BelleBELLE2-CONF-PH-2022-017 November 7 2022 Determination of jVubjfrom untagged B0decays using

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Belle

BELLE2-CONF-PH-2022-017

November 7, 2022

Determination of |Vub|from untagged B0→π−`+ν`decays using

2019-2021 Belle II data

(The Belle II Collaboration)

F. Abudin´en, I. Adachi, K. Adamczyk, L. Aggarwal, P. Ahlburg, H. Ahmed, J. K. Ahn, H.

Aihara, N. Akopov, A. Aloisio, F. Ameli, L. Andricek, N. Anh Ky, D. M. Asner, H.

Atmacan, V. Aulchenko, T. Aushev, V. Aushev, T. Aziz, V. Babu, S. Bacher, H. Bae, S.

Baehr, S. Bahinipati, A. M. Bakich, P. Bambade, Sw. Banerjee, S. Bansal, M. Barrett, G.

Batignani, J. Baudot, M. Bauer, A. Baur, A. Beaubien, A. Beaulieu, J. Becker, P. K.

Behera, J. V. Bennett, E. Bernieri, F. U. Bernlochner, V. Bertacchi, M. Bertemes, E.

Bertholet, M. Bessner, S. Bettarini, V. Bhardwaj, B. Bhuyan, F. Bianchi, T. Bilka, S.

Bilokin, D. Biswas, A. Bobrov, D. Bodrov, A. Bolz, A. Bondar, G. Bonvicini, A. Bozek, M.

Braˇcko, P. Branchini, N. Braun, R. A. Briere, T. E. Browder, D. N. Brown, A. Budano, L.

Burmistrov, S. Bussino, M. Campajola, L. Cao, G. Casarosa, C. Cecchi, D. ˇ

Cervenkov,

M.-C. Chang, P. Chang, R. Cheaib, P. Cheema, V. Chekelian, C. Chen, Y. Q. Chen, Y. Q.

Chen, Y.-T. Chen, B. G. Cheon, K. Chilikin, K. Chirapatpimol, H.-E. Cho, K. Cho, S.-J.

Cho, S.-K. Choi, S. Choudhury, D. Cinabro, L. Corona, L. M. Cremaldi, S. Cunliﬀe, T.

Czank, S. Das, N. Dash, F. Dattola, E. De La Cruz-Burelo, S. A. De La Motte, G. de

Marino, G. De Nardo, M. De Nuccio, G. De Pietro, R. de Sangro, B. Deschamps, M.

Destefanis, S. Dey, A. De Yta-Hernandez, R. Dhamija, A. Di Canto, F. Di Capua, S. Di

Carlo, J. Dingfelder, Z. Doleˇzal, I. Dom´ınguez Jim´enez, T. V. Dong, M. Dorigo, K.

Dort, D. Dossett, S. Dreyer, S. Dubey, S. Duell, G. Dujany, P. Ecker, S. Eidelman, M.

Eliachevitch, D. Epifanov, P. Feichtinger, T. Ferber, D. Ferlewicz, T. Fillinger, C. Finck,

G. Finocchiaro, P. Fischer, K. Flood, A. Fodor, F. Forti, A. Frey, M. Friedl, B. G. Fulsom,

M. Gabriel, A. Gabrielli, N. Gabyshev, E. Ganiev, M. Garcia-Hernandez, R. Garg,

A. Garmash, V. Gaur, A. Gaz, U. Gebauer, A. Gellrich, J. Gemmler, T. Geßler, G.

Ghevondyan, G. Giakoustidis, R. Giordano, A. Giri, A. Glazov, B. Gobbo, R. Godang, P.

Goldenzweig, B. Golob, P. Gomis, G. Gong, P. Grace, W. Gradl, S. Granderath, E.

Graziani, D. Greenwald, T. Gu, Y. Guan, K. Gudkova, J. Guilliams, C. Hadjivasiliou, S.

Halder, K. Hara, T. Hara, O. Hartbrich, K. Hayasaka, H. Hayashii, S. Hazra, C. Hearty,

M. T. Hedges, I. Heredia de la Cruz, M. Hern´andez Villanueva, A. Hershenhorn, T.

Higuchi, E. C. Hill, H. Hirata, M. Hoek, M. Hohmann, S. Hollitt, T. Hotta, C.-L. Hsu, K.

Huang, T. Humair, T. Iijima, K. Inami, G. Inguglia, N. Ipsita, J. Irakkathil Jabbar, A.

Ishikawa, S. Ito, R. Itoh, M. Iwasaki, Y. Iwasaki, S. Iwata, P. Jackson, W. W. Jacobs, D.

E. Jaﬀe, E.-J. Jang, M. Jeandron, H. B. Jeon, Q. P. Ji, S. Jia, Y. Jin, C. Joo, K. K. Joo,

H. Junkerkalefeld, I. Kadenko, J. Kahn, H. Kakuno, M. Kaleta, A. B. Kaliyar, J. Kandra,

K. H. Kang, S. Kang, P. Kapusta, R. Karl, G. Karyan, Y. Kato, H. Kawai, T. Kawasaki,

C. Ketter, H. Kichimi, C. Kiesling, C.-H. Kim, D. Y. Kim, H. J. Kim, K.-H. Kim, K. Kim,

arXiv:2210.04224v2 [hep-ex] 7 Nov 2022

S.-H. Kim, Y.-K. Kim, Y. Kim, T. D. Kimmel, H. Kindo, K. Kinoshita, C. Kleinwort, B.

Knysh, P. Kodyˇs, T. Koga, S. Kohani, K. Kojima, I. Komarov, T. Konno, A. Korobov, S.

Korpar, N. Kovalchuk, E. Kovalenko, R. Kowalewski, T. M. G. Kraetzschmar, F. Krinner,

P. Kriˇzan, R. Kroeger, J. F. Krohn, P. Krokovny, H. Kr¨uger, W. Kuehn, T. Kuhr, J.

Kumar, M. Kumar, R. Kumar, K. Kumara, T. Kumita, T. Kunigo, M. K¨unzel, S. Kurz, A.

Kuzmin, P. Kvasniˇcka, Y.-J. Kwon, S. Lacaprara, Y.-T. Lai, C. La Licata, K. Lalwani, T.

Lam, L. Lanceri, J. S. Lange, M. Laurenza, K. Lautenbach, P. J. Laycock, R. Leboucher,

F. R. Le Diberder, I.-S. Lee, S. C. Lee, P. Leitl, D. Levit, P. M. Lewis, C. Li, L. K. Li, S.

X. Li, Y. B. Li, J. Libby, K. Lieret, J. Lin, Z. Liptak, Q. Y. Liu, Z. A. Liu, D. Liventsev,

S. Longo, A. Loos, A. Lozar, P. Lu, T. Lueck, F. Luetticke, T. Luo, C. Lyu, C. MacQueen,

M. Maggiora, R. Maiti, S. Maity, R. Manfredi, E. Manoni, A. Manthei, S. Marcello, C.

Marinas, L. Martel, A. Martini, L. Massaccesi, M. Masuda, T. Matsuda, K. Matsuoka, D.

Matvienko, J. A. McKenna, J. McNeil, F. Meggendorfer, F. Meier, M. Merola, F. Metzner,

M. Milesi, C. Miller, K. Miyabayashi, H. Miyake, H. Miyata, R. Mizuk, K. Azmi, G. B.

Mohanty, N. Molina-Gonzalez, S. Moneta, H. Moon, T. Moon, J. A. Mora Grimaldo, T.

Morii, H.-G. Moser, M. Mrvar, F. J. M¨uller, Th. Muller, G. Muroyama, C. Murphy, R.

Mussa, I. Nakamura, K. R. Nakamura, E. Nakano, M. Nakao, H. Nakayama, H. Nakazawa,

A. Narimani Charan, M. Naruki, Z. Natkaniec, A. Natochii, L. Nayak, M. Nayak, G.

Nazaryan, D. Neverov, C. Niebuhr, M. Niiyama, J. Ninkovic, N. K. Nisar, S. Nishida, K.

Nishimura, M. H. A. Nouxman, K. Ogawa, S. Ogawa, S. L. Olsen, Y. Onishchuk, H. Ono,

Y. Onuki, P. Oskin, F. Otani, E. R. Oxford, H. Ozaki, P. Pakhlov, G. Pakhlova, A.

Paladino, T. Pang, A. Panta, E. Paoloni, S. Pardi, K. Parham, H. Park, S.-H. Park,

B. Paschen, A. Passeri, A. Pathak, S. Patra, S. Paul, T. K. Pedlar, I. Peruzzi, R.

Peschke, R. Pestotnik, F. Pham, M. Piccolo, L. E. Piilonen, G. Pinna Angioni, P. L. M.

Podesta-Lerma, T. Podobnik, S. Pokharel, L. Polat, V. Popov, C. Praz, S. Prell, E.

Prencipe, M. T. Prim, M. V. Purohit, H. Purwar, N. Rad, P. Rados, S. Raiz, A. Ramirez

Morales, R. Rasheed, N. Rauls, M. Reif, S. Reiter, M. Remnev, I. Ripp-Baudot, M. Ritter,

M. Ritzert, G. Rizzo, L. B. Rizzuto, S. H. Robertson, D. Rodr´ıguez P´erez, J. M. Roney, C.

Rosenfeld, A. Rostomyan, N. Rout, M. Rozanska, G. Russo, D. Sahoo, Y. Sakai, D. A.

Sanders, S. Sandilya, A. Sangal, L. Santelj, P. Sartori, Y. Sato, V. Savinov, B. Scavino, M.

Schnepf, M. Schram, H. Schreeck, J. Schueler, C. Schwanda, A. J. Schwartz, B. Schwenker,

M. Schwickardi, Y. Seino, A. Selce, K. Senyo, I. S. Seong, J. Serrano, M. E. Sevior, C.

Sﬁenti, V. Shebalin, C. P. Shen, H. Shibuya, T. Shillington, T. Shimasaki, J.-G. Shiu, B.

Shwartz, A. Sibidanov, F. Simon, J. B. Singh, S. Skambraks, J. Skorupa, K. Smith, R. J.

Sobie, A. Soﬀer, A. Sokolov, Y. Soloviev, E. Solovieva, S. Spataro, B. Spruck, M. Stariˇc,

S. Stefkova, Z. S. Stottler, R. Stroili, J. Strube, J. Stypula, Y. Sue, R. Sugiura, M.

Sumihama, K. Sumisawa, T. Sumiyoshi, W. Sutcliﬀe, S. Y. Suzuki, H. Svidras, M.

Tabata, M. Takahashi, M. Takizawa, U. Tamponi, S. Tanaka, K. Tanida, H. Tanigawa,

N. Taniguchi, Y. Tao, P. Taras, F. Tenchini, R. Tiwary, D. Tonelli, E. Torassa, N.

Toutounji, K. Trabelsi, I. Tsaklidis, T. Tsuboyama, N. Tsuzuki, M. Uchida, I. Ueda, S.

Uehara, Y. Uematsu, T. Ueno, T. Uglov, K. Unger, Y. Unno, K. Uno, S. Uno, P.

Urquijo, Y. Ushiroda, Y. V. Usov, S. E. Vahsen, R. van Tonder, G. S. Varner, K. E.

Varvell, A. Vinokurova, L. Vitale, V. Vobbilisetti, V. Vorobyev, A. Vossen, B. Wach,

E. Waheed, H. M. Wakeling, K. Wan, W. Wan Abdullah, B. Wang, C. H. Wang,

E. Wang, M.-Z. Wang, X. L. Wang, A. Warburton, M. Watanabe, S. Watanuki, J.

Webb, S. Wehle, M. Welsch, C. Wessel, J. Wiechczynski, P. Wieduwilt, H. Windel, E.

Won, L. J. Wu, X. P. Xu, B. D. Yabsley, S. Yamada, W. Yan, S. B. Yang, H. Ye,

J. Yelton, J. H. Yin, M. Yonenaga, Y. M. Yook, K. Yoshihara, T. Yoshinobu, C. Z.

Yuan, Y. Yusa, L. Zani, Y. Zhai, J. Z. Zhang, Y. Zhang, Y. Zhang, Z. Zhang, V.

Zhilich, J. Zhou, Q. D. Zhou, X. Y. Zhou, V. I. Zhukova, V. Zhulanov, and R. ˇ

Zlebˇc´ık

(The Belle II Collaboration)

Abstract

We present an analysis of the charmless semileptonic decay B0→π−`+ν`, where `=e, µ, from

198.0 million pairs of B¯

Bmesons recorded by the Belle II detector at the SuperKEKB electron-

positron collider. The decay is reconstructed without identifying the partner Bmeson. The partial

branching fractions are measured independently for B0→π−e+νeand B0→π−µ+νµas functions

of q2(momentum transfer squared), using 3896 B0→π−e+νeand 5466 B0→π−µ+νµdecays.

The total branching fraction is found to be (1.426 ±0.056 ±0.125) ×10−4for B0→π−`+ν`decays,

where the uncertainties are statistical and systematic, respectively. By ﬁtting the measured partial

branching fractions as functions of q2, together with constraints on the nonperturbative hadronic

contribution from lattice QCD calculations, the magnitude of the Cabibbo-Kobayashi-Maskawa

matrix element Vub, (3.55 ±0.12 ±0.13 ±0.17) ×10−3, is extracted. Here, the ﬁrst uncertainty is

statistical, the second is systematic and the third is theoretical.

1. INTRODUCTION

The Cabibbo-Kobayashi-Maskawa (CKM) matrix elements are fundamental parameters

of the Standard Model (SM) of particle physics [1]. The magnitude of the matrix element

Vub can be determined by measuring the diﬀerential decay rate of B→Xu`ν events,

which is proportional to |Vub|2. Here, Xuis a charmless hadronic ﬁnal state and `is a

light charged lepton. One method to measure |Vub|is inclusive, where no speciﬁc Xuﬁnal

state is reconstructed, but rather the sum of all possible ﬁnal states is analysed. This is

in contrast to the exclusive method in which a speciﬁc ﬁnal state is studied. The two

methods have complementary uncertainties introduced by theoretical QCD descriptions. In

inclusive decays, these descriptions involve the calculation of the total semileptonic rate,

while in the exclusive case they take the form of parameterizations of the low-energy strong

interactions (form factors). However, the results for |Vub|obtained by the two methods

diﬀer signiﬁcantly [2]. In order to resolve this disagreement, further measurements using

novel approaches are beneﬁcial.

The decay B0→π−`+ν`(with charge conjugation implied throughout) is experimentally

and theoretically the most reliable mode to measure |Vub|through an exclusive channel

at the BFactories. Here, we present a study of this decay using data from the Belle II

detector located at the SuperKEKB electron-positron collider at KEK, in Japan. The signal

decay is reconstructed from decays of B0mesons in e+e−→Υ(4S)→B0B0events. The

reconstruction method employed here is called untagged since the signal lepton and pion

candidates are selected without prior reconstruction (tagging) of the partner Bmeson. This

leads to a high signal eﬃciency, but also a low purity due to higher combinatorial background

from the partner Bmeson and increased backgrounds from e+e−collisions that produce light

quark pair (continuum) events.

The events are separated into six disjoint intervals (bins) of squared momentum transfer

from the Bmeson to the pion, q2. After selecting signal events and suppressing backgrounds,

the signal yields are extracted from an extended likelihood ﬁt to the binned two-dimensional

distribution of the energy diﬀerence ∆E, and the beam-constrained mass Mbc, both deﬁned

below, in bins of q2. Theoretical form-factor predictions from lattice QCD are combined

with the measured diﬀerential branching fractions to determine |Vub|[3].

2. DETECTOR, DATA SET AND SIMULATION

2.1. Belle II detector

The Belle II detector [4] is located at the SuperKEKB [5] asymmetric-energy electron-

positron collider, running at or slightly below the Υ(4S) resonance energy. The detector

is composed of subdetectors arranged around the collision point in a cylindrical geometry.

The longitudinal direction is deﬁned by the z-axis, which points approximately along the

electron-beam direction, while the transverse plane is deﬁned by the x- and y-axes, which

point radially out of the detector ring. A superconducting magnet producing a uniform

1.5 T magnetic ﬁeld oriented along the detector axis is installed outside all but the last

subdetector. Particles produced at the interaction point ﬁrst traverse the vertex detector

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BELLE2-CONF-PH-2022-017November7,2022DeterminationofjVubjfromuntaggedB0!`+`decaysusing2019-2021BelleIIdata(TheBelleIICollaboration)F.Abudinen,I.Adachi,K.Adamczyk,L.Aggarwal,P.Ahlburg,H.Ahmed,J.K.Ahn,H.Aihara,N.Akopov,A.Aloisio,F.Ameli,L.Andricek,N.AnhKy,D.M.Asner,H.Atmacan,V.Aulchenko,T.Aushev,V....

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