1. Precision Measurement of the dipole polarizability α D of 208 Pb, with high intensity, monoenergetic MeV γ- radiation for the evaluation of neutron skin and the enhancement of U NEDF 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. Overview Theoretical Motivation for the measurement of α D (208 Pb) (Inspired by W. Nazarewicz, Director HRIBF Oak Ridge & visiting Carnegie Professor UWS) –Universal Nuclear Energy Density Functional (U NEDF ), a leap forward »U NEDF and Neutron-rich Matter in the Heavens and Earth Neutron equation of state, neutron-rich matter and the n-skin (r skin ) of 208 Pb »Neutron matter, theoretical advise New theoretical approach, correlation between two observables Dipole polarizability as the best observable for r skin The need for high presision Experimental considerations –Photonuclear reaction rate of 208 Pb(γ,σ tot ) –ELI-NP ‘ γ source’ »Intensity, Accuracy, Challenges & Timeline Summary

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

4. U NEDF, a leap forward in theory Universal Nuclear Energy Density Functional (U NEDF ) –‘Functionals’ aim to describe all measured and predict unknown 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 U NEDF functionals for n-EoS can best be probed with selected ( 208 Pb) 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 3 rd and 4 th generation systems

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

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

7. Neutron matter, theoretical advise Recent theory: dipole polarizability α D ( 208 Pb) t he best observable to deduce r skin ( 208 Pb) 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: G.F. Bertsch et al., Phys. Rev. C 71, 054311 (2005). M. Kortelainen et al., Phys. Rev. C 77, 064307 (2008). J. Toivanen et al., Phys. Rev. C 78, 034306 (2008). P. Klüpfel et al., Phys. Rev. C 79, 034310 (2009). P.-G. Reinhard and W. Nazarewicz, Phys. Rev. C 81, 051303(R) (2010). M. Kortelainen et al., Phys. Rev. C 82, 024313 (2010)

8. Correlation between two observables 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! =1: full alignment/correlation =0: not aligned/statistically independent

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

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

11. Uncertainty for n-EoS, the need for high precision The U NEDF (n-EoS) theory improves dramatically for an uncertainty of δ r skin /r skin < 0.4%, allowing to devise and(!) conclude on suggested functionals (SV-min-R n )

12. Experimental Considerations

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

14. Measurements of r n in 208 Pb with ELI Monochromatic, high intensity γ -beams with E1 multipolarity will allow highest precision measurements of α D ( 208 Pb) –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 48 Ca (2 nd best system) »Auxiliary neutron detectors could be used eventually –σ GDR ( 208 Pb) ~200-300 mbar → Σ~0.01cm -1 »with >10 13 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

15. ELI-NP γ source Peak brilliance of 10 22-23 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 α D ( 208 Pb) and hence deduction of r skin ( 208 Pb) 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 U NEDF theory r skin ( 208 Pb) with ELI-NP more precise than any forthcoming PREX results(?) ( δ r skin /r skin ~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 U NEDF theory

16. Summary 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 ( α D ) is strongest correlated to r skin of 208 Pb (r skin = c × α D ) (Nazarewicz & Reinhard) –NRF measurement of α D to establish r skin ( 208 Pb) –Testing of prediction from ‘SV-min-R’ : 0.191(24) fm »“The most exciting NRF measurement to make”, W. Nazarewicz »δ r Skin is as important as the value r Skin for the validation of the functional ‘SV-min-R’ and hence for the deduction of n-EoS! High precision NRF program for α D is 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 r skin, n-EoS and U NEDF functionals »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

17. End of Talk Thanks for your attention

18. Based on: P.G. Reinhard and WN, Phys. Rev. C (R) 2010; arXiv:1002.4140) M. Kortelainen et al., 2010 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 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. fit-observables (may include pseudo-data) fit-observables (may include pseudo-data) Objective function Objective function

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

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

21. To estimate the impact of precise experimental determination of neutron skin, we generated a new functional SV-min-R n by adding the value of neutron radius in 208 Pb, r n =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 Good isovector indicators Poor isovector indicators Poor isovector indicators

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

25. P. Klüpfel et al, Phys. Rev. C79, 034310 (2009) 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 RMF-  -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, a sym =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. r n ( 208 Pb), current experimental status and what needs to be done Existing data can only predict α D within 10% at best, so the theoretical work by Reinhard and Nazarewicz demands a precision re-assessment of the dipole polarizability of 208 Pb 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 r n by end of 2010 with 1% accuracy –Skin of 208 Pb 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 r n

27. A word on PREX PREX (Pb-Radius Experiment) is a big project aimed to measure the neutron skin of 208 Pb –Scheduled to run in autumn 2010 at the Jefferson Lab (Jlab) USA –1 st 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 208 Pb (Z 0 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 - 4sin 2 θ W ) 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 3 rd generation light sources

29. High intensity laser systems will be sources of mono- energetic γ beams (3 rd generation light source) –Aimed to provide high photon yields of 10 13 photons/s (2015) –With hitherto unreachable high values for spectral brilliance: 10 22-25 photons/ mm 2 mrad 2 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 2 nd generation light source with 5% BW 2 to 20 MeV photons at I γ ~ 10 7 with 5% BW, best 2 nd generation light source Laser systems as providers of mono- energetic γ beams

30. E LI & S CAPA, C’est quoi? 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~10 24-25 Wcm -2 »1 st 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 3 rd 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 γ source for energies of up to 20-50 MeV (2015) –FEL laser concept with laser produced high energy electrons »Laser Plasma Wakefield accelerations: Schlenvoigt et al., Nature Phys 4, 130 (2008)

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

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

33. from Schoenlein RW et al., Science 274, 236 (1996) Laser/e-beam collision geometry 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 Thompson Scattering For given ϕ, the energy E  is a defined function of the scattering angle θ ϕ = 180 0 (head on) ϕ = 90 0 (transverse)

35. 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 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 E [keV]

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

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

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

39. Measurements of r n in 208 Pb ( 48 Ca) with ELI & SCAPA Monochromatic, high intensity γ -beams with E1 multipolarity will allow highest precision measurements of α D ( 208 Pb) –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 –σ GDR ( 208 Pb) ~200-300 mbar → Σ~0.01cm -1 »with 10 13 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

40. Summary 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 – 208 Pb 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 α D ( 208 Pb) with the existence and magnitude of a neutron skin in 208 Pb and predicts the thickness with highest accuracy »Thus demands a re-assessment of α D ( 208 Pb) with high precision »A proof of the predictions will allow to establish a good functional for UNEDF –Emerging, laser driven γ sources 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 3 rd generation laser driven light sources can provide the highest accuracy, which is of need to benchmark the theoretical predictions

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 Witek Nazarewicz, Visiting Carnegie Professor, UWS

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

43. αD→αD→ Skin( 208 Pb) [fm]

44. Skin and Polarizability are strongly correlated c align =0.978 for 208 Pb Skins for 132 Sn and 208 Pb 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