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Double hypernuclei at PANDAM. Agnello, F. Ferro and F. Iazzi
Dipartimento di Fisica
Politecnico di Torino
SUMMARY The physics of double-hypernuclei; Double strangeness production with antiprotons
new way for 2-hypernuclei;
Simulation of the physics: preliminary results many physical processes involved.
Strange baryons in nuclear systems S=1S=1: -, -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=2S=2: -atoms, -, 2-hypernuclei• nuclear structure
• baryon-baryon interaction in SU(3)f
• H-dibaryon
S=3S=3: -atom, (-,-,3-hypernuclei)J. Pochodzalla – LEAP 2003
Double hypernuclei: present status
2-hypernuclei have been already observed:
6He Prowse (1966) KEK (2001)
B[MeV] 10.9 ± 0.5 7.25 ± 0.19
B[MeV] 4.7 ± 0.6 1.01 ± 0.20
10Be Danysz (1963) KEK (1991)
B[MeV] 17.5 ± 0.4 8.5 ± 0.7
B[MeV] 4.5 ± 0.4 - 4.9 ± 0.7
Double hypernucleus production techniques
1) Double Strangeness Exchange: K- + p K+ + -
106 K- on emulsion ( - production - capture
hyper-fragment detection): few hypernuclei
@ BNL (AGS 1996): K- on 12C (diamond) ( scintillating fibers
detector): 9000 stopped - (in 4 months)
@ JHF: <7000 captured - per day are expected
2) - production from pbar: pbar + n - + 0bar
pbarstop + A K*bar in nucleus K*bar + N in nucleus
-slow K + other
pbarflight + A -fast + 0bar + (A-1)
low probability- to be strongly decelerated 0bar is a strong signature
Status of the - production
From pbar to Double Hypernucleus
From pbar to D-Hypernucleus (step 1)
Strangeness Creation Reaction (SCR):
pbar + n + (A-1) - + 0bar + (A-1)
Initial state:
SCR threshold: PTH,SCR 2.65GeV/c; production threshold: PTH,3.01GeV/c
pbar momentum chosen: P(pbar) = 3 GeV/c (from theory (3 GeV/c) = MAX)
Final state:
no produced; two-body final state
0bar processes: annihilation (inside or outside production nucleus),decay
- processes: • deceleration inside nucleus through elastic nuclear scatterings
• decay (negligible)
SCR kinematics (LAB frame)
max - angle max(-) 0.3 rad 17.2o
two kinematical solutions with:
1.3 GeV/c P(-) 2.1 GeV/c
0.9 GeV/c P(0bar) 1.8 GeV/c
0.9 GeV/c P(-) 1.3 GeV/c
1.85 GeV/c P(0bar) 2.1 GeV/c
0 (-) (0bar) 0.3 rad 17.2o
Two-body reaction with threshold:
} I solution
} II solution
-, 0barmomentum vs.- angle
P(bar) distribution after SCR
0bar angle after SCR
From pbar to D-Hypernucleus (step 1)
The 0bar fate
Kinematics parameters: (0bar0.8
c 6.5 cm
max(0bar17.2o (0.3 rad)
High annihilation probability:0bar + nucleus K+ + K0 + X
or K0 + K0 + X
K+, probably forward-boosted,
may be used for trigger purposes
Simulation of 0bar annihilation and of K path is to be done
|
From pbar to D-Hypernucleus (step 1)
- path in residual nucleus
INC-like approach
(A-1) residual (excited) nucleus survives for a time longer
than the time spent by - during elastic scatterings SCR reaction occurs uniformly in a spherical Ga nucleus
(improvement: near the surface, to be done)
(-) is chosen uniformly in the CM frame of reference
(improvement: Fermi momentum, to be done)
Elastic T(- N) 10 mb (Charlton, P.L. 32B; Müller, P.L. 39B)
Elastic d/d exp(Bt), B = 5 GeV-2
Assumptions:
From pbar to D-Hypernucleus (step 1)- path inside residual nucleus. Results from simulation:
A non-negligible number of -’s undergoes a few scatterings
a non-negligible fraction of -’s is decelerated below 800
MeV/c
P(-) distribution outside the Ga nucleus(Intranuclear scattering effects)
From pbar to D-Hypernucleus (step 2)
Energy loss and complete stop of- in secondary target
Assumptions: Two parallelepipedal targets (1 mm gap):
• - production target (gallium wire 4(cm) x 50 x 50(m2) , A=70)
• hypernuclear target (diamond), 8 x 8 x 4 (thickness) cm3
beam spot diameter: 50 m
each - is given a lifetime , according to the distribution around the mean life
at every deceleration step, the proper elapsed time interval is compared with ,
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
P(-) distribution before C target(Intranuclear scattering + energy loss in Ga target effects)
Elapsed proper time before - entering C target
From pbar to D-Hypernucleus (step 2)
Energy loss (2105 simulated -’s).
GalliumGallium production target.
Results:
I solution II solution
Decayed in Gallium 83 150
Decayed in the gap 5528 7879
Decayed in Diamond 98977 131700
Stopped in Diamond 197 3823
Fraction stopped in Diamond 9.85E-4 1.91E-2
From pbar to D-Hypernucleus (step 2)
Energy loss (2105 simulated -’s).
GoldGold production target.
Results:
I solution II solution
Decayed in Gold 90 186
Decayed in the gap 5752 8572
Decayed in Diamond 100203 131697
Stopped in Diamond 429 5770
Fraction stopped in Diamond 2.14E-3 2.88E-2
Ga production target: expected ratesLet us assume the following parameters:
Luminosity L 1032 cm-2s-1; A = 70, Z = 31(pbar+nbar) 2 b at 3 GeV/c (Kaidalov & Volkovitsky)
(pbar+A) (pbar+n)A2/3(A-Z)/A p conversion probability, P 0.05 (Yamada, Hirata)
probability of transition per event PT 0.5
level population fraction: PS 0.1
reconstruction efficiency: K 0.5
photo peak efficiency: 0.1
from simulation: stopped - fraction, f 9.8510-4 1.9110-
2We obtain (for Ga target):
Number of produced -: N = L 1600 Hz
Number of stopped and detected -: Nstop NfK 0.79 15.3
s-1
Number of detected -hypernuclei: N NstopPPT PS
(1.97 38.2)10-4 s-1 (per month: 510 9914;
UrQMD: 200)
Au production target: expected ratesLet us assume the following parameters:
Luminosity L 1032 cm-2s-1; A = 197, Z = 79(pbar+nbar) 2 b at 3 GeV/c (Kaidalov & Volkovitsky)
(pbar+A) (pbar+n)A2/3(A-Z)/A p conversion probability, P 0.05 (Yamada, Hirata)
probability of transition per event PT 0.5
level population fraction: PS 0.1
reconstruction efficiency: K 0.5
photo peak efficiency: 0.1
from simulation: stopped - fraction, f 2.1410-3 2.8810-
2We obtain (for Au target):
Number of produced -: N = L 1600 Hz
Number of stopped and detected -: Nstop NfK 1.71 23 s-
1
Number of detected -hypernuclei: N NstopPPT PS
(4.3 57)10-4 s-1 (per month: 1114 14774)
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