International Symposium in Honor of Professor Nambu
for the 10th Anniversary of his Nobel Prize in Physics

Particle Physics at theSuperKEKB/Belle II Experiment
Toru Iijima

Kobayashi-Maskawa InstituteNagoya University
December 12, 2018
Osaka City University
1

2SuperKEKB/Belle II
New intensity frontier facility at KEK• Target luminosity ; Lpeak = 8 x 1035cm-2s-1~1010 BB, τ+τ- and charms per year !
•Lint > 50 ab-1
Rich physics program••

Search for New Physics through processes sensitive to virtual heavy particles.
New QCD phenomena (XYZ, new states including heavy flavors) + more
Peak Luminosity Trends (e+e- collider)SuperKEKB
L peak (KEKB)=2.1x1034cm-2s-The first particle collider after the LHC !

Perfect SM••

CP violation explained by the mechanism proposed by
Kobayashi and Maskawa.
Higgs has been discovered and its couplings to fermionsare being measured.

Is this the end of the story ?

3

4

Why do we need go further ?
SM explains almost every phenomena sofar, but cannot explain• The Higgs mass (fine tuning problem)• Grand unification• Dark matter• Baryon asymmetry in the Universe• Origin of the 3 generations

New Physics ! @ O(1→ 10) TeV ?

4Why do we need go further ?
SM explains almost every phenomena sofar, but cannot explain• The Higgs mass (fine tuning problem)• Grand unification• Dark matter• Baryon asymmetry in the Universe• Origin of the 3 generations

New Physics ! @ O(1→ 10) TeV ?

Two Ways to Find New Physics•Energy Frontier : produces and detects a new particle
directly in collisions of extremely high energy beams.

•Luminosity Frontier : measures reactions of known
particles very precisely, and finds deviations from the Standard
Model predictions.
~GeVATLAS

CMS~TeVBelle II

5~MeVLHCb

No NP at LHC so far
The mass region ~1TeV almost excluded ?

6

Role of the Belle II Experiment• Complementary to direct search in LHC high PT programs.
• Reach in mass scale is not limited by the collision energy.
• Depend on NP flavor violating couplings.
Belle IIeritn BelleroFrov
aFlEnergy Frontier

7

B-Factory Experiments

8In 2001, the Belle experiment at KEK and the BaBar experiment
at SLAC successfully measured CP violation in B meson decays
as predicted by the Kobayashi-Maskawa theory.

KEKB / BellePEP II / BaBar

2008 Nobel Prize in Physics

9

Kobayashi-Maskawa Theory10– A quark change its flavor by emitting virtual W.
– 3X3 unitarity triangle has 3 rotational angles and onecomplex phase.

CP Violationd(s,buV*ud(s,b－W! u " !c " ! t "# d $ # s $ #b $% & % & % &! d ' " ! VudVusVub " ! d "$# $# $ #s'=VVVscdcscb$# $# $ ## b ' $ #V V V $ # b $% & % td ts tb & % &Flavor
eigenstate

CKMMasseigenstate11

Confirmation of Kobayashi-Maskawa
0 tag
B_B0 tag11

Confirmation of Kobayashi-Maskawa
0 tag
B_B0 tag

Press release from the Academy“As late as 2001, the two particle detectors BaBar at
Stanford, USA and Belle at Tsukuba, Japan, both
detected broken symmetries independently of eachother. The results were exactly as Kobayashi andMaskawa had predicted almost three decades earlier. “1210 years later,
we are starting a new experiment
SuperKEKB/Belle II
to search for new phenomena beyond KM.

SuperKEKB Accelerator• Low emittance (“nano-beam”) scheme employed (originally proposed by P. Raimondi)
Machine parameters
SuperKEKB
LER/HER

KEKB
LER/HER

E(GeV)

4.0/7.0

3.5/8.0

εx (nm)3.2/4.6

18/24

βy at IP(mm)0.27/0.30

5.9/5.9βx at
IP(mm)

32/25

120/120

Half crossingangle(mrad)

41.5

11I(A)

3.6/2.6

1.6/1.2

Lifetime~10min130min/200min

L(cm-2s-1)

80×1034

2.1×1034x20x213

Belle II Detector•

Deal with higher background (10-20×), radiation damage, higher occupancy,higher event rates (L1 trigg. 0.5→30 kHz)

•Improved performance and hermeticity

14

The Belle II Collaboration• Belle II now has grown to ~800
researchers from 25 countries• ~270 graduate students• Large international collaboration
hosted by KEK, Japan

15

Contribution by Japanese Universities
TOP（Nagoya, KEK）

ECL（Nara W）

Computing（by each
university, KEK）

Nagoya, KMI

Original development byNagoya groupJapan
Contribution inMC generation

A-RICH（TMU, Niigata, Chiba,
CDC（Osaka City, NPC, KEK）

Toho, KEK）

SVD（Tokyo, IPMU, Tohoku, KEK）

Trigger・DAQ（KEK）

16

SVD ladder assembly lab.
at IPMU

Contribution by Osaka City Univ.
Y. Teramoto, E. Nakano, M. Iwasaki
Original development,
construction, operation of Belle
KLM → used also in Belle II
Track extrapolation to KLM
Muon Identification

KLM
TOP
CDC

TOP

Development, construction,
operation of Belle II CDC
Computing/Software
Development of Machinelearning-based analysis+ SuperKEKB (talk by Iwasaki-san tomorrow)

ECLKLM17LHCb vs Belle II••

18

LHCb is the experiment dedicated for similar studies at LHC.
Two experiments compete each other;•pp collisions (LHCb) → rapid production of B mesons.

•e+e- collisions at Belle II → clean, less background measurements

+Advantage of e e Flavor Factory•

Clean environment••

Efficient detection of neutrals (γ, π0, η, …)

Quantum correlated B0B0 pairs•

High effective flavor tagging efficiency :~34%(Belle II)~3% (LHCb)•Large sample of τ leptons• Search for LFV τ decays at O(10-9)•Full reconstruction tagging possible••

19

A powerful tool to measure;• b→u semileptonic decays (CKM)• decays with large missing energy

πTag sideπϒ(4S)

KBtag

πSystematics different from LHCb•

Signal side

Two experiments are required to establish NPπℓ

Bsig

ν
B→πlν
B → τ ν, D τ νB→Kνν+Advantage of e e Flavor Factory•

Clean environment•••

Efficient detection of neutrals (γ, π0, η, …)

Quantum correlated B0B0 pairs••High effective flavor tagging efficiency :~34%(Belle II)~3% (LHCb)

Large sample of τ leptons
pp forcollision• Search
LFV τ decays at O(10-9)
large production ratee+e- collision
low backgroundπ

Full reconstruction tagging possible
Powerful !
• A powerful tool to measure;•••

19b→u semileptonic decays (CKM)
decays with large missing energy

Systematics different from LHCb•

Tag side

Signal side

Clean ! ϒ(4S)
KBtag

πππℓ

Bsig

ν

B→πlν
TOYOTA FCVTwo experiments are required to establish NP
B → τ ν, D τ νNOW ON MARKET !
B→Kνν20Physics at the Belle II Experiment
We know this old road…
Mt. New Physics ?

by Hiroshige Utagawa (1797-1858)

B-B Mixing and Top QuarkVibb

B¯0Wd¯i±Vid⇤dW⌥⇤Vjdj̄

Vjb

21B0b̄

A(B̄ 0 ! B 0 ) = |A| ⇥ e ↵B

↵ ⇠ 2arg(Vtd Vtb⇤ )Mt > 50 GeV/c2

CKM fit w/ Belle II + LHCb
1808.10567

22

CKM fit w/ Belle II + LHCb
1808.10567

Relative amplitude (h) phase (σ))1$+$LHCb$70)1$
Belle$II$5ab
Present

Belle$II$50ab)1$+$LHCb$500)1$

22B-B Mixing and New Physics
Vibb

B¯0Wd¯i±Vid⇤dW⌥⇤Vjdj̄Vjb23B0b̄
J. Charles et al.,
PRD89,033016(2014)

Mass reach (CKM-like): O(1)TeV → O(10) TeV !

Key Measurements @ Belle II

24

arXiv:1002.5012• CPV in b→s penguin decays• FCNC• Tauonic decays• LFV τ decays

Ultimate measurements down to theory error !

25

Hints of New Physics !
Observed deviation from SM
B→D(*) τ ν
B→K* llXWbt

R(K*)
X W+l+R(D(*))γ, Z−ls−Vub incl/excl.

τνcP5’(B→K*µµ)(g-2)µBs→φµµε’/ε K(g-2)µX
WWνIs Lepton Non-universality the clue to NP ?

26

Lepton non-Universality (tree)
There are 3 modes in the B meson weak decay into thelepton final states; B→D e ν, D μ ν, D τ ν.
Q: Are they just the same (as in the SM) ?
uc

B−ub

H-W−

D0−

eµ−

τ−

νeνµντ

(New Physics)

Hints of deviations in recent BaBar, Belle, LHCb data …

R(D), R(D*)
Summer 2018 update

SM3.8σDeviation from SM slightly decreased
from 4.1 →3.8σ, mainly due to change
in theoretical SM prediction.

27

R(D*)

R(D)

Only had. tag.
at B-factories

Belle II Projections

28• Lepton universality violation may be established even with 5ab-1 (2020).
• High statistics data will provide more detailed information, such as τpolarization, q2 distribution, to discriminate type of NP.

• More observables (distributions) !
••P(τ), P(D*)
dΓ/dq2, dΓ/dpD(*), dΓ/dpe, …

• More modes !

Will soon hit the systematic limit !

••B → π τ ν,BS → DS τ ν (at 5S runs) , …

Lepton non-Universality (loop)
RK*0RKP5’BS → φμμ29

30

CP Violation by New Physics
Belle II can measure types of B meson decays which rarely happen(~ one per million B decays), known as “Penguin” decays.
Q: Does CP violation in “Penguin” decays deviates from the SM ?
New particle mayappear here !

η’BKS0Φ1 (≡β) Projection
φ31NPb

B0d

Wc J /Ψ
csdKS

Belle II projection for sin2φ1from B→J/ψKsb

B0dgs φssdKSBelle II projection for sin2φ1efffrom b→s s s processes

32

Lepton Flavor Violation
SuperKEKB produces also a lot of tau-leptons, which can bestudies in detail by Belle II.
Q: Does the tau-lepton changes to the muon or electron,
similarly to the case of the neutrino (neutrino oscillation).

νee

ντ

νµ?

µ?

τneutrino oscillation
are there decays like
τ→μγ?
τ→eγ?

LFV τ Decays

33• Lepton flavor violated in
the neutrino sector.

• Some NP models predicts
LFV to be observed in‘near’ future experiments.

• Complementary to LHC• τ LFV complementary tomuon programs• μ→eγ, eee• µ→e conversion

Talk by Ami Rostomyan
at TAU2018

34

Tau LFV prospect at Belle II

Belle II will push down the current bounds further
by more than an order of magnitude.

35

Project Status
SuperKEKB and Belle II

Belle IIInjector

Damping ring

SuperKEKB main ring

5th KEK Flavor Factory Workshop, KEK-FF, 2015 October 26

936SuperKEKB/Belle II Plan
Phase 1 (w/o QCS/Belle II)• Accelerator basic tuningwith single beams
Phase 2 (w/ QCS/Belle II but
w/o VXD)• Verification of nano-beamscheme• Understand beam
backgroundPhase 3 (w/ full detector)• 1ab-1 after 1 year
• 5ab-1 by ~2020• 50ab-1 by ~2025Belle II Integration37

2013 - 2017 Feb. at roll-out position
B-KLM, 2013

TOP, 2016 Feb-May

B field meas., 2016 Jun-July

CDC 2016 Oct-Dec

BW endcap, 2017 Jan-Feb

B-KLM module installation, 2013

E-KLM module installation, 2014

E-KLM, 2014

Belle II Roll-In

38

April 11, 2017

Belle II rolled-in to the beam line on April 11th, 2017
One of the most significant milestones in the construction phaseBelle II Roll-In38

April 11, 2017

Belle II rolled-in to the beam line on April 11th, 2017
One of the most significant milestones in the construction phase

Belle II Roll-In

38

April 11, 2017

Belle II rolled-in to the beam line on April 11th, 2017
One of the most significant milestones in the construction phaseForward End-cap Installation

39

Sep.-Oct., 2017•

Two sub-detectors (A-RICH + FW ECL) are combined and installed
into Belle II.

First Collision !
0:38, April 26, 201840

First Collision !
0:38, April 26, 201840

First Collision !
0:38, April 26, 201840

41

Luminosity during Phase 2

by*= 80mm

by*= 8mm

6mm

by*= 4mm

by*= 3mm

5.55 x 1033/cm2/s (by*3mm, LER: 800mA, HER: 780mA, 1576 bunches/beam July 5th)
2.29 x 1033/cm2/s (by*3mm, LER: 270mA, HER: 225mA, 394 bunches/beam July 3rd)

42

Belle II performance in Phase 2• Clear mass peak observed by combining charged tracks
and photons

43

B reconstruction in Phase 2• B meson signals have been seen in Phase 2 data.

Prospect toward Phase 3
Integration of PXD and SVD on the beam pipe

44

Prospect toward Phase 3
Integration of PXD and SVD on the beam pipe

45Summary46• The Belle II experiment at SuperKEKB aims to find
New Physics with ultimate precision measurement(a few %, typically) of heavy flavor decays (O(1010)
samples / year).

• Complementary to LHC high Pt (ATLAS/CMS).
• Complementary and competing to LHCb.

• Belle II physics run will start ~end of FY2018.
• We are getting to the new stage, after 10 years since2008 Nobel Prize for Nambu, Kobayashi, Maskawa !

Stay Tuned !

Belle II OutreachAlso public HP: belle2.jp

Thank you !

Backup Slides