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Evidence for a New 17 Mev Boson

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Evidence for a New 17 Mev Boson PROTOPHOBIC 8Be TRANSITION EVIDENCE FOR A NEW 17 MEV BOSON Flip Tanedo arXiv:1604.07411 & work in progress SLAC Dark Sectors 2016 (28 — 30 April) with Jonathan Feng, Bart Fornal, Susan Gardner, Iftah Galon, Jordan Smolinsky, & Tim Tait BART SUSAN IFTAH 1 flip . tanedo @ uci . edu EVIDENCE FOR A 17 MEV NEW BOSON 14 week ending A 6.8σ nuclear transitionPRL 116, 042501 (2016) anomalyPHYSICAL REVIEW LETTERS 29 JANUARY 2016 shape of the resonance [40], but it is definitelyweek different ending pairs (rescaled for better separation) compared with the PRL 116, 042501 (2016) PHYSICAL REVIEW LETTERS 29 JANUARY 2016 from the shape of the forward or backward asymmetry [40]. simulations (full curve) including only M1 and E1 con- Therefore, the above experimental data make the interpre- tributions. The experimental data do not deviate from the Observation of Anomalous Internal Pairtation Creation of the in observed8Be: A Possible anomaly Indication less probable of a as Light, being the normal IPC. This fact supports also the assumption of the Neutralconsequence Boson of some kind of interference effects. boson decay. The deviation cannot be explained by any γ-ray related The χ2 analysis mentioned above to judge the signifi- A. J. Krasznahorkay,* M. Csatlós, L. Csige, Z. Gácsi,background J. Gulyás, M. either, Hunyadi, since I. Kuti, we B. cannot M. Nyakó, see any L. Stuhl, effect J. Timár, at off cance of the observed anomaly was extended to extract the T. G. Tornyi,resonance, and Zs. where Vajta the γ-ray background is almost the same. mass of the hypothetical boson. The simulated angular Institute for Nuclear Research, Hungarian Academy ofTo Sciences the best (MTA of Atomki), our knowledge, P.O. Box 51, the H-4001 observed Debrecen, anomaly Hungary can correlations included contributions from bosons with 2 notT. J. have Ketel a nuclear physics related origin. masses between m0c 15 and 17.5 MeV. As a result Nikhef National Institute for Subatomic Physics,The Science deviation Park 105, observed 1098 XG Amsterdam, at the bombarding Netherlands energy of of the χ2 analysis, we¼ determined the boson mass to be 2 Ep 1.10 MeV and at Θ ≈ 140° has a significance of 6.8 m0c 16.70 0.35 stat MeV. The minimum value for A. Krasznahorkay¼ 2¼ Æ ð Þ CERN, CH-1211 Geneva 23, Switzerland and Institute forstandard Nuclear Research,deviations, Hungarian corresponding Academy of to Sciences a background (MTA Atomki), fluc- the χ =f was 1.07, while the values at 15 and 17.5 MeV 12 P.O. Box 51, H-4001tuation Debrecen, probability Hungary of 5.6 × 10− . On resonance, the M1 were 7.5 and 6.0, respectively. A systematic error caused by (Received 7 April 2015;contribution published 26 should January be 2016) even larger, so the background the instability of the beam position on the target, as well as Electron-positron angular correlations wereshould measured decrease for the isovector faster than magnetic in other dipole cases, 17.6 MeV which would the uncertainties in the calibration and positioning of the π π (J 1þ, T 1) state → ground state (J make0þ, T the0) deviation and the isoscalar even magnetic larger dipoleand more 18.15 significant. MeV detectors is estimated to be 6°, which corresponds to ¼ ¼ ¼ ¼ ΔΘ (Jπ 1 , T 0) state → ground state transitions in 8Be. Significant− enhancement relative to the internal ¼ ¼ þ ¼ The eþe decay of a hypothetical boson emitted iso- 0.5 MeV uncertainty in the boson mass. pair creation was observed at large angles intropically the angular from correlation the target for the has isoscalar been transition simulated with together a with Since, in contrast to the case of 17.6 MeV isovector confidence level of > 5σ. This observation could possibly be due to nuclear reaction interference− effects or might indicate that, in an intermediatethe step, normal a neutral IPC isoscalaremission particle of eþe withpairs. a mass The of sensitivity of transition, the observed anomalous enhancement of the 2 theπ angular correlation measurements to the mass of the 18.15 MeV isoscalar transition could only be explained by 16.70 0.35 stat 0.5 syst MeV=c and J 1þ was created. Æ ð ÞÆ ð Þ assumed¼ boson is illustrated in Fig. 4. also assessing a particle, then it must be of isoscalar nature. DOI: 10.1103/PhysRevLett.116.042501 Taking into account an IPC coefficient of 3.9 × 10−3 for The invariant mass distribution calculated from the the 18.15 MeV M1 transition [32], a boson to γ branching measured energies and angles was also derived. It is shown DOI: 10.1103/PhysRevLett.116.042501 −6 ratio of 5.8 × 10 was found for− the best fit and was then2 in Fig. 5. Recently, several experimental anomalies were discussed particle decaying into an eþe pair, the angular correlation flipas . possible tanedo signatures@ uci for . a edu new light particle [1–3]. SomeusedEVIDENCE forbecomes the other FOR sharply boson A 17 peaked massesMEV at NEW larger in Fig. BOSON angles,4. the correlation14 The dashed line shows the result of the simulation predictions suggest light neutral bosons in the 10 MeVAccording– angle of to a two-particle the simulations, decay is the 180° contribution in the center-of-mass of the performed for M1 23%E1 mixed IPC transition (the 10 GeV mass range as dark matter candidates, whichassumedsystem. boson should be negligible for asymmetric pairs mixing ratio was determinedþ from fitting the experimental 8 couple to electrons and positrons [4–7], to explainwith the 0.5 ≤Toy populate≤ 1.0. the The 17.6, open and circles 18.15 MeV with1þ errorstates bars in Be in angular correlations), the dotted line shows the simulation anomalies. A number of attempts were made to find such selectively,j j we used the 7Li p; γ 8Be reaction at the Fig. 4 show the experimental data obtainedð Þ for asymmetric for the decay of a particle with mass of 16.6 MeV=c2 while particles [1,8–17]. Since no evidence was found, limits Ep 0.441, and 1.03 MeV resonances [29]. Proton beams were set on their mass and their coupling strength to from¼ a 5 MV Van de Graaff accelerator with typical current the dash-dotted line is their sum, which describes the 2 ordinary matter. In the near future, ongoing experiments are of -11.0 μA impinged on 15 μg=cm thick LiF2 and experimental data reasonably well. 10 2 − expected to extend those limits to regions in mass and 700 μg=cm thick LiO2 targets evaporated on 10 μmAl In conclusion, we have measured the eþe angular coupling strength which are so far unexplored. All of them backings. correlation in internal pair creation for the M1 transition − are designed to exploit the radiative production of the so- The eþe pairs were detected by five plastic ΔE E depopulating the 18.15 MeV state in 8Be, and observed a detector telescopes similar to those built by Stiebing− and called dark photons (γ0) by a very intense electron or peaklike deviation from the predicted IPC. To the best of positron beam on a high-Z target [18–23]. co-workers [34], but we used larger telescope detectors in In the present work, we reinvestigated the anomalies combination with position sensitive detectors to signifi- =17.6 MeV =15.6 MeV 2 observed previously in the internal pair creation of iso- cantly increase the coincidence efficiency by2 about 3 orders c c =16.6 MeV 0 0 2 3 vector (17.6 MeV) and isoscalar (18.15 MeV) M1 tran- c m of magnitude. E detectors of 38 × 45 × 1 mmm and the E Δ 0 800 8 3 sitions in Be [24–29]. The expected signature of the detectors of 78 × 60 × 70 mm werem placed perpendicu- anticipated particle is a very characteristic angular corre- larly to the beam direction at azimuthal angles of 0°, 60°, 700 − lation of the eþe pairs from its decay [30,31]. The angular 120°, 180°, and 270°. These angles ensured homogeneous correlation between the e and e− emitted in the internal IPCC (relative unit) 600 þ acceptance of the e e− pairs as a function of the correlation pair creation (IPC) drops rapidly with the separation angle þ angle. The positions of the hits were determined by 500 θ [32,33]. In striking contrast, when the transition takes =16.6 MeV −13 multiwire-2 proportional counters (MWPC) [35] placed in 2 c place by emission of a short-lived (τ < 10 s) neutral 10 400 0 front of the ΔE and E detectors. m The target strip foil was perpendicular to the beam 300 IPC, M1+E1 direction. The telescope detectors were placed around the (Weighted Counts/0.5 MeV) Published by the American Physical Society under the terms of 80 90 100 110 120 130 140 150 160 170 vacuum chamber made of a carbon-fiber tube. A detailed e+e- 200 the Creative Commons Attribution 3.0 License. Further distri- Θ (deg.) N bution of this work must maintain attribution to the author(s) and description of the experimental setup is published else- the published article’s title, journal citation, and DOI. where [36]. 100 − FIG. 4. Experimental angular eþe pair correlations measured 7 0 in the Li p; e e− reaction at E 1.10 MeV with 9 10 11 12 13 14 15 16 17 18 0031-9007=16=116(4)=042501(5) 042501-1ð þ PublishedÞ by the Americanp ¼ Physical Society −0.5 ≤ y ≤ 0.5 (closed circles) and y ≥ 0.5 (open circles). me+e- (MeV) The results of simulations of boson decayj j pairs added to those of IPC pairs are shown for different boson masses as described in FIG.
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