%APark, S.-H.%AKwon, Y.-J.%AAdachi, I.%AAihara, H.%AAl Said, S.%AAsner, D.%AAtmacan, H.%AAushev, T.%AAyad, R.%ABabu, V.%ABehera, P.%ABennett, J.%ABessner, M.%ABhardwaj, V.%ABhuyan, B.%ABilka, T.%ABiswal, J.%ABonvicini, G.%ABozek, A.%ABračko, M.%ABrowder, T.%ACampajola, M.%ACao, L.%AČervenkov, D.%AChang, M.-C.%AChang, P.%AChen, A.%ACheon, B.%AChilikin, K.%ACho, H.%ACho, K.%ACho, S.-J.%AChoi, S.-K.%AChoi, Y.%AChoudhury, S.%ACinabro, D.%ACunliffe, S.%ADas, S.%ADash, N.%ADe Nardo, G.%ADi Capua, F.%ADingfelder, J.%ADoležal, Z.%ADong, T.%AEidelman, S.%AEpifanov, D.%AFerlewicz, D.%AFulsom, B.%AGarg, R.%AGaur, V.%AGarmash, A.%AGiri, A.%AGoldenzweig, P.%AGuan, Y.%AGudkova, K.%AHadjivasiliou, C.%AHara, T.%AHartbrich, O.%AHayasaka, K.%AHayashii, H.%AHedges, M.%AHernandez Villanueva, M.%AHou, W.-S.%AHsu, C.-L.%AHuang, K.%AIijima, T.%AInami, K.%AInguglia, G.%AIshikawa, A.%AItoh, R.%AIwasaki, M.%AIwasaki, Y.%AJacobs, W.%AJaegle, I.%AJang, E.-J.%AJeon, H.%AJia, S.%AJin, Y.%AJoo, C.%AJoo, K.%AKang, K.%AKaryan, G.%AKawasaki, T.%AKiesling, C.%AKim, D.%AKim, K.-H.%AKim, S.%AKim, Y.-K.%AKinoshita, K.%AKodyš, P.%AKonno, T.%AKorpar, S.%AKotchetkov, D.%AKrižan, P.%AKroeger, R.%AKrokovny, P.%AKuhr, T.%AKumar, M.%AKumara, K.%ALalwani, K.%ALee, I.%ALee, S.%ALi, C.%ALi, J.%ALi, L.%ALi, Y.%ALi Gioi, L.%ALibby, J.%ALieret, K.%ALiptak, Z.%ALiventsev, D.%ALuo, T.%AMacNaughton, J.%AMacQueen, C.%AMasuda, M.%AMatsuda, T.%AMatvienko, D.%AMerola, M.%AMetzner, F.%AMiyabayashi, K.%AMizuk, R.%AMohanty, G.%AMohanty, S.%AMori, T.%AMoser, H.-G.%AMrvar, M.%AMussa, R.%ANakao, M.%ANatkaniec, Z.%ANatochii, A.%ANayak, L.%ANayak, M.%ANiiyama, M.%ANisar, N.%ANishida, S.%AOgawa, S.%AOno, H.%AOnuki, Y.%AOskin, P.%APakhlov, P.%APakhlova, G.%APardi, S.%APark, C.%APark, H.%APatra, S.%APaul, S.%APedlar, T.%APestotnik, R.%APiilonen, L.%APodobnik, T.%APopov, V.%APrencipe, E.%APrim, M.%ARitter, M.%ARöhrken, M.%ARostomyan, A.%ARout, N.%ARusso, G.%ASakai, Y.%ASandilya, S.%ASangal, A.%ASantelj, L.%ASanuki, T.%ASavinov, V.%ASchnell, G.%ASchueler, J.%ASchwanda, C.%ASeino, Y.%ASenyo, K.%ASevior, M.%AShapkin, M.%ASharma, C.%AShen, C.%AShiu, J.-G.%ASokolov, A.%ASolovieva, E.%AStanič, S.%AStarič, M.%AStottler, Z.%AStrube, J.%ASumihama, M.%ASumisawa, K.%ASumiyoshi, T.%ASutcliffe, W.%ATakizawa, M.%ATanida, K.%ATenchini, F.%AUchida, M.%AUglov, T.%AUnno, Y.%AUno, S.%AUrquijo, P.%AVahsen, S.%AVan Tonder, R.%AVarner, G.%AVarvell, K.%AVinokurova, A.%AVorobyev, V.%AWaheed, E.%AWang, C.%AWang, E.%AWang, M.-Z.%AWang, P.%AWatanabe, M.%AWatanuki, S.%AWehle, S.%AWon, E.%AXu, X.%AYabsley, B.%AYan, W.%AYang, S.%AYe, H.%AYelton, J.%AYin, J.%AYusa, Y.%AZhang, Z.%AZhilich, V.%AZhukova, V.%AZhulanov, V.%Anull Ed.%BJournal Name: Journal of High Energy Physics; Journal Volume: 2021; Journal Issue: 4 %D2021%I %JJournal Name: Journal of High Energy Physics; Journal Volume: 2021; Journal Issue: 4 %K %MOSTI ID: 10273327 %PMedium: X %TSearch for the dark photon in B0 → A′A′, A′ → e+e−, μ+μ−, and π+π− decays at Belle %XA bstract We present a search for the dark photon A ′ in the B 0 → A ′ A ′ decays, where A ′ subsequently decays to e + e − , μ + μ − , and π + π − . The search is performed by analyzing 772 × 10 6 $$ B\overline{B} $$ B B ¯ events collected by the Belle detector at the KEKB e + e − energy-asymmetric collider at the ϒ(4 S ) resonance. No signal is found in the dark photon mass range 0 . 01 GeV /c 2 ≤ m A ′ ≤ 2 . 62 GeV /c 2 , and we set upper limits of the branching fraction of B 0 → A ′ A ′ at the 90% confidence level. The products of branching fractions, $$ \mathrm{\mathcal{B}}\left({B}^0\to A^{\prime }A^{\prime}\right)\times \mathrm{\mathcal{B}}{\left(A\prime \to {e}^{+}{e}^{-}\right)}^2 $$ ℬ B 0 → A ′ A ′ × ℬ A ′ → e + e − 2 and $$ \mathrm{\mathcal{B}}\left({B}^0\to A^{\prime }A^{\prime}\right)\times \mathrm{\mathcal{B}}{\left(A\prime \to {\mu}^{+}{\mu}^{-}\right)}^2 $$ ℬ B 0 → A ′ A ′ × ℬ A ′ → μ + μ − 2 , have limits of the order of 10 − 8 depending on the A ′ mass. Furthermore, considering A ′ decay rate to each pair of charged particles, the upper limits of $$ \mathrm{\mathcal{B}}\left({B}^0\to A^{\prime }A^{\prime}\right) $$ ℬ B 0 → A ′ A ′ are of the order of 10 − 8 –10 − 5 . From the upper limits of $$ \mathrm{\mathcal{B}}\left({B}^0\to A^{\prime }A^{\prime}\right) $$ ℬ B 0 → A ′ A ′ , we obtain the Higgs portal coupling for each assumed dark photon and dark Higgs mass. The Higgs portal couplings are of the order of 10 − 2 –10 − 1 at $$ {m}_{h\prime}\simeq {m}_{B^0} $$ m h ′ ≃ m B 0 ± 40 MeV /c 2 and 10 − 1 –1 at $$ {m}_{h\prime}\simeq {m}_{B^0} $$ m h ′ ≃ m B 0 ± 3 GeV /c 2 . %0Journal Article