We present the results of a search for the charged-lepton-flavor violating decays $\textit{B}$ → $\textit{K}$ $\textit{τ}$ $\textit{ℓ}$ , where $\textit{ℓ}$ is either an electron or a muon. The results are based on 365 fb and 711 fb datasets collected with the Belle II and Belle detectors, respectively. We use an exclusive hadronic $\textit{B}$-tagging technique, and search for a signal decay in the system recoiling against a fully reconstructed $\textit{B}$ meson. We find no evidence for $\textit{B}$ → $\textit{K}$ $\textit{τ}$ $\textit{ℓ}$ decays and set upper limits on the branching fractions in the range of (2.9–6.4)×10 at 90% confidence level.

I. Adachi

Y. Ahn

H. Aihara

N. Akopov

S. Alghamdi

M. Alhakami

A. Aloisio

K. Amos

M. Angelsmark

N. Anh Ky

C. Antonioli

D. Asner

H. Atmacan

V. Aushev

M. Aversano

R. Ayad

V. Babu

H. Bae

N. Baghel

S. Bahinipati

P. Bambade

Sw. Banerjee

S. Bansal

M. Barrett

J. Baudot

A. Baur

A. Beaubien

F. Becherer

J. Becker

J. Bennett

F. Bernlochner

V. Bertacchi

M. Bertemes

E. Bertholet

M. Bessner

S. Bettarini

B. Bhuyan

F. Bianchi

T. Bilka

D. Biswas

A. Bobrov

D. Bodrov

J. Borah

A. Boschetti

A. Bozek

M. Bračko

P. Branchini

R. Briere

T. Browder

A. Budano

S. Bussino

M. Campajola

L. Cao

G. Casarosa

C. Cecchi

M.C. Chang

P. Cheema

B. Cheon

K. Chilikin

J. Chin

H.E. Cho

K. Cho

S.J. Cho

S.K. Choi

S. Choudhury

I. Consigny

L. Corona

J. Cui

E. De La Cruz-Burelo

S. De La Motte

G. Marino

G. Pietro

R. Sangro

M. Destefanis

A. Canto

J. Dingfelder

Z. Doležal

I. Domínguez Jiménez

T. Dong

X. Dong

M. Dorigo

G. Dujany

P. Ecker

D. Epifanov

R. Farkas

P. Feichtinger

T. Ferber

T. Fillinger

C. Finck

G. Finocchiaro

F. Forti

A. Frey

B. Fulsom

A. Gale

E. Ganiev

M. Garcia-Hernandez

R. Garg

G. Gaudino

V. Gaur

V. Gautam

Search for lepton flavor-violating decay modes $\textit{B}$

This paper presents a novel tagging technique to measure the beauty-quark partial decay-width ratio $$R_b$$ and its forward–backward asymmetry $$A_{\textrm{FB}}^b$$ at the FCC-ee, using $$\mathcal {O}(10^{12})$$ $\textit{Z}$-boson decays. The method is based on the exclusive reconstruction of a selected list of $\textit{b}$-hadron decay modes in $$Z\rightarrow b\bar{b}$$ events at the $\textit{Z}$ pole, which can provide the flavour and possibly the charge of the hemisphere. This approach effectively eliminates the contamination from light-quark physics events and reduces the leading systematic uncertainties arising from background contamination, tagging-efficiency correlations, and gluon-radiation corrections by exploiting the geometric and kinematic properties of beauty hadrons. This results in a total relative uncertainty of the order of 0.01 % for both observables. Furthermore, this precision allows to obtain a commensurate precision on the weak mixing angle $$\sin ^2(\theta _\text {W}^{\text {eff}})$$ compared to the muon forward–backward asymmetry on the order of 0.002 %.

Germany

France

Lars Röhrig

Kevin Kröninger

Romain Madar

Stéphane Monteil

Italy

Fabrizio Palla

Switzerland

Emmanuel Perez

Measuring $$A_\textrm{FB}^b$$ and $$R_b$$ with exclusive $\textit{b}$-hadron decays at the FCC-ee

A search for a pseudoscalar $\textit{a}$ produced in association with a top-quark pair, or in association with a single top quark plus a $\textit{W}$ boson, with the pseudoscalar decaying into $\textit{b}$-quarks ( $$a\rightarrow b\bar{b}$$ ), is performed using the full Run 2 data sample using a dileptonic decay mode signature. The search covers pseudoscalar boson masses between 12 and 100 GeV and involves both the kinematic regime where the decay products of the pseudoscalar are reconstructed as two standard $\textit{b}$-tagged small-radius jets, or merged into a large-radius jet due to its Lorentz boost. No significant excess relative to expectations is observed. Assuming a branching ratio $$\text {BR}(a\rightarrow b\bar{b})=100\% $$ , the range of pseudoscalar masses between 50 and 80 GeV is excluded at 95% confidence level for a coupling of the pseudoscalar to the top quark of 0.5, while a coupling of 1.0 is excluded at 95% confidence level for the masses considered, with the coupling defined as the strength modifier of the Standard Model Yukawa coupling.

G. Aad

Norway

E. Aakvaag

United States

B. Abbott

United Arab Emirates

S. Abdelhameed

K. Abeling

N.J. Abicht

S. Abidi

M. Aboelela

Morocco

A. Aboulhorma

Israel

H. Abramowicz

Y. Abulaiti

United Kingdom

B. Acharya

A. Ackermann

C. Bourdarios

Poland

L. Adamczyk

S. Addepalli

M. Addison

J. Adelman

Türkiye

A. Adiguzel

T. Adye

A. Affolder

Y. Afik

Spain

M. Agaras

A. Aggarwal

Romania

C. Agheorghiesei

Azerbaijan

F. Ahmadov

S. Ahuja

China

X. Ai

G. Aielli

A. Aikot

M. Tamlihat

B. Aitbenchikh

M. Akbiyik

Sweden

T. Åkesson

A. Akimov

Japan

D. Akiyama

N. Akolkar

S. Aktas

G. Alberghi

Canada

J. Albert

P. Albicocco

G. Albouy

S. Alderweireldt

Z. Alegria

M. Aleksa

I. Aleksandrov

C. Alexa

Greece

T. Alexopoulos

F. Alfonsi

M. Algren

M. Alhroob

Czechia

B. Ali

Saudi Arabia

H. Ali

S. Ali

S. Alibocus

South Africa

M. Aliev

G. Alimonti

W. Alkakhi

C. Allaire

B. Allbrooke

J. Allen

P. Allport

Argentina

F. Alonso

C. Alpigiani

Z. Alsolami

A. Alvarez Fernandez

Search for a new pseudoscalar decaying into a pair of bottom and antibottom quarks in top-associated production in $$\sqrt{s}=13$$ TeV proton–proton collisions with the ATLAS detector