level: • increases with Z • increases with the hadron mass DATA: p- , K- , pbar, and S- cover the whole periodic table X- missing Measurements of several X- exotic atomsare required STRANGENESS IN NUCLEI F. Iazzi INFN-Torino&Politecnico

  5. n p X- p n Doubly strange hypernuclei Doubly Strange Hypernucleus: • Physics:X -N interaction: • short range interaction • long range interaction • ….. • One Boson Exchange features: • X N X N : no strange meson (I=1/2), all I=0,1 meson exchange (w, h , p, r ...) • X N LL coupling: only strange meson exchange(k ...) • Measurements: • g emission in X-absorption by nucleus • momentum of p– from X- decay • X-spectroscopy needs high statistics STRANGENESS IN NUCLEI F. Iazzi INFN-Torino&Politecnico

  6. n p X- p n Doubly strange hypernuclei: status of art Doubly Strange Hypernucleus: • Other measurements: • X- + N: sel≤ 24mb (X- produced in (K-,K+),with p(K-)=1.66GeV/c) (Ahn06,PLB633) • X- + nucleus: mean free path in nucleus ≈ 4.7fm (p(X-) = 0.6GeV/c ) (Aoki98NPA644) • K- + 12C  K+ + 12BX :(Khaustov00,PRC61) STRANGENESS IN NUCLEI F. Iazzi INFN-Torino&Politecnico

  7. Double Hypernuclei • Physics:LL strong interaction • only possible in double hypernuclei • YY potential: attractive/repulsive? • hyperfragments probability dependence on YY potential One Boson Exchange features LLLL : only nonstrange, I =0 meson exchange (w,h...) • LL weak interaction: hyperon induced decay: • LL L n : GLn << Gfree (expected) • LL S-p : GSp << Gfree (expected) Double Hypernucleus: • Measurements: • DBLL(AZLL) = BLL(AZLL ) - 2BL(A-1ZL) • Several A needed to extract the core of the LL interaction • momentum of p– from L ,S-decay • momentum of p from L decay and from LL S -p STRANGENESS IN NUCLEI F. Iazzi INFN-Torino&Politecnico n L p L p n

  8. Double Hypernuclei decay Weak Decay of Single Hypernuclei: (MWD, NMWD) • Mesonic Weak Decay : L Np ; G ≈ 0.174*Gfree(12C) ; p(N) ≈ 101 MeV/c • Non Mesonic Weak Decay L + N NN ; G ≈ 0.841*Gfree(12C) ; p(N) ≈ 416 MeV/c • (Nucleon Induced Decay) Weak Decay of Double Hypernuclei: (MWD, NMWD, HINMWD) • Both LLmesonic: LL pN + L  pN + pN • Both LL non mesonic: LL + NN  LN + NN  NN + NN • Mixed mesonic & non mesonic: LLN  pN + LN  pN + NN • A new kind of Non MesonicWeak Decay: one L decays interacting with the other one • New mechanism: Hyperon Induced NonMesonicWeak Decay (HINMWD): • LL LN (pL/N = 433 MeV/c)  NN (only in DH) • LL SN (pS/N = 321 MeV/c)  NN (only in DH) • HINMWD related to YY interaction: complementary to DH spectra • Decay into Hyperfragments: • Excited LL-Hypernucleus  breakup channels: • L + AZL + others • A1Z1L + A2Z2L + others • AZLL + others STRANGENESS IN NUCLEI F. Iazzi INFN-Torino&Politecnico

  9. Double Hypernuclei: status of art Double Hypernucleus: MeV A Nagara, Mikage,Demachi-Yanagi, Danisz,Hida, Hida, E176 Double Hypernuclei: few events, spread over A, existence confirmed Weak Decay: is used as a tag of the DH formation but statistics is missing STRANGENESS IN NUCLEI F. Iazzi INFN-Torino&Politecnico n L p L p n

  10. Production of Doubly Strange Systems • Direct reactions: DSS produced in a single nucleus • K- + AZ  ( p(K-,K+)X- X-re-scattering in nucleus)  A(Z-1)X • K- + AZ  p0 + A(Z-1)LK+ + A(Z-2)LL (p0re-scattering in nucleus) Multistep processes  low cross section  vanishing statistics • Indirect reactions: • quasi free X-production in a nucleus, followed by: • X-stoppingandcapture in a different nucleus • K- + p  K+ + X- stop  (LL) (KEK, BNL-AGS, JPARC) • pbar + N  Xbar + X- stop  (LL) (FAIR : PANDA, FLAIR) • heavy ion X- production (FAIR , ALICE?) STRANGENESS IN NUCLEI F. Iazzi INFN-Torino&Politecnico

  11. Pbar momentum[ GeV/c] Kinematical features of the pbar indirect reactions • Which antiproton momentum? • pbar(3GeV/c) + N Xbar + X-(quasi-free in nucleus) • pbar(≈15GeV/c) + N Xbar + X-(nearly recoilless) • pbar(rest) + N K*bar + K* (in same nucleus) K*+N’  Kbar+ X-(≈ at rest) pbar+ N  X-+Xbar(Threshold: 2.65 GeV/c ) • pbar (3GeV/c) + N Xbar + X- X- (0) momentum PANDA STRANGENESS IN NUCLEI F. Iazzi INFN-Torino&Politecnico

  12. Doubly Strange Systems in PANDA Pbar +N- + bar :  ≈ 2 b; @Pbar = 3GeV/c :  ≈ max @Pbar = 3GeV/c : belowproduction threshold)  K  p K N bar +N  Kbar+ Kbar +p + … [ -production tag]  Elastic scattering in nucleus: strong slowing down (a challenge) slowing down in matter (with decay) MeV   -capture into atomic levels and hyperatomic cascade  - N conversion +  sticking Xray Capture into nucleus: Strong and Coulomb forces decay (MWD,NMWD… ) N STRANGENESS IN NUCLEI F. Iazzi INFN-Torino&Politecnico

  13. DSS in PANDA: Xbar products distribution Pbar +N- + bar :  ≈ 2 b; Pbar @ 3GeV/c (belowproduction threshold)  K  p K N  STRANGENESS IN NUCLEI F. Iazzi INFN-Torino&Politecnico

  14. DSS in PANDA: X- scattering distribution  K Pbar +N- + bar :  ≈ 2 b; Pbar @ 3GeV/c (belowproduction threshold)  p K N  STRANGENESS IN NUCLEI F. Iazzi INFN-Torino&Politecnico

  15. DSS in PANDA: 2-target technique Pbar +N- + bar :  ≈ 2 b; Pbar @ 3GeV/c (belowproduction threshold)  K I Target  p K N bar +N  Kbar+ Kbar +p + … [ -production tag]  Elastic scattering in nucleus: strong slowing down [PochodzallaNIM2004] II Ta r ge t slowing down in matter (with decay) MeV   -capture into atomic levels and hyperatomic cascade  - N conversion +  sticking Xray Capture into nucleus: Strong and Coulomb forces decay (MWD,NMWD… ) N STRANGENESS IN NUCLEI F. Iazzi INFN-Torino&Politecnico

  16. DSS in PANDA: 2-target setup • Primary target : thin wire located inside beam pipe (15 mm F), to produce: • X-hyperon in: p + A X- + X + (A-1), (quasi free) • Strong slowing down of X- in dense matter (A-1) • X annihilations in (A-1), ( trigger) Secondary target • Secondary target: layers between the mstrips • made by different materials for different D.H. • located around beam pipe (as first 12C is planned) • to allow: • X- stopping in ordinary matter, absorption into atomic levels, cascade, capture … • Detection of X– and L decay products X- p Beam pipe Primary target STRANGENESS IN NUCLEI F. Iazzi INFN-Torino&Politecnico

  17. X- Production Efficiency Efficiency Ratio: Rs ≡ Stopped X- (in secondary target)/Produced X- Rs depends on: primary target (scattering in nuclear matter) secondary target (slowing down by ionization) setup geometry (relative distances  decay) Assuming a 12C secondary target (fully passive): Transverse distribution of the X- stopping points Radius&length ≈ 6 cm  ≈ 98 % Stopped X- • … and: • Life time: mostly spent during stopping in ordinary matter • Heavier secondary targets  shorter stopping time • shorter stopping time  lower decay probability • For A>12 targets: Rs(A) ≥ Rs(12C) • Active-passive target : Rs ≤ Rs(12C) Radial –longitudinal distribution of the X- stopping points STRANGENESS IN NUCLEI F. Iazzi INFN-Torino&Politecnico

  18. X- Production: dependence on internal target • In a 12C secondary target: • Rs ≡ stopped X- (in matter) ≈ (2÷4) ·10-3 • Rc ≡ captured X- (by atom) ≈ (2÷4) ·10-3 • Ra ≡ absorbed X- (by nucleus) ≈ (1.5÷3) ·10-3 Rs = 1,31 ·10-3 ·A0,21 Rs (x10-3) Ratio R of stopped to produced X- calculated for a 12C secondary target A of internal target Heavier nuclei are (slightly) more efficient Capture by atoms and absorption in nuclei: same trend as stopping Crucial role played by the beam-target interaction F.Ferro et al. Nucl.Phys. A789 (2007)209 STRANGENESS IN NUCLEI F. Iazzi INFN-Torino&Politecnico

  19. from RESR Beam -Target Interaction: HESR • H E S R Performance • Racetrack shaped Ring: 574 m length • Luminosity/Intensity: • Pbar production rate: 2x107 /s • High luminosity mode: 2x1032 [cm-2s-1] • Pbar production rate: 1x107 /s • High resolution mode: 2x1031 [cm-2s-1] • (for target thickness 4x1015 atoms/cm2) • Momentum range: • 1.5 – 15 [GeV/c] (0.295- 14.1 [GeV]) • Revolution frequency: ≈ 5x105 Hz • Momentum resolution: • High luminosity mode: Dp/p=10-4 (stochastic cooling above 3.8 GeV/c)) • High resolution mode: Dp/p=10-5 (electron cooling) • Effects on the beam: • Losses of pbardue to: • Single Coulomb Scattering (SCS): • Hadronic interactions: (pbar annihilation, scattering…) • Energy straggling • Touschek effect • (Lehrach et al.,NIM2007) • Effects on the detectors: • Background(max tolerable rate of annihilation : ≈ 5x106s-1) • Beam parameters: • I0 = initial bunch contents • Tinj = repetition time • I0 / Tinj = Pbar production rate PANDA Pbar bunch STRANGENESS IN NUCLEI F. Iazzi INFN-Torino&Politecnico

  20. Beam -Target Interaction: target material The pbar losses at 3 GeV/c: (≈1.03 [b] for12C) Single Coulomb Scattering (SCS): Hadronic interactions: (annihilation, nuclear scattering…) [b] (for 12C) Energy straggling Touschek effect Losses increases as Z2 & A2/3 X- rates increases by a factor 2 from 12C to 197Au Light nuclei are preferable as primary target Carbon properties: electric and heat conductor, good workability, low density, cheap…. STRANGENESS IN NUCLEI F. Iazzi INFN-Torino&Politecnico

  21. Beam -Target Interaction: target sizes (1) Pbar beam after n-th round Produced X- after n rounds Pbar annihilations after n rounds • Only free parameter : target sizes ( as product) • Max Pbar annihilation rate at the beginning ( n=1) ( < 5 ·106 [ann/s])  I0vsWth ·Ww • X - production rate depends on final nf= Tinj*(rev. frequency), i.e. on the pbar production • rate for fixed I0 STRANGENESS IN NUCLEI F. Iazzi INFN-Torino&Politecnico

  22. Beam -Target Interaction: X-rates X- rates & target sizes vs bunch contents ( for different pbar production, satisfying background constraints) • Remarks: • target sizes can be very small • thickness of 3 mm is under test • mechanical and thermal properties • to be evaluated Stopped X-/day(x100) Wth·Ww [μm2] 2x107 /s 1.5x107 /s 1x107 /s Result: 14000 ÷ 27000stopped X-/day expected • Possible improvements • increasing the beam acceptance with dedicated setting of the magnets for solid target • Max tolerable annihilation rate could be found higher after tests of prototypes STRANGENESS IN NUCLEI F. Iazzi INFN-Torino&Politecnico

  23. CONCLUSIONS • Doubly strange systems can shed light on important features of the baryon-baryon interaction ( L-L, X - N, X – nucleus, S=-2 decays…): but high statistics is absolutely required • FAIR will supply intense antiproton beams inside a ring (HESR) : new way to produce DSS • PANDA design for DSS: 2 target technique presents advantages (hyperon production optimized independently on hypernuclear targets, small amount of matter in the ring, only indirect production … • Antiproton beam at HESR: features under study, final performance not yet completely determined • Beam-target interaction: internal target designed with different options depending on the final features of HESR: stopped X- rate expected in the range 1.4104 ÷ 2.7 104 /day • Feasibility of the primary target, damage from beam, lifetime: under test • Detectors around the internal target are under study and someone already successfully tested STRANGENESS IN NUCLEI F. Iazzi INFN-Torino&Politecnico

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