Related papers: Anomalous internal pair conversion signaling elusi…

$e^{+}e^{-}$ pairs from a nuclear transition signaling an elusive light neutral boson

Electron-positron pairs have been observed in the 10.95-MeV $0^-\to0^+$ decay in $^{16}$O. The branching ratio of the e$^+$e$^-$ pairs compared to the 3.84-MeV $0^-\to2^+$ $\gamma$ decay of the level is deduced to be $20(5)\times10^{-5}$.…

High Energy Physics - Experiment · Physics 2009-11-11 A. Krasznahorkay , F. W. N. de Boer , M. Csatlós , L. Csige , Z. Gácsi , J. Gulyás , M. Hunyadi , T. J. Ketel , J. van Klinken , A. Krasznahorkay , A. Vitéz

Further search for a neutral boson with a mass around 9 MeV/c2

Two dedicated experiments on internal pair conversion (IPC) of isoscalar M1 transitions were carried out in order to test a 9 MeV/c2 X-boson scenario. In the 7Li(p,e+e-)8Be reaction at 1.1 MeV proton energy to the predominantly T=0 level at…

High Energy Physics - Phenomenology · Physics 2009-11-07 F. W. N. de Boer , K. Bethge , H. Bokemeyer , R. van Dantzig , J. van Klinken , V. Mironov , K. A. Mueller , K. E. Stiebing

A multi-detector array for high energy nuclear e+e- pair spectrosocopy

A multi-detector array has been constructed for the simultaneous measurement of energy- and angular correlation of electron-positron pairs produced in internal pair conversion (IPC) of nuclear transitions up to 18 MeV. The response…

Nuclear Experiment · Physics 2008-11-26 K. E. Stiebing , F. W. N. de Boer , O. Froehlich , H. Bokemeyer , K. A. Mueller , K. Bethge , J. van Klinken

Observation of Anomalous Internal Pair Creation in $^8$Be: A Possible Signature of a Light, Neutral Boson

Electron-positron angular correlations were measured for the isovector magnetic dipole 17.6 MeV state ($J^\pi=1^+$, $T=1$) $\rightarrow$ ground state ($J^\pi=0^+$, $T=0$) and the isoscalar magnetic dipole 18.15 MeV ($J^\pi=1^+$, $T=0$)…

Nuclear Experiment · Physics 2016-02-03 A. J. Krasznahorkay , M. Csatlós , L. Csige , Z. Gácsi , J. Gulyás , M. Hunyadi , T. J. Ketel , A. Krasznahorkay , I. Kuti , B. M. Nyakó , L. Stuhl , J. Timár , T. G. Tornyi , Zs. Vajta

Protophobic Fifth Force Interpretation of the Observed Anomaly in $^8$Be Nuclear Transitions

Recently a 6.8$\sigma$ anomaly has been reported in the opening angle and invariant mass distributions of $e^+ e^-$ pairs produced in $^8\text{Be}$ nuclear transitions. The data are explained by a 17 MeV vector gauge boson $X$ that is…

High Energy Physics - Phenomenology · Physics 2016-08-17 Jonathan L. Feng , Bartosz Fornal , Iftah Galon , Susan Gardner , Jordan Smolinsky , Tim M. P. Tait , Philip Tanedo

Search for a hypothetical gauge boson and dark photons in charmonium transitions

We report a direct search for a new gauge boson, $X$, with a mass of $17~\text{MeV}/c^2$, which could explain the anomalous excess of $e^+e^-$ pairs observed in the $^8\text{Be}$ nuclear transitions. The search is conducted in the…

High Energy Physics - Experiment · Physics 2026-02-18 BESIII Collaboration , M. Ablikim , M. N. Achasov , P. Adlarson , X. C. Ai , R. Aliberti , A. Amoroso , Q. An , Y. Bai , O. Bakina , Y. Ban , H. -R. Bao , V. Batozskaya , K. Begzsuren , N. Berger , M. Berlowski , M. B. Bertani , D. Bettoni , F. Bianchi , E. Bianco , A. Bortone , I. Boyko , R. A. Briere , A. Brueggemann , H. Cai , M. H. Cai , X. Cai , A. Calcaterra , G. F. Cao , N. Cao , S. A. Cetin , X. Y. Chai , J. F. Chang , T. T. Chang , G. R. Che , Y. Z. Che , C. H. Chen , Chao Chen , G. Chen , H. S. Chen , H. Y. Chen , M. L. Chen , S. J. Chen , S. M. Chen , T. Chen , X. R. Chen , X. T. Chen , X. Y. Chen , Y. B. Chen , Y. Q. Chen , Z. K. Chen , J. C. Cheng , L. N. Cheng , S. K. Choi , X. Chu , G. Cibinetto , F. Cossio , J. Cottee-Meldrum , H. L. Dai , J. P. Dai , X. C. Dai , A. Dbeyssi , R. E. de Boer , D. Dedovich , C. Q. Deng , Z. Y. Deng , A. Denig , I. Denisenko , M. Destefanis , F. De Mori , X. X. Ding , Y. Ding , Y. X. Ding , J. Dong , L. Y. Dong , M. Y. Dong , X. Dong , M. C. Du , S. X. Du , S. X. Du , X. L. Du , Y. Y. Duan , Z. H. Duan , P. Egorov , G. F. Fan , J. J. Fan , Y. H. Fan , J. Fang , J. Fang , S. S. Fang , W. X. Fang , Y. Q. Fang , L. Fava , F. Feldbauer , G. Felici , C. Q. Feng , J. H. Feng , L. Feng , Q. X. Feng , Y. T. Feng , M. Fritsch , C. D. Fu , J. L. Fu , Y. W. Fu , H. Gao , Y. Gao , Y. N. Gao , Y. N. Gao , Y. Y. Gao , Z. Gao , S. Garbolino , I. Garzia , L. Ge , P. T. Ge , Z. W. Ge , C. Geng , E. M. Gersabeck , A. Gilman , K. Goetzen , J. D. Gong , L. Gong , W. X. Gong , W. Gradl , S. Gramigna , M. Greco , M. H. Gu , C. Y. Guan , A. Q. Guo , J. N. Guo , L. B. Guo , M. J. Guo , R. P. Guo , X. Guo , Y. P. Guo , A. Guskov , J. Gutierrez , T. T. Han , F. Hanisch , K. D. Hao , X. Q. Hao , F. A. Harris , C. Z. He , K. L. He , F. H. Heinsius , C. H. Heinz , Y. K. Heng , C. Herold , P. C. Hong , G. Y. Hou , X. T. Hou , Y. R. Hou , Z. L. Hou , H. M. Hu , J. F. Hu , Q. P. Hu , S. L. 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A Standard Model Explanation for the "ATOMKI Anomaly"

Using the $e^+e^-$ pair spectrometer at the 5 MV Van de Graaff accelerator at the Institute for Nuclear Research, Hungarian Academy of Sciences (ATOMKI), Krasznahorkay et al. have claimed a 6.8$\sigma$ excess at high $e^+e^-$ opening angles…

High Energy Physics - Phenomenology · Physics 2021-04-08 A. Aleksejevs , S. Barkanova , Yu. G. Kolomensky , B. Sheff

New anomaly observed in $^{12}$C supports the existence and the vector character of the hypothetical X17 boson

Employing the $^{11}$B(p,$\gamma$)$^{12}$C nuclear reaction, the angular correlation of $e^+e^-$ pairs was investigated in the angular range of $40^\circ\Theta\leq 175^\circ$ for five different proton energies between E$_p$ = 1.50 - 2.50…

Nuclear Experiment · Physics 2022-12-21 A. J. Krasznahorkay , A. Krasznahorkay , M. Begala , M. Csatlós , L. Csige , J. Gulyás , A. Krakó , J. Timár , I. Rajta , I. Vajda , N. J. Sas

Anomaly in decay of 8Be and 4He -- can an observed light boson mediate low energy nucleon-nucleon interactions ?

We present a hypothesis that the anomaly in the folding angle distribution of electron-positron pairs, emitted in the decay of the excited levels of nucleus $^{8}$Be and $^{4}$He can be related to the cluster structure of the decaying…

Nuclear Theory · Physics 2021-06-11 M. Veselsky , V. Petousis , J. Leja

Search for Higgs Bosons and Other Massive States decaying into two Photons in e+e- Collisions at 189 GeV

A search is described for the generic process e+e- to X Y, where X is a neutral heavy scalar boson decaying into a pair of photons, and Y is a neutral heavy boson (scalar or vector) decaying into a fermion pair. The search is motivated…

High Energy Physics - Experiment · Physics 2008-11-26 The OPAL collaboration , G. Abbiendi et al

Search for light pseudoscalar bosons, pair-produced in Higgs boson decays in the four-electron final state in proton-proton collisions at $\sqrt{s}$ = 13 TeV

A search for pairs of light neutral pseudoscalar bosons (A) resulting from the decay of a Higgs boson is performed. The search is conducted using LHC proton-proton collision data at $\sqrt{s}$ = 13 TeV, collected with the CMS detector in…

High Energy Physics - Experiment · Physics 2026-05-12 CMS Collaboration

Particle Physics Models for the 17 MeV Anomaly in Beryllium Nuclear Decays

The 6.8$\sigma$ anomaly in excited 8Be nuclear decays via internal pair creation is fit well by a new particle interpretation. In a previous analysis, we showed that a 17 MeV protophobic gauge boson provides a particle physics explanation…

High Energy Physics - Phenomenology · Physics 2017-02-22 Jonathan L. Feng , Bartosz Fornal , Iftah Galon , Susan Gardner , Jordan Smolinsky , Tim M. P. Tait , Philip Tanedo

First Energy and Angle differential Measurements of e^+e^- -pairs emitted by Internal Pair Conversion of excited Heavy Nuclei

We present the first energy and angle resolved measurements of e+e- pairs emitted from heavy nuclei (Z>=40) at rest by internal pair conversion (IPC) of transitions with energies of less than 2MeV as well as recent theoretical results using…

Nuclear Experiment · Physics 2009-10-30 U. Leinberger , E. Berdermann , F. Heine , S. Heinz , O. Joeres , P. Kienle , I. Koenig , W. Koenig , C. Kozhuharov , A. Schroeter , H. Tsertos , C. Hofmann , G. Soff

A Re-evaluation of Evidence for Light Neutral Bosons in Nuclear Emulsions

Electron-positron pair-production data obtained by bombardment of emulsion detectors with either cosmic rays or projectiles with mass between one and 207 and kinetic energies between 18 GeV and 32 TeV have been re-analysed using a…

Nuclear Experiment · Physics 2011-08-10 F. W. N. de Boer , C. A. Fields

Improved limits on a hypothetical X(16.7) boson and a dark photon decaying into $e^+e^-$ pairs

The improved results on a direct search for a new X(16.7 MeV) boson which could explain the anomalous excess of $e^+e^-$ pairs observed in the excited 8Be nucleus decays ("Berillium anomaly") are reported. Due to its coupling to electrons,…

High Energy Physics - Experiment · Physics 2020-04-22 D. Banerjee , J. Bernhard , V. E. Burtsev , A. G. Chumakov , D. Cooke , P. Crivelli , E. Depero , A. V. Dermenev , S. V. Donskov , R. R. Dusaev , T. Enik , N. Charitonidis , A. Feshchenko , V. N. Frolov , A. Gardikiotis , S. G. Gerassimov , S. N. Gninenko , M. Hoesgen , M. Jeckel , V. A. Kachanov , A. E. Karneyeu , G. Kekelidze , B. Ketzer , D. V. Kirpichnikov , M. M. Kirsanov , V. N. Kolosov , I. V. Konorov , S. G. Kovalenko , V. A. Kramarenko , L. V. Kravchuk , N. V. Krasnikov , S. V. Kuleshov , V. E. Lyubovitskij , V. Lysan , V. A. Matveev , Yu. V. Mikhailov , L. Molina Bueno , D. V. Peshekhonov , V. A. Polyakov , B. Radics , R. Rojas , A. Rubbia , V. D. Samoylenko , D. Shchukin , V. O. Tikhomirov , I. Tlisova , D. A. Tlisov , A. N. Toropin , A. Yu. Trifonov , B. I. Vasilishin , G. Vasquez Arenas , P. V. Volkov , V. Yu. Volkov , P. Ulloa

Search for a Hypothetical 16.7 MeV Gauge Boson and Dark Photons in the NA64 Experiment at CERN

We report the first results on a direct search for a new 16.7 MeV boson (X) which could explain the anomalous excess of e+e- pairs observed in the excited Be-8 nucleus decays. Due to its coupling to electrons, the X could be produced in the…

High Energy Physics - Experiment · Physics 2018-06-12 D. Banerjee , V. E. Burtsev , A. G. Chumakov , D. Cooke , P. Crivelli , E. Depero , A. V. Dermenev , S. V. Donskov , R. R. Dusaev , T. Enik , N. Charitonidis , A. Feshchenko , V. N. Frolov , A. Gardikiotis , S. G. Gerassimov , S. N. Gninenko , M. Hosgen , M. Jeckel , A. E. Karneyeu , G. Kekelidze , B. Ketzer , D. V. Kirpichnikov , M. M. Kirsanov , I. V. Konorov , S. G. Kovalenko , V. A. Kramarenko , L. V. Kravchuk , N. V. Krasnikov , S. V. Kuleshov , V. E. Lyubovitskij , V. Lysan , V. A. Matveev , Yu. V. Mikhailov , D. V. Peshekhonov , V. A. Polyakov , B. Radics , R. Rojas , A. Rubbia , V. D. Samoylenko , V. O. Tikhomirov , D. A. Tlisov , A. N. Toropin , A. Yu. Trifonov , B. I. Vasilishin , G. Vasquez Arenas , P. V. Volkov , V. Volkov , P. Ulloa

Anomalous Internal Pair Creation

In recent electron-positron angular correlation measurements the observed significant enhancements relative to the internal pair creation at large angles was interpreted as indication of the creation of $J^{\pi }=1^{+}$ boson called X17…

Nuclear Theory · Physics 2022-10-19 Péter Kálmán , Tamás Keszthelyi

Light Axial Vectors, Nuclear Transitions, and the $^8$Be Anomaly

New hidden particles could potentially be emitted and discovered in rare nuclear transitions. In this work we investigate the production of hidden vector bosons with primarily axial couplings to light quarks in nuclear transitions, and we…

High Energy Physics - Phenomenology · Physics 2017-07-06 Jonathan Kozaczuk , David E. Morrissey , S. R. Stroberg

Search for pseudoscalar bosons decaying into $e^+e^-$ pairs in the NA64 experiment at the CERN SPS

We report the results of a search for a light pseudoscalar particle $a$ that couples to electrons and decays to $e^+e^-$ performed using the high-energy CERN SPS H4 electron beam. If such pseudoscalar with a mass $\simeq 17$ MeV exists, it…

High Energy Physics - Experiment · Physics 2022-01-05 Yu. M. Andreev , D. Banerjee , J. Bernhard , V. E. Burtsev , N. Charitonidis , A. G. Chumakov , D. Cooke , P. Crivelli , E. Depero , A. V. Dermenev , S. V. Donskov , R. R. Dusaev , T. Enik , A. Feshchenko , V. N. Frolov , A. Gardikiotis , S. G. Gerassimov , S. N. Gninenko , M. Hoesgen , M. Jeckel , V. A. Kachanov , A. E. Karneyeu , G. Kekelidze , B. Ketzer , D. V. Kirpichnikov , M. M. Kirsanov , V. N. Kolosov , I. V. Konorov , S. G. Kovalenko , V. A. Kramarenko , L. V. Kravchuk , N. V. Krasnikov , S. V. Kuleshov , V. E. Lyubovitskij , V. Lysan , V. A. Matveev , Yu. V. Mikhailov , L. Molina Bueno , D. V. Peshekhonov , V. A. Polyakov , B. Radics , R. Rojas , A. Rubbia , V. D. Samoylenko , H. Sieber , D. Shchukin , V. O. Tikhomirov , I. Tlisova , A. N. Toropin , A. Yu. Trifonov , B. I. Vasilishin , G. Vasquez Arenas , P. V. Volkov , V. Yu. Volkov , P. Ulloa

A search for pair production of new light bosons decaying into muons in proton-proton collisions at 13 TeV

A search for new light bosons decaying into muon pairs is presented using a data sample corresponding to an integrated luminosity of 35.9 fb$^{-1}$ of proton-proton collisions at a center-of-mass energy $\sqrt{s} =$ 13 TeV, collected with…

High Energy Physics - Experiment · Physics 2019-07-24 CMS Collaboration