PUMA : Exotic Nuclei & Antiprotons Alexandre Obertelli TU - - PowerPoint PPT Presentation

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PUMA : Exotic Nuclei & Antiprotons Alexandre Obertelli TU Darmstadt Bormio Winter Meeting on Nuclear Physics January 23 rd , 2018 03.10.2017 | Fachbereich BBBBB | Institut AAAA | Prof. TTTTTT | 23.01.2018 l PUMA | A.

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03.10.2017 | Fachbereich BBBBB | Institut AAAA | Prof. TTTTTT |

PUMA : Exotic Nuclei & Antiprotons

Alexandre Obertelli TU Darmstadt Bormio Winter Meeting on Nuclear Physics January 23rd, 2018

23.01.2018 l PUMA | A. Obertelli | IKP, TU Darmstadt | 1

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03.10.2017 | Fachbereich BBBBB | Institut AAAA | Prof. TTTTTT |

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Context: neutron- rich / deficient nuclei proton-neutron asymmetry

Z proton number N neutron number

208Pb

126 82 50 82 50 28 28 20 20

hypernuclei multi-neutron systems neutron skins & halos

16 20

shell evolution

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Talk by T. Aumann Talk by K. Blaum Talk by H. Tamura

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Neutron skins

Δrnp = rn − rp ≈ rm − rc

neutron skin thickness

  • X. Vinas et al., Eur. Phys. J A 50, 27 (2014)

(N-Z)/A

  • X. Roca-Maza et al., Phys. Rev. Lett. 106, 252501 (2011)

E A (ρn,ρp) = E0 A (ρ)+ S(ρ)(ρn − ρp ρ )2 L ∝ ∂S(ρ) ∂ρ

ρ0

❑ neutron skins have been extensively studied ❑ motivated by the Nuclear Equation of State (EOS) as well ❑ structure phenomenon difficult to characterise and to measure accurately

23.01.2018 l PUMA | A. Obertelli | IKP, TU Darmstadt | 3

208Pb

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03.10.2017 | Fachbereich BBBBB | Institut AAAA | Prof. TTTTTT |

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Charge and matter/neutron radii, ex. of 208Pb

Charge radii: ❑ Charge density distributions extracted from (e,e’) for stable nuclei ❑ Not accessible for short-lived nuclei, except at SCRIT at RIKEN since 2017 ❑ Charge radii of unstable nuclei from fine structure (relative) studies (ex. ISOLDE) Matter radii: ❑ proton scattering, coherent π0 photoproduction, parity-violation expts, reaction cross sections

  • ex. dedicated SFB workshop, MITP Mainz 2016
  • T. Aumann et al., Phys. Rev. Lett. 119, 262501 (2017)

208Pb

  • A. Meucci et al., PRC 90, 027301 (2014)

23.01.2018 l PUMA | A. Obertelli | IKP, TU Darmstadt | 4

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03.10.2017 | Fachbereich BBBBB | Institut AAAA | Prof. TTTTTT |

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Neutron halos

1n Halo 2n Halo 4n Halo/Skin H He Li Be B C N O F Ne Na Mg

6He 8He 11Li 14Be 17B 19B 22C 31Ne

S-wave dominate: 11Be, 15C , 19C, P-wave dominate: 6He, 8He, 31Ne, 37Mg

37Mg

Necessary conditions for halos: ❑ Small separation energy (<1MeV) ❑ Low orbital angular momenta (l=0 or 1)

23.01.2018 l PUMA | A. Obertelli | IKP, TU Darmstadt | 5

1p Halo

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03.10.2017 | Fachbereich BBBBB | Institut AAAA | Prof. TTTTTT |

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Neutron skins, halos in medium-mass nuclei

13/09/2017 13/09/2017

  • V. Rotival, K. Bennaceur and T. Duguet, Phys. Rev. C 79, 054309 (2009)

Nhalo = ρ(r)r 2 dr

r0 +∞

∫

Beyond the radius r0 : core density is one order of magnitude smaller than the halo one.

23.01.2018 l PUMA | A. Obertelli | IKP, TU Darmstadt | 6

EDF Skyrme Sly4

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03.10.2017 | Fachbereich BBBBB | Institut AAAA | Prof. TTTTTT |

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Neutron skins, halos in medium-mass nuclei

13/09/2017 13/09/2017

  • V. Rotival, K. Bennaceur and T. Duguet, Phys. Rev. C 79, 054309 (2009)

Nhalo = ρ(r)r 2 dr

r0 +∞

∫

Beyond the radius r0 : core density is one order of magnitude smaller than the halo one.

23.01.2018 l PUMA | A. Obertelli | IKP, TU Darmstadt | 6

  • S. Typel et al., Phys. Rev. C 89, 064321 (2014)

Correlations within the neutron-skin still to be investigated EDF Skyrme Sly4

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What would be an ideal probe? ❑ isospin sensitivity: differentiating between protons and neutrons ❑ sensitivity to the tail of the nuclear density ❑ usable for short-lived nuclei … low-energy antiprotons fulfill these requirements [was proposed in the past at CERN and GSI/FAIR (FLAIR project)] Sn isotopes SLy4 force Δrnp = 1 fm ρn/ρp =200

From V. Rotival et al., PRC 79 (2009)

Antiproton annihilation: a probe for the nuclear density tail

23.01.2018 l PUMA | A. Obertelli | IKP, TU Darmstadt | 7

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03.10.2017 | Fachbereich BBBBB | Institut AAAA | Prof. TTTTTT |

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Antiproton annihilation: a probe for the nuclear density tail

Captured antiproton Decay X-rays Auger electrons

1 2 3

Surface annihilation & pion emission

π π π

4

Cascade & residue production, decay

Brookhaven NL: W. M. Buggs et al., Phys. Rev. Lett. 31, 475 (1973)

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Antiproton annihilation: a probe for the nuclear density tail

  • Ex. 172Y @ CERN, R. Schmidt et al., PRC 58, 3195 (1998)

Γn = ImV(r) Ψn(r)

2 r 2

∫

dr withV(r) = 2π µ aρ(r)

Γ reaction probability Φnl antiproton radial wave function V(r) antiproton-nucleus potential a effective N-antiproton scattering length

  • ex. a=-1.53 – 2.5 i fm (Batty, NPA 1997)

ρ(r) nuclear density convoluted with pbar-N range (0.75-1 fm if finite range)

23.01.2018 l PUMA | A. Obertelli | IKP, TU Darmstadt | 9

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03.10.2017 | Fachbereich BBBBB | Institut AAAA | Prof. TTTTTT |

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Antiproton annihilation: a probe for the nuclear density tail

❑ Features: ▪ High cross section (Mbarns) at low energy (100 eV) ▪ Net electric charge conservation

  • 1: neutron annihilation

0: proton annihilation ❑ Sensitive to neutron-proton density ratio at surface

  • M. Wada, Y. Yamazaki, Nucl. Instr. Meth. B 214 (2004)

Nn Np ρn ρp surface

Extracted from data theory Emitted pions Multiplicity M Total charge Σ Captured antiproton Decay X-rays Auger electrons

1 2 3

Surface annihilation & pion emission

π π π

4

Cascade & residue production, decay

23.01.2018 l PUMA | A. Obertelli | IKP, TU Darmstadt | 10

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PUMA: Pbar Unstable Matter Annihilation

Storage of antiprotons at CERN/AD/ELENA at the GBAR experiment Transport the antiprotons… … to ISOLDE at CERN for unstable ion annihilation. PUMA trap for antiprotons

❑ Transport antiprotons from ELENA (CERN) to ISOLDE ❑ Device to be build (funded from 01/2018, for 5 years) ❑ First experiment at ISOLDE foreseen in 2022 ❑ Pioneer experiment with antiprotons as a probe for short-lived nuclei

23.01.2018 l PUMA | A. Obertelli | IKP, TU Darmstadt | 11

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03.10.2017 | Fachbereich BBBBB | Institut AAAA | Prof. TTTTTT |

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The GBAR experiment

How does antimatter falls in the gravitational field?

Spokesperson: P. Pérez (CEA/IRFU)

23.01.2018 l PUMA | A. Obertelli | IKP, TU Darmstadt | 12

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03.10.2017 | Fachbereich BBBBB | Institut AAAA | Prof. TTTTTT |

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The GBAR experiment

How does antimatter falls in the gravitational field?

Spokesperson: P. Pérez (CEA/IRFU)

23.01.2018 l PUMA | A. Obertelli | IKP, TU Darmstadt | 12

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03.10.2017 | Fachbereich BBBBB | Institut AAAA | Prof. TTTTTT |

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PUMA: a magnetic bottle for antiprotons

antiprotons radioactive ions Technical challenges: ❑ Store a large number of antiproton (<108) for a long time ❑ Transport low-energy ions inside the ultra high vacuum

23.01.2018 l PUMA | A. Obertelli | IKP, TU Darmstadt | 13

270 about 900 mm

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03.10.2017 | Fachbereich BBBBB | Institut AAAA | Prof. TTTTTT |

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Day-1 experiments at ISOLDE

23.01.2018 l PUMA | A. Obertelli | IKP, TU Darmstadt | 14

Nucleus T1/2 Statistics 1 day beam

Expected ρn/ρp

6He

807 ms 107 Neutron halo > 100

8He

119 ms

  • 4. 106

Thick skin 70(10)

11Li

8 ms 2 103 Neutron halo > 100

17Ne

109 ms 104 Proton halo < 0.010

31Ne

3 ms

  • 5. 102

Neutron halo > 100

104-138Sn

>103 Progression of skin: From 1.0(2) to 4.0(6) Production rates at ISOLDE ❑ Example of yield estimate:

  • At relative energy of about 100 eV, the capture cross section is 10-16 cm2 (100 Mbarns)
  • 107 cm-2 antiproton « target », 6-cm long
  • trapping time of 10 ms: ions go through antiprotons 104 times each
  • 1000 pps production rate of radioactive Ion (10 ions / bunch of 10 ms)
  • this least to an annihilation rate of 1 / minute (102 / day)
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Trapping challenges

  • Transporting charges in a Penning trap

C.H. Tseng and G. Gabrielse, Hyperfine Interactions 76, 381 (1993)

  • Trapping a large amount of antiprotons

In 2006, few 106 antiprotons trapped by the ASACUSA collaboration

  • Trapping antiprotons for a long time

BASE experiment (antiprotons stored without loss for >1.5 year)

  • C. Smorra et al., Nature 550, 371 (2017)
  • Efficient extraction of a subpart of stored antiprotons
  • C. Smorra et al., Int. Jour. Mass Spectroscopy (2015)
  • High efficiency transfer of charges from a trap

to another with smaller diameter

  • G. Schneider et al., Science 358, 1081 (2017)

Main challenge of PUMA: all the above in one

23.01.2018 l PUMA | A. Obertelli | IKP, TU Darmstadt | 15

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03.10.2017 | Fachbereich BBBBB | Institut AAAA | Prof. TTTTTT |

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< 10-17 mbar ultra high vacuum

❑ PUMA: thin sealing window needed for ion insertion

  • Material candidate: Si3N4. Well known properties, highly used membranes.
  • Membranes commercially available from 8 nm, few mm size

❑ Lifetime of antiprotons determined by the vacuum ❑ ONE solution: cryogenic (4 K) sealed vacuum

P

H (mbar) = 6×10−16 T(K) /τ( jours)

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  • Ex. OCTALAB, Singapore, created in 2008
  • J. Wieser et al., EPJD 48, 383 (2008)

12 keV e- beam through a 250 nm membrane

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03.10.2017 | Fachbereich BBBBB | Institut AAAA | Prof. TTTTTT |

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Summary

❑ PUMA: new program at CERN / ELENA and ISOLDE (started in January 2018) ❑ antiprotons as a probe for the nuclear density tail of short-lived nuclei ❑ Proton-to-neutron annihilation rate after capture, related to the proton-to-neutron density ratio ❑ search for halos and characterise thick neutron skins in short-lived nuclei ❑ (1) store, (2) transport antiprotons, (3) insert short-lived nuclei, (4) annihilate nucleons ❑ first physics experiments expected in 2022 ❑ Foreseen challenges:

  • trap and transport 109 antiprotons
  • ultra-high vacuum with thin entrance window
  • corrections from final state interactions
  • estimate of uncertainties from theory

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Sensitivity to final state interactions

  • M. Wada, Y. Yamazaki, Nucl. Instr. Meth. B 214 (2004)

❑ Pions may re-interact with residual nucleus Stable nuclei: probability 20-50% ❑ Solution: analyse charged pion multiplicity (M) AND sum charge (Sigma_c) ❑ treatment of final state interactions: λ+: π0 + p -> π+ + n λ-: π0 + n -> π- + p ω+: π- + p -> π0 + n ω-: π+ + n -> π0 + p ❑ analysis of M-Sigma matrices should lead to N(pbar-n)/N(pbar-p) with good accuracy and precision (<5% for 105 annihilations) ❑ new and systematic analysis based on simulated Monte-Carlo annihilations in progress (A. Corsi et al.)

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