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Double hypernuclei at PANDA

Double hypernuclei at PANDA. SUMMARY The physics of double-hypernuclei; Double strangeness production with antiprotons new way for 2 L -hypernuclei; Simulation of the physics: preliminary results many physical processes involved. M. Agnello , F. Ferro and F. Iazzi

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Double hypernuclei at PANDA

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  1. Double hypernuclei at PANDA SUMMARY • The physics of double-hypernuclei; • Double strangeness production with antiprotons • new way for 2L-hypernuclei; • Simulation of the physics: preliminary results • many physical processes involved. M. Agnello, F. Ferro and F. Iazzi Dipartimento di Fisica Politecnico di Torino

  2. Strange baryons in nuclear systems • S=1: L-, S-hypernuclei • nuclear structure, new symmetries • The presence of a hyperon may modify the size, shape… of nuclei • New specific symmetries • hyperon-nucleon interaction • strange baryons in nuclei • weak decay The physics of double-hypernuclei • S=2: X-atoms, X-, 2L-hypernuclei • nuclear structure • baryon-baryon interaction in SU(3)f • H-dibaryon • S=3: W-atom, (W-,LX-,3L-hypernuclei) J. Pochodzalla – LEAP 2003

  3. Double hypernuclei: present status 2L-hypernuclei have been already observed:

  4. Double hypernucleus production techniques 1) Double Strangeness Exchange: K- + p ® K+ + X- • 106 K- on emulsion (®X- production ®X- capture ® hyper-fragment detection): few hypernuclei • @ BNL (AGS 1996): K- on 12C (diamond) (®scintillating fibers detector): 9000 stopped X- (in 4 months) • @ JHF: <7000 captured X- per day are expected 2) X- production from pbar: pbar + n ® X- + X0bar • pbarstop + A ® K*bar in nucleus ® K*bar + N in nucleus ® X-slow K + other • pbarflight + A ® X-fast + X0bar + (A-1) • low probability • X- to be strongly decelerated • X0bar is a strong signature

  5. Status of the X- production

  6. From pbar to Double Hypernucleus

  7. From pbar to D-Hypernucleus (step 1) Strangeness Creation Reaction (SCR): pbar + n + (A-1)®X- + X0bar + (A-1) • Initial state: • SCR threshold: PTH,SCR » 2.65GeV/c; p production threshold: PTH,p » 3.01GeV/c • pbar momentum chosen: P(pbar) = 3 GeV/c (from theory s(3 GeV/c) = MAX) • Final state: • no p produced; two-body final state • X0bar processes:annihilation (inside or outside production nucleus),decay • X- processes: • deceleration inside nucleus through elastic nuclear scatterings • decay (negligible)

  8. SCR kinematics (LAB frame) Two-body reaction with threshold: • max X- angle qmax(X-) » 0.3 rad »17.2o • two kinematical solutions with: 1.3 GeV/c £P(X-) £ 2.1 GeV/c 0.9 GeV/c £P(X0bar)£ 1.8 GeV/c 0.9 GeV/c £P(X-) £ 1.3 GeV/c 1.85 GeV/c £P(X0bar)£ 2.1 GeV/c 0 £q(X-) £q(X0bar) £ 0.3 rad »17.2o } I solution } II solution

  9. X-, X0barmomentum vs. X- angle

  10. P(X0bar) distribution after SCR

  11. X0bar angle after SCR

  12. From pbar to D-Hypernucleus (step 1) The X0bar fate | Kinematics parameters: • b(X0bar) » 0.8 • bct»6.5 cm • max q(X0bar) » 17.2o (0.3 rad) • High annihilation probability: • X0bar + nucleus ® K+ + K0 + X • or K0 + K0 + X • K+, probably forward-boosted, may be used for trigger purposes Simulation of X0bar annihilation and of K path is to be done

  13. From pbar to D-Hypernucleus (step 1) X- path in residual nucleus INC-like approach Assumptions: • (A-1) residual (excited) nucleus survives for a time longer than the time spent by X- during elastic scatterings • SCR reaction occurs uniformly in a spherical Ga nucleus (improvement: near the surface, to be done) • q(X-) is chosen uniformly in the CM frame of reference (improvement: Fermi momentum, to be done) • Elastic sT(X- N) »10 mb (Charlton, P.L. 32B; Müller, P.L. 39B) • Elastic ds/dW» exp(B×t), B = 5 GeV-2

  14. From pbar to D-Hypernucleus (step 1) X- path inside residual nucleus. Results from simulation: • A non-negligible number of X-’s undergoes a few scatterings • a non-negligible fraction of X-’s is decelerated below 800 MeV/c

  15. P(X-) distribution outside the Ga nucleus (Intranuclear scattering effects)

  16. From pbar to D-Hypernucleus (step 2) Assumptions: • Two parallelepipedal targets (1 mm gap): • X- production target (gallium wire 4(cm) x 50 x 50(mm2) , A=70) • hypernuclear target (diamond), 8 x 8 x 4 (thickness) cm3 • beam spot diameter: 50 mm Energy loss and complete stop of X- in secondary target • each X- is given a lifetime t, according to the distribution around the mean life • at every deceleration step, the proper elapsed time interval Dt is compared with t, in order to determine whether the particle survives or not • a complete stop is achieved in the diamond target: the stop position and the total elapsed time are evaluated

  17. P(X-) distribution before C target (Intranuclear scattering + energy loss in Ga target effects)

  18. Elapsed proper time before X- entering C target

  19. From pbar to D-Hypernucleus (step 2) Energy loss (2×105 simulated X-’s). Gallium production target. Results:

  20. From pbar to D-Hypernucleus (step 2) Energy loss (2×105 simulated X-’s). Gold production target. Results:

  21. Ga production target: expected rates Let us assume the following parameters: • Luminosity L » 1032 cm-2s-1; A = 70, Z = 31 • s(pbar+n®XXbar) »2 mb at 3 GeV/c (Kaidalov & Volkovitsky) • S º s(pbar+A) » s(pbar+n)×A2/3×(A-Z)/A • X-p®LL conversion probability, PLL»0.05(Yamada, Hirata) • probability of transition per event PT»0.5 • level population fraction: PS»0.1 • reconstruction efficiency: eK»0.5 • g photo peak efficiency: eg»0.1 • from simulation: stopped X- fraction, fX»9.85×10-4 ¸ 1.91×10-2 We obtain (for Ga target): • Number of produced X-: NX = L×S»1600 Hz • Number of stopped and detected X-: Nstop»NX×fX×eK»0.79¸15.3 s-1 • Number of detected LL-hypernuclei: NLL»Nstop×PLL×PT ×PS×eg» » (1.97¸ 38.2)×10-4 s-1 (per month: 510 ¸ 9914; UrQMD: » 200)

  22. Au production target: expected rates Let us assume the following parameters: • Luminosity L » 1032 cm-2s-1; A = 197, Z = 79 • s(pbar+n®XXbar) »2 mb at 3 GeV/c (Kaidalov & Volkovitsky) • S º s(pbar+A) » s(pbar+n)×A2/3×(A-Z)/A • X-p®LL conversion probability, PLL»0.05(Yamada, Hirata) • probability of transition per event PT»0.5 • level population fraction: PS»0.1 • reconstruction efficiency: eK»0.5 • g photo peak efficiency: eg»0.1 • from simulation: stopped X- fraction, fX»2.14×10-3 ¸ 2.88×10-2 We obtain (for Au target): • Number of produced X-: NX = L×S»1600 Hz • Number of stopped and detected X-: Nstop»NX×fX×eK»1.71¸23 s-1 • Number of detected LL-hypernuclei: NLL»Nstop×PLL×PT ×PS×eg» » (4.3¸ 57)×10-4 s-1 (per month: 1114 ¸ 14774)

  23. Conclusions • Simulation of -production and stopping (based on INC-Like Model) • has been implemented • Previous UrQMD rate prediction has been confirmed (slightly enhanced) • - & double hypernuclei high rate production seems feasible in PANDA Future work • Optimizing the physical parameters • (production target, densities, geometry,…) • Simulating 0bar , +bar annihilations for trigger purposes • Simulating the  conversion and decay for detection purposes • Producing spectra and distributions • to insert in the event generator of PANDA-MC • Exploring the experimental aspects (trigger, detection efficiency,...) • by using PANDA-MC

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