Physics Prospects at
SuperKEKB / Belle II
Alessandro Gaz,
KMI, Nagoya University
The 3rd KMI International Symposium
on “Quest for the Origin of Particles and the Universe”(KMI2017)
Nagoya (Japan) January 5th­7th 2017

The B­factories heritage

The B­factories operated for about adecade colliding e+e­ at (or close to)the energy of the Y(4s) resonance;
Achievements (in > 1000 papers):
➔

➔

➔
➔

➔

Discovery of CP violation in B
decays;Spectacular confirmation of the
CKM paradigm of Flavor Physics;
Discovery of several new particles;
Stringent limits on New Physics
scenarios;…

The SM is very healthy, but some
intriguing tensions are there...
January 5th 2017

A. Gaz2

Searching for New Physics●

Belle II: continue on the path set by the B­factories;●

Complementary strategy to LHC direct searches:➔➔●measure observables that can be predicted with small
theoretical uncertainties: a significant discrepancy would be aclear sign of New Physics!
if New Physics particles are observed at the LHC, Belle II
would be in a strong position to determine the flavor
structure and weak phases of the New Physics;

Exploit the clean environment and constrained kinematics tomeasure final states containing neutrals (p0, h('), K0L, … ) andneutrinos;
Key to success: increase dataset size by ~2 orders of magnitude!
January 5th 2017

A. Gaz3

From KEKB to SuperKEKB
Crucial ingredient: nanobeams!
KEKB

sx ~100 mm, sy ~ 2 mm

SuperKEKB

sx ~10 mm, sy ~ 60 nm

x40 increase ininstantaneous luminosity
January 5th 2017

A. Gaz4

The Belle II Detector
Structure from the old Belle… practically a brand new detector!

January 5th 2017

A. GazMany upgrades needed in order
to increase the performance andcope with much more severe
background conditions
5

The Belle II Detector ­ highlights
Improvement in performance especially in two areas:
1) Tracking and vertexing:
new (and bigger) silicon vertex tracker using
both pixel (PXD) and strips (SVD) sensors
Outer layer at r = 135 mm

Inner layer
at r = 14 mm

First built
PXD
module2) Particle Identification:please see K. Matsuoka's
talk on Friday
January 5th 2017

A. Gaz6

The Physics Program
We plan to collect 50 ab­1 of e+e­ collisions at (or close to) the Y(4s)resonance, so that we have:➔a (Super) B­factory (~1.1 x 109 BB pairs per ab­1);➔a (Super) charm factory (~1.3 x 109 cc pairs per ab­1);➔a (Super) t factory (~0.9 x 109 t+t­ pairs per ab­1);➔➔

thanks to the Initial State Radiation, we can effectively scan
the range [0.5 – 10] GeV and measure the e+e­ → light hadrons
cross­section very precisely;
finally we can exploit the clean e+e­ environment to probe theexistence of exotic hadrons, dark photons/Higgs, light Dark
Matter particles, …

I will give highlights on some of the processes that will be studied at Belle II.
This reflects (also) my personal tastes, apologies if I am neglecting your favorite topic!
January 5th 2017

A. Gaz7

B Physics

January 5th 2017

A. Gaz8

Time Dependent CP Violation●

Flagship measurements of the B­factories: access the weak phaseof the CKM Matrix by exploiting the interference between mixing
and decay:
All aspects of the experimentcrucially important:tracking efficiency;● neutrals reconstruction;● vertexing;● PID;● B Flavor Tagging;● background rejection;
● …
●

●

Significant improvements over the previous generation ofexperiments:➔
Dt resolution ~0.77 ps (30% to a factor 2 better compared to Belle);➔
effective flavor tagging efficiency ~35.8% (was 30.1% at Belle).
January 5th 2017

A. Gaz9

Time Dependent CP Violation●

The measurement of sin2f1 from B → cc K0 with the full dataset
will be dominated by systematic uncertainties:

●

Belle

Belle II (50 ab-1)

S

0.667 ± 0.023 ± 0.012

x.xxxx ± 0.0027 ± 0.0044

A

0.006 ± 0.016 ± 0.012

x.xxxx ± 0.0033 ± 0.0037

Most gluonic penguin dominatedmodes will be limited by statisticaluncertainties.
Many of these modes
are theoreticallyclean, and allow for
precise tests fornon­SM contributions.
January 5th 2017

B2TiP reportA.- Gaz
preliminary

10Semileptonic Decays●

Semileptonic B decays have been used at
the B­factories to measure |Vcb| and |Vub|:

M. Rotondo, KEKFF 2015

●

●

●

Huge progress, but also tension
between inclusive and exclusive
determinations;
LHCb can contribute to this field,
but Belle II will have the advantage
of more modes accessible;
Collaboration with theorists will be vital.
January 5th 2017

A. Gaz11

B→D tn(*)●

A hot topic in B Physics comes from the measurement of:l = e, m●

W+ / H +Very clean prediction from the theory:
PRD 78, 014003 (2008)
PRD 85, 094025 (2012)●

Measured values seemto be consistently
higher than SM
prediction: level of
discrepancy at 4s now.
January 5th 2017

A. Gaz12

Prospects on B → D t n
(*)

●

●

●

The excess needs to be confirmed with more data:dR(D)/R(D)dR(D*)/R(D*)

World Average

12%

5.5%

Belle II (50 ab-1)

3.4%

2.1%

The experimental precision
will match the current
theoretical uncertainty

It will be important to look at more observables, measure t andD* polarization, measure rates as a function of q2, … ;Belle already measured the tpolarization with the full dataset:

P(t) = -0.38 ± 0.51+0.21-0.16●

Possibly the anomaly is linked toother tensions we see in B
physics.
January 5th 2017

A. GazBelle Preliminary, submitted to PRL
see S. Hirose's poster tonight13

Electroweak Penguins●●

Several tensions at the 2­3s levelfrom decays mediated byelectroweak penguin amplitudes;

Lepton Flavor Universality
violation in B+ → K+l+l­?

2.6s tension fromlatest LHCb
measurement

1●

LHCb will have the edge on many of these decays, but
confirmation from Belle II will be crucial.
January 5th 2017

A. Gaz14

Electroweak Penguins●

Attempts to fit all the different anomalies in electroweak penguin
dominated B decays have been made;e.g. J. Virto at CKM2016●●

Many observables are analyzed and NP contributions to the Wilson
coefficients are studied;
Negative C9NP seems a goodcandidate;●

If this is confirmed, Belle II will
have the potential to discover
New Physics with >5s
significance.
January 5th 2017

A. Gaz15

Charm Physics

January 5th 2017

A. Gaz16

Motivations
●

●

●

●

B­factories discovered D0­D0 mixing;
Next: improve knowledge of mixing parameters, look for direct
and indirect (in mixing) CP Violation, search for rare decays…;
Clear advantage on LHCb on some important areas:➔

semileptonic D decays (neutrinos in final state);➔

rare decays (D0 → gg, D0 → e+e­, …);

Substantial improvement over
Belle/BaBar on:➔➔

proper time resolution;

Belle II MCPRELIMINARY
D0 → K+Kst ~ 0.14 ps

flavor tagging: besides the D*+ self
tagging decays, new methods, basedon the analysis of the Rest Of Event(ROE) are being developed.

January 5th 2017

A. Gaz17

Prospects on Charm Physics
Mixing/CPV in D0 → Ksp+p­:

●

Belle

Belle II (50 ab-1)s(x) (10-2)

0.20

0.11

s(y) (10-2)

0.16

0.05

s(|q/p|) (10-2)

17.8

7.4

s(arg(q/p)) (o)

12.2

4.2

(this is based on an extrapolation from Belle results – a large fraction of 'irreducible' systematic
uncertainties will be reduced by moving to model­independent Dalitz Plot analysis)●

Sensitivity to D → gg (expected BF: a few 10 );●Belle II sensitivity with 50 ab­1:

●

­8

➔

~2 x 10­8 if sensitivity scales with L;➔~10­7 if sensitivity scales with sqrt(L);BF < 8.5 x 10-7

Controlling beam backgrounds will be the key!
January 5th 2017

A. GazBelle Collaboration,
PRD 93, 051102 (2016)18

t Physics

January 5th 2017

A. Gaz19

Lepton Flavor Violation in t decays●●●

In the SM, lepton flavor violating decays, like t → m g, are~forbidden, while NP could enhance their BF's up to O(10­8);
LHCb will be competitive with Belle II only on a very few
channels (most notably t → mmm);
Belle II will be the only to access final states with neutrals(g, p0, h('), …), control ofthe beam backgrounds
will be crucial.

January 5th 2017

A. Gaz20

t Electric Dipole Moment●

Other null test from the SM: t EDM;

BELLE - PRELIMINARY“Optimal observable” - PRD 45, 2405 (1992)●●

Belle's limit reaches the region where some NP models predict
potential enhancements;
Good margin for improvement on Re(dt), Im(dt) is currently
dominated by systematics. Better understanding of the detector
will be needed for Belle II to continue making progress.

January 5th 2017

A. Gaz21

e e → light hadrons+ ­January 5th 2017

A. Gaz22

Motivations●

Long standing discrepancy between theory and experiment in the (g-2)m:
E821 Collaboration, PRL 92, 1618102 (2004)

anomalous magnetic moment●

Experiment:(g-2)m/2 = 11 659 208.9 (6.3) x 10-10

Theory:(g-2)m/2 = 11 659 181.5 (4.9) x 10-10Discrepancy :(27.4 ± 8.0) x 10-10
3.5s discrepancy

Most of the uncertainty in the theory prediction comes from the hadronic
contribution:“hadronic vacuum polarization”

Phys. Rept. 447, 1-110 (2009)
January 5th 2017

size
uncertaintyof the hadronic contribution
A. GazSee next talk by Y. Sato on prospects 23
for the measurement of (g-2)mProspects
●

●

●

●

The vacuum polarization is connected e+
to the e+e- → hadrons through theoptical theorem;
At the B-factories we can exploit theinitial state radiation (ISR) and theelarge integrated luminosity toeffectively have a “scan” at low
invariant masses;
A large number of exclusive final
states has been investigated by
BaBar;
Due to trigger limitations, Belle
could not participate to thecampaign, but this will be an
important topic at Belle II!

January 5th 2017

A. GazY

24

Searches for dark/exotic particles

January 5th 2017

A. Gaz25

Dark photons decaying to invisible●●

Many BSM theories predict the existence of a Dark Sector;
Common ingredient: a dark photon A' that mixes kinetically with
the SM photon with strength e;●

Several search strategies already pioneered at the B­factories;●

Only at Belle II:

mono­photon signal: this requires a
special trigger (under development)
Enormous improvement wrt BaBar
January 5th 2017

A. Gaz26

Charmed Baryons●●

Substantial progress at Belle in the study
Yuji Kato received JPS
Young Scientist Awardof charmed baryons;
Several new states and decay modes have been observed for the
first time;First observationof Xc(3055)0

Belle Collaboration, PRD 94 032002 (2016)●●

The properties (spin­parity) of many of these states are not yet
determined;
Boost in statistics will allow the determination of the quantum
numbers of the newly discovered states (and the discovery of
more states).
January 5th 2017

A. Gaz27More exotic particles?
Belle top cited papers:
1) Observation of a narrow charmonium­like state in exclusive
B+ → K+ J/y p+ p­ decays – PRL 91, 262001 (2016);
2) Observation of large CP violation in the neutral B meson
system – PRL 87, 091802 (2001);

1269 citations

8313) Observation of a resonance­like structure in the p±y' mass distribution489
in exclusive B → K p±y' decays – PRL 100, 142001 (2008);
4) A measurement for the branching fraction of inclusive
B → Xs g at Belle – PLB 511, 151 (2001);

4275) Observation of a near­threshold w J/y mass enhancement in
exclusive B → K w J/y decays – PRL 94, 182002 (2005).

414

Several non­anticipated states have been found at Belle, whose
nature has not yet been fully clarified. More surprises are likely to
be in store for Belle II...
January 5th 2017

A. Gaz28

The Belle II Collaboration

700
100
23

Members
Institutions
Countries

January 5th 2017

Impressing computing infrastructure
for data reconstruction/analysis andMonte Carlo generation.
See Y. Kato’s talk on Belle IIcomputing on Friday
A. Gaz29

World Research Unit for
Heavy Flavor Particle Physics”WPI-next” under “Program for Promoting the Enhancement of Research Universities”

SuperKEKB/
Belle II

LHC-ATLAS

Toru Iijima•B, Tau Physics•Exotic hadrons

Makoto Tomoto●
Top physics●
Higgs

TheoryJunji Hisano●
FlavorPhysics●
Dark MatterPeter Krizan(Ljubljana)

Alessandro
Gaz

Tim Gershon(Warwick)
Kodai
Matsuoka

Yuji
Omura

Gino Isidori Yu Nakahama(Zurich)30

SuperKEKB commissioning
Feb­June 2016, PHASE1 commissioning(without Belle II):➔➔➔

Basic machine tuning;
Vacuum scrubbing;
Background studies;

Achieved 1010 (870) mA in the LER (HER)

January 5th 2017

A. Gaz31

Road to Physics
PHASE 2: January 2018 – June 2018
Machine commissioning with the Belle II detector (w/o silicon vertex detectors);More background studies and detector commissioning on e +e­ collisions;Target luminosity: 1034 cm­2s­1;
Some physics opportunities at the energy of the Y(6s).

PHASE 3: December 2018 –Belle II detector complete;
Luminosity tuning;
Start of Physics Run!

January 5th 2017

A. Gaz32

Conclusions
●

●

●

●
●

●
●

The Belle II detector is in its final stages of construction, roll­in to
the beam line is scheduled for March 14th;
Aim: discover Physics beyond the Standard Model exploring avery broad physics case, ranging from B physics to (g­2) m;
There will be competition with LHCb, but high degree ofcomplementarity and many channels will be exclusive to Belle II;
Several exciting anomalies need to be confirmed;
First phase of SuperKEKB accelerator successfully completed;
We are looking forward for the first physics papers in 2018;
The B2TiP report on Belle II Physics Program and expected
sensitivity is on track to be released this coming Spring.
January 5th 2017

A. Gaz33

Backup Slides

January 5th 2017

A. Gaz34

Competition and Complementarity
In the next years LHCb and Belle II will fiercely compete in someareas … in others, they will exploit their own strengths;
●

LHCb:
➔
➔
➔

●

Very high b­quark cross section (B0, B+, Bs, Bc, Lb, …);
Unbeatable in rare decays to charged final state particles;
Large boost, long flight lengths → can exploit it forkinematical constraints;

Belle II:➔➔➔

Coherent BB production from Y(4s) decays;
Very clean environment, great efficiency in final states withneutrals (p0, h('), w, …);Possibility to do energy scans above/below thresholds.

January 5th 2017

A. Gaz35

Semileptonic Decays●●●|Vcb| and |Vub| are fundamental inputs for the CKM fit;
Semileptonic B decays allow for their extraction at tree level,
their determination is crucial for New Physics searches;
Tremendous progress in the last decade:PDG 2014:|Vcb|

Inclusive: (42.2 ± 0.7) x 10­3
Exclusive: (39.5 ± 0.8) x 10­3●|Vub|
(4.41 ± 0.21) x 10­3
(3.28 ± 0.29) x 10­3

Error on |Vcb| < 2%, on |Vub| ~ 5­9%;… but the FNAL/MILC collaboration now obtains ~4% error on the
exclusive determination of |Vub| from BaBar + Belle...

●●M. Rotondo, KEKFF 2015

Great improvement on the errors, but ~3s tension between
inclusive and exclusive determinations of both |Vcb| and |Vub|;
LHCb entered the game with Lb → Lc/p m n (!).
January 5th 2017

A. Gaz36

Semileptonic Decays
Result:experimental●●

The presence of right­
handed (V+A) currents
could explain thediscrepancy between
inclusive and exclusive
determinations;

FF LQCD
prediction

uncertainty
from |Vcb|

The Lb result from LHCb
strongly disfavors thishypothesis.
January 5th 2017

A. Gaz37

Semileptonic Decays●

Exclusive |Vub| determination from B → p l n data (BaBar +Belle) from the FNAL/MILC Collaboration (2015):
PRD 92, 014024 (2015)

January 5th 2017

A. Gaz38

Semileptonic Decays
Corrected mass:

mhm: visible mass of the hm pairp⊥ : transverse momentum wrt the Lbflight direction (which is determinedfrom the position of the decay vertex
wrt the primary vertex)
KpJanuary 5th 2017

A. Gaz39

Semileptonic Decays

January 5th 2017

A. Gaz40

B → D tn
(*)

●

●

●

One of the hot topics of the moment, potential charged Higgs­likeparticles can cant effects;
Measure:l = e, mClean predictions from SM, most uncertainties cancel in theratio:
PRD 78, 014003 (2008)
PRD 85, 094025 (2012)●●

BaBar saw a 3.4s discrepancy
a few years ago;

Experiment
TheoryType II 2HDM almost ruled out
by this result.
More about potential New Physics
effects in M. Tanaka's talk tomorrow
January 5th 2017

A. Gaz

BaBar Collaboration,
PRD 88, 072012 (2013)41

B → D tn(*)●

In the last year, Belle and LHCb measured the same quantities:
LHCb performs a template fit on
the 3 kinematic variables:
LHCb-TALK-2015-178

Belle reconstructs signal events on
the recoil of hadronic Btag, using
leptonic t decays (similar to BaBar)
~1.4s
~1.8s

Belle Collaboration,
PRD 92, 072014 (2015)
January 5th 2017

~2.1s
Still tension with SM
A. Gaz

LHCb Collaboration,
PRL 115, 111803 (2015)42

B → D tn
(*)

●

●

●

New Belle result on R(D*) for B0 → D*∓t±n;
Analysis performed on the recoil of B0 → D*∓l±n mesons(statistically independent from previous Belle analysis);

Signal yield extracted by
2D fit on NN output(combining kinematic
variables) and extra
energy EECL;

NN > 0.8

1.6s above SM
January 5th 2017

A. Gaz43

B → D tn
(*)

2.0s

2.7s

BaBar Collaboration,
PRD 88, 072012 (2013)
January 5th 2017

A. Gaz44

B → D tn(*)

January 5th 2017

A. Gaz45

B → D tn(*)

LHCb-TALK-2015-178

January 5th 2017

A. Gaz46

B → D tn(*)

January 5th 2017

A. Gaz47

B → D tn(*)

PRELIMINARY – from P. Goldenzweig @ Moriond EW 2016
January 5th 2017

A. Gaz48

CP violation in BB mixing●

Some formalism of BB oscillations:Time evolution of a B0B0 system
Mass eigenstatesIf
the probability for a B0
to oscillate to a B0 is different from theprobability of a B0 going to B0●

Experimentally we measure:●

The Standard Model predicts tiny CP violation in mixing:
Experimental precision ~10­3,still room for surprises...
A. Lenz, arXiv 1205.1444 [hep-ph]
January 5th 2017

A. Gaz49

CP violation in BB mixing
Different strategies to measure ASL:
1) Tag two B0's (at B­factories and D0):
Time integrated,
exploiting symmetry inproduction of B0 and B0… can also use
l±K± pairs!

2) Untagged measurement (at LHCb):
Time dependent,
complications from theasymmetric production
at a pp collider

January 5th 2017

A. Gaz50

CP violation in BB mixing●

From PRL 114, 081801 (2015)

Experimental status:

BaBar (ll):BaBar (D*ln):
D0 (DmX):
LHCb (DmX):(­0.39 ± 0.35 ± 0.19)%( 0.06 ± 0.17 ± 0.35)%( 0.68 ± 0.45 ± 0.14)%( 0.02 ± 0.19 ± 0.30)%= AsSL

AdSL:

AsSL:
D0 (DsmX):(­1.12 ± 0.74 ± 0.17)%

LHCb (DsmX):(­0.06 ± 0.50 ± 0.36)%= AdSL●The next years will be quite interesting: still quite a bit of
margin for improvement (many systematics depend on statistics
of control samples).

January 5th 2017

A. Gaz51

Electroweak Penguins
Sensitive to the:C7: elctromagnetic penguin
C9: vector electroweak
C10: axial­vector electroweak
Wilson Coefficients●

Very suppressed in the SM (BF ~ 10­6);●Many observables and often very precise predictions from theory;
Belle, PRL 103 171801 (2009)
CDF, PRL 107 161801 (2011)

LHCb, PRL 108 181806 (2012)

BABAR, PRD 79 031102 (2009)

LHC turn-on
CMS, PLB 727 77 (2013)

q2 (GeV2)
January 5th 2017

A. Gaz52

Electroweak Penguins: P'5

●

●

●

Angular analysis of B0 → K*0m+m­;

Many observables investigated, can cancel the leading
uncertainty on hadronic
form factor by defining“optimised” observables:
Interesting discrepancy
is observed in P'5;

LHCb Collaboration,
JHEP 1602, 104 (2016)(full definitions of observables in backup)

●

●

DHMV:
JHEP 1412,
125 (2014)

Global fit to complete set of observables gives a 3.4s tension with
SM: New Physics or hadronic effects larger than expected?
While the experiments improve the precision, input from theory
is essential.
January 5th 2017

A. Gaz53

Electroweak Penguins: LUV?
●●

Tests of Lepton Universality in b → sl+l­ decays can reveal thepresence of Higgs­like particles;
LHCb measured the ratio RK in B+ → K+l+l­: 1 (modulo tiny corrections)●

Challenging analysis, need to correct for Bremstrahlung;●In 1 < q2 < 6 GeV2:●

2.6s tension wrt
expectation: this needs
confirmation!
January 5th 2017

A. Gaz

LHCb Collaboration,
PRL 113, 151601 (2014)54

Electroweak Penguins: Outlook●

Quite a few channels where LHCb will improve a lot in the next
couple years:➔➔●

B → p l+l­;
Bs → f l+l­;➔

Lb → L l l ;

➔

…

+ ­

}

Keep refining precision on differential BF's,
CP asymmetries, angular observables,
Lepton Universality...

… and quite a few more where we need to wait for Belle II:
➔
➔
➔
➔
➔
➔

B → K(*) t+t­; current limit ~2 orders of magnitude above predictions
B → K(*) n n; might see a signal with full dataset
but it is crucial to control the machine backgrounds
B → gg;(semi­)inclusive b → d/s g;Time dependent CPV in B0 → KSp0g, B0 → r0 g;}…

January 5th 2017

A. Gaz55

Electroweak Penguins●

Definitions of main observables:

I(q2): q2 dependent angular observables.
They are expressed as a combination of 6
decay amplitudes (3 transversity states x
2 chirality states of the mm system)

January 5th 2017

A. Gaz56

Electroweak Penguins: AFB

q : angle between the l+ (l-)
momentum and the B (B)momentum in the l+l­ rest frame

January 5th 2017

A. Gaz57

The Angles of the UT●

One of the main goals of the B­factories: still a lot to do!

➔

f 1/b: now well into the precision era;➔f 2/a: larger theoretical and experimental uncertainties, will need➔to combine several modes;
f 3/g: measured through tree level amplitudes: crucial input for
the CKM fit.
January 5th 2017

A. Gaz58

f1/b from charmonium K

BaBar Collaboration
PRD 79, 072009 (2009)

Belle Collaboration
PRL 108, 171802 (2012)0

LHCb Collaboration
PRL 115, 031601 (2015)

So far we assumed that penguin pollution played a negligible rolein these measurements: we cannot afford this luxury any longer...
January 5th 2017

A. Gaz59

f1/b – Penguin Pollution●●●

Bd → J/y K0
Bs → J/y f
●
●

c

J/y
J/y
c
Penguin diagrams carrying
b
b
c
u
c
different weak phases
+
0
0
+
W
B
B
W
s
s
contribute to these decaysdd0
and can shift the measuredKK0dsee e.g.
value of the phase by asdK. De Bruyn, R. Fleisher
JHEP 1503, 145 (2015)
much as 1o;
Those contributions cannot be reliably computed by QCD;
Need a coherent plan to constrain these effects experimentally,measuring weak phases of SU(3) or U­spin related decays:

Bd → J/y p0, Bs → J/y K0
Bs → J/y K , Bd → J/y r*00

Recent measurements from LHCb:
JHEP 1506, 131 (2015)
PLB 742, 38 (2015)

Already got useful constraints, but need more precision;
Strong interplay between LHCb and Belle II!
January 5th 2017

A. Gaz60

f3/g status●

GLW - Phys. Lett. B253, 483 (1991)
Methods exploiting the interference
ADS – Phys. Rev. D63, 036005 (2001)(*)
between tree level B → DK
GGSZ – Phys. Rev. D68, 054018 (2003)
amplitudes pioneered at the B­factories:

favored

Vcb
●

Vub

~11o uncertainty fromthe B-factories

suppressed

LHCb is now dominating the scene:
Excluding B → Dp
All

LHCb-CONF-2014-004
January 5th 2017

A. Gaz61

f3/g outlook●

LHCb also measures it from time dependent Bs → Ds∓K± decays:

LHCb Collaboration,
JHEP 1411, 60 (2014)●

P. Urquijo
Belle II LHCb sensitivity
extrapolations

Enormous progress expected in thenext decade, the competition
between LHCb and Belle II will betight!
January 5th 2017

A. Gaz62

f2/a status●

Can be extracted in a way conceptually similar to f1/b from B0 → pp,

B0 → rr, but sizable penguin pollution requires isospin analysis (andleads to ambiguities);

B → r+rBelle Collaboration,
PRD 93 032010 (2016)●●

B → r0r0
LHCb Collaboration,
PLB 747 468 (2015)

Current precision ~8o;
LHCb will dominate on r0r0, Belle II on
r+r-, r+r0. Expected precision ~3o fromboth pp and rr by the end of Belle II.
January 5th 2017

A. Gaz63

f2/a from TD B → p p
0

●

0 0

Precision on f2/a from B → pp is limited by small B0 → p0p0

branching ratio and the fact that we could not measure the S p0p0
parameter;●

A TD analysis, exploiting photon conversion and Dalitz decays
can be attempted at Belle II (need high integrated luminosityand clean environment!);
Ambiguity
reduced to 2-fold!
P. Vanhoefer,
B2TiP Fall 2014

F. Abudinen
B2TiP Fall 2015●

Estimate of the sensitivity with 50 ab­1 currently in progress.

January 5th 2017

A. Gaz64

f3/g determinations
Decay amplitudes:

Weak phase changes signJanuary 5th 2017

A. GazStrong phase (measured fromthe data) stays the same65

f3/g : ADS method●●

Select events where the (anti)D 0 from the favored amplitude decays to a
DCS final state (and the (anti)D 0 from the suppressed amplitude decays tothe same Cabibbo favored final state):

We define the two observables...

...related to g :January 5th 2017

A. GazD : strong phase difference between theabove amplitudes (provided by CLEO)
66

f3/g : GLW method●

Both D 0 and D 0 decay to the same CP eigenstate;●

The four (only three independent) GLW observables are:●

They are sensitive to g through:no need of external inputs

January 5th 2017

A. Gaz67

f3/g : GGSZ method●

Dalitz plot analysis: exploit the variation of the strong phaseacross the DP to increase sensitivity on g;
D 0 → K S +  -January 5th 2017

D 0 → K SK + K -A. Gaz68