PoS(LHCP2019)182 https://pos.sissa.it/ ∗† [email protected] Speaker. Thanks to the organizers for the invitation to give this presentation. We will present recently publishednon-LHC and experiments, soon namely BABAR, to NA62, be NA64, BELLE expected II, results and for PADME. dark matter searches in † ∗ Copyright owned by the author(s) under the terms of the Creative Commons c 7th Annual Conference on Large Hadron20-25 Collider May, Physics 2019 - LHCP2019 Puebla, Mexico Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND 4.0). Instituto de Física, Universidad Autónoma deE-mail: San Luis Potosí, Mexico Jürgen Engelfried Dark sector searches in non-LHC experiments PoS(LHCP2019)182 0 0 ) A A 1 ( m - U ε beam, − c e . 0 / A Be decays [5]. 8 Jürgen Engelfried produced together with . 0 2 2 c A c / / [4], with special emphasis for − , with the experimental signature e 2GeV 0 8GeV . + A e < 10 0 A . → , interacting with the SM sector through 0 0 m 0 µν A dark A A F m the longer is the lifetime of the . ε QED µν 2 F c / 1 2 ε − , looks for − ε = µ + 02GeV . mix µ , is very long lived and/or decays into dark particles only and L − 0 − e for 0 e A for a large mass range + + 3 e invisible 3 e − right). − , the a new boson postulate to explain anomalies in 2 1 → → 10 → c 10 0 0 0 / A A . A . , , , 0 0 ε 0 ε A A γ γ ZA 7MeV . − → → left): e masses and also smaller 16 1 − − 0 e e A left) are → = + + 2 M Z e e X is the lightest “Dark Sector” particle, it can only decay to SM particles, otherwise it − m 0 e A is the kinetic mixing strength. The smaller with ε X The seminal study of BABAR in 2014 [3] searches for a short-lived In this recent analysis [6] BABAR search for a long-lived If the For the experimental signatures and searches we have to distinguish two main cases: 1) The The need for an extension of the Standard Model (SM) – the dark sector – is well known In this presentation we will present recent already public results and expectations from non- A simple and natural extension of the SM is the introduction of a new interaction with a A more recent search by NA64, a fixed target experiment at CERN with a 100GeV = 0 plane are (see fig. a photon, decaying into a pair of electrons or muons. No signal is observed, and limits in the is the lightest “dark” particle andthe has experimental a setup, sufficiently and short 2) lifetime The tothe decay experimental into signature SM would particles within beexperimental missing results energy/momentum. which will For be presented both in cases the there following. are2.1 recent BABAR: 2.3 BABAR: can also decay in (lighter) dark sector particles. being a single photonlimits and (see large fig. missing momentum and energy. After observing no signal, the where A No signal is observed (see fig. a kinetic mixing and will not be discussedfields here. used, and Introducing are usually new separated particles“Axions” into and and Scalars ALP’s interactions (also (Axion called depend like “dark on Higgs”), particles),called the Axial and particles the type new called of Vector “Dark Interactions, Photon”. withleptons a (heavy Other new neutrinos), vector possible and boson some candidates other for solutions. dark sector particlesLHC are experiments heavy which neutral are already runningNA62, or NA64, will Belle start II, in and the PADME. near future, namely from BABAR, 2. Dark Photons Dark sector searches in non-LHC experiments 1. Introduction symmetry [1,2], with the new boson, the “dark photon” 2.2 NA64: probing lower PoS(LHCP2019)182 , , , Þ Þ < as Be 8 4 .In ϵ was 02 05 ) s [45] − Þ . . 0 at ϵ 0 0 A 10 ; are also 0 from the × ϵ CL A ;m run, were runs) was ϵ difference ϵ 3 93 85 0 0 . ) plane from ð . . m 0 [69,70] Be anomaly 1 ϵ . Left: . Left: beam cross- 0 [71] X -factors X 0 8 A , KLOE ; 0 0 ð ð via the k n X e − − Þ event detection. A 10% A e m e 0 together with the [40] 2 Þ ≲ explaining the and mass value of resulted in 3 in a mass − A for 30 4 e 02 g . ϵ − into account , and bounds from the with Þ ð 3 ,ECAL 0 and Refs. 0 Þ GeV. . A 4 10 − 10% BABAR . The [50] 072002 (2018) − 03 . × ≃ calculated by adding all cross sections was used to m , [64] 0 0 98 ð 2 0 . 10 . (26) 10 100 A A 0 4 ; runs, respectively. The total and [25] ð 97, 0 N Jürgen Engelfried ϵ 0 96 ≲ 0 ¼ 90% A [13,14] . , NA48 . X 90% C.L. upper limit e 0 X with , E787 and E949 experi- 0 ð ϵ [64,69,70] on 2 ε , constraints on the mixing [48] E V , E774 favored area are also shown. . The dimuon efficiency corrections
0 → , WASA-at-COSY → 1 14 NOVEMBER 2014 0 A μ
0 Þð þ ECAL → → A – 2 þ 2014 KLOE - ¼ e þ as a square A e i [38,39] E X 0 γ 2017 significance n m 0 decays 10 μ μ μ 0 GeV are set, signifi- events per > , the final distributions of e.m. neutral events, ;m anomaly E + m ε π ; 4 , and the test run from þ ¼ 2 ” [10] ϵ – → π e A [70 or − μ , setting limits (see fig. AR 2 ð GeV is shown 0 π 0 0 . Our data rule 0 μ Δ 1 week ending μ ( 0 2 th entry in this K summarizes the conservatively estimated back- 1 π A is the signal efficiency in the run ε − π B , i A ( vs Þ . Þ ; i þ 4 , 034 0 π ð 0 I n ; A . N 1 , measured on different nuclei μ ν A 2 0 ε i tot . Figure þ 3 -4 -3 -2 -1 0 1 2 3 4 0 A e 21 B 2 B ϵ 1 ≥ π = A . π B invisible [19] eZ ð 2 pair production by punchthrough 2 O
10
[14,15] , by using the modified frequentist approach, taking − 29 SEPTEMBER 2017 10
→ 6
γ global Z 10 APEX . − Entries → , the electron anomalous bremsstrahlung in the WCAL, → ;m → 0 ), and “ g Table The combined 90% confidence level (C.L.) upper limits e (GeV) in channels where [29] 90% A ∼ 07 0 0 S ϵ mixing strength squared . ;K N − ð þ < ¼ → A . Each ð 0 where ground inside the0 signal box, which is expected to be sponding limit for theN expected number of signal events, from the beam kaon decays in flight, Source of backgrounde Events the profile likelihood as a test statistic in the decay volume with energy π shown in the ( value is given by the sum decay photons escaping the dumpaccompanied without by interactions and poorlysource of detected fake secondaries, signal. Tothe is evaluate this extrapolation another background we of used σ the charge-exchange cross sections, decays, with theerror. uncertainty In Fig. dominated bywhich the are presumably statistical photons, and signalthat candidate passed events the selection criteria (i) TABLE I.signal Expected box estimated numbers for of background events in the π π either ECAL was found to be negligible. contribution to background is 0.06 events from the error were determined to stem from the overall calculated under thepredominant; assumption see, e.g., that Eq. (3.7) this in Ref. decay mode is in this sum wasthe calculated corresponding by beam running simulating conditions signalthem and events processing through for theselection reconstruction criteria program and efficiency withsample corrections from the as the for same run the data Punchthrough K found in theground signal is small box. is The confirmed conclusion by the thatfor data. the the back- mixing strength X and dimuon production in the dump eZ Total . We compute both the ε 0 0 e → 0 0 4 A i A [15] value is the signal yield m A the limits obtained with points in the absence of A E 0 n A -1 Þ 1 from Fig. 0 m 0 were determined from the A1 − Δ V , π A ed to the previous constraints i tot A GeV obtained from direct (blue) and 2 (green) MeV. 2 0 with a smaller data set. No signal invisible, with the ν ϵ (GeV) 10 ϵ 10 (solid red line) and the profile- , ε ν (GeV) E m A' 1 π 0 . A' , KLOE
3 m
N
ϵ − 0 0.5 2.5 1.5
Þ 20] − σ 100
Upper Limit at 90% CL 90% at Limit Upper -2 -3 -4 -4 -3 -2 -1 0 1 2 3 4
ε A 2 1 In a similar search, with the signature being a single electron and large missing energy, NA64 NA62, the rare kaon decay experiment at the CERN SPS, searched for a long-living 2 2 4 2 3 – 6 10 , HADES − − −
. 10 ≳
(23) N
10 10 10 10 ) from the fits to the dielectron (left) and dimuon (right) final 10
2 Entries − as a function of The 90% confidence level (C.L.) upper limits on 0
10 10 10 ε The limits were also calculated with a simplified method S ε A 2 g S pares our results to other limits on At each value of ε in Fig. by this work (green area) compar [7,18 frequentist profile-likelihood limits with a uniform prior for FIG. 5. Regions of the anomaly is allowed to decayparameter space invisibly, consistent as with well the as to the region of FIG. 4. Upper limits at 90% C.L. on any signal is function of out the dark-photonð coupling as the explanation for the likelihood limit (blue dashed line). Bayesian limits with a uniform prior for deviation in any of the 166 root of the Bayesian limit on of SEARCH FOR VECTOR MEDIATOR OF DARK MATTER the ETL and WW calculations for different mass range where searches of can be seen in Fig. sum was calculatedcorresponding by beam simulating runningthem the conditions through signal the and eventsselection reconstruction for processing criteria program and efficiency withsample corrections the as from for same the theestimated data systematic run-i. errors were also The takingthe into expected limits account in calculation. backgrounds Thelimits and combined on 90% the mixing C.L. strength exclusion as a function of the 90% C.L. upper limitevents, for the expected number of signal corresponding mixing strength detection with the mass FIG. 14.as The a sensitivity, defined function as of an average the expected ECAL limit, energy cut for the case of the per EOT generatedECAL by target in a the energy single range 100 GeV electron in the confidence levels (C.L.), takingtest the statistic profile in likelihood the as asymptotic a approximation are also showncorrections are for mostly comparison. relevantm in One the can higher mass see region that the by merging allpreviously three by runs Eq. into a single run as described Eq. total number of expected signal events inthe the sum signal box of was expected events from the three runs: consistent with the excess reportedment by the close HyperCP experi- to 214 MeV is observed boson at constrain the rangeinterpretations of of the theand discrepancy parameter measured between anomalous space the magnetic calculated favored moment by of the muon APEX constraints based on a search for a light magnetic moment [16] cantly improving previous constraintsdump derived from beam- experiments displayed as a red line. required to explain themeasured discrepancy anomalous between magnetic the moment calculated and of the muon are finally translatedmixing into strength 90% between the C.L.function photon upper and of limits dark the photon on as dark the a photon mass displayed in Fig. section, assuming alimits flat are typically prior at the for level of the cross section. The FIG. 4 (color online).strength Upper limit (90% C.L.) on the mixing FIG. 3 (color online).( Distribution of the statistical significance states, togetherhypothesis with (dashed line). the expected distribution for the null neighboring points isof around 90%. Bounds at the level BARAR [6]. Right: NA64 [7]. 2.4 NA64: also searched [7] for a long-living reaction Figure 2: 2.5 NA62: range Figure 1: BARAR [3]. Right: NA64 [4]. ratios are related via [8] Dark sector searches in non-LHC experiments . 0 ¼ ≡ , 131804-6 A 0 0 p S A m A 201801-6 γ m
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PHYSICAL REVIEW LETTERS
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(top) and S ( (GeV) for the 166 as a function of the mass (GeV m from zero occurs at 2 X A' M 2 σ − S m max data sets, shown for illustration 4%) are propagated as 2 ε e 4 ϵ L . – Þ þ significance of observation are shown in Fig. 3 , where S e cross section for each final 3 (GeV) (GeV) Þ ” is the value of the likelihood with the 0 ð 0 A’ A’ 0 A 0 → ϒ m m A L 0 m =L γ 4%), the luminosity (0.6%), and local and combine the results into a A , where “ – Þ L and , (global significance of 0 ð 0 → shows the maximum-likelihood estimators Þ ) as a function of the dark photon mass. 1 A [9] . S S =L − γ 3 2 131804 (2017) 1 log S mixing strength e ð max 012345678 0 ¼ ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 2 ϒ þ 1 25 30 35 40 45 50 55 60 . The statistical significance of each fit 0 2 3 → L
A
e 1 3
2 0 2 S 1.5 0.5 2.5
ð
1
−
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− ) 119, Pull − p GeV and corresponds to
σ 10
Events / ( 0.5 GeV 0.5 ( / Events
ln ) e 2 10 Figure ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 2 þ ¼ 21 . e FIG. 2. Signal significance purposes. The signal peakcance (red) corresponds to the local signifi- tion of shows the full PDF, while thethe magenta background dashed contribution. line corresponds Top: Distribution to fit of the residuals normalized (pulls). signal yield fixed to zero, are shown in Fig. FIG. 3. Bottom: Signal fit for the simulation estimates of the triggersystematic uncertainty efficiency, within of the 0.4%. We compareobservables the input in BDT simulationphoton and data in events, counting a theuncertainty sample difference as of of a the systematic themultiplicative single- error signal on the signal selection crosssmall section efficiency. compared is 5%, The to and the is total statistical uncertainty. of the PRL the likelihood, and The values of p ulations determine that the probability to find such a 6 significant deviation of GeV (6.09 GeV) for the dielectron (dimuon) S from Ref. (bottom) cross sections together with their respective 201801 (2014) − − 02 0246810 0246810 . l μ 0 0 4 2 0 4 2 0
-2 -2 -4 -4 7
þ 10 50
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S l
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113, S
μ
e e A’ A’, (e e ) fb )
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μ γ → σ → μ ¼
+ - - - + + - + 0 → → We extract the A 0 0 A likelihood values forbackground fits with hypothesis, afactors free respectively. by signal We generating and a estimateThe the largest large pure local trial sample significance of is m MC experiments. state using theA expected dark photon branching fractions The gray bands indicate thethe mass analysis. regions that are excluded from obtained by combiningsample divided by the the efficiency signalsections and luminosity. as yields The cross a of function each of data FIG. 2. The PRL single measurement. The uncertaintiesbranching on fractions the (0.1% dark photon statistical significance ( final state. Includingvalue is trial 0.57 factors, (0.94), consistent the with corresponding the null hypothesis. distributions of the statisticaldisplayed in significances Fig. of the fits are the limited MC statistics (0.5% is taken as systematic uncertainties. We derive(C.L.) 90% confidence Bayesian level upper limits on the PoS(LHCP2019)182 in 0 A is not @90 % γ 0 < ) A 7 decays. As − BR ν , 10 ¯ ν + e Jürgen Engelfried × γν ) where one 4 → plane with for a long-lived → . ] 0 in the quantum 1 0 0 2 σ + γγ A A 0 c 2 140 π ± K − m A µ M → Dibaryon with a mass of 2 . BaBar 0 vs [MeV/ 1 (g-2) H , in the SM predicted to be and . ( π A' 2 2 ¯ ν M ν /c . ν 120 + + ¯ Λ µ π ¯ Λ distribution is performed. S the state should have a typical weak → → 2 2 + ) c → + γ / K 100 P K ϒ NA62 ( could be deeply bound [15, 16]. This is an − B + cannot decay and will be stable, thus being an π P S was set. should have a very long, cosmological lifetime; , 15 80 − 2 2 3 S uuddss 2055MeV c c + 0, which is used for normalization. No signal for a / / the corresponding limits are shown. K with its expected value [14, 15, 16]. = P = e 5 and the mass of the dark photon Λ 2) ε m = ( − 2 miss 60 [11] in terms of a contribution from the g + 05GeV the state m ( . e 2 µ miss 2 2 [18], the signature being a missing mass recoiling against the m 1878MeV c 2) M ¯ / < Λ + − <
¯ S e Λ P g S ( S m 40
m
m (g-2) NA64 → > ϒ H band in the mass ranges 83–113 and 176–243 MeV 6 7 5 2055MeV m − − − µ
10 10 10
2)
∈ < . 2 3 . If S − at 90% CL, improving the current limit by more than three orders of magnitude. 2 g m c 7 ( / − , a peak search is performed in the region of positive missing mass square, suffi- 10 4 Finally, an upper limit has been set for the branching ratio of the decay The cost of the experiment and of its auxiliary systems were supported by the funding agen- × 9 . Limits on the kinetic mixing term conservative scenario, not shownwith in the Fig. 7, the upper limit from E787-E949 partially overlaps Acknowledgements It is a pleasure tostaff express of our appreciation the toexperiment participating the staff and laboratories of data the and processing. CERN universities laboratory for and the their technical cies efforts of in the the CollaborationRecherche Institutes. operation Scientifique We of - are the particularly FNRS),Bulgaria; indebted Belgium; NSERC to: (Natural BMES Sciences F.R.S.-FNRS (Ministry and (Fonds EngineeringResearch of de Research Council), Council) la Education, Canada; Youth contribution NRC (National andand to Science), Sports), TRIUMF, Czech Republic; Canada; BMBF05H12UM5, MEYS (Bundesministerium 05H15UMCNA für (Ministry and Bildung 05H18UMCNA, of undNucleare), Germany; Forschung) Italy; Education, contracts MIUR INFN (Ministero Youth (Istituto dell’Istruzione,CyT Nazionale dell’Università (Consejo e di Nacional della de Fisica Ricerca), Cienciamania; Italy; y INR-RAS Tecnología), CONA- Mexico; (Institute IFA for (Institute NuclearRussia; of Atomic Research JINR Physics), of Ro- (Joint the Institute RussianCenter) Academy for “Kurchatov of Institute” Nuclear Sciences), Research), Moscow, andFederation), Dubna, MESRF Russia; Russia; (Ministry MESRS NRC ofCERN (Ministry (National Education (European of Research and Organization Education, Science for of Science, Nuclear the Research Russian Research), and Switzerland; Sport), STFC Slovakia; (Science and Tech- decaying into invisible final states.experiments The are limits from shown. the The BaBarto [8] green an (blue) band explanation and of shows NA64 the the [9]muon discrepancy (light region between magnetic grey) of the measured moment the and parameterloops expected space values [12, of corresponding the 13]. anomalous magnetic The moment region of above the the electron black line is excluded by the agreement of the anomalous 1 Figure 7: Upper limit at 90% CL from NA62 (red region) in the . First results were already published [10] from the 2016 data taking period, and the status decays from NA62 [12]. Only about 1 % of the available data on tape are used for this analysis. 0 11 A 2150GeV − γ BABAR searched in The completely symmetric six-quark state The analysis profits heavily from the extremely high-efficiency photon veto system needed for For this analysis [12] only about 1% of the available data already on tape are used, leading to NA62 searched for heavy neutral leptons [13, 14] in system. No signal was observed, and a limit of ≈ 10 → ¯ H Λ × 0 ¯ but if it is even deeper bound, ideal candidate for a dark matter particle. Λ m lifetime, while if ciently far away from the SM peak at 4. BABAR: Search for Stable Six-Quark State of the analysis of the 2017 data set are reported [11]the at this main conference. measurement. The most abundant background is still due to Figure 3: 8 shown in fig. heavy neutral lepton is observed, and in fig. extension of a prediction by Jaffe [17] in 1976, when he predicted the C.L. for the full mass range of limits shown in fig. 3. Heavy Neutral Leptons (neutrinos) Dark sector searches in non-LHC experiments NA62 [9] is designed to measure the branching ratio of detected due to acceptance, inefficiencyevaluated with (very data low), from and a photon minimumsignal bias conversions. sample, trigger a The stream peak (independent background search of in is the the signal stream). In the π PoS(LHCP2019)182 (right) ν + µ → + Jürgen Engelfried K (blue) decays from ν + µ → (left) and + ν K + e → + K (red) and ν + ) for e µ , e → + = 4 l K ( 2 ) + l P − + K P regions used for normalization and where the peak search is performed. = ( 2 miss 2 miss m m Limits on heavy neutral leptons from Distributions of Figure 5: NA62 [14] with the 2016 data set. Figure 4: Dark sector searches in non-LHC experiments decays. Arrows indicate the NA62 [14]. PoS(LHCP2019)182 , γγ → 113 visible, → ) are being 3 Jürgen Engelfried . Phys. Rev. Lett. (section , 0 A mass range. γ 2 c / → invisible will be improved for visible, DarkScalar (1986) 196 0 invisible. π → → 0 → A 166B 10GeV 0 , and also will search for ALP A 1 < − , HNL Collisions at BaBar − − ALP ), and for µ e + m + 2.5 µ Phys. Lett. < , , 2 − c e 5 / invisible they project [22] to improve the BABAR + e . → after the experimental setup will be moved to Cornell → 0 2 0 A c A / after acquiring 50ab Electron on Target, and is also preparing to use a muon beam 5 − 12 (1980) 285 10 10 ]. 95B × × 100MeV 5 . & 0 Search for a Dark Photon in e A ε m POT have been taken and are currently analyzed, and during 2021-2023 up to ) Phys. Lett. 1406.2980 , MOT, improving their existing limits for [ 16 , and 13 2 , and during dedicated periods in Beam Dump Mode. During the 2016-2018 data 10 Two U(1)’s and Epsilon Charge Shifts c for beam dump data are currently ongoing. Also analysis on the full statistics from ( ¯ ) limit to ν 10 / ν O Effects of the Spin 1 Partner of the Goldstino (Gravitino) on Neutral Current collaboration, γγ 2.3 × + π AR → POT are expected. Analysis for B → ) 10MeV A 18 + Phenomenology (2014) 201801 I would like to thank Mauro Raggi (PADME), and Gerard Bonneaud and Fabio Anulli (BABAR) There are several experiments currently analyzing data, or just starting with data taking. We PADME [19] is a new fixed target experiment in Frascati. It took already some test data and is BELLE II [21] is just starting to take data, and they are well prepared for analysis with the NA64 expects [23] up to 5 NA62 takes data for dark searches in 2 modes: parasitically together with the main trigger . K 10 0 ( A [3]B [1] P. Fayet, [2] B. Holdom, for providing material for this presentation. References performed. Acknowledgment (see section expecting best limits in particular for the 1GeV will not present projected exclusion plots here, we will better wait5.1 for PADME real experimental results. preparing for real data taking. They project [20] that limits for experience from Belle and BABAR. For for Dark sector searches in non-LHC experiments 5. More results to come in the near future m and/or JLAB. 5.2 BELLE II 5.3 NA64 with up to 5 5.4 NA62 taking period O and ALP 2016-8 for HNL searches in Kaon decays (section PoS(LHCP2019)182 , ]. , (2019) 05 (2019) B778 (2017) 712 (2017) ]. Collisions at , 2019. Phys. Lett. 12 122 , − JHEP , 2019. e B772 Jürgen Engelfried , + 1903.07899 [ ]. JINST Phys. Lett. ]. , , ]. decays 0 Combined search for light 1504.01527 π [ Phys. Lett. , decays . Phys. Rev. Lett. (2019) 117 + , . 1803.07748 decays 1403.3041 1711.10971 [ B796 [ [ µ ν LHCP19, these proceeding + (1977) 195 ]. µ (2016) 042501 38 , in La Thuile – Les Recoontres de physics de la → 116 + , in Phys. Lett. 1808.10567 (2018) 929 , using the decay-in-flight technique , ¯ ν (2018) 231802 (2014) 959802 ν 6 ]. . + ]. 120 π 1702.03327 [ 2014 → Phys. Rev. Lett. ICRC2017 , + Phys. Rev. Lett. , Exploring Portals to a Hidden Sector Through Fixed Targets PoS , ]. 1710.00971 0906.5614 1708.08951 [ [ , Proposal to Search for a Dark Photon in Positron on Target Collisions Phys. Rev. Lett. (2017) 131804 ]. , Observation of Anomalous Internal Pair Creation in Be8 : A Possible La Thuile – Les Recoontres de physics de la valee D’Aoste The Belle II Physics Book ]. ]. 119 Search for a Stable Six-Quark State at BABAR Search for Invisible Decays of a Dark Photon Produced in e , in Search for heavy neutral lepton production in K First search for K Search for heavy neutrinos in K Search for vector mediator of Dark Matter production in invisible decay mode The Beam and detector of the NA62 experiment at CERN Search for a Hypothetical 16.7 MeV Gauge Boson and Dark Photons in the Search for production of an invisible dark photon in ]. Recent kaon decay results from NA62 1811.08508 Adv. High Energy Phys. [ , ]. (2018) 072002 (2009) 095024 , 2019. 6-quark Dark Matter Stable Sexaquark BELLE II 1712.00297 Perhaps a Stable Dihyperon [ Searching for Dark Photons with PADME D97 D80 1703.08501 1810.04724 collaboration, collaboration, [ [ Phys. Rev. Lett. NE Linac -II collaboration, , (2019) 156 Φ 1903.08767 AR AR [ B B ELLE A A 1705.07510 Indication of a Light, Neutral Boson BaBar dark matter with electron and muon beams at NA64 (2018) 137 072002 at DA [ valee D’Aoste Phys. Rev. Phys. Rev. P05025 B791 182 NA64 Experiment at CERN [5] A. J. Krasznahorkay et al., [6]B [7] NA64 collaboration, [8] B. Batell, M. Pospelov and A. Ritz, [9] NA62 collaboration, [4] NA64 collaboration, [23] S. N. Gninenko, D. V. Kirpichnikov, M. M. Kirsanov and N. V. Krasnikov, [16] G. R. Farrar, [17] R. L. Jaffe, [18]B [22] G. Inguglia, [19] M. Raggi and V. Kozhuharov, [14] NA62 collaboration, [11] N. Estrada-Tristán, [13] NA62 collaboration, [15] G. R. Farrar, [20] P. Valente, [10] NA62 collaboration, [21]B Dark sector searches in non-LHC experiments [12] NA62 collaboration,