Semileptonic B decays at the Belle experiment

Christoph Schwanda Instute of High Energy Physics Austrian Academy of Sciences

Seminar on Parcle Physics SS 2014 Vienna University, March 4, 2014 Outline of this talk

• A short introducon to the Belle experiment at KEK • Measurements of semileptonic B decays at the

B factories and determinaon of |Vcb| and |Vub| • The Belle II upgrade • Prospects for semileptonic B decays at Belle II

March 4, 2014 2 The Belle experiment at KEK

March 4, 2014 3 1999 – 2010: B factory at KEK (Japan)

Linac KEKB double ring e+e-

e+e- → Y(4S) → BB

Belle detector

• World largest B sample ~771 million BB events • ~400 Belle physics publicaons March 4, 2014 4 About 771 million e+e- → BB events in the Belle data

March 4, 2014 5 Cherenkov cnt. SC solenoid n=1.015~1.030 1.5T 3.5 GeV e+ CsI(Tl) 16X0 TOF counter

- 8 GeV e Central Drift Chamber small cell +He/C2H5

Si vtx. det. µ / KL detection 3(4) lyr. DSSD 14/15 lyr. RPC+Fe ID efficiency ~90% Fake rate ~0.1% (), ~1% (March 4, 2014 muons) 6 Cabibbo-Kobayashi-Maskawa mixing

• W couples to the weak eigenstates • Charged current processes can change quark flavour • CKM matrix elements appears at the quark-W vertex

March 4, 2014 7 The main goal of the B factories was…

… to confirm the CKM mechanism, as established by M. Kobayashi and T. Maskawa in the year 1973

Wolfenstein parametrizaon of VCKM

• VCKM contains not only coupling constants of weak transions • But also a complex phase, responsible for all CP-violang phenomena in the SM

March 4, 2014 8 The CKM unitarity triangle

CPV in B → ππ, ρρ, ρπ B → Xlν

CPV in B → J/ψKs B-/+ → D(*)K(*)-/+

March 4, 2014 9 March 4, 2014 10 Review of semileptonic B decays

March 4, 2014 11 l+ ν W+ l

b c,u Semileptonic B decay u/d u/d

+/0 B Xc,u

b W+ l+ Leptonic B decay u νl

B+

March 4, 2014 12 Why study semileptonic B decays…

… because they are the best way to measure the CKM matrix elements |Vcb| and |Vub|, two fundamental parameters of the SM

March 4, 2014 13 |Vcb| from exclusive decays

B → D*lν

B → Dlν

• Theory input: Form factors F(1) and G(1) at zero recoil (w=1) from lace QCD calculaons • Experimental method: Measure the differenal width dΓ as a funcon of w and extrapolate to zero recoil (typically assuming a parameterizaon of the form factors)

March 4, 2014 14 B0 → D*-l+ν at Belle [W. Dungel, CS, PRD 82, 112007 (2010)]

• 711/ of Belle Y(4S) data • About 120,000 reconstructed B0 → D*-l+ν decays

• Fit in 40 bins of w, cos θl, θV and χ to obtain HQET F.F. parameters • Dominant experimental systemacs: tracking

March 4, 2014 15 |Vcb| from inclusive decays

B → Xlν

• Based on the Operator Product Expansion (OPE)

• : hadronic matrix elements (non-perturbave) ci: coefficients (perturbave) • Parton- duality → the hadronic ME depend only on the inial state

Kinec scheme 1S scheme [JHEP 1109 (2011) 055] [PRD70, 094017 (2004)]

O(1) mb, mc mb 2 2 2 O(1/m b) µ π, µ G λ1, λ2 3 3 3 O(1/m b) ρ D, ρ LS ρ1, τ1-3 March 4, 2014 16 2 Moments of the El and M X spectrum

Also other observables in B à Xlν can be expanded into an OPE with the same heavy quark parameters, e.g.,

• The nth moment of the (truncated) lepton energy spectrum

th 2 • The n moment of the (truncated) M X spectrum

Master plan: • Measure the quark masses and heavy quark parameters using moments • Substute them in the formula of the semileptonic width March 4, 2014 17 • Determine | Vcb| from the semileptonic branching fracon • Analysis in the kinec scheme with 50 moments from BaBar, Belle, CDF, CLEO and DELPHI [P. Gambino, CS, Phys.Rev.D89, 014022 (2014)] March 4, 2014 18 Global fit (kinec scheme) [Phys.Rev.D89, 014022 (2014)]

March 4, 2014 19 ] 45

-3 2 ∆ χ = 1 CLEO | [10 cb |Vcb| |V

× 40 DELPHI OPAL (excl.) (excl.)

F(1) DELPHI (part. reco.) OPAL (part. reco.) * AVER AGE Exclusive (D lν) 35 BABAR (Global Fit) ALEPH BABAR (D*0) BABAR (excl.) -3 BELLE |Vcb| = (39.48 +/- 0.50exp +/- 0.74th) x 10 HFAG 30 PDG 2013 F(1) = (0.908 +/- 0.017) [arXiv:1011.2166] χ2/dof = 30.0/23

0 0.5 1 1.5 2 ρ2 Inclusive (kinec) -3 |Vcb| = (41.88 +/- 0.73) x 10 HFAG preprint [arXiv:1207.1158]

• Exclusive and inclusive agree at the level of ~2 sigma

March 4, 2014 20 B → D**lν mystery

• Inclusive-exclusive gap of (1.45 +/- 0.29)% • 1/2 vs. 3/2 puzzle • Belle II might clarify the situaon by measuring B → D(*)nπlν Sascha Turczyk CKM 2012 workshop

March 4, 2014 21 Determinaon of |Vub|

Exclusive B → πlν

• Form factor f+ from lace QCD [PRD73, 074502; PRD79, 054507] or from QCD sum rules [PRD83, 094031; PRD 71, 014015]

Inclusive • Also based on the OPE [NPB699, 335; JHEP01, 097; JHEP10, 058] B → Xulν • Experimental selecons can comprise the convergence of the OPE → shape funcon

March 4, 2014 22 B → πlν untagged [PRD 86, 092004 (2012)]

• 416/ of BaBar Y(4S) data • Reconstruct only πe/πµ, infer neutrino momentum

from pmiss (loose neutrino reconstrucon technique) • About 12,000 signal events, S/N ~0.1 • Paral branching fracons obtained in 12 q2 bins • Systemacs: detector effects, b → u background

March 4, 2014 23 B → πlν untagged [PRD 86, 092004 (2012)]

• FF parameterizaon: Boyd-Grinstein-Lebed

• Combined fit with FNAL/MILC lace data yields |Vub| = (3.25 +/- 0.31) x 10-3 • Alternave extracons of |Vub| (using LCSR/LQCD in regions of q2) consistent with the combined fit

March 4, 2014 24 New Belle hadronic tag

[NIM A654, 432 (2011)]

• New hadronic tag based on Neurobayes • 2-3x stascal gain over previous analyses

March 4, 2014 25 B → πlν with hadronic tag [PRD 88, 032005 (2013)]

• 703/ of Belle Y(4S) data • Hadronic tag 2 • Yield extracted from M miss in 13 (7) bins of q2 for B0 → π+lν (B+ → π0lν) • Main systemacs: tag calibraon

March 4, 2014 26 ×10-6 )

-2 Belle untagged 12 Belle tagged BaBar untagged (6 bins) |V | (GeV BaBar untagged (12 bins) ub 2 FNAL/MILC q 10

Δ FNAL/MILC used in fit

B/ BCL fit (3+1 par.)

Δ 8 6 Exclusive (BCL fit) 4 -3 2 |Vub| = (3.28 +/- 0.29) x 10 0 0 5 10 15 20 25 q2 (GeV2) Inclusive (BLNP)

-3 |Vub| = (4.40 +/- 0.15exp +/- 0.20th) x 10

HFAG preprint [arXiv:1207.1158] + web updates

• Exclusive and inclusive agree at the level of ~3 sigma

March 4, 2014 27 Right-handed currents

L • Add right-handed currents (|Vub|=|Vub |) L R 2 – B → πlν goes as |Vub +Vub | L R 2 – B → τν goes as |Vub -Vub | L 2 R 2 – B → Xulν goes as |Vub | +|Vub | • Can fit the data with ~17% RHC contribuon

Florian Bernlochner CKM 2012 workshop

March 4, 2014 28 The Belle II upgrade

March 4, 2014 29 © NASA/WMAP

Extensions to the Standard Model Large Extra Dimensions

Technicolor

Grand Unification

March 4, 2014 30 Energy Froner

Physics beyond the Standard Model

Precision Froner

March 4, 2014 Cosmological Froner 31 Belle II search channels for NP

Flavor changing neutral currents Precision test of CKM unitarity (virtual contribuons of new, heavy (search for new CP violang phases) parcles in loops)

???

Search for the charged Higgs boson Search for lepton flavor violaon in in B à τ nu and B à D(*) τ nu B and decays (SUSY breaking decays mechanism, right-handed neutrino couplings)

March 4, 2014 32 Search for the charged Higgs boson with B+ → τ+ ν

Standard model Type II Higgs doublet models

H-

W.S.Hou, PRD 48, 2342 (1993)

Belle II 5σ H+ discovery (50/ab)

14 TeV ATLAS 5σ H+ discovery (30/) arXiv:0901.0512 [hepMarch 4, 2014-ex] 33 τ lepton flavor violaon

γ τ µ τ → lγ τ → 3l, lη h µ()s χ! 0 ()e τ τ! µ!(e!) µ µ()s • SUSY + seesaw 2 • Neutral Higgs mediated decay (m!l )23(13) • Large LFV • Important when MSUSY >> EW scale experimental sensivity

mode Br(τ → µγ) Br(τ → 3l) mSUGRA + seesaw 10-7 10-9 SUSY + SO(10) 10-8 10-10 SM + seesaw 10-9 10-10 Non-universal Z’ 10-9 10-8 SUSY + Higgs 10-10 10-7

March 4, 2014The full range of τ LFV modes is only accessible at a Super B factory! 34 Belle II physics sensivity [arXiv:1002.5012[hep-ex]]

March 4, 2014 35 I ξ L 8 10 −35 cm −2s−1 e± ± y . From KEKB to SuperKEKB = × [ ]∝ * β y Take advantage of existing items ・ the KEKB tunnel, New QCS magnet for Nano-beam scheme ・ the KEKB components Build new beam New superconducting / as much as possible! line Tsukuba permanent final focusing section quads near the IP New beam pipe& bellows TiN-coated beam pipe with New design antechambers for Near-IR Add / modify RF systems for higher beam Main ring arc and straight section: current Redesign the lattices of both rings to reduce the emittance New low emittance New and re-use wiggler KEKB e- gun magnets are mixed: Oho section Nikko section (LER) Super (LER&HER) KEKB damping ring Main ring arc section: LER: Replace all main dipoles New e+ HER: Preserve the present cells source

36 March 4, 2014 Compare the Parameters for KEKB and SuperKEKB

KEKB KEKB Achieved SuperKEKB Design : with crab Nano-Beam Energy (GeV) (LER/HER) 3.5/8.0 3.5/8.0 4.0/7.0

* y (mm) 10/10 5.9/5.9 0.27/0.30 * x (mm) 330/330 1200/1200 32/25

x (nm) 18/18 18/24 3.2/5.3

y x (%) 1 0.85/0.64 0.27/0.24

y(m) 1.9 0.94 0.048/0.062

y 0.052 0.129/0.090 0.09/0.081

z (mm) 4 6 - 7 6/5

Ibeam (A) 2.6/1.1 1.64/1.19 3.6/2.6

Nbunches 5000 1584 2500 Luminosity (1034 cm-2 s-1) 1 2.11 80 Nano-beams are the key (vertical spot size is ~50nm !!) March 4, 2014 37 5 This is not a typo Y. Ohnishi et al. Belle II Detector

KL and muon detector: Resistive Plate Counters (barrel outer layers) + WLSF + MPPC (end-caps , inner two barrel layers) EM Calorimeter: CsI(Tl), waveform sampling (barrel) Pure CsI + waveform sampling (end-caps)

Particle Identification electrons (7GeV) Time-of-Propagation counter (barrel) Prox. focusing Aerogel RICH (fwd)

Beryllium beam pipe: radius 1 cm

Vertex Detector 2 layers DEPFET + 4 layers DSSD (4GeV) Central Drift Chamber He(50%):C2H6(50%), small cells, long lever arm, fast electronics

March 4, 2014 38 Inner tracking (PXD, SVD) SVD

PXD • PXD + SVD in Belle II (in Belle only strip layers ) 20 [c m ] la y e r s DSSD strip layers 6 5 10 4 3 1+2 pixel layers Belle 0

-3 0 -2 0 -1 0 0 10 20 30 40 Belle II [c m ] rφ IP resolution m)

• µ

Pixels in novel DEPFET technology: thin (75μm) sensors ( give lile mulple scaering, close to the IR σ • Fast strip readout with APV25 chip (50 ns), low occupancy pβsin3/2θ[GeV/c] • Improved IP resoluon and low momentum tracking + - (pT < 100MeV), 30% larger eff. of Ks→π π with vertex info Belle z IP resolution Mechanical mockup of pixel detector DEPFET sensor Belle II m) µ ( σ

March 4, 2014 pβsin5/2θ[GeV/c]39 Phase I: w/o QCS and Belle II Jan-May, 2015 Phase II: with QCS and Belle II Partial TOP, w/o vtx detectors Feb-June, 2016

Phase III: Physics Run with full Belle II Starts Oct 2016 March 4, 2014 40 March 4, 2014 41 Belle II map (as of Nov 2013)

~580 collaborators, 23 countries/regions, 97 instuons March 4, 2014 ~220 from Europe 42 Prospects for semileptonic B decays

March 4, 2014 43 General comment

• Two aims at Belle II

– Reduce the uncertaines on |Vcb| and |Vub| – Understand the reason of the discrepancy between inclusive and exclusive (or firmly establish it → NP) • Strategy – Use only the theorecally/experimentally cleanest methods – Provide consistency checks for theory/experiment

March 4, 2014 44 Prospects for |Vcb| at Belle II

• Tagged measurement of B → D*lν and B → Dlν will yield |Vcb| with a similar level of precision • Fit with lace data at different kinemac points?

Expected relave uncertainty in |Vcb| from B → D*lν Sample Stat Syst Th Total

711/ 0.6 3.0 1.8 3.6

5/ab 0.2 1.5 1.5 2.2

50/ab 0.1 1.1 1.0 1.5

lace prospects from hp://www.usqcd.org/documents/13flavor.pdf March 4, 2014 45 Prospects for |Vub| exclusive at Belle II

• The tagged measurement of B → πlν reaches a similar precision than the untagged one

Expected relave uncertainty in |Vub| from B → πlν Sample Stat Syst Th Total untagged 605/ 2.7 2.2 8.7 9.4 5/ab 0.9 1.1 4.0 4.2

50/ab 0.3 0.8 2.0 2.2

711/ 5.8 2.5 8.7 10.8 tagged 5/ab 2.2 1.3 4.0 4.7

50/ab 0.7 1.0 2.0 2.4 lace prospects from hp://www.usqcd.org/documents/13flavor.pdf March 4, 2014 46 Prospects for |Vub| inclusive at Belle II

• We can measure inclusive observables in b → u and confirm the theory descripon (similar to b → c)

Expected relave uncertainty in |Vub| inclusive Sample Stat Syst Th Total

605/ 4.5 4.1 4.5 7.6

5/ab 1.6 2.6 4.5 5.4

50/ab 0.5 2.3 4.5 5.1

March 4, 2014 47 Measurement of B → τν [PRL 110, 131801 (2013)]

• 703/ of Y(4S) data • 4 signal tau modes: τ → eνν, µνν, πν, ρν • New hadronic tag (sample x3 compared to 2006 analysis) 2 • 2d fit to EECL and M miss (2006: EECL only) – Improve sensivity by 20% – More robust against peaking backgrounds

March 4, 2014 48 Measurement of B → τν [PRL 110, 131801 (2013)]

• Signal yield: • Current analysis ~3 sigma 62 +23/-22 +/- 6 evidence (3σ including systemacs) • At Belle II, we expect to

• Br(B → τν) = measure |Vub| from (0.72 +0.27/-0.25 +/- 0.11) x 10-4 B → τν at the level of 3-5%

March 4, 2014 49 SUMMARY

March 4, 2014 50 Summary

• Semileptonic B decays have allowed to determine the CKM matrix elements |Vcb| and |Vub| to the level of 1-2% and 6-10%, respecvely • However, there is a long-standing discrepancy between inclusive and exclusive measurements of |Vcb| and |Vub| • At Belle II we can address this issue with new experimental methods and provide crucial cross checks to confirm the OPE/lace descripon

March 4, 2014 51 LOC: Schwanda, Abele, Hoang hp://ckm2014.hephy.at/

52 BACKUP

March 4, 2014 53 B → ρlν with hadronic tag PRD 88, 032005 (2013)

• 703/ of Belle Y(4S) data • Hadronic tag 2 • Yield extracted from M miss in 11 (6) bins of q2 for B+ → ρ0lν (B0 → ρ+lν)

March 4, 2014 54 B+ → ωlν and B+ → η(‘)lν PRD 88, 032005 (2013)

• 703/ of Belle Y(4S) data

March 4, 2014 55 B D ( D⇡)`⌫ :angulardistributions ! ⇤ ! `

d2 = a (q2)+bc (q2)cos + bs (q2)sin + cc (q2)cos2 + cs (q2)sin2 dq2d

2 2 2 2 2 GF Vcb 2 m` 2 a(q )= | | q 1 D (q ) 384⇡4m3 q2 ⇤ ⇥ B ✓ ◆ ⇢ p 2 2 2 2 2 m` 3 m` 2 [ H+ + H + H0 ] 1+ + Ht | | | | | | 2q2 2 q2 | | ✓ ◆ 2 2 2 3 c 2 GF Vcb 2 m` 2 c(q )= | | q 1 D (q ) e [H+H⇤ ] 384⇡4m3 q2 ⇤ ⇥ R B ✓ ◆ 2 2 2 3 p s 2 GF Vcb 2 m` 2 c(q )= | | q 1 D (q ) m [H+H⇤ ] 384⇡4m3 q2 ⇤ ⇥ I B ✓ ◆ p c,s 2 b (q )=0unless there is interference with (D⇡)S amplitude [interesting!!!] Two NEW NP-sensitive observables: c 2 s 2 (`) 2 c(q ) (`) 2 c(q ) C (q )= 2 ,S (q )= 2 . a(q ) a(q )

March 4, 2014 56 D. Bečirević (LPT Orsay) @EPS HEP 2013 Looking for NP through semileptonic decays 11 / 15 Issues in |Vcb|

0 *- + • |Vcb| exclusive mainly comes from B → D l ν + *0 + 0 - + – |Vcb| from B → D bar l ν, B → D l ν and B+ → D0bar l+ ν is considerably less precise – Measurements of B0 → D*- l+ nu by different experiments are consistent but could be affected by common systemacs (slow tracking) • F(w) and G(w) form-factors – Calculated only at a single kinemac point (zero recoil w=1) – can lace predict the F.F. shape also in B decays? – Precise calculaon of F(1) available only from a single lace group (FNAL MILC) – Discrepancy with sum rule calculaons (~1 sigma) • Radiave and EW correcons?

March 4, 2014 57 Issues in |Vub|

• |Vub| exclusive comes exclusively from B → π l ν – No precise F.F. calculaons for B → ρlν or other modes – Lace and sum rule calculaons of the F.F. apply to different q2 regions and don’t provide a mutual cross- check

CLEO (Ee) – Can we claim that lace 4.19 ± 0.49 + 0.26 - 0.34 BELLE sim. ann. (m , q2) X 4.46 ± 0.47 + 0.25 - 0.27 predicts the F.F. shape? BELLE (E ) e 4.88 ± 0.45 + 0.24 - 0.27 BABAR (Ee) • 4.48 ± 0.25 + 0.27 - 0.28 max |V | inclusive BABAR (E , s ) ub e h 4.66 ± 0.31 + 0.31 - 0.36 – BELLE multivariate (p*) Dominant experimental syste- 4.47 ± 0.27 + 0.19 - 0.21 BABAR (m <1.55) X macs: b u signal modelling – 4.17 ± 0.19 ± 0.24 → BABAR (m <1.7) X 3.97 ± 0.22 ± 0.20 how well do we understand BABAR (m <1.7, q2>8) X 4.25 ± 0.23 + 0.23 - 0.25 light quark fragmentaon? BABAR (P+<0.66) 4.02 ± 0.25 + 0.24 - 0.23 BABAR (m , q2 fit, p*>1GeV) X 4.28 ± 0.24 + 0.18 - 0.20 – 5 theorecal frameworks BABAR (p*>1.3GeV) 4.29 ± 0.27 + 0.19 - 0.20 but none of them provides a Average +/-exp + theory - theory 4.40 ± 0.15 + 0.19 - 0.21 χ2/dof = 11.0/11 (CL = 44.00 %) Bosch, Lange, Neubert and Paz (BLNP) (convincing) internal cross-check Phys.Rev.D72:073006,2005 HFAG End Of 2011 March 4, 2014 2 4 58 6 |V | [× 10-3] ub Leptonic B decays

• Helicity suppression Γ(eν) << Γ(µν) << Γ(τν) • Very clean theorecally, might be affected by NP (2HDM, lepto-quark) • B → eν and B → µν are also experimentally clean but beyond the reach of Belle • B → τν has 2-3 neutrinos in the final state and kinemacs cannot be fully reconstructed (high background measurement) March 4, 2014 59 Search for the charged Higgs in B → τν

H- 2HDM SM Type II

W.S.Hou, PRD 48, 2342 (1993)

• SM expectaon – Br(B → τν) = (1.20 +/- 0.25) x 10-4 • UT fit result – Br(B → τν) = (0.72 +0.12/-0.08) x 10-4

March 4, 2014 60 (10-4) 2HDM Type II effect in B → D(*)τν

• Observables – R(D*) = Br(D*τν)/Br(D*lν) – R(D) = Br(Dτν)/Br(Dlν)

Belle D(*)τν average BaBar [PRL 109, 101802]

March 4, 2014 61