title: First direct measurement of the 2H(α,γ)6Li cross section at big bang energies and the primordial lithium problem.
abstract: Recent observations of (6)Li in metal poor stars suggest a large production of this isotope during big bang nucleosynthesis (BBN). In standard BBN calculations, the (2)H(α,γ)(6)Li reaction dominates (6)Li production. This reaction has never been measured inside the BBN energy region because its cross section drops exponentially at low energy and because the electric dipole transition is strongly suppressed for the isoscalar particles (2)H and α at energies below the Coulomb barrier. Indirect measurements using the Coulomb dissociation of (6)Li only give upper limits owing to the dominance of nuclear breakup processes. Here, we report on the results of the first measurement of the (2)H(α,γ)(6)Li cross section at big bang energies. The experiment was performed deep underground at the LUNA 400 kV accelerator in Gran Sasso, Italy. The primordial (6)Li/(7)Li isotopic abundance ratio has been determined to be (1.5 ± 0.3) × 10(-5), from our experimental data and standard BBN theory. The much higher (6)Li/(7)Li values reported for halo stars will likely require a nonstandard physics explanation, as discussed in the literature.
authors.affiliation: Helmholtz-Zentrum Dresden-Rossendorf, Bautzner Landstrasse 400, 01328 Dresden, Germany and Technische Universität Dresden, Mommsenstrasse 9, 01069 Dresden, Germany.
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authors.lastname: Anders
authors.affiliation: Università degli Studi di Milano and INFN, Sezione di Milano, Via G. Celoria 16, 20133 Milano, Italy.
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authors.lastname: Trezzi
authors.affiliation: INFN, Sezione di Padova, Via F. Marzolo 8, 35131 Padova, Italy.
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authors.lastname: Menegazzo
authors.affiliation: SUPA, School of Physics and Astronomy, University of Edinburgh, EH9 3JZ Edinburgh, United Kingdom.
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authors.lastname: Aliotta
authors.affiliation: Università degli Studi di Genova and INFN, Sezione di Genova, Via Dodecaneso 33, 16146 Genova, Italy.
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authors.lastname: Bellini
authors.affiliation: Helmholtz-Zentrum Dresden-Rossendorf, Bautzner Landstrasse 400, 01328 Dresden, Germany.
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authors.lastname: Bemmerer
authors.affiliation: INFN, Sezione di Padova, Via F. Marzolo 8, 35131 Padova, Italy.
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authors.lastname: Broggini
authors.affiliation: INFN, Sezione di Padova, Via F. Marzolo 8, 35131 Padova, Italy.
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authors.lastname: Caciolli
authors.affiliation: Università degli Studi di Genova and INFN, Sezione di Genova, Via Dodecaneso 33, 16146 Genova, Italy.
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authors.lastname: Corvisiero
authors.affiliation: Università degli Studi di Genova and INFN, Sezione di Genova, Via Dodecaneso 33, 16146 Genova, Italy.
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authors.lastname: Costantini
authors.affiliation: SUPA, School of Physics and Astronomy, University of Edinburgh, EH9 3JZ Edinburgh, United Kingdom.
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authors.lastname: Davinson
authors.affiliation: Helmholtz-Zentrum Dresden-Rossendorf, Bautzner Landstrasse 400, 01328 Dresden, Germany.
authors.forename: Z
authors.initials: Z
authors.lastname: Elekes
authors.affiliation: INFN, Sezione di Padova, Via F. Marzolo 8, 35131 Padova, Italy.
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authors.lastname: Erhard
authors.affiliation: Laboratori Nazionali del Gran Sasso (LNGS), Via G. Acitelli 22, 67100 Assergi, Italy.
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authors.lastname: Formicola
authors.affiliation: Institute of Nuclear Research (MTA ATOMKI), PO Box 51, HU-4001 Debrecen, Hungary.
authors.forename: Zs
authors.initials: Z
authors.lastname: Fülöp
authors.affiliation: Università degli Studi di Torino and INFN, Sezione di Torino, Via P. Giuria 1, 10125 Torino, Italy.
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authors.lastname: Gervino
authors.affiliation: Università degli Studi di Milano and INFN, Sezione di Milano, Via G. Celoria 16, 20133 Milano, Italy.
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authors.affiliation: INFN, Sezione di Roma "La Sapienza", Piazzale A. Moro 2, 00185 Roma, Italy.
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authors.lastname: Gustavino
authors.affiliation: Institute of Nuclear Research (MTA ATOMKI), PO Box 51, HU-4001 Debrecen, Hungary.
authors.forename: Gy
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authors.lastname: Gyürky
authors.affiliation: Laboratori Nazionali del Gran Sasso (LNGS), Via G. Acitelli 22, 67100 Assergi, Italy.
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authors.lastname: Junker
authors.affiliation: Università degli Studi di Genova and INFN, Sezione di Genova, Via Dodecaneso 33, 16146 Genova, Italy.
authors.forename: A
authors.initials: A
authors.lastname: Lemut
authors.affiliation: Helmholtz-Zentrum Dresden-Rossendorf, Bautzner Landstrasse 400, 01328 Dresden, Germany.
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authors.lastname: Marta
authors.affiliation: Università degli Studi di Milano and INFN, Sezione di Milano, Via G. Celoria 16, 20133 Milano, Italy.
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authors.lastname: Mazzocchi
authors.affiliation: Università degli Studi di Genova and INFN, Sezione di Genova, Via Dodecaneso 33, 16146 Genova, Italy.
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authors.lastname: Prati
authors.affiliation: INFN, Sezione di Padova, Via F. Marzolo 8, 35131 Padova, Italy.
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authors.lastname: Rossi Alvarez
authors.affiliation: SUPA, School of Physics and Astronomy, University of Edinburgh, EH9 3JZ Edinburgh, United Kingdom.
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authors.initials: DA
authors.lastname: Scott
authors.affiliation: Institute of Nuclear Research (MTA ATOMKI), PO Box 51, HU-4001 Debrecen, Hungary.
authors.forename: E
authors.initials: E
authors.lastname: Somorjai
authors.affiliation: Osservatorio Astronomico di Collurania, Via M. Maggini, 64100 Teramo, Italy and INFN, Sezione di Napoli, Via Cintia, 80126 Napoli, Italy.
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authors.lastname: Straniero
authors.affiliation: Institute of Nuclear Research (MTA ATOMKI), PO Box 51, HU-4001 Debrecen, Hungary.
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authors.lastname: Szücs