Thursday, August 27, 2020

New Analysis Disfavors X17 Particle

An outside analyst considers the data of the Hungarian researchers who proposed a new fundamental 17 MeV boson dubbed X17 and finds that their data is not consistent with the X17 explanation.

Can a protophobic vector boson explain the ATOMKI anomaly?

In 2016, the ATOMKI collaboration announced [PRL 116, 042501 (2016)] observing an unexpected enhancement of the e+e pair production signal in one of the 8Be nuclear transitions induced by an incident proton beam on a 7Li target. Many beyond-standard-model physics explanations have subsequently been proposed. One popular theory is that the anomaly is caused by the creation of a protophobic vector boson (X) with a mass around 17 MeV [e.g., PRL 117, 071803 (2016)] in the nuclear transition. We study this hypothesis by deriving an isospin relation between photon and X couplings to nucleons. This allows us to find simple relations between protophobic X-production cross sections and those for measured photon production. The net result is that X production is dominated by a direct E1X transition without going through any nuclear resonance (i.e. Bremsstrahlung radiation) with a smooth energy dependence that occurs for all proton beam energies above threshold. This contradicts the experimental observations and invalidates the protophobic vector boson explanation.
Comments:6 pages, 3 figures, 1 table
Subjects:High Energy Physics - Phenomenology (hep-ph); High Energy Physics - Experiment (hep-ex); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
Report number:NT@UW-20-07
Cite as:arXiv:2008.11288 [hep-ph]
 (or arXiv:2008.11288v1 [hep-ph] for this version)


neo said...

" An outside analyst considers the data of the Hungarian researchers who proposed a new fundamental 17 MeV boson dubbed X17 and finds that their data is not consistent with the X17 explanation."

it was Feng et all who proposed a new fundamental 17 MeV boson, the Hungarian researchers who collected the data.

i'd be interested in Feng's response,

the paper only evaluates Feng's proposal, there are other BSM hypothesis offered to explain ATOMKI anamoly,


Anomalies in 8^88Be nuclear transitions and (g−2)e,μ(g-2)_{e,\mu}(g−2)e,μ​: towards a minimal combined explanation

Apr 30, 2020
Motivated by a simultaneous explanation of the apparent discrepancies in the light charged lepton anomalous magnetic dipole moments, and the anomalous internal pair creation in 8^{8}8Be nuclear transitions, we explore a simple New Physics model, based on an extension of the Standard Model gauge group by a U(1)B−L_{B−L}B−L​. The model further includes heavy vector-like fermion fields, as well as an extra scalar responsible for the low-scale breaking of U(1)B−L_{B−L}B−L​, which gives rise to a light Z′ boson. The new fields and currents allow to explain the anomalous internal pair creation in 8^{8}8Be while being consistent with various experimental constraints. Interestingly, we find that the contributions of the Z′ and the new U(1)B−L_{B−L}B−L​-breaking scalar can also successfully account for both (g −2)e,μ_{e,μ}e,μ​ anomalies; the strong phenomenological constraints on the model’s parameter space ultimately render the combined explanation of (g − 2)e_{e}e​ and the anomalous internal pair creation in 8^{8}8Be particularly predictive. The underlying idea of this minimal “prototype model” can be readily incorporated into other protophobic U(1) extensions of the Standard Model.

here he proposals Z′ boson and a scalar and new fermion fields

both Feng and this author make use of SM extension U(1)B−L gauge theory

Z′ boson have also been proposed in other BSM theories

and this paper

Possible Explanation of the Electron Positron Anomaly at 17 MeV in 8Be^8Be8Be Transitions Through a Light Pseudoscalar Ulrich Ellwanger Sep 6, 2016

We estimate the values of Yukawa couplings of a light pseudoscalar A with a mass of about 17 MeV, which would explain the8^{8}8 Be anomaly observed in the Atomki pair spectrometer experiment. The resulting couplings of A to up and down type quarks are about 0.3 times the coupling of the standard Higgs boson. Then constraints from K and B decays require that loop contributions to flavour changing vertices cancel at least at the 10% level. Constraints from beam dump experiments require the coupling of A to electrons to be larger than about 4 times the coupling of the standard Higgs boson, leading to a short enough A life time consistent with an explanation of the anomaly.

neo said...

Hunting down the X17 boson at the CERN SPS
E. Depero, D. Banerjee, J. Bernhard, V. Burtsev, A . Chumakov, D. Cooke, A. Dermenev, S. Donskov, R. Dusaev, T. Enik, N. Charitonidis, A. Feshchenko, V. Frolov, A. Gardikiotis, S. Gerassimov, S. Girod, S. Gninenko, M. Hoesgen, V. Kachanov, A. Karneyeu, G. Kekelidze, B. Ketzer, D. Kirpichnikov, M. Kirsanov, V. Kolosov, I. Konorov, S. Kovalenko, V. Kramarenko, L. Kravchuk, N. Krasnikov, S. Kuleshov, V. Lyubovitskij, V. Lysan, V. Matveev, Yu. Mikhailov, L. Molina, D. Peshekhonov, V. Polyakov, B. Radics, R. Rojas, A. Rubbia, V. Samoylenko, D. Shchukin, V. Tikhomirov, I. Tlisova, D. Tlisov, A. Toropin, A. Trifonov, B. Vasilishin, G. Vasquez, P. Volkov, V. Volkov, P. Ulloa, P. Crivelli

Recently, the ATOMKI experiment has reported new evidence for the excess of e+e− events with a mass ∼17 MeV in the nuclear transitions of 4He, that they previously observed in measurements with 8Be. These observations could be explained by the existence of a new vector X17 boson. So far, the search for the decay X17→e+e− with the NA64 experiment at the CERN SPS gave negative results. Here, we present a new technique that could be implemented in NA64 aiming to improve the sensitivity and to cover the remaining X17 parameter space. If a signal-like event is detected, an unambiguous observation is achieved by reconstructing the invariant mass of the X17 decay with the proposed method. To reach this goal an optimization of the X17 production target, as well as an efficient and accurate reconstruction of two close decay tracks, is required. A dedicated analysis on the available experimental data making use of the trackers information is presented. This method provides an independent confirmation of the NA64 published results [D. Banerjee {\it et al.} (NA64 Collaboration), Phys. Rev. D101, 071101 (2020)], validating the tracking procedure. The detailed Monte Carlo study of the proposed setup and the background estimate show that the goal of the proposed search is feasible.

Subjects: High Energy Physics - Experiment (hep-ex); Instrumentation and Detectors (physics.ins-det)
Cite as: arXiv:2009.02756 [hep-ex]