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

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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