Overview

1. Precision Measurement of the dipole polarizabilityαD of 208Pb, with high intensity, monoenergeticMeVγ-radiation for the evaluation of neutron skin and the enhancement of UNEDF theory K M Spohr, KWD Ledingham SUPA collaboration; University of the West of Scotland (UWS), Paisley & University of Strathclyde, Glasgow, Collaborators: Oak Ridge Nat. Lab, USA; IFIN-HH, Romania

2. Theoretical Motivation for the measurement of αD(208Pb) (Inspired by W. Nazarewicz, Director HRIBF Oak Ridge & visiting Carnegie Professor UWS) Universal Nuclear Energy Density Functional (UNEDF), a leap forward UNEDF and Neutron-rich Matter in the Heavens and Earth Neutron equation of state, neutron-rich matter and the n-skin (rskin) of 208Pb Neutron matter, theoretical advise New theoretical approach, correlation between two observables Dipole polarizability as the best observable for rskin The need for high presision Experimental considerations Photonuclear reaction rate of 208Pb(γ,σtot) ELI-NP‘γ source’ Intensity, Accuracy, Challenges & Timeline Summary Overview

3. Theoretical motivation for the measurement of αD(208Pb)

4. Universal Nuclear Energy Density Functional(UNEDF) ‘Functionals’ aim to describe all measured and predictunknown nuclear properties from finite nuclei to neutron stars n-EoS & p-EoS Functionals (e.g. ‘Skyrme based’) instead of ab initio calculations with individual wave functions of all nucleons consisting of 2- or 3-body Hamiltonians Based on ‘Density Functional Theory’ derived for atomic systems (W. Kohn) Ab initio to A~60, (2011); progress: A+1 per year Unprecedented theoretical effort in history of Nuclear Physics 15 leading US institutions, chaired by W. Nazarewicz (Oak Ridge) Use of worlds leading open computing facilities (Jaguar Oak Ridge) Highlighted by DoE and 43 million processor hrs approved New Theory: Crucial UNEDFfunctionals for n-EoS can best be probed with selected (208Pb) high precision photonuclear (NRF) measurements achievable with the ELI ‘γ source’ in the near future! ELI will inform core nuclear physics issues, basic research by photons! Directive for experimentalist and ideally suited for 3rd and 4th generation systems UNEDF, a leap forward in theory

5. UNEDF and neutron-rich matter in the Heavens and on Earth 132Sn Equation of state Laboratory observables In-medium interactions Many-body theory Neutron star crust Astronomical observables Microphysics (transport,…)

6. Neutron Equation of State is very elusive to study in labs Best cases ‘skin’ of: 208Pb and 48Ca (Doubly magic nuclei) little interfering of shell and pairing effects for 208Pb No direct evidence of neutron skin yet (PREX soon?) PREX: 208Pb(e,e’) experiment at JLAB (12 year programme) Neutron-rich nuclei: rskin= rn– rp= 0.19 fm (208Pb) rp(208Pb) is well known: 5.45 fm Evaluating UNEDF,neutron matter in the labs 208Pb

7. Recent theory: dipole polarizabilityαD (208Pb) the best observable to deduce rskin(208Pb) with high precision. Nucleons communicate with us through a lot of observables Some are important, others not Some subsets of observables may be statistically correlated (linked) Some are very easy to measure, others extremely complicated Challenge for theory to guide experimentalists to select observables with the optimal information content Needs a lot of theoretical calculations, statistical modelling Results can be astonishing und unexpected A theoretical statistical uncertainty will prevail for the predictions Recent works: Neutron matter, theoretical advise • G.F. Bertschet al., Phys. Rev. C 71, 054311 (2005). • M. Kortelainenet al., Phys. Rev. C 77, 064307 (2008). • J. Toivanenet al., Phys. Rev. C78, 034306 (2008). • P. Klüpfelet al., Phys. Rev. C 79, 034310 (2009). • P.-G. Reinhard and W. Nazarewicz, Phys. Rev. C 81, 051303(R) (2010). • M . Kortelainenet al., Phys. Rev. C 82, 024313 (2010)

8. The product correlation between two observable A,B is: Reinhard’s and Nazarewicz’s newest covariance analysis is the least biased and most exhausting way to find out the correlations between all conceivable observables in one model and derive theoretical uncertainties within the model! Different models do not allow to deduce correlation between observables! Correlation between two observables =1: full alignment/correlation =0: not aligned/statistically independent

9. Nuclear observables evaluated for rskin (208Pb) bulk equilibrium symmetry energy symmetry energy at surface density slope of binding energy of neutron matter low-energy dipole strength dipole polarizability neutron skin

10. Result: aD the best observable! • A.Veyssiereet al., Nucl. Phys. A 159, 561 (1970) • E. Lipparini and S. Stringari, Phys. Rep. 175, 103 (1989) A 10% uncertainty makes it impossible to use the currently best value for aD as an independent check on neutron skin. New experiment in need!

11. Uncertainty for n-EoS, the need for high precision The UNEDF (n-EoS) theory improves dramatically for an uncertainty of δrskin /rskin< 0.4%, allowing to devise and(!) conclude on suggested functionals (SV-min-Rn)

12. ExperimentalConsiderations

13. 208Pb(γ,σtot), the GDR 1/E weighting of αD ~10% error for each point σ [b] NRF: Decrease in Intensity is prop. σ(E) Low-lying E1 transitions Threshold Energy [MeV]

14. Monochromatic, high intensity γ-beams with E1 multipolarity will allow highest precision measurements of αD (208Pb) Reduction of photo transmission is proportional to photo-excitation cross section Polarisation of γ beam allows disentanglement of E1,M1 and E2 Nuclear Resonance Fluorescence NRF experiments with semiconductor detectors can be applied Could use small targets e.g. for 48Ca (2nd best system) Auxiliary neutron detectors could be used eventually σGDR (208Pb) ~200-300 mbar → Σ~0.01cm-1 with >1013 photons/s high yields will be achieved, even for thin targets Challenges: Beam stability (yield, energy, bandwidth), influence of high flux in target Characterisation, use and development of radiation hardened detectors Simulation Measurements of rn in 208Pb with ELI

15. Peak brilliance of 1022-23 ph mm-2 msrad-2 s-1 (0.1%BW)-1 at a bandwidth of 1 ×10-3 will allow a high precision NRF measurement of αD(208Pb) and hence deduction of rskin (208Pb) with ELI-NP (2014) The 100 mA ELI-ERL system will allow to even enhance the precision by orders of magnitude (2017) The experimental campaign can go along with the development of source features Precision of NRF experiment can be realised in the regime demanded by theory of Reinhard and Nazarewicz! Feeding into UNEDF theory rskin(208Pb) with ELI-NP more precise than any forthcoming PREX results(?) (δrskin /rskin~1.2% at best estimation for PREX) Mass/Chargeless accelerator vs Charged accelerator technology! Possible PREX results could be independently verified, with higher precision Unique possibility to proof the correlation of observables as predicted by Reinhard and Nazarewicz and inform UNEDF theory ELI-NP γ source

16. UNEDF which aims to get a full description of nuclear interaction for ALL nuclei informing a gamut of related research fields can be informed by ELI-NP in a unique manner Dipole polarizability (αD) is strongest correlated to rskin of 208Pb (rskin = c × αD) (Nazarewicz & Reinhard) NRF measurement of αDto establish rskin (208Pb) Testing of prediction from ‘SV-min-R’ : 0.191(24) fm “The most exciting NRF measurement to make”, W. Nazarewicz δrSkin is as important as the value rSkinfor the validation of the functional ‘SV-min-R’ and hence for the deduction of n-EoS! High precision NRF program for αDis feasible with the forthcoming ELI’s ‘γ source’ as accuracy demands by theory can be matched with the superb beam qualities of ELI-NP and esp. ELI-100mA ERL ELI γ source offers a unique way to deduce rskin , n-EoS and UNEDFfunctionals Experimental program can progress with advance of ELI γ source features Intensity, maximum gamma energy, resolution ELI-NP as fine-tuneable Game Changer for Nuclear Physics, the dawn of a new era for understanding nuclear matter and the whole Universe Summary

17. End of TalkThanks for your attention

18. Based on: P.G. Reinhard and WN, Phys. Rev. C (R) 2010; arXiv:1002.4140) M. Kortelainen et al., 2010 To what extent is a new observable independent of existing ones and what new information does it bring in? Without any preconceived knowledge, all different observables are independent of each other and can usefully inform theory. On the other extreme, new data would be redundant if our theoretical model were perfect. Reality lies in between. Consider a model described by coupling constants Any predicted expectation value of an observable is a function of these parameters. Since the number of parameters is much smaller than the number of observables, there must exist correlations between computed quantities. Moreover, since the model space has been optimized to a limited set of observables, there may also exist correlations between model parameters. How to confine the model space to a physically reasonable domain? Statistical methods of linear-regression and error analysis Objective function fit-observables (may include pseudo-data)

19. Consider a model described by coupling constants The optimum parameter set Hessian The reasonable domain is defined as that multitude of parameters around minimum that fall inside the covariance ellipsoid : Uncertainty in variable A: Correlation between variables A and B:

20. towards n-stars http://unedf.org 208Pb 48Ca

21. To estimate the impact of precise experimental determination of neutron skin, we generated a new functional SV-min-Rn by adding the value of neutron radius in 208Pb, rn=5.61 fm, with an adopted error 0.02 fm, to the set of fit observables. With this new functional, calculated uncertainties on isovector indicators shrink by about a factor of two.

22. Good isovector indicators Poor isovector indicators

24. Nuclear Density Functional Theory and Extensions Input NN+NNN interactions Density Matrix Expansion Density dependent interactions Energy Density Functional Optimization • Fit-observables • experiment • pseudo data DFT variational principle HF, HFB (self-consistency) Symmetry breaking Symmetry restoration Multi-reference DFT (GCM) Time dependent DFT (TDHFB) Observables • two fermi liquids • self-bound • superfluid (ph and pp channels) • self-consistent mean-fields • broken-symmetry generalized product states • Direct comparison with experiment • Pseudo-data for reactions and astrophysics

25. The model used: DFT (EDF + fitting protocol) The fit-observables embrace nuclear bulk properties (binding energies, surface thicknesses, charge radii, spin-orbit splittings, and pairing gaps) for selected semi-magic nuclei which are proven to allow a reasonable DFT description. SV-min Skyrme functional P. Klüpfel et al, Phys. Rev. C79, 034310 (2009) RMF-d-t RMF functional Includes isoscalar scalar, vector, isovector vector, tensor couplings of vector fields, isovector scalar field with mass 980 MeV, and the Coulomb field; the density dependence is modeled only by non-linear couplings of the scalar field. Since the resulting NMP of this model (K=197MeV, asym=38MeV,m*/m=0.59) strongly deviate from the accepted values, we use this model only to discuss the robustness of our certain predictions and to illustrate the model dependence of the statistical analysis.

26. Existing data can only predict αDwithin 10% at best, so the theoretical work by Reinhard and Nazarewiczdemands a precision re-assessment of the dipole polarizability of 208Pb with a fine tuned experiment using a high precision tool, such as a mono-energetic gamma ray source emerging from high power laser systems PREX experiment is supposed to deliver rn by end of 2010 with 1% accuracy Skin of 208Pb lead has been measured in different experiments Hadron scattering: ratio of π+/π-=0.0(1), elastic proton scattering at 0.8GeV: 0.14(4), inelastic alpha scattering 0.19(9) Deviating results, systematic problems resulting in high systematic uncertainties, estimation S=0.17, Karatiglidis et al., PRC 65 (4), 044306, 2002 Estimation of PREX working group ~5% accuracy at best for rn rn (208Pb), current experimental status and what needs to be done

27. A word on PREX • PREX (Pb-Radius Experiment) is a big project aimed to measure the neutron skin of 208Pb • Scheduled to run in autumn 2010 at the Jefferson Lab (Jlab) USA • 1st proof of the existence of the neutron skin • Neutron skin detection is very elusive!, project inaugurated 1999 • Promises accuracy of ~1% • New UNEDF functional depicted before as this demands <0.4% • Intends to measure the parity-violating electroweak asymmetry in the elastic scattering of polarised 850MeV electrons on 208Pb (Z0 Boson) • Based on a coincidence that the axial potential A(r) depends mainly on the neutron radius only, as the proton distribution gets weighted by the factor (1 - 4sin2θW) which is close to zero • PREX does not render any further investigations obsolete! • Model dependence • Further independent proof • Higher accuracy possible with mono-energetic gamma sources

28. HOW? New generation of high intensity laser systems 3rd generation light sources

29. Laser systems as providers of mono-energetic γ beams • High intensity laser systems will be sources of mono-energetic γ beams (3rd generation light source) • Aimed to provide high photon yields of 1013 photons/s (2015) • With hitherto unreachable high values for spectral brilliance: 1022-25 photons/ mm2 mrad2 s (0.1%BW) (2015-2020) • In principle TWO technological approaches • Inverse Compton Backscattering of laser light on electron bunches • Provided by ‘traditional’ ELINAC (warm-LINAC), energy recovering LINAC (new concept, ALICE accelerator Daresbury, U.K., 2010) ERL • ELI foresees to follow the technological path of the MEGa-Ray ‘warm-Linac’ solution (Lawrence Livermore) in the first stage 2015 • From 2016 on the ERL solution is envisaged in a second phase • Free Electron Laser systems • SCAPA (Scottish Centre for the Application of Plasma Acceleration), 2014 • Storage ring driven FEL ‘High Intensity Gamma-Ray Source’ (HIGS) exists Duke University (USA), but 2nd generation light source with 5% BW • 2 to 20 MeV photons at Iγ ~ 107 with 5% BW, best 2nd generation light source

30. ELI (Extreme Light Infrastructure) Biggest European Laser Infrastructure initiated by G. Mourou with 20 PW system to be build at the NIPNE in Magurele, Bucharest solely for laser based nuclear physics Aimed to achieve 20 PW with 1 Hz rep rate and I~1024-25 Wcm-2 1st phase to be completed 2014-15 with ~280M€ (allocated!) ~80M€ allocated for the Gamma-ray infrastructure April 2010 decision taken to follow the MEGa-Ray approach (first 3rd generation light source, with unique intensity and spectral quality features, esp. reduced bandwidth) Collaboration of 13 (+x) European countries Three additional sites in, Prague (High energy e-beam facility) and Szeged (Attosecond science) + another, fourth high power system envisaged SCAPA (Scottish Centre for the Application of Plasma Acceleration) £20M research infrastructure to be build @ Strathclyde University Tuneable γsource for energies of up to 20-50 MeV (2015) FEL laser concept with laser produced high energy electrons Laser Plasma Wakefield accelerations: Schlenvoigtet al., Nature Phys 4, 130 (2008) ELI & SCAPA, C’est quoi?

31. Magurele Site NIPNE Director: V. Zamfir Blue-print High-Power Site

32. Laser Induced Compton Backscattering,COBALD at Daresbury Superconducting Elinac energy recovery of e-beam • ELBE/150TW system @ FZ-Rossendorf is similar • Blueprint for ELI mono-energetic photon beamline in 2nd phase (2015 onwards)

33. Laser/e-beam collision geometry For givenϕ, the energy E is a defined function of the scattering angle θ ϕ= 1800 (head on) ϕ= 900 (transverse) Thompson Scattering • normalised vector potential of the laser field • electromagnetic energy gained across laser wavelength compared to electron rest-mass • ~0 (classical Compton scattering), > 1 non-linear from Schoenlein RW et al., Science 274, 236 (1996)

35. E [keV] Simulation of backscattered photons of LICB system, 40 keV photons are shifted by ~10 keV, but due to non- linear effects, higher harmonics should occur • In relativistic regime non-linear QED effects lead to a red-shift • in the Compton scattered photons and the onset higher harmonics • Transformation of optical radiation into the keV and MeV regime • by multiple Compton backscattering on relativistic electrons • Origin of Gamma-ray bursts suggested by Wozniak et al., Astrophys J 691, 495, 2009

36. Features of MEGa-Ray, blueprint for ELI Bartyet al., ELI-NP meeting, Apr 2010

37. SCAPA-like FEL system Laser Plasma Wakefield accelerator Concept-Study Conceptional Design: Nakajima, Nature Physics 4, 92 - 93 (2008)

38. 208Pb(γ,σtot) Critical regions can be scanned with ELI-like systems with high δE resolution Resolution should be highest for low energies, 7-14 MeV and highest amplitudes 1/E weighting σ [b] Amplitude around Threshold Low-lying E1 transitions Energy [MeV]

39. Monochromatic, high intensity γ-beams with E1 multipolarity will allow highest precision measurements of αD (208Pb) Reduction of photo transmission is proportional to photo-excitation cross section Polarisation of γ beam allows disentanglement of E1,M1 and E2 Nuclear Resonance Fluorescence NRF experiments with semiconductor detectors can be applied Could use small targets e.g. For 48Ca Auxiliary neutron detectors could be used eventually σGDR (208Pb) ~200-300 mbar → Σ~0.01cm-1 with 1013 photons/s high yields will be achieved, even for thin targets Challenges: Influence of high flux onto target matter (heating, plasma effects?) Characterisation, use and development of radiation hardened detectors Simulation Measurements of rn in 208Pb (48Ca) with ELI & SCAPA

40. The aim of the talk was to show how important the neutron equation of state (EoS) is to address a manifold of fundamental open physics questions in a variety of fields such as nuclear and astrophysics, determined by the quest to optimise the UNEDF 208Pb is the best testing case for dense neutron matter in the laboratory, as it is a stable doubly magic isotope, readily available Measurements can inform the behaviour of neutron stars New theory links αD (208Pb) with the existence and magnitude of a neutron skin in 208Pb and predicts the thickness with highest accuracy Thus demands a re-assessment of αD (208Pb) with high precision A proof of the predictions will allow to establish a good functional for UNEDF Emerging, laser driven γsources such as MEGa-Ray and the future ELI and SCAPA systems promise high photon yields with MeV energies thus enabling such high precision measurements offering a complementary route to test predictions and existing data with regard to the neutron EoS, by ~2015 Potentially this 3rd generation laser driven light sources can provide the highest accuracy, which is of need to benchmark the theoretical predictions Summary

41. Merci, on behalf of the SUPA nuclear group, including the laser buffins: Klaus Spohr (UWS) Mahmud Hassan (UWS, SUPA PhD ) Malte Roesner (UWS, SUPA-PhD, 09/2010) Jody Melone (Strath) Tom McCanny (Strath) Ken Ledingham (Strath) +2 new SUPA employments In memoriam: Wilfred Galster (Strath) 1948-2009 With special thanks to WitekNazarewicz, Visiting Carnegie Professor, UWS

42. Various correlations reported… Typel and Brown, Phys. Rev. C 64, 027302 (2001) Furnstahl, Nucl. Phys. A 706, 85 (2002) Klimkiewicz et al., Phys. Rev. C 76, 051603(R) (2007) Yoshida and Sagawa, Phys. Rev. C 69, 024318 (2004)

43. Skin(208Pb) [fm] αD→

44. Skin and Polarizability are strongly correlated calign=0.978 for 208Pb • Skins for 132Sn and 208Pb are strongly correlated • Similar nature of neutron skins for doubly magic nuclei • Other measurable entities are not as strongly correlated with ‘Skin’ functional • Some parameters e.g. κ show no correlation to ‘Skin’ at all