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Strangest observed nuclei

  1. Apr 18, 2013 #1
    What are the strangest known nuclei? Specifically, have any nuclei with strangeness over 3 been seen?

    Are there any known charming or beautiful hypernuclei? Considering that Be-8, with half-life 10-16 s is a well described nucleus, the 10-12...10-13 s lifetime of charming and beautiful hyperons should be plenty to form nuclei.

    Also, have any nuclei been seen which contain no nucleons?

    And what are the observed properties of neutral and negative hypernuclei?
     
  2. jcsd
  3. Apr 18, 2013 #2

    mathman

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    You seem to be confusing two different things. Strange and charm quarks are found in hadrons. Nuclei consist of protons and neutrons made up of up and down quarks.

    Nuclei (by definition) are made up of nucleons.
     
  4. Apr 18, 2013 #3
    Can hyperons be bound to nucleons by strong force, the way nucleons are bound to each other in nuclei?

    Can hyperons be bound to each other by strong force?

    What is a strong force bound system connecting of several hyperons but including no nucleons? Is it a nucleus or not?
     
  5. Apr 18, 2013 #4

    Bill_K

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    Almost all hypernuclei studied contain just one Λ. Among the ones produced: 3ΛH, 4ΛH, 5ΛH, 6ΛH, 6ΛHe and 7ΛHe. There have been a few observations of double hypernuclei, which were formed after a conversion of a Ξ-hyperon into two Λ particles.

    See this review paper.
     
  6. Apr 18, 2013 #5
    Right - in presence of abundant nucleons of both tastes, hyperons can convert to lambda by quark exchange.

    Note that baryons that differ by one quark cannot undergo quark exchange.

    What happens when omegas are captured? In large nuclei, 3 lambdas, but in small nuclei?
     
  7. Apr 18, 2013 #6

    mfb

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    Right (both).
    It is a hypernucleus, which is a subgroup of all nuclei.

    The problem I see with charmed/beauty hypernuclei: both the formation of nuclei with multiple baryons and the production of charm/beauty-quarks are rare, and happen at different energy scales. The chance to have both at the same time could be low.
     
  8. Apr 19, 2013 #7
    Hava any hypernuclei containing no nucleons been positively observed?
    Nuclei with multiple baryons are commonly present from the start. At high energy scales, they disintegrate, but is the energy equally distributed? The energy may be carried away mostly by a few baryons being some of the original nucleons, leaving the charmed or beautiful hyperons bound in a hypernucleus of some size.

    There are 6 strange hyperons (without charm or beauty) and 2 nucleons. Between them, there are 14 pairs of baryons which differ by one quark and therefore cannot undergo quark exchange.
     
  9. Apr 19, 2013 #8

    mfb

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    That would be like a bunch of apples without apples. How is that supposed to look like?

    What do you mean with "from the start"?

    Well, you need hard, inelastic scattering to produce charm or beauty quarks. A quark gluon plasma could be nice in that respect - it can slow down the heavy quarks. At the LHC, something like 50 ##c\bar{c}##- and 2 ##b\bar{b}##-pairs are produced (on average) per lead-lead-collision.
     
  10. Apr 19, 2013 #9
    Imagine, say, aftermath of an omega capture:
    Ω-+p->ksi0+lambda
    ending up as a bound state.
    If 2 (presumably different) hyperons but no nucleons are bound to each other by strong force in a way two nucleons are bound to each other in a deuteron, is the resulting bound system a "nucleus" or something else?
    Collisions where charm and beauty are formed often happen inside nuclei.
    And what comes in is 416 nucleons.

    Where do these 50 charms on average wind up? How many on average fly away as mesons, how many depart as free charmed hyperons, and how many wind up bound in charmed hypernuclei?

    Do all 416 nucleons (plus the extra nucleons formed in nucleon-antinucleon pairs) fly away as free nucleons, or do appreciable numbers of (presumably mostly small) nuclei form?
     
    Last edited: Apr 19, 2013
  11. Apr 19, 2013 #10

    mfb

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    Ah, well, that depends on the interpretation of the word "nucleon" now. A bound state of several baryons without neutrons or protons is possible, but I don't know of observations of them.

    I am sure ALICE has published some papers about that. Some of them are annihilated before they form hadrons, some of them produce charmonium, some of them produce charmed hadrons, but I don't have numbers.

    Many protons and neutrons are destroyed in the collisions, and their valence quarks end up in other hadrons (several thousand particles are created in central collisions).
     
  12. Apr 19, 2013 #11
    Turns out that it is not exactly the baryons differing by 1 quark that are stable towards quark exchange.

    Ksions can be turned into two lambdas. Like
    ksi0(1315)+n(939)->2lambda(1116)+22MeV.
    Note that the energy is small. But on the other hand, ksions cannot be turned into lambda plus sigma - to the contrary:
    lambda(1116)+Ʃ+(1189)->ksi0(1315)+p(938)+52MeV.

    Considering how small the energy production of ksion conversion is - can it be reversed by a suitable shell structure?
     
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