856. WE-Heraeus-Seminar: Challenges in Semileptonic B Decays 2026

Apr 11, 2026, 9:00 AM → Apr 16, 2026, 8:00 PM Europe/Zurich

Physikzentrum Bad Honnef (PBH)

Christoph Schwanda (Austrian Academy of Sciences (AT)), Florian Urs Bernlochner (University of Bonn (DE)), Martin Jung (Università di Torino & INFN), Andreas Kronfeld, Marcello Rotondo (INFN e Laboratori Nazionali di Frascati (IT)), Thomas Mannel, Keri Vos (Nikhef National institute for subatomic physics (NL))

The workshop is the 856. WE-Heraeus-Seminar and aims to review recent progress in semileptonic B decays, both on the theory and the experimental front, and to form a consensus on how to extract the CKM matrix elements Vcb and Vub from inclusive and exclusive decays. Another topic of the workshop is the test of lepton flavour universality in semileptonic B decays in particular in the third generation.

This workshop follows previous workshops held at MITP (2015 and 2018), in Barolo (2022) and in Vienna (2024). The venue of this edition is the Physikzentrum Bad Honnef.

The workshop is scheduled from Sunday April 12 to Thursday April 16. We start on Sunday at 09:00 and finish on Thursday at 9:00 am after a common breakfast. People can arrive on Saturday April 11th. A welcome reception is foreseen for Monday evening. Accomodation will be arranged at the centre. Please be aware of and do not respond to phishing emails regarding this. 

Located in the picturesque town of Bad Honnef, the Physics Center is the headquarters of the German Physical Society. Nestled amidst the landscape of the Rhine valley, it offers on-site a modern conference venue with the possibility to host all guests within the center. 

The workshop is supported kindly by the Wilhelm and Else Heraeus foundation: 

Sat, April 11

3:00 PM → 6:00 PM Arrival Saturday Evening & joint Dinner

Arrival possible from 15:00 and joint dinner starting from 19:00

6:00 PM → 8:00 PM Dinner

Sun, April 12

9:00 AM → 12:10 PM Sunday Morning

Chair: Marcello Rotondo

9:15 AM Welcome

Speaker: Markus Tobias Prim (University of Bonn (DE))

Welcome to Challenges in Semileptonic Decays!.pdf

9:20 AM R(D/D*) from Babar

Speaker: Abi Soffer (Tel Aviv University (IL))

Soffer-challenges in SL decays.pdf

9:50 AM An experimental overview of Belle II LFU tests

Speakers: Ilias Tsaklidis (University of Bonn), Ilias Tsaklidis, Ilias Tsaklidis

2026_Challenges_LFU_itsaklid.pdf

10:15 AM Tea break

10:45 AM Status of R(D/D*) measurements at Belle II with inclusive tagging

Speaker: Tia Crane

Challenges_in_SL_B_2026_Tia_Crane.pdf

11:15 AM Status of combined B -> D/D* l nu measurements with Belle II

Speakers: MICHELE MANTOVANO, Michele Mantovano (University and INFN Trieste), Michele Mantovano (Universita & INFN Pisa (IT)), Michele Mantovano (DESY)

Vcb_Challenges_B_decays_final.pdf

11:45 AM Discussion

2:00 PM → 5:50 PM Sunday afternoon

Chair: Paolo Gambino

2:00 PM Soft Photon corrections to semileptonic decays

Speaker: Federico Cima

Cima-Bonn.pdf

2:30 PM Fermilab/MILC B->D exclusive form factors

Speakers: Alejandro Marino Vaquero Avilés-Casco (Universidad de Zaragoza), Dr Alejandro Vaquero Avilés-Casco (University of Utah)

Bonn-Talkv3.pdf

3:00 PM B-> D(*) l nu with light leptons

Speaker: Stefan Schacht (Durham University)

bad-honnef-2026-schacht.pdf

3:30 PM Tea break

4:15 PM RBC/UKQCD exclusive form factors focus Bs to Ds star

Speakers: Oliver Witzel (Universität Siegen), Oliver Witzel (University of Edinburgh)

charm-f1s.avi

witzel_oliver.pdf

4:45 PM On the simulated kinematic distributions of semileptonic B decays

Speakers: Florian Herren (UZH), Raynette Van Tonder (Karlsruhe Institute of Technology), Raynette van Tonder (KIT)

EvtGen.pdf

5:05 PM Discussion

Speaker: Marzia Bordone (JGU Mainz)

talk.pdf

Mon, April 13

9:00 AM → 12:15 PM Heavy to light

Chair: Christoph Schwanda (Morning), Zoltan Ligeti (Afternoon)

9:00 AM Status of inclusive Vub determinations

Speakers: Lu Cao (Fudan University), Dr Lu Cao (University of Bonn)

challenges2026_Cao.pdf

9:30 AM B to Xu l nu and Vub measurement at Belle II

Speakers: Tommy Martinov, Tommy Martinov (INFN Trieste)

Inclusive_Vub_BelleII.pdf

10:00 AM Tea break

10:45 AM Novel b-> u ell nu hybrid model

Speaker: Philipp Horak (University of Victoria)

horak_new_hybrid_challenges.pdf

11:15 AM Inclusive b -> u discussion

Speaker: Keri Vos (Nikhef National institute for subatomic physics (NL))

challenges_KKV.pdf

12:15 PM → 12:35 PM Group Photo

2:00 PM → 5:45 PM Heavy to light

Chair: Christoph Schwanda (Morning), Zoltan Ligeti (Afternoon)

2:00 PM Theory review of B -> pi pi l nu decays

Speaker: Florian Herren (UZH)

Challenges_2026.pdf

2:30 PM B to rho l nu at LHCb

Speaker: Michel De Cian (The University of Manchester (GB))

rhomunuV2.pdf

3:00 PM Tea break

3:45 PM Fermilab/MILC B->π etc. exclusive form factors

Speaker: Andreas Kronfeld

ask4Vxb.pdf

4:15 PM FLAG perspective

Speakers: Dr Enrico Lunghi (Indiana University), Enrico Lunghi

t-260413-Challenges in SL decays (Bad Honnef)-FLAG.pdf

4:45 PM On-shell Vcb measurement at Atlas

Speaker: Elisabeth Schopf (Universitaet Siegen (DE))

26_04_13_Schopf_VcbATLAS_banom.pdf

5:15 PM Discussion session

8:30 PM → 10:00 PM Lightning Talks

8:30 PM Testing Lepton Flavour Universality with Λb → Λc τ ν

Speaker: Mrityunjoy Singha (Eotvos Lorand University (HU))

Testing_LFU_with_Lb2Lctaunu.pdf

8:35 PM Towards relaxing the standard model assumption in R(D(*)+)

Speakers: Dylan Cameron Houston (University of Glasgow (GB)), Dylan Houston (University of Glasgow (GB))

Challenges_SLB_Poster_DH_final.pdf

8:40 PM Poster: B(s) → D(s) semileptonic decay form factors from highly improved staggered quarks

Speaker: Akhil Chauhan

Challenges_2026_Poster.pdf

8:45 PM Poster: B -> pi l nu using n_f = 2+1+1 highly improved staggered quarks

Speaker: Nick Cassar

bee2pie_poster.pdf

8:50 PM Poster: New Physics in B \to \ell \nu decays

Speaker: Danilo Ricciardella

Poster Bad Honnef.pdf

8:55 PM Poster: Status and prospects for |Vub| measurements

Speaker: Alois Caillet (Centre National de la Recherche Scientifique (FR))

Poster_Vub_Prospects.pdf

9:00 PM Poster: Angular Analysis of $B^0 \to D^{* -}\mu^+ \nu_\mu$ at LHCb

Speaker: David Vico Benet (University of Oxford (GB))

Poster_SLChallengesWorkshop_DavidVicoBenet.pdf

9:05 PM Poster: Measurement of the Branching Ratio and CKM Matrix element |V_{cb}| in $B→ X_c l nu Semileptonic Decays at Belle II

Speaker: Rajeshwari Roy

Poster_SL_Challenges_Roy.pdf

Tue, April 14

9:00 AM → 12:10 PM Tuesday Morning

Chair: Florian Bernlochner

9:15 AM SL D(*) pi and Review of the Gap with possible candidate modes

Speakers: Raynette Van Tonder (Karlsruhe Institute of Technology), Raynette van Tonder (KIT)

BSL2026_vanTonder.pdf

9:45 AM An experimental overview of Belle II measurements of D** decays

Speaker: Nada Gharbi

10:15 AM Tea break

11:00 AM Angular Analysis of B -> D* l nu with LHCb

Speakers: Biljana Mitreska (CERN), Biljana Mitreska (The University of Manchester (GB))

11:30 AM R(D/D*) Combinations: how can we improve

Speaker: Lucia Grillo (University of Glasgow (GB))

2:00 PM → 5:25 PM Tuesday Afternoon

Chair: Thomas Mannel

2:00 PM Phenomenological studies of Lambda_b -> Lambda_c Tau Nu

Speaker: Biplab Dey (Eotvos U.)

2:30 PM LHCb & Belle II b -> c tau nu Combinations

Speakers: Marco Colonna (Technische Universitaet Dortmund (DE)), Maria Colonna

3:00 PM Semileptonic Baryonic decays

Speaker: Anna Lupato (Università di Bergamo & INFN Padova)

3:30 PM Tea break

4:15 PM Heavy quark physics in the ALPHA Collaboration: strategy and application to semileptonic $B$-decay form factors

Speaker: Gregorio Herdoiza

4:45 PM Angular analysis in Bs to Ds* ell nu

Speaker: Federico Manganella (INFN e Universita Roma Tor Vergata (IT))

Wed, April 15

9:00 AM → 12:20 PM Wednesday Morning

Chair: Keri Vos

9:00 AM NP in B-> Xc (or higher orders)

Speakers: Gael Finauri, Gael Finauri

9:30 AM Measurement of the inclusive semileptonic B meson branching fraction with dileptons

Speaker: Christoph Schwanda (Austrian Academy of Sciences (AT))

10:00 AM Status of moment measurements relevant for inclusive Vcb determinations with Belle II

Speaker: Munira Khan (University of Bonn)

10:30 AM Tea break

11:10 AM Massive yet Beautiful; the b Quark Kinetic Mass in full QCD

Speaker: Rens Verkade

11:40 AM ETM inclusive rate

Speakers: Alessandro De Santis, Alessandro De Santis

1:35 PM → 5:20 PM Afternoon

Chair: Markus Prim

2:00 PM Bumpy road toward understanding of the incl/excl puzzle through lattice

Speakers: Shoji Hashimoto (KEK), Shoji Hashimoto (KEK)

2:30 PM Inclusive charm (theory)

Speaker: Qin Qin

3:00 PM Inclusive SL charm decays at BES III and outlook for STCF

Speakers: Alex Gilman, Alex Gilman, Alexander Leon Gilman (University of Cincinnati (US))

3:30 PM Tea break

4:15 PM FCC-ee as a discovery machine for Flavor: a theorists view

Speaker: Zoltan Ligeti (Lawrence Berkeley National Lab. (US))

4:45 PM FCC-ee as a discovery machine for Flavor: an experimentalists view

Speakers: Marie-Helene Schune (Université Paris-Saclay (FR)), Marie-Helene Schune (Université Paris-Saclay (FR))

Thu, April 16

8:00 AM → 9:00 AM Departure