Time, Formation Probability and Signatures of SBNs

LIFE TIME, FORMATION PROBABILITY AND SIGNATURES OF SBNS 

For such low values of Q many important annihilation channels involving two heavy mesons (p, co, ri, rj, . ..) are simply closed. Other two-body channels such as np, Ttco are considerably suppressed due to the closeness to the threshold. As is well known, the two-pion final states contribute only about 0.4% of the annihilation cross section. Even in vacuum all above mentioned channels contribute to OA not more than 15% [53]. Therefore, we expect that only multi-pion final states contribute significantly to antiproton annihilation in the SBN. But these channels are strongly suppressed due to the reduction of the available phase space. Our calculations show that changing Q from 2 to 1 GeV results in suppression factors 5, 40 and 1000 for the annihilation channels with 3, 4 and 5 pions in the final state, respectively. Applying these suppression factors to the experimental branching ratios [54] we come to the conclusion that in the SBNs the annihilation rates can be 

Let us discuss now how these exotic nuclear states can be produced in the laboratory. We believe that the most direct way is to use antiproton beams of multi-GeV energy. This high energy is needed to suppress annihilation on the nuclear surface which dominates at low energies. To form a deeply bound state, the fast antiproton must transfer its energy and momentum to one of the surrounding nucleons. This can be achieved through reactions of the type pN BB in the nucleus. 

Without detailed transport calculations it is difficult to find the formation probability, W, of final nuclei with trapped antinucleons in these reactions. A rough estimate can be obtained by assuming that antiproton stopping is achieved in a single inelastic collision somewhere in the nuclear interior, i.e., taking the penetration length of the order of the nuclear radius R. From the Poisson distribution in the number of collisions the probability of such an event is 

Ap is simply Ap/piab- For piab = 10 GeV and Ap = 0.4 GeV this gives 0.04. Assuming the geometrical fraction of central events 20% we get the final estimate W 0.17x0.04x0.2 1.410 . One should bear in mind that additional reduction factors may come from the matrix element between the bare massive antibaryon and the dressed almost massless antibaryon in a deeply bound state. But even with extra factors 10 -10 which may come from the detailed calculations the detection of SBNs is well within the modern experimental possibilities. 

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Life Time, Formation Probability and Signatures of SBNs 130... 

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