Search for $\boldsymbol{B\to h\nu\bar{\nu}}$ decays with semileptonic tagging at Belle
The Belle Collaboration: J. Grygier, P. Goldenzweig, M. Heck, I., Adachi, H. Aihara, S. Al Said, D. M. Asner, T. Aushev, R. Ayad, T. Aziz, V., Babu, I. Badhrees, S. Bahinipati, A. M. Bakich, V. Bansal, E. Barberio, P., Behera, B. Bhuyan, J. Biswal, A. Bobrov, A. Bondar

TL;DR
This study searches for rare B meson decays involving neutrinos using semileptonic tagging at Belle, setting the most stringent upper limits to date due to no significant signals observed.
Contribution
First search for B→hνν̄ decays with semileptonic tagging at Belle, providing the most restrictive upper limits on these branching fractions.
Findings
No significant signals observed in any decay channel.
Set the world's most stringent upper limits on branching fractions.
Enhanced sensitivity compared to previous searches.
Abstract
We present the results of a search for the rare decays , where stands for and . The results are obtained with pairs collected with the Belle detector at the KEKB collider. We reconstruct one meson in a semileptonic decay and require a single meson but nothing else on the signal side. We observe no significant signal and set upper limits on the branching fractions. The limits set on the , , , , , and channels are the world's most stringent.
| Channel | Observed signal yield | Significance | ||||||
|---|---|---|---|---|---|---|---|---|
| \IfEqCase321 32131032333213310313211111213113[] | ||||||||
| \IfEqCase310 32131032333213310313211111213113[] | ||||||||
| \IfEqCase323 32131032333213310313211111213113[] | ||||||||
| \IfEqCase313 32131032333213310313211111213113[] | ||||||||
| \IfEqCase211 32131032333213310313211111213113[] | ||||||||
| \IfEqCase111 32131032333213310313211111213113[] | ||||||||
| \IfEqCase213 32131032333213310313211111213113[] | ||||||||
| \IfEqCase113 32131032333213310313211111213113[] | ||||||||
| Channel | Observed signal yield | Significance | ||||||
|---|---|---|---|---|---|---|---|---|
| \IfEqCase321 32131032333213310313211111213113[] | ||||||||
| \IfEqCase310 32131032333213310313211111213113[] | ||||||||
| \IfEqCase323 32131032333213310313211111213113[] | ||||||||
| \IfEqCase313 32131032333213310313211111213113[] | ||||||||
| \IfEqCase211 32131032333213310313211111213113[] | ||||||||
| \IfEqCase111 32131032333213310313211111213113[] | ||||||||
| \IfEqCase213 32131032333213310313211111213113[] | ||||||||
| \IfEqCase113 32131032333213310313211111213113[] | ||||||||
| Channel | Efficiency | Expected limit | Observed limit |
|---|---|---|---|
| \IfEqCase321 32131032333213310313211111213113[] | \IfEqCase310 32131032333213310313211111213113[] | \IfEqCase323 32131032333213310313211111213113[] | \IfEqCase313 32131032333213310313211111213113[] | \IfEqCase211 32131032333213310313211111213113[] | \IfEqCase111 32131032333213310313211111213113[] | \IfEqCase213 32131032333213310313211111213113[] | \IfEqCase113 32131032333213310313211111213113[] | |
| veto | 0.2 | 0.2 | 0.1 | 0.2 | 0.6 | 0.4 | 0.6 | 0.0 |
| Fixed fractions | 0.4 | 0.3 | 0.1 | 0.2 | 1.3 | 0.1 | 0.1 | 1.0 |
| Continuum scaling | 2.0 | 0.0 | 0.0 | 0.0 | 3.1 | 0.0 | 0.0 | 0.0 |
| Tag efficiency correction | 0.5 | 0.2 | 0.1 | 0.1 | 1.9 | 0.1 | 0.2 | 0.5 |
| Shape uncertainty | 2.6 | 1.3 | 1.8 | 1.7 | 4.5 | 1.5 | 2.3 | 3.4 |
| Fit bias | 0.2 | 0.1 | 0.2 | 0.1 | 0.2 | 0.1 | 0.2 | 0.2 |
| Total | 3.4 | 1.4 | 1.8 | 1.8 | 5.9 | 1.6 | 2.4 | 3.6 |
Peer Reviews
No public reviews on file for this paper yet. If you reviewed it on a platform where reviews are public (OpenReview, ICLR, NeurIPS, ICML), you can paste yours below so the community can read it here.
Videos
No videos yet. Explain this paper in a talk, walkthrough, or lecture? Add one.
The Belle Collaboration
Belle Preprint 2017-10
KEK Preprint 2017-6
Search for \boldsymbol{\IfEqCase{0}{{321}{\mbox{\boldsymbol{B^{+}\to K^{+}\nu\mathrm{bar}{\nu}}}}{310}{\mbox{\boldsymbol{B^{0}{\phantom{+}}\to K{\text{S}}^{0}>\nu\mathrm{bar}{\nu}}}}{323}{\mbox{\boldsymbol{B^{+}\to{K^{\ast}}^{+}\nu\mathrm{bar}{\nu}}}}{3321}{\mbox{\boldsymbol{B^{+}\to{K^{\ast}}^{+}\left(\to K^{+}\pi^{0}\right)\nu\mathrm{bar}{\nu}}}}{3310}{\mbox{\boldsymbol{B^{+}\to{K^{\ast}}^{+}\left(\to K_{\text{S}}^{0}>\pi^{+}\right)\nu\mathrm{bar}{\nu}}}}{313}{\mbox{\boldsymbol{B^{0}{\phantom{+}}\to{K^{\ast}}^{0}\nu\mathrm{bar}{\nu}}}}{211}{\mbox{\boldsymbol{B^{+}\to\pi^{+}\nu\mathrm{bar}{\nu}}}}{111}{\mbox{\boldsymbol{B^{0}{\phantom{+}}\to\pi^{0}\nu\mathrm{bar}{\nu}}}}{213}{\mbox{\boldsymbol{B^{+}\to\rho^{+}\nu\mathrm{bar}{\nu}}}}{113}{\mbox{\boldsymbol{B^{0}_{\phantom{+}}\to\rho^{0}\nu\mathrm{bar}{\nu}}}}}[B\to h\nu\mathrm{bar}{\nu}]} decays with semileptonic tagging at Belle
J. Grygier
Institut für Experimentelle Kernphysik, Karlsruher Institut für Technologie, 76131 Karlsruhe
P. Goldenzweig
Institut für Experimentelle Kernphysik, Karlsruher Institut für Technologie, 76131 Karlsruhe
M. Heck
Institut für Experimentelle Kernphysik, Karlsruher Institut für Technologie, 76131 Karlsruhe
I. Adachi
High Energy Accelerator Research Organization (KEK), Tsukuba 305-0801
SOKENDAI (The Graduate University for Advanced Studies), Hayama 240-0193
H. Aihara
Department of Physics, University of Tokyo, Tokyo 113-0033
S. Al Said
Department of Physics, Faculty of Science, University of Tabuk, Tabuk 71451
Department of Physics, Faculty of Science, King Abdulaziz University, Jeddah 21589
D. M. Asner
Pacific Northwest National Laboratory, Richland, Washington 99352
T. Aushev
Moscow Institute of Physics and Technology, Moscow Region 141700
R. Ayad
Department of Physics, Faculty of Science, University of Tabuk, Tabuk 71451
T. Aziz
Tata Institute of Fundamental Research, Mumbai 400005
V. Babu
Tata Institute of Fundamental Research, Mumbai 400005
I. Badhrees
Department of Physics, Faculty of Science, University of Tabuk, Tabuk 71451
King Abdulaziz City for Science and Technology, Riyadh 11442
S. Bahinipati
Indian Institute of Technology Bhubaneswar, Satya Nagar 751007
A. M. Bakich
School of Physics, University of Sydney, New South Wales 2006
V. Bansal
Pacific Northwest National Laboratory, Richland, Washington 99352
E. Barberio
School of Physics, University of Melbourne, Victoria 3010
P. Behera
Indian Institute of Technology Madras, Chennai 600036
B. Bhuyan
Indian Institute of Technology Guwahati, Assam 781039
J. Biswal
J. Stefan Institute, 1000 Ljubljana
A. Bobrov
Budker Institute of Nuclear Physics SB RAS, Novosibirsk 630090
Novosibirsk State University, Novosibirsk 630090
A. Bondar
Budker Institute of Nuclear Physics SB RAS, Novosibirsk 630090
Novosibirsk State University, Novosibirsk 630090
G. Bonvicini
Wayne State University, Detroit, Michigan 48202
A. Bozek
H. Niewodniczanski Institute of Nuclear Physics, Krakow 31-342
M. Bračko
University of Maribor, 2000 Maribor
J. Stefan Institute, 1000 Ljubljana
T. E. Browder
University of Hawaii, Honolulu, Hawaii 96822
D. Červenkov
Faculty of Mathematics and Physics, Charles University, 121 16 Prague
P. Chang
Department of Physics, National Taiwan University, Taipei 10617
V. Chekelian
Max-Planck-Institut für Physik, 80805 München
A. Chen
National Central University, Chung-li 32054
B. G. Cheon
Hanyang University, Seoul 133-791
K. Chilikin
P.N. Lebedev Physical Institute of the Russian Academy of Sciences, Moscow 119991
Moscow Physical Engineering Institute, Moscow 115409
R. Chistov
P.N. Lebedev Physical Institute of the Russian Academy of Sciences, Moscow 119991
Moscow Physical Engineering Institute, Moscow 115409
K. Cho
Korea Institute of Science and Technology Information, Daejeon 305-806
Y. Choi
Sungkyunkwan University, Suwon 440-746
D. Cinabro
Wayne State University, Detroit, Michigan 48202
N. Dash
Indian Institute of Technology Bhubaneswar, Satya Nagar 751007
S. Di Carlo
Wayne State University, Detroit, Michigan 48202
Z. Doležal
Faculty of Mathematics and Physics, Charles University, 121 16 Prague
Z. Drásal
Faculty of Mathematics and Physics, Charles University, 121 16 Prague
D. Dutta
Tata Institute of Fundamental Research, Mumbai 400005
S. Eidelman
Budker Institute of Nuclear Physics SB RAS, Novosibirsk 630090
Novosibirsk State University, Novosibirsk 630090
H. Farhat
Wayne State University, Detroit, Michigan 48202
J. E. Fast
Pacific Northwest National Laboratory, Richland, Washington 99352
T. Ferber
Deutsches Elektronen–Synchrotron, 22607 Hamburg
B. G. Fulsom
Pacific Northwest National Laboratory, Richland, Washington 99352
V. Gaur
Tata Institute of Fundamental Research, Mumbai 400005
N. Gabyshev
Budker Institute of Nuclear Physics SB RAS, Novosibirsk 630090
Novosibirsk State University, Novosibirsk 630090
A. Garmash
Budker Institute of Nuclear Physics SB RAS, Novosibirsk 630090
Novosibirsk State University, Novosibirsk 630090
M. Gelb
Institut für Experimentelle Kernphysik, Karlsruher Institut für Technologie, 76131 Karlsruhe
R. Gillard
Wayne State University, Detroit, Michigan 48202
B. Golob
Faculty of Mathematics and Physics, University of Ljubljana, 1000 Ljubljana
J. Stefan Institute, 1000 Ljubljana
O. Grzymkowska
H. Niewodniczanski Institute of Nuclear Physics, Krakow 31-342
E. Guido
INFN - Sezione di Torino, 10125 Torino
J. Haba
High Energy Accelerator Research Organization (KEK), Tsukuba 305-0801
SOKENDAI (The Graduate University for Advanced Studies), Hayama 240-0193
T. Hara
High Energy Accelerator Research Organization (KEK), Tsukuba 305-0801
SOKENDAI (The Graduate University for Advanced Studies), Hayama 240-0193
K. Hayasaka
Niigata University, Niigata 950-2181
H. Hayashii
Nara Women’s University, Nara 630-8506
M. T. Hedges
University of Hawaii, Honolulu, Hawaii 96822
C.-L. Hsu
School of Physics, University of Melbourne, Victoria 3010
T. Iijima
Kobayashi-Maskawa Institute, Nagoya University, Nagoya 464-8602
Graduate School of Science, Nagoya University, Nagoya 464-8602
K. Inami
Graduate School of Science, Nagoya University, Nagoya 464-8602
G. Inguglia
Deutsches Elektronen–Synchrotron, 22607 Hamburg
A. Ishikawa
Department of Physics, Tohoku University, Sendai 980-8578
R. Itoh
High Energy Accelerator Research Organization (KEK), Tsukuba 305-0801
SOKENDAI (The Graduate University for Advanced Studies), Hayama 240-0193
Y. Iwasaki
High Energy Accelerator Research Organization (KEK), Tsukuba 305-0801
W. W. Jacobs
Indiana University, Bloomington, Indiana 47408
I. Jaegle
University of Florida, Gainesville, Florida 32611
H. B. Jeon
Kyungpook National University, Daegu 702-701
Y. Jin
Department of Physics, University of Tokyo, Tokyo 113-0033
D. Joffe
Kennesaw State University, Kennesaw, Georgia 30144
K. K. Joo
Chonnam National University, Kwangju 660-701
T. Julius
School of Physics, University of Melbourne, Victoria 3010
J. Kahn
Ludwig Maximilians University, 80539 Munich
A. B. Kaliyar
Indian Institute of Technology Madras, Chennai 600036
K. H. Kang
Kyungpook National University, Daegu 702-701
G. Karyan
Deutsches Elektronen–Synchrotron, 22607 Hamburg
P. Katrenko
Moscow Institute of Physics and Technology, Moscow Region 141700
P.N. Lebedev Physical Institute of the Russian Academy of Sciences, Moscow 119991
T. Kawasaki
Niigata University, Niigata 950-2181
T. Keck
Institut für Experimentelle Kernphysik, Karlsruher Institut für Technologie, 76131 Karlsruhe
H. Kichimi
High Energy Accelerator Research Organization (KEK), Tsukuba 305-0801
C. Kiesling
Max-Planck-Institut für Physik, 80805 München
D. Y. Kim
Soongsil University, Seoul 156-743
H. J. Kim
Kyungpook National University, Daegu 702-701
J. B. Kim
Korea University, Seoul 136-713
K. T. Kim
Korea University, Seoul 136-713
M. J. Kim
Kyungpook National University, Daegu 702-701
S. H. Kim
Hanyang University, Seoul 133-791
K. Kinoshita
University of Cincinnati, Cincinnati, Ohio 45221
P. Kodyš
Faculty of Mathematics and Physics, Charles University, 121 16 Prague
S. Korpar
University of Maribor, 2000 Maribor
J. Stefan Institute, 1000 Ljubljana
D. Kotchetkov
University of Hawaii, Honolulu, Hawaii 96822
P. Križan
Faculty of Mathematics and Physics, University of Ljubljana, 1000 Ljubljana
J. Stefan Institute, 1000 Ljubljana
P. Krokovny
Budker Institute of Nuclear Physics SB RAS, Novosibirsk 630090
Novosibirsk State University, Novosibirsk 630090
T. Kuhr
Ludwig Maximilians University, 80539 Munich
R. Kulasiri
Kennesaw State University, Kennesaw, Georgia 30144
T. Kumita
Tokyo Metropolitan University, Tokyo 192-0397
A. Kuzmin
Budker Institute of Nuclear Physics SB RAS, Novosibirsk 630090
Novosibirsk State University, Novosibirsk 630090
Y.-J. Kwon
Yonsei University, Seoul 120-749
J. S. Lange
Justus-Liebig-Universität Gießen, 35392 Gießen
C. H. Li
School of Physics, University of Melbourne, Victoria 3010
L. Li
University of Science and Technology of China, Hefei 230026
Y. Li
Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061
L. Li Gioi
Max-Planck-Institut für Physik, 80805 München
J. Libby
Indian Institute of Technology Madras, Chennai 600036
D. Liventsev
Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061
High Energy Accelerator Research Organization (KEK), Tsukuba 305-0801
M. Lubej
J. Stefan Institute, 1000 Ljubljana
T. Luo
University of Pittsburgh, Pittsburgh, Pennsylvania 15260
M. Masuda
Earthquake Research Institute, University of Tokyo, Tokyo 113-0032
T. Matsuda
University of Miyazaki, Miyazaki 889-2192
D. Matvienko
Budker Institute of Nuclear Physics SB RAS, Novosibirsk 630090
Novosibirsk State University, Novosibirsk 630090
F. Metzner
Institut für Experimentelle Kernphysik, Karlsruher Institut für Technologie, 76131 Karlsruhe
K. Miyabayashi
Nara Women’s University, Nara 630-8506
H. Miyake
High Energy Accelerator Research Organization (KEK), Tsukuba 305-0801
SOKENDAI (The Graduate University for Advanced Studies), Hayama 240-0193
H. Miyata
Niigata University, Niigata 950-2181
R. Mizuk
P.N. Lebedev Physical Institute of the Russian Academy of Sciences, Moscow 119991
Moscow Physical Engineering Institute, Moscow 115409
Moscow Institute of Physics and Technology, Moscow Region 141700
G. B. Mohanty
Tata Institute of Fundamental Research, Mumbai 400005
H. K. Moon
Korea University, Seoul 136-713
T. Mori
Graduate School of Science, Nagoya University, Nagoya 464-8602
R. Mussa
INFN - Sezione di Torino, 10125 Torino
E. Nakano
Osaka City University, Osaka 558-8585
M. Nakao
High Energy Accelerator Research Organization (KEK), Tsukuba 305-0801
SOKENDAI (The Graduate University for Advanced Studies), Hayama 240-0193
T. Nanut
J. Stefan Institute, 1000 Ljubljana
K. J. Nath
Indian Institute of Technology Guwahati, Assam 781039
Z. Natkaniec
H. Niewodniczanski Institute of Nuclear Physics, Krakow 31-342
M. Nayak
Wayne State University, Detroit, Michigan 48202
High Energy Accelerator Research Organization (KEK), Tsukuba 305-0801
N. K. Nisar
University of Pittsburgh, Pittsburgh, Pennsylvania 15260
S. Nishida
High Energy Accelerator Research Organization (KEK), Tsukuba 305-0801
SOKENDAI (The Graduate University for Advanced Studies), Hayama 240-0193
S. Ogawa
Toho University, Funabashi 274-8510
S. Okuno
Kanagawa University, Yokohama 221-8686
H. Ono
Nippon Dental University, Niigata 951-8580
Niigata University, Niigata 950-2181
Y. Onuki
Department of Physics, University of Tokyo, Tokyo 113-0033
G. Pakhlova
P.N. Lebedev Physical Institute of the Russian Academy of Sciences, Moscow 119991
Moscow Institute of Physics and Technology, Moscow Region 141700
B. Pal
University of Cincinnati, Cincinnati, Ohio 45221
C.-S. Park
Yonsei University, Seoul 120-749
C. W. Park
Sungkyunkwan University, Suwon 440-746
H. Park
Kyungpook National University, Daegu 702-701
S. Paul
Department of Physics, Technische Universität München, 85748 Garching
T. K. Pedlar
Luther College, Decorah, Iowa 52101
L. Pesántez
University of Bonn, 53115 Bonn
L. E. Piilonen
Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061
M. Prim
Institut für Experimentelle Kernphysik, Karlsruher Institut für Technologie, 76131 Karlsruhe
C. Pulvermacher
High Energy Accelerator Research Organization (KEK), Tsukuba 305-0801
M. Ritter
Ludwig Maximilians University, 80539 Munich
A. Rostomyan
Deutsches Elektronen–Synchrotron, 22607 Hamburg
Y. Sakai
High Energy Accelerator Research Organization (KEK), Tsukuba 305-0801
SOKENDAI (The Graduate University for Advanced Studies), Hayama 240-0193
S. Sandilya
University of Cincinnati, Cincinnati, Ohio 45221
L. Santelj
High Energy Accelerator Research Organization (KEK), Tsukuba 305-0801
T. Sanuki
Department of Physics, Tohoku University, Sendai 980-8578
Y. Sato
Graduate School of Science, Nagoya University, Nagoya 464-8602
V. Savinov
University of Pittsburgh, Pittsburgh, Pennsylvania 15260
T. Schlüter
Ludwig Maximilians University, 80539 Munich
O. Schneider
École Polytechnique Fédérale de Lausanne (EPFL), Lausanne 1015
G. Schnell
University of the Basque Country UPV/EHU, 48080 Bilbao
IKERBASQUE, Basque Foundation for Science, 48013 Bilbao
C. Schwanda
Institute of High Energy Physics, Vienna 1050
A. J. Schwartz
University of Cincinnati, Cincinnati, Ohio 45221
Y. Seino
Niigata University, Niigata 950-2181
K. Senyo
Yamagata University, Yamagata 990-8560
I. S. Seong
University of Hawaii, Honolulu, Hawaii 96822
M. E. Sevior
School of Physics, University of Melbourne, Victoria 3010
V. Shebalin
Budker Institute of Nuclear Physics SB RAS, Novosibirsk 630090
Novosibirsk State University, Novosibirsk 630090
C. P. Shen
Beihang University, Beijing 100191
T.-A. Shibata
Tokyo Institute of Technology, Tokyo 152-8550
J.-G. Shiu
Department of Physics, National Taiwan University, Taipei 10617
B. Shwartz
Budker Institute of Nuclear Physics SB RAS, Novosibirsk 630090
Novosibirsk State University, Novosibirsk 630090
F. Simon
Max-Planck-Institut für Physik, 80805 München
Excellence Cluster Universe, Technische Universität München, 85748 Garching
E. Solovieva
P.N. Lebedev Physical Institute of the Russian Academy of Sciences, Moscow 119991
Moscow Institute of Physics and Technology, Moscow Region 141700
M. Starič
J. Stefan Institute, 1000 Ljubljana
J. F. Strube
Pacific Northwest National Laboratory, Richland, Washington 99352
T. Sumiyoshi
Tokyo Metropolitan University, Tokyo 192-0397
M. Takizawa
Showa Pharmaceutical University, Tokyo 194-8543
J-PARC Branch, KEK Theory Center, High Energy Accelerator Research Organization (KEK), Tsukuba 305-0801
Theoretical Research Division, Nishina Center, RIKEN, Saitama 351-0198
U. Tamponi
INFN - Sezione di Torino, 10125 Torino
University of Torino, 10124 Torino
F. Tenchini
School of Physics, University of Melbourne, Victoria 3010
K. Trabelsi
High Energy Accelerator Research Organization (KEK), Tsukuba 305-0801
SOKENDAI (The Graduate University for Advanced Studies), Hayama 240-0193
T. Tsuboyama
High Energy Accelerator Research Organization (KEK), Tsukuba 305-0801
SOKENDAI (The Graduate University for Advanced Studies), Hayama 240-0193
M. Uchida
Tokyo Institute of Technology, Tokyo 152-8550
T. Uglov
P.N. Lebedev Physical Institute of the Russian Academy of Sciences, Moscow 119991
Moscow Institute of Physics and Technology, Moscow Region 141700
Y. Unno
Hanyang University, Seoul 133-791
S. Uno
High Energy Accelerator Research Organization (KEK), Tsukuba 305-0801
SOKENDAI (The Graduate University for Advanced Studies), Hayama 240-0193
P. Urquijo
School of Physics, University of Melbourne, Victoria 3010
Y. Ushiroda
High Energy Accelerator Research Organization (KEK), Tsukuba 305-0801
SOKENDAI (The Graduate University for Advanced Studies), Hayama 240-0193
C. Van Hulse
University of the Basque Country UPV/EHU, 48080 Bilbao
G. Varner
University of Hawaii, Honolulu, Hawaii 96822
V. Vorobyev
Budker Institute of Nuclear Physics SB RAS, Novosibirsk 630090
Novosibirsk State University, Novosibirsk 630090
A. Vossen
Indiana University, Bloomington, Indiana 47408
E. Waheed
School of Physics, University of Melbourne, Victoria 3010
B. Wang
University of Cincinnati, Cincinnati, Ohio 45221
C. H. Wang
National United University, Miao Li 36003
M.-Z. Wang
Department of Physics, National Taiwan University, Taipei 10617
P. Wang
Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049
M. Watanabe
Niigata University, Niigata 950-2181
Y. Watanabe
Kanagawa University, Yokohama 221-8686
S. Wehle
Deutsches Elektronen–Synchrotron, 22607 Hamburg
K. M. Williams
Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061
E. Won
Korea University, Seoul 136-713
H. Yamamoto
Department of Physics, Tohoku University, Sendai 980-8578
Y. Yamashita
Nippon Dental University, Niigata 951-8580
H. Ye
Deutsches Elektronen–Synchrotron, 22607 Hamburg
Y. Yook
Yonsei University, Seoul 120-749
C. Z. Yuan
Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049
Y. Yusa
Niigata University, Niigata 950-2181
Z. P. Zhang
University of Science and Technology of China, Hefei 230026
V. Zhilich
Budker Institute of Nuclear Physics SB RAS, Novosibirsk 630090
Novosibirsk State University, Novosibirsk 630090
V. Zhukova
Moscow Physical Engineering Institute, Moscow 115409
V. Zhulanov
Budker Institute of Nuclear Physics SB RAS, Novosibirsk 630090
Novosibirsk State University, Novosibirsk 630090
M. Ziegler
Institut für Experimentelle Kernphysik, Karlsruher Institut für Technologie, 76131 Karlsruhe
A. Zupanc
Faculty of Mathematics and Physics, University of Ljubljana, 1000 Ljubljana
J. Stefan Institute, 1000 Ljubljana
Abstract
We present the results of a search for the rare decays \IfEqCase0 32131032333213310313211111213113[] , where h stands for and . The results are obtained with pairs collected with the Belle detector at the KEKB collider. We reconstruct one meson in a semileptonic decay and require a single meson but nothing else on the signal side. We observe no significant signal and set upper limits on the branching fractions. The limits set on the \IfEqCase310 32131032333213310313211111213113[] , \IfEqCase313 32131032333213310313211111213113[] , \IfEqCase211 32131032333213310313211111213113[] , \IfEqCase111 32131032333213310313211111213113[] , \IfEqCase213 32131032333213310313211111213113[] , and \IfEqCase113 32131032333213310313211111213113[] channels are the world’s most stringent.
pacs:
13.25.Hw, 12.15.Mm, 14.40.Nd
The decays \IfEqCase0 32131032333213310313211111213113[] [1] can proceed only via a penguin or a box diagram at leading order in the standard model (SM), as shown in Fig. 1, and are thus highly suppressed [2]. Theoretical calculations for the branching fractions cover the range from [3] ( \IfEqCase111 32131032333213310313211111213113[] ) to [2] ( \IfEqCase323 32131032333213310313211111213113[] ). Recent results by LHCb [4, 5] show evidence for a deviation of experimental data from expected values in the angular observable in decays, and in the ratio of the to branching fractions. A measurement of by Belle [6] is compatible with both, the SM prediction and the LHCb result. Different new physics models proposed to explain these observations can also influence decays. Therefore, \IfEqCase0 32131032333213310313211111213113[] channels provide an important test for any model proposed to solve these tensions. Additionally, \IfEqCase0 32131032333213310313211111213113[] channels are theoretically clean due to the mediation of the transition by a boson alone, in contrast to decays [2] where the photon contributes.
\IfEqCase
0 32131032333213310313211111213113[] decays have been studied previously by Belle with a hadronic tagging algorithm [7], and by BaBar utilizing both hadronic [8] and semileptonic tagging [9]. Recent results by Belle [10] have shown that the usage of semileptonic tagging enhances the sensitivity of some analyses significantly. The semileptonically tagged sample provides a statistically independent and more efficiently tagged data set of reconstructed events as compared to the hadronically tagged sample.
We search for \IfEqCase0 32131032333213310313211111213113[] decays with the full Belle data sample produced by the KEKB collider [11] at the center-of-mass (CM) energy with an integrated luminosity of , corresponding to pairs. A data set of taken at an energy below the resonance energy is used to study background from processes (continuum), where . We refer to this data set as the off-resonance sample. We model the decays with the EVTGEN package [12] and simulate the detector response with the GEANT3 package [13]. We include a randomly-triggered sample to account for beam-related background. The signal process is modeled according to three-body phase space.
The Belle detector [14] is a large-solid-angle magnetic spectrometer that consists of a silicon vertex detector (SVD), a 50-layer central drift chamber (CDC), an array of aerogel threshold Cherenkov counters (ACC), a barrel-like arrangement of time-of-flight scintillation counters (TOF), and an electromagnetic calorimeter comprised of CsI(Tl) crystals (ECL) located inside a super-conducting solenoid coil that provides a 1.5 T magnetic field. An iron flux-return located outside of the coil is instrumented to detect mesons and to identify muons (KLM). The detector is described in detail elsewhere [14]. Two inner detector configurations were used. A 2.0 cm beampipe and a 3-layer silicon vertex detector were used for the first sample of pairs, while a 1.5 cm beampipe, a 4-layer silicon detector and a small-cell inner drift chamber were used to record the remaining pairs [15].
The three-body \IfEqCase0 32131032333213310313211111213113[] decay, with two invisible particles in the final state, does not convey sufficient kinematic information to isolate the signal. Thus, we first reconstruct the accompanying meson in the semileptonic decay channels (), where neutral (charged) candidates are reconstructed in 10 (7) different decay channels. This amounts to 108 different decay channels. The tagging algorithm, described elsewhere [16, 17], uses multiple instances of neural network classifiers built using the NeuroBayes package [18] in a hierarchical approach to find candidates. The output of the neural network used to identify real candidates transformed into the interval is referred to as and can be interpreted as the probability of the meson to be a true in a generic sample. We combine candidates with our signal selection to form signal event candidates. We separate charged pion and kaon candidates based on particle identification (PID) selection criteria utilizing CDC, ACC and TOF information. We combine the PID information in a likelihood ratio , where is a function of the polar angle and the momentum of the track in the laboratory system. We require for candidates. The kaon (pion) identification efficiency is with a misidentification probability of .
We reduce the number of poor quality tracks by requiring that , where () is the distances of closest approach of a track to the interaction point along (transverse to) the axis, which is antiparallel to the positron beam. Signal daughter candidates are reconstructed through the decays , and , , , , and . candidates are selected following Ref. [19]. Photons used for reconstruction are required to have a minimal energy of for the barrel (), forward (), and backward () region of the ECL, respectively, where is taken with respect to the axis. The invariant mass of the two candidates is required to fulfill , while the invariant mass of the () candidates is required to be within of the nominal mass from Ref. [20]. The mass requirements are subsequently optimized using Monte Carlo (MC) simulations by maximizing the figure of merit , where is the number of correctly reconstructed mesons and the number of fake candidates, both passing the requirement. We combine a candidate with the reconstructed signal- decay product ( ) to form an candidate.
Events with additional charged tracks or candidates that satisfy our selection criteria are rejected. Furthermore, we remove events with two or more tracks not fulfilling our requirement on or “raw tracks.” We veto events with reconstructed candidates and weight our background simulations to account for known data–MC differences, as described in Ref. [21]. An important variable to identify correctly–reconstructed signal events is the extra energy, . We sum all ECL clusters not used in the reconstruction of the candidate, not associated with a track, and fulfilling the same energy requirements as the clusters used to form candidates. We require . We also require the momentum of the candidate in the CM system to fulfill , the missing energy in the CM system , the momentum of the lepton candidate in the CM system , and a minimal tag quality of . These requirements are motivated by kinematic boundaries, data–MC differences in case of low–momentum , and badly reconstructed tag candidates. To suppress pions from decays misreconstructed as muons, we veto events where the invariant mass of the () candidate and the tag–side lepton fulfill . The channel–dependent fraction of events with more than one candidate can be as large as , dominated by candidate exchange between signal– and tag–side. In such cases, we select the candidate with the highest value, *i.e.*, the candidate with the highest probability of being correctly reconstructed. In MC studies, we find that the efficiency of this selection is between ( \IfEqCase213 32131032333213310313211111213113[] ) and ( \IfEqCase310 32131032333213310313211111213113[] ).
We reconstruct tagged and decays to correct for experimental data–MC efficiency differences. Both channels can be reconstructed with negligible background and are well described in MC. We bin equally in 4 (3) bins for charged (neutral) mesons and calculate the number of reconstructed events in data and MC. We assign the ratio as a weight in each bin of . This calibration includes a correction of the tagging efficiency the number of pairs produced () the branching fraction of to charged and neutral meson pairs, as we have a separate calibration for and . We train one neural network per channel to suppress continuum events. We use 16 modified Fox-Wolfram moments [22], nine CLEO cones [23], the cosine of the angle of the thrust axis relative to the axis, and the angle of the momentum of the candidate with respect to the axis. We refer to the output of this neural network as .
To optimally separate signal from background, another neural network is trained for each reconstructed channel. We optimize the requirement on the network output ( ) by maximizing a figure-of-merit , which is independent of the signal-to-background ratio and optimized for searches [24]. Here, is the signal efficiency while denotes the number of background events passing the requirement on . Both values are determined from MC. We choose a desired significance . The most powerful variables to identify the signal are , , the cosine between the momentum of the system and the momentum of the in the CM system [25], the cosine of the angle of the missing momentum relative to the axis, the cosine of the angle of the thrust axis, , and, for the and channels, the reconstructed invariant mass. The number of input variables varies for each channel, spanning a range from 17 to 31.
We evaluate the description of the data by our MC by looking into an sideband (), by reconstructing tagged decays, and by utilizing the off-resonance sample. We find good agreement between data and MC in the sidebands for six of the eight channels. However, we find an underestimation of continuum background in MC in the \IfEqCase321 32131032333213310313211111213113[] and the \IfEqCase211 32131032333213310313211111213113[] channels, which we correct by scaling the continuum component in the background model by the observed data–MC ratio in the off-resonance sample.
To extract the signal yield in each channel, we perform an extended binned maximum likelihood (ML) fit to the distribution. We use histogram templates to model signal as well as backgrounds from charm -decay (), charmless -decay (), and continuum. We fix the relative fractions of the background components to MC expectations and leave only the signal and the overall background yields as freely floating parameters. We perform extensive toy MC studies to estimate the sensitivity of our procedure. For this purpose, we simulate 1000 background-only samples for each channel and calculate an expected limit on the signal yield by integrating the profile likelihood up to the point where it includes of the positive region. We also simulate samples with various numbers of signal events to test for a possible bias. We find a non-negligible but modest bias in almost all investigated channels. We fit this bias with a linear function, whose slope is consistent with 1.0 and whose intercept lies between [math] and events. We correct for this bias in our fit to data.
The fit results are listed in Table 1(a); Fig. 2 shows the distributions of the data together with the fitted signal and background models. The fit yields no significant signal in any channel. The largest signal contribution is observed in the \IfEqCase323 32131032333213310313211111213113[] channel with a significance of . The significance is defined by evaluating the likelihood of the complete model and the background-only likelihood : . Both are evaluated at their respective best fitting point. We calculate the branching fraction of the -th mode by , where the reconstruction efficiency includes all daughter branching fractions. These efficiencies, along with the expected and measured confidence level (C.L.) upper limit [26] for each channel, are displayed in Table 1(b).
We estimate the uncertainty on the fixed fractions, the veto efficiency, the continuum scaling, the tagging efficiency, and the fit bias correction by refitting the data with each of these quantities varied by . We estimate the shape uncertainty by simulating 1000 toy templates obtained by drawing a random number from a Gaussian distribution with the mean and error of the respective bin of our fit model as the central value and deviation. The quantiles of the resulting distribution are used as estimators of the uncertainty. We estimate the uncertainty on the and charged track vetoes by comparing the respective efficiency differences between data and MC for the sample with and without the veto applied. We obtain a value of in both cases for charged and neutral channels alike. We evaluate the influence of the requirement on the number of raw tracks via the same sample by setting it to two and zero, respectively. We subsequently average the contributions and obtain a value of . The uncertainty on the calibration (9.6%) includes the uncertainty on the correction of (1.4%) and the uncertainty on . Based on studies using dedicated control samples, we assign , , and for the uncertainties on PID efficiency, efficiency and efficiency, respectively. The systematic uncertainty is included by convolving the likelihood function with a Gaussian with zero mean and a width equal to the square root of the quadratic sum of the additive and multiplicative error. The additive uncertainty is defined as the uncertainty on the signal yield, and contributions are summarized in Table 2. A comparison of our results with previous ones is presented in Fig. 3.
The systematic uncertainties are evaluated using independent samples of MC and data control samples for charged and neutral modes. They can therefore be considered uncorrelated. Thus, we combine charged and neutral modes by adding the negative log likelihoods. We scale the branching fraction of the neutral modes by a factor of since the lifetime difference is the only factor distinguishing charged from neutral \IfEqCase0 32131032333213310313211111213113[] decays in the SM. We subsequently repeat the calculation of the limit and obtain the following values at C.L.:
[TABLE]
Based on the values and theoretical uncertainties from Ref. [2], we also give a limit on the ratios between the measured branching fractions of and of and the respective SM prediction . We obtain values of and , respectively, where we included the theoretical uncertainty. Both values are quoted at C.L.
In summary, we report the results of a search for eight different decay channels with a pair of neutrinos in the final state, where the second is reconstructed in one of 108 semileptonic decay channels. No significant signal is observed and limits are set on the respective branching fractions at a confidence level of . The limits on the branching fraction for the \IfEqCase310 32131032333213310313211111213113[] , \IfEqCase313 32131032333213310313211111213113[] , \IfEqCase211 32131032333213310313211111213113[] , \IfEqCase111 32131032333213310313211111213113[] , \IfEqCase213 32131032333213310313211111213113[] , and \IfEqCase113 32131032333213310313211111213113[] channels are the most stringent to date. Although our analysis yields important improvements, none of these limits excludes SM predictions and all of them leave room for contributions from new physics.
We thank the KEKB group for the excellent operation of the accelerator; the KEK cryogenics group for the efficient operation of the solenoid; and the KEK computer group, the National Institute of Informatics, and the PNNL/EMSL computing group for valuable computing and SINET5 network support. We acknowledge support from the Ministry of Education, Culture, Sports, Science, and Technology (MEXT) of Japan, the Japan Society for the Promotion of Science (JSPS), and the Tau-Lepton Physics Research Center of Nagoya University; the Australian Research Council; Austrian Science Fund under Grant No. P 26794-N20; the National Natural Science Foundation of China under Contracts No. 10575109, No. 10775142, No. 10875115, No. 11175187, No. 11475187, No. 11521505 and No. 11575017; the Chinese Academy of Science Center for Excellence in Particle Physics; the Ministry of Education, Youth and Sports of the Czech Republic under Contract No. LTT17020; the Carl Zeiss Foundation, the Deutsche Forschungsgemeinschaft, the Excellence Cluster Universe, and the VolkswagenStiftung; the Department of Science and Technology of India; the Istituto Nazionale di Fisica Nucleare of Italy; the WCU program of the Ministry of Education, National Research Foundation (NRF) of Korea Grants No. 2011-0029457, No. 2012-0008143, No. 2014R1A2A2A01005286, No. 2014R1A2A2A01002734, No. 2015R1A2A2A01003280, No. 2015H1A2A1033649, No. 2016R1D1A1B01010135, No. 2016K1A3A7A09005603, No. 2016K1A3A7A09005604, No. 2016R1D1A1B02012900, No. 2016K1A3A7A09005606, No. NRF-2013K1A3A7A06056592; the Brain Korea 21-Plus program, Radiation Science Research Institute, Foreign Large-size Research Facility Application Supporting project and the Global Science Experimental Data Hub Center of the Korea Institute of Science and Technology Information; the Polish Ministry of Science and Higher Education and the National Science Center; the Ministry of Education and Science of the Russian Federation and the Russian Foundation for Basic Research; the Slovenian Research Agency; Ikerbasque, Basque Foundation for Science and MINECO (Juan de la Cierva), Spain; the Swiss National Science Foundation; the Ministry of Education and the Ministry of Science and Technology of Taiwan; and the U.S. Department of Energy and the National Science Foundation.
The reference list from the paper itself. Each links out to its DOI / PubMed record.
- 1[1] Throughout this letter, h ℎ h refers to one of the following charmless states: K + superscript 𝐾 K^{+} , K S 0 superscript subscript 𝐾 S 0 K_{\text{S}}^{0}\> , K ∗ + superscript 𝐾 ∗ absent K^{\ast+} , K ∗ 0 superscript 𝐾 ∗ absent 0 K^{\ast 0} , π + superscript 𝜋 \pi^{+} , π 0 superscript 𝜋 0 \pi^{0} , ρ + superscript 𝜌 \rho^{+} , ρ 0 superscript 𝜌 0 \rho^{0} . Charge-conjugate channels are implied throughout this paper unless explicitly stated otherwise.
- 2[2] A. Buras, J. Girrbach-Noe, C. Niehoff, and D. Straub, JHEP 02 , 184 (2015).
- 3[3] C. Hambrock, A. Khodjamirian, Alexander, and A. Rusov, Phys. Rev. D 92 , 074020 (2015).
- 4[4] R. Aaij et al. (LH Cb Collaboration), JHEP 02 , 104 (2016).
- 5[5] R. Aaij et al. (LH Cb Collaboration), Phys. Rev. Lett. 113 , 151601 (2014).
- 6[6] S. Wehle et al. (Belle Collaboration), Phys. Rev. Lett. 118 , 111801 (2017).
- 7[7] O. Lutz et al. (Belle Collaboration), Phys. Rev. D 87 , 111103 (2013).
- 8[8] J.P. Lees et al. (Ba Bar Collaboration), Phys. Rev. D 87 , 112005 (2013).
