LUNA results at BBN energiesBBN is the result of the competition between the relevant nuclear...

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Marciana Marina, Isola d'Elba June 23-27, 2014 Laboratory Underground Nuclear Astrophysics LUNA results at BBN energies Carlo Gustavino INFN ROME •Nuclear Astrophysics •LUNA experiment •Big Bang Nucleosynthesis 3 He( 4 He,γ) 7 Be reaction ( 7 Li abundance) •D(α,γ) 6 Li reaction ( 6 Li abndance) •D(p, γ) 3 He reaction (D abundance) •Conclusion

Transcript of LUNA results at BBN energiesBBN is the result of the competition between the relevant nuclear...

Page 1: LUNA results at BBN energiesBBN is the result of the competition between the relevant nuclear processes and the expansion rate of the early universe, governed by the Freidmann Equation:

Marciana Marina, Isola d'Elba June 23-27, 2014

Laboratory Underground Nuclear Astrophysics

LUNA results at BBN energies Carlo Gustavino

INFN ROME

• Nuclear Astrophysics • LUNA experiment • Big Bang Nucleosynthesis • 3He(4He,γ)7Be reaction (7Li abundance) • D(α,γ)6Li reaction (6Li abndance) • D(p, γ)3He reaction (D abundance) • Conclusion

Page 2: LUNA results at BBN energiesBBN is the result of the competition between the relevant nuclear processes and the expansion rate of the early universe, governed by the Freidmann Equation:

0

<σv> = (KT)3/2

1 8 πµ

S(E) exp dE E KT

EG E

tunneling probability KT << Z1Z2e2

RN ⇒

3He(3He,2p)4He 22 keV

d(p,γ)3He 7 keV

14N(p,γ)15O 27 keV

E0

Reaction rate for charged particles

E

EEG

eEESE

−=

)()(σ

Reaction

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Page 3: LUNA results at BBN energiesBBN is the result of the competition between the relevant nuclear processes and the expansion rate of the early universe, governed by the Freidmann Equation:

event/month < Rlab < event/day

ε ~ 10 % IP ~ mA ρ ~ µg/cm2

Rlab= σ·ε·Ip·ρ·Nav/A

pb < σ < nb

Reaction rate in the laboratory

EEG

eEESE

−=

)()(σ

Beware of extrapolations!!

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Page 4: LUNA results at BBN energiesBBN is the result of the competition between the relevant nuclear processes and the expansion rate of the early universe, governed by the Freidmann Equation:

Rlab > Bcosm+ Benv + Bbeam

Experimental requirements

Rlab= Reaction rate à High beam intensity, target density, high efficiency detectors Bcosm= Cosmic ray induced background à Underground Laboratory Benv= Natural radioactivity à Passive shielding (Lead, Copper), Anti-Radon Box and high purity detectors. Bbeam= Beam induced background à high purity targets, detector techniques (coincidence), analysis…

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Page 5: LUNA results at BBN energiesBBN is the result of the competition between the relevant nuclear processes and the expansion rate of the early universe, governed by the Freidmann Equation:

Gran Sasso National Laboratory (LNGS)

LUNA

Cosmic background reduction: "µ: 10-6 n: 10-3 γ: 10-2-10-5 ""

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Page 6: LUNA results at BBN energiesBBN is the result of the competition between the relevant nuclear processes and the expansion rate of the early universe, governed by the Freidmann Equation:

Cosmic ray induced background

Radiation LNGS/Surface Muons 10-6

neutrons 10-3

40K 214Bi

232Th

Clear advantage of underground measurements for reaction with high Q-values. Concerning BBN: D(p,γ)3He (Q=5.5 MeV)

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Page 7: LUNA results at BBN energiesBBN is the result of the competition between the relevant nuclear processes and the expansion rate of the early universe, governed by the Freidmann Equation:

Natural radioactivity background

Passive shielding is more effective underground since the µ flux, that create secondary γs in the shield, is suppressed. Underground measurements are well suited also for low Q-value reactions. Concerning BBN: 3He(α,γ)7Be (Q=1586 keV) D(α,γ)6Li (Q=1473 keV)

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Page 8: LUNA results at BBN energiesBBN is the result of the competition between the relevant nuclear processes and the expansion rate of the early universe, governed by the Freidmann Equation:

Voltage Range: 50-400 kV Output Current: 1 mA (@ 400 kV) Absolute Energy error: ±300 eV Beam energy spread: <100 eV Long term stability: 5 eV Terminal Voltage ripple: 5 Vpp

A. Formicola et al., NIMA 527 (2004) 471.

BBN reactions: 3He(4He,γ)7Be à 7Li/H D(4He,γ)6Li à 6Li/H D(p, γ)3He à D/H

The LUNA accelerator

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Page 9: LUNA results at BBN energiesBBN is the result of the competition between the relevant nuclear processes and the expansion rate of the early universe, governed by the Freidmann Equation:

BBN is the result of the competition between the relevant nuclear processes and the expansion rate of the early universe, governed by the Freidmann Equation:

Big Bang Nucleosynthesis

H 2 =8π3Gρ

H = Hubble constant

G = Newton's gravitational constant

ρ  = energy density (i.e. photons and neutrinos density in the early Universe)

Therefore, the abundance of primordial isotopes ONLY depends on:

•  Baryon density Ωb (BBN and CMB experiments)

•  Particle Physics (τn, Neff, α..)

•  Nuclear astrophysics, i.e. cross sections of BBN nuclear reactions

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Page 10: LUNA results at BBN energiesBBN is the result of the competition between the relevant nuclear processes and the expansion rate of the early universe, governed by the Freidmann Equation:

-The BBN begins with the formation of Deuterium. -Nearly all the free neutrons end up bound in the most stable light element 4He. -  7Li and 6Li have small abundance

because of the absence of stable nuclei with mass number 5 or 8.

-  Direct observations are restricted to stable isotopes (D, 3He, 4He, 6Li, 7Li)

Big Bang Nucleosynthesis

BBN error budgets: 4He: Almost entirely due to Δτn (1) D: Mainly due to the D(p,γ)3He reaction (3) 3He: Mainly due to the 3He(d,p)4He reaction (9)

6Li: Mainly due D(α,γ)6Li reaction (13) 7Li: ..Many reactions of the BBN network (10, 9, 3,...)

Big Bang Nucleosynthesis

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Page 11: LUNA results at BBN energiesBBN is the result of the competition between the relevant nuclear processes and the expansion rate of the early universe, governed by the Freidmann Equation:

Determination of primordial abundances

Direct Observations: •  Observation of a set of primitive objects (born when the universe was young) •  Extrapolate to zero metallicity: Fe/H, O/H, Si/H à 0 •  Systematics mainly due to post-primordial processes 4He: Observation in HII regions, quite large systematics. D: Observation of absorption lines in QSO. Accurate measurements. 3He: Solar System, very large systematics, not a powerful probe for BBN. 7Li: observation of metal poor stars absorption line (Spite plateau) 6Li: observation of metal poor stars absorption lines (controversial) 4He, D, 3He abundances measurements are broadly consistent with expectations. 7Li: Long standing “Lithium problem” 6Li: “Second Lithium problem”? A coherent theory (Cosmology, Astrophysics, Particle physics, Gravitation…) must provide the matching between theory Vs observations for the abundances of all the primordial light isotopes.

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Lithium observations 7Li primordial abundance: observation of the absorption lines at the surface of metal-poor stars in the halo of our Galaxy 6Li abundance : observation of the asymmetry of the 7Li absorption lines.

Observed 7Li abundance is 2-4 times lower than foreseen: Well established ”7Li problem”.

Observed 6Li abundance orders of magnitude higher than expected (Asplund2006). However the “Second Lithium problem” is debated, because:

-Convective motions on the stellar surface can give an asymmetry of the absorption line, mimicking the presence of 6Li.

-The BBN prediction for 6Li is affected by a v e r y l a r g e e r r o r, i n f a c t n o d i r e c t measurements of the D(4He,γ)6Li reaction have been done (before LUNA)

The Lithium problem(s)

Line strength: 7Li abundance Line Profile: 6Li/7Li ratio

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Page 13: LUNA results at BBN energiesBBN is the result of the competition between the relevant nuclear processes and the expansion rate of the early universe, governed by the Freidmann Equation:

The Lithium problem(s)

Line strength: 7Li abundance Line Profile: 6Li/7Li ratio

Lithium observations The disagreement between the observed 7Li and 6Li abundance in metal poor stars with respect to BBN calculations is very large. Possible reasons are:

• Systematics in the measured 7Li and 6Li abundances in the metal-poor stars.

• Unknown processes before the birth of the galaxy, able to burn 7Li and synthetize 6Li.

• New physics, e.g. sparticle annihilation/decay (Jedamzik2008), long lived negatively charged particles (Kusakabe2010)

• …Nuclear physics, i.e. the lack of knowledge of the relevant nuclear reactions makes the BBN calculations not reliable.

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Page 14: LUNA results at BBN energiesBBN is the result of the competition between the relevant nuclear processes and the expansion rate of the early universe, governed by the Freidmann Equation:

The 3He(4He,γ)7Be reaction is a key process to calculate the 7Li abundance. Four objectives for the 3He(4He,γ)7Be LUNA measurement: • Lowest uncertainty (4%). • Measurements well inside the BBN energy region, 90<Ecm(keV)<170. • Lowest energy ever reached. • Simultaneous measurement of prompt and delayed γs.

Prompt γs

Delayed γs (τ=53 days )

3He(4He,γ)7Be: The 7Li/H abundance

Tension between prompt and delayed γs measurements 14/28

Page 15: LUNA results at BBN energiesBBN is the result of the competition between the relevant nuclear processes and the expansion rate of the early universe, governed by the Freidmann Equation:

Ecm=93 keV T=31,2 days

Ecm=93 keV T=11,6 days

3He(α,γ)7Be at LUNA: prompt γ and activation

Signal+background bck

Signal+background bck

Prompt γs setup

Delayed γs setup 15/28

Page 16: LUNA results at BBN energiesBBN is the result of the competition between the relevant nuclear processes and the expansion rate of the early universe, governed by the Freidmann Equation:

3He(α,γ)7Be

Activation Prompt

Rescaled Kajino (1987) Rescaled Descouvemont (2004)

3He(α,γ)7Be at LUNA: result

BBN

D. Bemmerer et al., PRL 97, 122502 (2006) Gy. Gyurky et al. Phys.Rev, C 75, 035805 (2007) F. Confortola et al., Phys.Rev. C 75, 065803 (2007)

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Page 17: LUNA results at BBN energiesBBN is the result of the competition between the relevant nuclear processes and the expansion rate of the early universe, governed by the Freidmann Equation:

The D(α,γ)6Li reaction dominates the 6Li production during BBN. Before LUNA, there was a lack of knowledge of the reaction rate in the BBN.

D(α,γ)6Li: The 6Li/H abundance

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. FOR THE FIRST TIME, the D(4He,γ)6Li reaction has directly been studied inside the BBN energy region.

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Page 18: LUNA results at BBN energiesBBN is the result of the competition between the relevant nuclear processes and the expansion rate of the early universe, governed by the Freidmann Equation:

d

d

α

D(α,α)d Rutherford scattering α

α beam Deuterium gas target

3He d d

n

D(d,n)3He reaction Q=3.269 MeV

Ecm(3He)= 0,820 MeV

Ecm(n)=2.450 MeV

(n,n’γ) reaction on the surrounding materials (lead, steel, copper and germanium) γ-ray background in the RoI for the D(α,γ)6Li DC transition (∼1.6 MeV)

Beam Induced Background in the D(4He,γ)6Li measurement

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Page 19: LUNA results at BBN energiesBBN is the result of the competition between the relevant nuclear processes and the expansion rate of the early universe, governed by the Freidmann Equation:

• 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)3He reaction yield. • Si detector to monitor the neutron production through the detection of D(d,p)3H protons. • Lead, anti-radon Box to reduce and stabilize Natural Background. • Selected materials.

D(4He,γ)6Li set-up

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Page 20: LUNA results at BBN energiesBBN is the result of the competition between the relevant nuclear processes and the expansion rate of the early universe, governed by the Freidmann Equation:

Measurement method

The measurement is performed into 2 steps:

1.  Measurement with Eα=400 keV on D2 target. The Ge spectrum is mainly due to

background induced by neutrons interacting with the surrounding materials (Pb, Ge, Cu). The D(α,γ)6Li signal is expected in a well defined RoI (1587-1625 keV).

2.  Same as 1., but with Eα =280 keV. The Ge spectrum is essentially the same as before, while the gammas from the D(α,γ)6Li reaction are expected at 1550-1580 keV.

D(α,γ)6Li Signal is obtained by subtracting the two spectra

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Page 21: LUNA results at BBN energiesBBN is the result of the competition between the relevant nuclear processes and the expansion rate of the early universe, governed by the Freidmann Equation:

First D(α,γ)6Li cross section measurement at BBN energies

D(α,γ)6Li: The 6Li/H abundance

BBN

PRL (accepted)

S24(134 keV ) = (4.0±0.8(stat) ± 0.5(syst)) X 10−6 keV b S24(94 keV ) = (2.7±1.5(stat) ± 0.3(syst)) X 10−6 keV b

6Li/H = (0.74±16)x10-14

6Li/7Li = (1.5±0.3)x10-5

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Page 22: LUNA results at BBN energiesBBN is the result of the competition between the relevant nuclear processes and the expansion rate of the early universe, governed by the Freidmann Equation:

D(p,γ)3He: The deuterium abundance

Big Bang Nucleosynthesis

Primordial deuterium error budget (Di Valentino et al. 2014)

Physics goals: 1) Cosmology: measurement of Ωb. 2) Particle physics: measurements of Neff. 3) Nuclear physics: comparison of data with “ab initio” modeling.

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Page 23: LUNA results at BBN energiesBBN is the result of the competition between the relevant nuclear processes and the expansion rate of the early universe, governed by the Freidmann Equation:

observations

100Ωb,0h2(CMB)=2.20±0.03 (PLANCK2013) 100Ωb,0h2(D/H)=2.20±0.02±0.04 (Cooke2013)

1) Cosmology: The deuterium abundance is very sensitive to the cosmic baryon density Ωb. Assuming Standard Model (Neff=3):

D/H observations Nuclear Astrophysics (Dpγ reaction uncertainty)

2) Particle physics: The deuterium abundance is also sensitive to the number of neutrino families. With the present 2H(p,γ)3He data at BBN energies we have: Neff (CMB) = 3.36±0.34 (PLANCK 2013) Neff (BBN) = 3.57±0.18 (COOKE&PETTINI 2013) Neff (SM) = 3.046 3) Nuclear Physics: Present S12 data differ from “ab initio” model of about 20%.

Physics Goals

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Page 24: LUNA results at BBN energiesBBN is the result of the competition between the relevant nuclear processes and the expansion rate of the early universe, governed by the Freidmann Equation:

Di Valentino 2014 Cooke 2013

Yp error band mainly due to systematics of direct observations. D/H error band is mainly due to the D(p,γ)3He reaction. Neff (BBN) = 3.57±0.18 (COOKE 2013)

D(p,γ)3He reaction rate. Neff (CMB) = 3.36±0.34 (PLANCK 2013)

•  Good agreement between CMB and BBN results, suggesting the presence of “dark radiation”.

•  The poorly known cross-section of the 2H(p,γ)3He reaction at BBN energies represent the most important obstacle to improve the constraints on the existence of “dark radiation”.

D(p,γ)3He Vs Neff

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Page 25: LUNA results at BBN energiesBBN is the result of the competition between the relevant nuclear processes and the expansion rate of the early universe, governed by the Freidmann Equation:

BGO detector Total cross section Vs Energy

26<Ecm(keV)<266

D(p,γ)3He reaction: Possible Setup

Ge(Li) detector Study of angular emission of photons

100<Ecm(keV)<263

Experimental goals: -Measurement of the Total cross section in wide energy range: 40<Elab(keV)<400 -Good accuracy, with systematics at the 3% level. -Measurement of the differential cross section at several energies.

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Proton beam

Page 26: LUNA results at BBN energiesBBN is the result of the competition between the relevant nuclear processes and the expansion rate of the early universe, governed by the Freidmann Equation:

Doppler effect and high resolution HPGe to extract the angular distribution

HPGe

Proton beam

D(p,γ)3He reaction: Possible Setup

γ

Beam stopper D2 gas target

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Page 27: LUNA results at BBN energiesBBN is the result of the competition between the relevant nuclear processes and the expansion rate of the early universe, governed by the Freidmann Equation:

D(p,γ)3He reaction: reaction yield

HPGe: 103-104 events/day (100<Ecm(keV)<263) BGO: 104-105 events/hour (20<Ecm(keV)<263)

Casella 2002

LUNA 400

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Page 28: LUNA results at BBN energiesBBN is the result of the competition between the relevant nuclear processes and the expansion rate of the early universe, governed by the Freidmann Equation:

-We are in the “Precision Era” of Cosmology. BBN parameters, such as Ωb, (D/H)p are known with high (and increasing) precision. Uncertainties of calculations are often limited by the poor knowledge of the cross section of few reaction, at BBN energies.

-Accurate measurements at low energy must be done with Underground accelerators, with present (LUNA) or future accelerators (e.g. the approved LUNA-MV project).

-The 3He(4He,γ)7Be LUNA measurement at BBN energies makes very unlikely a nuclear solution fo the “Lithium problem”.

-Likewise, the recent measurement of the D(α,γ)6Li rules out the possibility of a standard explication for the purpoted 6Li problem: For the first time, the calculated abundance of 6Li is based on a solid experimental footing.

-The future measurement of the D(p,γ)3He cross section is of crucial importance to precisely calculate the D abundance and therefore to increase the BBN and CMB sensitivity to Neff and lepton degeneracy.

Conclusions

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