Neutron scattering and extra interactions'

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Neutron scattering and extra interactions.
Guillaume Pignol Valery Nesvizhevsky Konstantin
Protasov
Rencontres des particules 2008 LAPTH
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The institute Laue-Langevin in Grenoble
European Synchrotron
Mountain

• The ILL
• Nuclear core 53 MW
• The most intense neutron
• source in the world

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Optical and Ultra Cold Neutrons (UCN)

• Optical neutrons
• wavelength gt2 Å
• interaction with bulk matter described by a mean
  potential (Fermi potential) 100 neV

10 MeV
production
Thermal neutrons
0.025 eV
Optical neutrons
100 neV
Ultra Cold Neutrons
velocity lt 7 m/s
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Slow neutrons and fundamental interactions

• Free neutrons feel all interactions very weakely
• Weak interaction
• ß decay 886 s
• Strong interaction
• Fermi potentials 100 neV
• Electromagnetism
• No electric charge
• B 1 T induce Zeeman split of 100 neV
• Gravity
• 1 m fall neutron increases its energy by 100
  neV

Neutrons can be very sensitive to new
interactions!
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Extra short range interaction
We assume a new interaction between neutron and
nucleus with A nucleons
Mediated by a new light boson of mass M
High Energy Physics
Modification of gravity
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Extra short range interaction
If a new boson gets its mass by a Higgs
mechanism at the Electroweak scale
If the new boson travels in large flat extra
dimensions (ADD) the coupling is suppressed.
High Energy Physics
Modification of gravity
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Slow neutron scattering with extra interaction

• Coherent scattering length (Fermi)
• Isotropic
• Energy independant
• Scales as A1/3

• Not isotropic
• Energy dependant
• Scales as A

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1 Simple nuclear model
We aim to exclude a contribution A in the set of
measured scattering lengths
Random potential model
Peskhin, Ringo, Am. J. Phys. 39 (1971)

• Square well potential for
• nuclear interaction
• Radius R x A1/3
• Random depth.

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1 Simple nuclear model extra interaction
We repeated the analysis with an extra force
included
Additional parameter
Random potential model
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2 Comparing forward and backward scattering
Interference measurement
Bragg diffraction measurement

• Measurements using interference method
• sensitive to the forward scattering amplitude
• one actually measures
• Measurements using Bragg-diffraction method
• sensitive to q 10 nm-1 scattering amplitude
• one actually measures

The two methods for measuring the scattering
lengths do not bear the same sensitivity to extra
force
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2 Comparing forward and backward scattering
No difference is observed for the nuclei for
which both measures exist
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3 Comparing forward scattering and total X-section

• Measurements using optical method
• sensitive to the forward scattering amplitude
• one actually measures
• Measurements using transmission method
• sensitive to the total cross-section at 1 eV
• one actually measures

This idea first appeared in Leeb and
Schmiedmayer, PRL 68 (1992)
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3 Comparing forward scattering and total X-section
Very precise measurements exist for both methods,
on lead and bismuth nuclei. No deviation is
observed There is a hidden difficulty for
scattering at 1 eV, electromagnetic effects have
to be taken into account.
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Measuring asymmetry of scattering
Diluted noble gaz
Possible dedicated experiment

• Forward/Backward asymmetry of scattering at
  noble gaz as a probe of new interactions
• Can detect asymmetry of 10-3
• Must take into account Doppler thermal effect

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Conclusions

• Neutron constraints on extra interactions are
  several orders of magnitude better than those
  usually cited in the range 1 pm 5 nm.
• We provided several independant strategies
• neutron constraints are reliable.
• Dedicated experiment (asymmetry of scattering)
  can easily improve the constraints by one order
  of magnitude.

For the detailed analysis, see hep-ph/0711.2298
(accepted in Phys Rev D)