Interactions of antiprotons with nuclei'

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Interactions of antiprotons with nuclei.

• K.Boreskov, A.B.Kaidalov
• ITEP, Moscow

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Contents

• Introduction. Space-time picture.
• Annihilation on nuclei .
• Solution of the paradox with A-dependence of
  sann.
• Charmonia production on nuclei.
• Bound charmonia in nuclei.
• Cumulative particle production.

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Space-time picture of high-energy interactions

• Large coherence length (time) of
• hadronic fluctuations at high energies
• ?t 2p/(M²-m²)
• At high energies hadronic (nuclear)
• fluctuations are prepared long before an
  interaction.

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Space-time picture of high-energy interactions

• The space-time picture of hA (AB) interaction
  changes at energies Ec when lcoh ?t RA . For
  typical interactions Ec mNµRA .
• At E lt Ec an elastic hA scattering amplitude
  can be considered as successive rescatterings of
  an initial hadron on nucleons of a nucleus
• (Glauber model)

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Space-time picture of high-energy interactions

• For E gt Ec there is a coherent interaction of
  constituents of a hadron with nucleons of a
  nucleus.
• However hA elastic amplitude can be
• calculated as in the Glauber model, but with
  account of inelastic intermediate states
• ( M² ltlt s ) - Gribov approach.

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Non-locality of high-energy interactions
Key feature of hadron HE interaction is
essential non-locality (even for NN)
In Regge language reggeon is essentially
non-local object (in contrast to
potential-scattering description)
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Two space-time pictures
Planar diagrams vanish as 1/E
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Antinucleon annihilation in interactions with
nuclei
Annihilation process - no antinucleons in final
state

• Glauber approach vs Reggeon picture

Its resolution gives definite predictions on
energy and atomic number dependencies of
annihilation cross section for E 10 15 GeV
Mechanisms of high-energy interactions can be
clarified
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Probabilistic description (Glauber approach)
(non-locality is completely neglected )
Beam particle propagates within nuclear
medium and successively interacts with target
nucleons
For annihilation
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Probabilistic (local) picture
single annihilation (at z) higher powers are
due to probability not to annihilate
Reggeon diagrams (low energies)
vanish at low energies as a whole particular
discontinuities contribute to different
processes
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Discontinuities of regge diagrams
planar
nonplanar
1st order in annihilation only
All nonannihilation interactions cancel each
other. The same for higher orders
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Reggeon diagrams (high energies)
A paradox unitarity violation?
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Reggeon diagrams

• several annihilation amplitudes
• for low energies
• for planar diagrams only

• single annihilation amplitude
• for high energies
• other contribution cancel

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Integration over intermediate masses
Large intermediate masses are not produced
coherently due to nuclear form-factors
Low intermediate masses are not produced because
of suppression of planar subdiagram
Narrow region at
crit value
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Annihilation cross section fastly decreases with
energy But nuclear effects are frozen at sscrit
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Conclusions (to this part)

• Unique possibility to differ two space-time
  pictures

• Freezing of nuclear effects with energy
• is predicted

• Value of critical energy
• where change of interaction picture occurs
• can be measured

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Charmonia production on nuclei.

• There are several goals of experiments for
  production of charmonia states on nuclei
• to measure the hard component of nucleon
  distribution in a nucleus,
• to study the phenomenon of color transparency,
• to measure cross sections of c -states
  interactions with nuclei (A-dependencies for
  different states).

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Bound charmonia in nuclei.

• It was supposed by S.Brodsky et al that charmonia
  can form bound states with nuclei, starting
  already from light nuclei.
• Estimate of the effective interaction of s-wave
  charmonia, using multipole expansion in QCD
  (A.K., P.E.Volkovitsky), show that this
  interaction is too week to lead to a bound state.
  (See, however, A.Sibirtsev, M.B. Voloshin).
• It is interesting to search for such states at
  PANDA.

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Cumulative particle production

• Nonnucleonic degrees of freedom (fluctons, quark
  clusters,..) exist in nuclei and are responsible
  for production of cumulative particles.
• Data show that spectra of cumulative particles
  obey universal scaling laws.
• It is important to check this scaling in
  interactions of antiprotons with nuclei and, in
  particular, in annihilation.

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Conclusions

• There are many important aspects of
  strong-interaction dynamics, which can be studied
  in interactions of antiprotons with nuclei by
  PANDA experiment.
• In particular, it will be possible to observe a
  change in space-time picture of annihilation
  process on nuclei.
• Production of charmonia by antiprotons and
  investigation of its interactions with nuclei
  look promising.