1. 1/38 Laboratory Underground Nuclear Astrophysics The D( 4 He,  ) 6 Li reaction at LUNA and the Big Bang Nucleosynthesis Carlo Gustavino For the LUNA collaboration The Big Bang Nucleosynthesis The Lithium problem Nuclear astrophysics The D( 4 He,  ) 6 Li measurement at LUNA LUNA MegaVolt

2. 2/38 Big Bang Nuclesynthesis In the standard scenario, the primordial abundance of light elements depends ONLY on: Barionic density  b  (measured by CMB experiments at the level of %) Standard Model (  n,, ..) Nuclear astrophysics, i.e. cross sections of nuclear reactions in the BBN chain Already measured by LUNA: P(D,  ) 3 He (D abundance) 3 He(D,p) 4 He ( 3 He abundance) 3 He( 4 He,g) 7 Be ( 7 Li abundance) This talk: D( 4 He,  ) 6 Li ( 6 Li abundance) Good agreement between calculations and observations for D, 4 He, 3 He. Problems for 7 Li, 6 Li

3. 3/38 BBN Cosmology Astrophysics New Physics CMB  b  b  b <<1 Nuclear Astrophysics Primordial Elements Observations Particle Physics (  n,, ..) BBN Flowchart

4. 4/38 Line strength: 7 Li abundance Line Profile: 6 Li/ 7 Li ratio Basic Concepts to unfold primordial abundances Observation of a set of primitive objects (born when the Universe was young) Extrapolation to zero metallicity: Fe/H, O/H, Si/H -----> 0 Lithium observations 7 Li: Observation of the absorption line at the surface of metal-poor stars in the halo of our Galaxy 6 Li: Observation of the asymmetry of the 7 Li absorption line. The observed Lithium abundance

5. 5/38 Observational Results: Observed 7 Li abundance is ~3 times lower than foreseen (Spite Plateau): Well established ” 7 Li problem”. Claim of a 6 Li abundance orders of magnitude higher than expected (Asplund 2006) However, the existence of a “Second Lithium problem” is presently debated, because convective motions on the stellar surface can give an asymmetry of the absorption line, mimicking the presence of 6 Li. Finally, the expected 6 Li abundance is affected by a large uncertainty, because of the poor knowledge of the D( 4 He,  ) 6 Li cross section See also “Lithium in the Cosmos”, 27-29 february, Paris Uncertainty from D( 4 He,  ) 6 Li The Lithium Problem(s)

6. 6/38 Production/destruction of 6 Li Leading process for the 6 Li production: D( ,  ) 6 Li Leading Process for the 6 Li destruction: 6 Li(p, 3 He) 4 He SERPICO 2004 6 Li(p, 3 He) 4 He S-factor BBN

7. 7/38 The claimed 6 Li abundance in metal-poor stars is very large (Asplund et al. 2006) compared to BBN predictions (NACRE compilation). Possible reasons are: Systematics in the 6 Li observation in the metal-poor stars Unknown 6 Li sources older than the birth of the galaxy New physics, i.e. sparticle annihilation/decay (Jedamzik2004), long lived sparticles (Kusakabe2010),… …Lack of the knowledge of the D( 4 He,  ) 6 Li reaction. IN FACT: NO DIRECT MEASUREMENTS in the BBN energy region in literature (large uncertainty due to extrapolation) INDIRECT coulomb dissociation measurements (Kiener91, Hammache2010) strongly depends on the theoretical assumptions, because the nuclear part is dominant. FOR THE FIRST TIME, the D( 4 He,  ) 6 Li reaction has directly been studied inside the BBN energy region D( 4 He,  ) 6 Li cross section

8. 8/38 0  = (KT) 3/2 1 8  S(E) exp dE E KT EGEG E tunneling probability KT << Z1Z2e2Z1Z2e2 RNRN  3 He( 3 He,2p) 4 He 22 keV d(p,  ) 3 He 7 keV 14 N(p,  ) 15 O 27 keV E0E0 Reaction rate for charged particles E Reaction

9. 9/38 event/month < R lab < event/day  ~ 10 % I P ~ mA  ~  g/cm 2 R lab =  ·  ·I p ·  ·N av /A pb <  < nb Reaction rate in the laboratory

10. 10/38 Danger in extrapolating (low energy nuclear resonances possible) Direct measurement at low energies needed > UnderGround Measurements, high beam current Why underground Measurements? DATAEXTRAPOLATION

11. 11/38 R lab > B cosm + B env + B beam induced Environmental radioactivity has to be considered underground (shielding, Radon Box…) and intrinsic detector background. Beam induced background from parasitic reactions  selected materials, detector techniques (coincidence), proper set-up. Experimental requirements Underground Laboratory B cosm B env B beam induced

12. 12/38 Cosmic background reduction:  : 10 -6 n: 10 -3  : 10 -2 -10 -5 Gran Sasso National Laboratory (LNGS) The LUNA measurements are performed at LNGS, with the unique accelerator in the world operating underground. The Ultra Low background makes possible to study Nuclear reactions well below the coulomb barrier. LUNA

13. 13/38 Cosmic ray induced background RadiationLNGS/out Muons10 -6 neutrons10 -3 40 K 214 Bi 232 Th 10 2 -10 3 reduction at E  >4 MeV Advantage of underground measurements for reaction with high Q-values: d(p,  ) 3 He, 14 N(p,  ) 15 O, 15 N(p,  ) 16 O, 25 Mg(p,  ) 26 Al Underground laboratory

14. 14/38 Natural radioactivity background Underground + Lead shield + Radon box Passive shielding is more effective underground since the  flux, that create secondary  s in the shield, is suppressed. Advantage for underground measurements also for low Q-value reactions: 3 He( ,  ) 7 Be, D( ,  ) 6 Li

15. 15/38 Voltage Range : 1 - 50 kV Output Current: 1 mA Beam energy spread: 20 eV Long term stability (8 h): 10 -4 Terminal Voltage ripple: 5 10 -5 The LUNA1 (50 kV) accelerator 3 He( 3 He,2p) 4 He Solar Standard Model, v flux P(D,  ) 3 He BBN, proto-stars D( 3 He,p) 4 He electron shielding, BBN U. Greife et al, NIM A 350 (1994).

16. 16/38 Voltage Range: 50-400 kV Output Current: 1 mA (@ 400 kV) Absolute Energy error: ±300 eV Beam energy spread: <100 eV Long term stability (1 h) : 5 eV Terminal Voltage ripple: 5 Vpp A. Formicola et al., NIMA 527 (2004) 471. 14 N(p,  ) 15 O 3 He( 4 He,  ) 7 Be 25 Mg(p,  ) 26 Al 15 N(p,  ) 16 O 17 O(p,  ) 18 F D( 4 He,  ) 6 Li 22 Ne(p,  ) 23 Na The LUNA (400 kV) accelerator

17. 17/38 d d  D(α,α)d Rutherford scattering  α beam Deuterium gas target  He d d n D(d,n) 3 He reaction Q=3.269 MeV E cm ( 3 He)= 0,820 MeV E cm (n)=2.450 MeV Beam Induced Background in the D( 4 He,  ) 6 Li measurement (n,n’  ) reaction on the surrounding materials (lead, steel, copper and germanium)  -ray background in the RoI for the D( ,  ) 6 Li DC transition ( ∼ 1.6 MeV)

18. 18/38 Germanium detector close to the beam line to increase the detection efficiency. Target length optimized. Pipe to reduce the path of scattered deuterium, to minimize the D(d,n) 3 He reaction yield. Si detector to monitor the neutron production through the detection of D(d,p) 3 H protons. Lead, Radon Box to reduce and stabilize Natural Background. Copper removal, selected materials. D( 4 He,  ) 6 Li set-up

19. 19/38 Beam Induced Background and Natural Background D+alpha RoI at E lab =400 keV Submitted to EPJA

20. 20/38 Beam Induced Background Vs GEANT simulation D+alpha ROI at E lab =400 keV Submitted to EPJA

21. 21/38 400 keV beam 280 keV beam D(d,n) 3 He reaction Q=3.269 MeV E cm (n)=2.450 MeV E cm ( 3 He)= 0,820 MeV The neutrons produced in the D(d,n) 3 H reaction have a narrow energy distribution, weakly dependent on the  -beam energy. ---> While changing the beam energy E , the shape of the HPGe spectrum due to (n,n’  ) reactions remains essentially the same. Beam Induced Background Vs Beam Energy  -energy [keV] Counts Neutron Energy Distribution (Simulation) Germanium detector spectra (data)

22. 22/38 -The Energy of  ’s coming from D+alpha reaction strongly depends on the beam energy, through the following relationship: D( 4 He,  ) 6 Li signal The Region of Interest (RoI) is defined by kinematics and depends only on the beam energy. The shape of  -ray peak depends on angular distribution composition

23. 23/38 Energy (keV) Signal (Hammache) (counts/day@300uA) Noise (Data) (counts/day@300uA) 35 keV window N/S 2409900100 2801873141 3604362014 4005867012 Signal/Noise estimation Long measurement time needed. No hope to see the D( ,  ) 6 Li signal at low beam energies

24. 24/38 Measurement method The measurement is performed into 2 steps: 1.Measurement with E  =400 keV on D 2 target. The Ge spectrum is mainly due to background (natural background and beam induced background). The D( ,  ) 6 Li signal is expected in a well defined RoI (1587-1625 keV). 2.Same measurement as 1., but with E  =280 keV. The background are is essentially the same as before, while the gammas from the D( ,  ) 6 Li reaction are expected at 1550-1580 keV. D( ,  ) 6 Li Signal is obtained by subtracting the two spectra

25. 25/38 400 keV: T=18,2 days; =0,306 mbar; Q=514 C 280 keV: T=20,5 days; =0,308 mbar; Q=539 C Preliminary results (E lab =400/280 keV) 400 keV ROI 280 keV ROI  -energy [keV] Counting excess observed in the E lab =400 (280) keV RoI

26. 26/38 Preliminary results (E lab =400/280 keV)  -energy [keV] 400 keV: T=18,2 days; =0,306 mbar; Q=514 C 280 keV: T=20,5 days; =0,308 mbar; Q=539 C No “D+alpha like” excess observed, by shifting the energy of  E=±75 keV 400 keV ROI 280 keV ROI

27. 27/38 1) The spectra taken at E  =400,280 keV are divided into 17 energy region of  E=75 keV. 2) BLIND search of fake ”D(  ) 6 Li-like" signals (excesses at 400 and 280 keV summed up) Search of ”D(  ) 6 Li-like" excess in the Ge spectra PRELIMINARY RESULTS (ROOT+MINUIT): -The counting excess in the true D+alpha energy region exceeds 5  's. -No significant ”D(  ) 6 Li-like” excesses are found in the other energy regions. -Counting deviations in the “off-RoI’s” energy bins are compatible with statistical expectation.

28. 28/38 A further check.. Not too bad N/S ratio foreseen at E  =360 keV Short measurement at E  =360/240 keV. The D(  ) 6 Li counting excess must shift of about 14 keV towards lower energy.

29. 29/38 400 keV: T=18,2 days; =0,306 mbar; Q=514 C 280 keV: T=20,5 days; =0,308 mbar; Q=539 C Counting excess observed in the E lab =400 keV RoI Preliminary results (E lab =400/280 keV) PRELIMINARY 400 keV ROI 280 keV ROI  -energy [keV] Counts

30. 30/38 360 keV: T=8,55 days; =0,300 mbar; Q=252 C 240 keV: T=9,07 days; =0,300 mbar; Q=211 C Counting excess shifted to the E lab =360 keV RoI Preliminary results (E lab =360/240 keV) PRELIMINARY 360 keV ROI 240 keV ROI  -energy [keV] Counts Poor statistics!

31. 31/38 Conclusion -The LUNA measurement excludes a nuclear solution for the 6 Li problem. The observation of a “huge” amount of 6 Li in metal-poor stars must be explained in a different way (systematics in the 6 Li observation, unknown 6 Li sources older than galaxies, new physics…). -Direct D( ,  ) 6 Li measurement at BBN energies. For the first time, a solid experimental footing is available to calculate the 6 Li primordial abundance. Data analysis still in progress. Three independent method are used, giving compatible results.

32. 32/38 LUNA MV Project April 2007: a Letter of Intent (LoI) was presented to the LNGS Scientific Committee (SC) containing key reactions of the He burning and neutron sources for the s-process: 12 C( ,  ) 16 O 13 C( ,n) 16 O 22 Ne( ,n) 25 Mg ( ,  ) reactions on 14,15 N and 18 O The project requires a new machine, i.e. a 3.5 MV single ended positive ion accelerator with high current (~mA)

33. 33/38 LOI to LNGS for a new accelerator (3.5 MEV single ended) The Holy Grail: 12 C( ,  ) 16 O Gamow window

34. 34/38 M. Heil: the 13 C( ,n) case LOI to LNGS for a new accelerator (3.5 MEV single ended)

35. 35/38 Possible location of the 3.5 MV accelerator LUNA (50 kV)LUNA2(400kV)LUNA MV(3.5 MV)

36. 36/38 Possible location of the 3.5 MV accelerator

37. 37/38 Progetto Premiale LUNA MV Total request: 6,4 Meuro in 5 years Approved for 2012 (2,8 Meuro, Accelerator tender)!! http://www.presid.infn.it/premiali.html

38. 38/38 Tender for the machine (to be completed by end of 2012) Tender for site preparation (to be completed by February 2013) Workshop at LNGS (february 2013) Next Actions