Search for<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>η</mml:mi></mml:math>-mesic<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msup><mml:mrow /><mml:mn>4</mml:mn></mml:msup></mml:math>He with the WASA-at-COSY detector

Adlarson, P.; Augustyniak, W.; Bardan, W.; Bashkanov, M.; Bednarski, T.; Bergmann, F. S.; Berłowski, M.; Bhatt, H.; Büscher, M.; Calén, H.; Clement, H.; Coderre, D.; Czerwiński, E.; Demmich, K.; Doroshkevich, E.; Engels, R.; Erven, W.; Eyrich, W.; Fedorets, P.; Föhl, K.; Fransson, K.; Goldenbaum, F.; Goslawski, P.; Goswami, A.; Grigoryev, K.; Gullström, C.-O.; Hauenstein, F.; Heijkenskjöld, L.; Hejny, V.; Hinterberger, F.; Hodana, M.; Höistad, B.; Jany, A.; Jany, Benedykt R.; Jarczyk, L.; Johansson, T.; Kamys, B.; Kemmerling, G.; Khan, Farha; Khoukaz, A.; Kistryn, S.; Klaja, J.; Kleines, H.; Kłos, B.; Krapp, M.; Krzemień, W.; Kulessa, P.; Kupść, A.; Lalwani, K.; Lersch, D.; Li, L.; Lorentz, B.; Magiera, A.; Maier, R.; Marciniewski, P.; Mariański, B.; Mikirtychiants, M.; Morsch, H. P.; Moskal, P.; Nandi, B. K.; Niedźwiecki, Szymon; Ohm, H.; Ozerianska, I.; Río, E. Pérez del; Pluciński, P.; Podkopał, P.; Prasuhn, D.; Pricking, A.; Pszczel, D.; Pysz, K.; Pyszniak, A.; Redmer, C. F.; Ritman, J.; Roy, A.; Rudy, Z.; Sawant, S.; Schadmand, S.; Schmidt, Axel; Sefzick, T.; Serdyuk, V.; Shah, N.; Siemaszko, M.; Siudak, R.; Skorodko, T.; Skurzok, M.; Smyrski, J.; Sopov, V.; Stassen, R.; Steṕaniak, J.; Stephan, E.; Sterzenbach, G.; Stockhorst, H.; Ströher, H.; Szczurek, Antoni; Tolba, T.; Trzciński, A.; Varma, R.; Vlasov, P.; Wagner, G. J.; Wȩglorz, W.; Wolke, M.; Wrońska, A.; Wüstner, P.; Wurm, P.; Yamamoto, A.; Yuan, X.; Yurev, L.; Zabierowski, J.; Zheng, C.; Zieliński, Marcin; Zipper, W.; Złomańczuk, J.; Żuprański, P.; Żurek, M.

doi:10.1103/physrevc.87.035204

Cited by 96 publications

(164 citation statements)

References 18 publications

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“…Surprisingly, there is no experimental confirmation of such an effect. Measurements [13][14][15][16] offer a cross section of about 200 nb which is apparently due to a quasi-free reaction. An upper limit of the fraction that proceeds through a quasi-bound state is obtained at a level of 25 nb [14].…”

Section: Introductionmentioning

confidence: 99%

Studies of Mesic Nuclei via Decay Reactions

Wycech¹,

Krzemień²

2014

Acta Phys. Pol. B

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Section: Introductionmentioning

confidence: 99%

Studies of Mesic Nuclei via Decay Reactions

Wycech¹,

Krzemień²

2014

Acta Phys. Pol. B

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“…[5,23,24]. A number of previous experiments, such as beam dump [25][26][27][28][29][30][31][32][33][34][35][36][37][38][39], fixed target [40][41][42], collider [43][44][45] and rare particle decay searches [46][47][48][49][50][51][52][53][54][55][56][57], put stringent constraints on the and mass m A of such dark photons, excluding, in particular, the parameter space region favored by the g µ − 2 anomaly. However, a large range of mixing strengths 10 −4 10 −3 corresponding to short-lived A remains unexplored.…”

mentioning

confidence: 99%

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

Banerjee¹,

Bernhard²,

Burtsev³

et al. 2020

Phys. Rev. D

107

103

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The improved results on a direct search for a new X(16.7 MeV) boson that could explain the anomalous excess of e + e − pairs observed in the decays of the excited 8 Be * nucleus ("Berillium anomaly") are reported. The X boson could be produced in the bremsstrahlung reaction e − Z → e − ZX by a high energy beam of electrons incident on the active target in the NA64 experiment at the CERN SPS and observed through its subsequent decay into e + e − pair. No evidence for such decays was found from the combined analysis of the data samples with total statistics corresponding to 8.4 × 10 10 electrons on target collected in 2017 and 2018. This allows to set the new limits on the X − e − coupling in the range 1.2 × 10 −4 e 6.8 × 10 −4 , excluding part of the parameter space favored by the Berillium anomaly. The non-observation of the decay A → e + e − allows also to set the new bounds on the mixing strength of photons with dark photons (A ) with a mass 24 MeV.Recently, the search for new light bosons weakly coupled to SM particles was additionally inspired by the observation in the ATOMKI experiment by Krasznahorkay et al. [1,2] of a ∼7σ excess of events in the invariant mass distribution of e + e − pairs produced in the nuclear transitions of the excited 8 Be * to its ground state via internal pair creation. It was shown that this anomaly can be interpreted as the emission of a protophobic gauge boson X with a mass of 16.7 MeV decaying into e + e − pair [3,4]. This explanation of the anomaly was found to be consistent with the existing constraints assuming that the X has non-universal coupling to quarks, coupling to electrons in the range 2 × 10 −4 e 1.4 × 10 −3 and lifetime 10 −14 τ X 10 −12 s. It is interesting that a new boson with such relatively large couplings to charged leptons could also resolve the so-called (g µ − 2 ) anomaly, a discrepancy between measured and predicted values of the muon anomalous magnetic moment. This has motivated worldwide efforts towards the experimental searches, see, e.g., Refs. [5,6], and studies of the phenomenological aspects of light vector bosons weakly coupled to quarks and leptons, see, e.g., and also earlier works of Refs. [13][14][15][16]. The latest experimental results from the ATOMKI group show a similar excess of events at approximately the same invariant mass in the nuclear transitions of another nucleus, 4 He [17]. This further increases the importance of independent searches for a new particle X.Another strong motivation to search for new light bosons decaying into e + e − pair comes from the dark matter puzzle. An interesting possibility is that in addition to gravity a new force between the dark sector and visible matter, carried by a new vector boson A , called dark photon, might exist [18,19]. Such A could have a mass

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“…The first experiment was performed in June 2008 by measuring the excitation function of the dd → 3 He pπ − reaction near the η-meson production threshold. An upper limit for the formation and decay of the bound state in the process dd → ( 4 He-η) bound → 3 He pπ − at the 90% confidence level, was determined from 20 nb to 27 nb for the bound state width ranging from 5 MeV to 35 MeV, respectively [25]. During the second experiment, in November 2010, two channels of the η-mesic helium decay were registered: dd → ( 4 He-η) bound → 3 He pπ − and dd → ( 4 He-η) bound → 3 He nπ 0 → 3 He nγγ [26][27][28] in the excess energy range from −70 MeV to 30 MeV.…”

Section: Methodsmentioning

confidence: 99%

Search for $\eta $-mesic Nuclei with WASA-at-COSY

Krzemień¹,

Moskal²,

Skurzok³

2015

Acta Phys. Pol. B

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We search for an evidence of η-mesic He with the WASA detector. Two dedicated experiments were performed at the Cooler Synchrotron COSY-Jülich. The experimental method is based on the measurement of the excitation functions for the two reaction channels: dd → 3 He pπ − and dd → 3 He nπ 0 , where the outgoing N -π pairs originate from the conversion of the η meson on a nucleon inside the He nucleus. In this contribution, the experimental method is shortly described and the current status of the analysis is presented.

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Search forη-mesic4He with the WASA-at-COSY detector

Cited by 96 publications

References 18 publications

Studies of Mesic Nuclei via Decay Reactions

Studies of Mesic Nuclei via Decay Reactions

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

Search for $\eta $-mesic Nuclei with WASA-at-COSY

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