Branching Fraction Measurement of B± → χc1 π+π- K±
and Search for a Narrow Resonance with the Belle Experiment
Elisabeth Patricia Panzenböck
Georg-August University, Göttingen, Germany
Nara Women's University, Nara, Japan
GöttingenDecember 2nd 2014

Contents●

Exotic Hadrons and Charmonium(-like) States●

The Belle Experiment●

Event Selection and Reconstruction of B± → χc1 π+π- K±●

MC Studies and Results●–

Branching Fraction Measurement–

Invariant Mass Spectrum of χc1 π+π-Conclusion

Why Exotic Hadrons ?
●we see two types of conventional
structures in hadrons: meson & baryon

Meson

Baryon

c

u

c

u

u

3

Why Exotic Hadrons ?
●●we see two types of conventional
structures in hadrons: meson & baryon

Baryon

c

u

c

u

u

other combinations are not explicitely
forbidden by QCD !
–

●

Meson

new forms of matter such as
mesonic molecules, tetraquarks,
quark-gluon hybrids and others

QCD motivated models for hadrons
predict these exotic states in theircalculations
g*4

Why Exotic Hadrons ?
●●we see two types of conventional
structures in hadrons: meson & baryon●➔

Baryon

c

u

c

u

u

other combinations are not explicitely
forbidden by QCD !
–

●

Meson

new forms of matter such as
mesonic molecules, tetraquarks,
quark-gluon hybrids and others

QCD motivated models for hadrons
predict these exotic states in theircalculations
lack of experimental evidence for along time, but many discoveries recentlyg*unusual hadron structures might be a
key to reveal a new aspect of QCD
5

Charmonium(-like) States●●➔light flavours (u, d, s) may mix,
still interesting i.e. for glueball searches
relation between observed states
and constituent quarks is desired
to be rather straightforward
advantage of heavy flavours (c, b):higher masses serve as cut-off andallow usage of non-relativistic QCD
to precisely calculate spectrum
J: angular momentum
P: parity
C: charge conjugation

6

Charmonium(-like) States
●

●

➔

●

light flavours (u, d, s) may mix,
still interesting i.e. for glueball searches
D0D*0

relation between observed states
and constituent quarks is desired
to be rather straightforward

D+D-

advantage of heavy flavours (c, b):higher masses serve as cut-off andallow usage of non-relativistic QCD
to precisely calculate spectrum

Γ=300 keV

trends in the spectrum:–

narrow states below open charm(DD) threshold, electromagnetic
decays compete with hadronic
decays (suppressed by OZI rule!)

Γ=93 keV
J/ψ

J/ψ

π+ ud
π0 dd
π- du

c
c
c
c

γ

l+
l-

7

Charmonium(-like) States
Γ=70 MeV●●➔

light flavours (u, d, s) may mix,
still interesting i.e. for glueball searches
relation between observed states
and constituent quarks is desired
to be rather straightforward

D0D*0

c
c

ψ(3770)

D+ cd
D- cd

Γ=27 MeV

D+D-

advantage of heavy flavours (c, b):higher masses serve as cut-off andallow usage of non-relativistic QCD
to precisely calculate spectrum

trends in the spectrum:–

narrow states below open charm(DD) threshold–broad states above threshold due tostrong decay to charmed meson pair8

Charmonium(-like) Production in B Factories●●

various processes to produce
charmonium(-like) particles

a

b

c

d

allowed/ favoured quantum numbers
depend on production process(a) B meson decays(b) initial state radiation(c) two-photon collisions(d) double charmonium production

9

Charmonium(-like) Production in B Factories●●

various processes to produce
charmonium(-like) particlesaballowed/ favoured quantum numbers
depend on production process(a) B meson decays(b) initial state radiation(c) two-photon collisions

JPC = 0-+, 1--, 1++cd(d) double charmonium production

10

Charmonium(-like) Production in B Factories●●

various processes to produce
charmonium(-like) particlesaballowed/ favoured quantum numbers
depend on production process(a) B meson decays(b) initial state radiation(c) two-photon collisions

JPC = 1-cd(d) double charmonium production

11

Charmonium(-like) Production in B Factories●●

various processes to produce
charmonium(-like) particles

a

b

c

d

allowed/ favoured quantum numbers
depend on production process(a) B meson decays(b) initial state radiation(c) two-photon collisions(d) double charmonium production

JPC = 0-+, 2++
12

Charmonium(-like) Production in B Factories●●

various processes to produce
charmonium(-like) particles

a

b

c

d

allowed/ favoured quantum numbers
depend on production process(a) B meson decays(b) initial state radiation(c) two-photon collisions(d) double charmonium production

C = +1
13

Charmonium(-like) Production in B Factories●●

various processes to produce
charmonium(-like) particlesab

JPC = 0-+, 1--, 1++

JPC = 1--cd

JPC = 0-+, 2++

C = +1

allowed/ favoured quantum numbers
depend on production process(a) B meson decays(b) initial state radiation(c) two-photon collisions(d) double charmonium production➔

ideal clean environment forcharmonium spectroscopy

14

The Discovery of X(3872)
●

●

➔

➔

Belle, 2003:
very narrow peak found above theDD threshold in B+→ (J/ψπ+π-)K+ !
does not match properties of known
conventional charmonium states

ψ(2S)Γ<1.2 MeV

X(3872)are there other decay modes ?
how is X(3872) related to D0D*0
as it is very close to this threshold ?

15

X(3872) Properties●ccquantum numbers JPC = 1++ determined fromangular distribution of J/ψπ+π➔

2013

might be a conventional cc state,maybe the as yet unseen χc1(2P)(θx being X(3872)'s helicity angle)

16

X(3872) Properties
●

●

c
c

quantum numbers JPC = 1++ determined fromangular distributions of J/ψπ+π- and J/ψ(π+π-π0)
isospin violation found in equally often decays to
two pions via ρ (I=1) and three pions via ω (I=0)
➔

●

c q
c q

mass difference of 50 MeV to χc1(2P) andisospin violation disfavour assignment asconventional cc !

no partner found: charged or differing mass,suggests strong isospin 0 compontent, C-odd➔➢

isospin violation and lack of partner states
disfavour tetraquark hypothesis according
to model predictions !

➢

➢

➢

charged partner search in
J/ψπ+π0C-odd partner search in
J/ψη and χc1γ
different mass search in
charged vs. neutral B decays
~ 0.5
17

X(3872) Properties
●

●

●

●

●

quantum numbers JPC = 1++ determined fromangular distributions of J/ψπ+π- and J/ψ(π+π-π0)
isospin violation found in equally often decays to
two pions via ρ (I=1) and three pions via ω (I=0)
no partner found: C-odd, charged or differing
mass suggests strong isospin 0 component
mass (3871.69 ± 0.17) MeV is very close to
the D0D*0 threshold at (3871.80 ± 0.09) MeV !
decays to D0D*0 have been observed withBr(X(3872)→D0D*0) ≈ 10x Br(X(3872)→J/ψπ+π-)➔

D* → D0π0
D* → D0γ

might be a D0D*0 (di-mesonic) molecule18

X(3872) Properties
●

●

●

●

●

●

●

2014

quantum numbers JPC = 1++ determined throughangular distribution of J/ψπ+π- and J/ψ(π+π-π0)
isospin violation found in equally often decays to
two pions via ρ (I=1) and three pions via ω (I=0)
no partner found: C-odd, charged or differing
mass suggests most likely isospin 0

2014

mass (3871.69 ± 0.17) MeV is very close to
the D0D*0 threshold at (3871.80 ± 0.09) MeV !
decays to D0D*0 have been seen withBr(X(3872)→D0D*0) ≈ 10x Br(X(3872)→J/ψπ+π-)radiative decays: measured opposite of prediction
Br(X(3872)→ψ(2S)γ) ≈ 2.5x Br(X(3872)→J/ψγ)
also: pure molecule would be too fragile to be
produced at Tevatron (CDF) or LHC (LHCb)➔

disfavours pure molecule hypothesis !

c

5 fm
0

0

D D*

J/ψ

c

0.4 fm19

Interpretation for X(3872)●➔

most plausible interpretation of X(3872):
admixture !
DD molecule is mixing with an ordinarycharmonium state with same JPC,
i.e. the as yet unseen χc1(2P)✔

quantum numbers✔

molecular part can explain isospin violation✔

conventional cc core can explain the
production in high energy machines
like Tevatron or LHC
Rψγ: ratio of branching fractions ofX(3872) decay into ψ(2S)γ and J/ψγ

20

Interpretation for X(3872)●●

most plausible interpretation of X(3872):
admixture !
Blah
DD molecule is mixing with an ordinarycharmonium state with same JPC,

χc1(2P)
D0D*0i.e. the as yet unseen χc1(2P)
π+
●

π-

D+D-

if χc1(2P) is not mixing to form X(3872),
it is still expected to decay to χc1(1P)π+πBlah–χc1(2P) mass prediction at 3920 MeV–

χc1(2P) →χc1π+π- dipion transition
expected due to no quantum number
conflict, as seen in ψ(2S) → J/ψ π+π21Interpretation for X(3872)●●

most plausible interpretation of X(3872):
admixture !
DD molecule is mixing with an ordinarycharmonium state with same JPC,
i.e. the as yet unseen χc1(2P)●

in both cases: χc1π+π- is a suitable and interestingsource to look for either X(3872) or χc1(2P) !

if χc1(2P) is not mixing to form X(3872),
it is still expected to decay to χc1(1P)π+π–χc1(2P) mass prediction at 3920 MeV–

χc1(2P) →χc1π+π- dipion transition
expected due to no quantum number
conflict, as seen in ψ(2S) → J/ψ π+π22

The Belle Experiment

3.5 GeV e+

8 GeV e-

KEKB: 8 GeV e- beam × 3.5 GeV e+ beam
mainly @ Υ(4S) resonance (√s = 10.58 GeV)

Belle Detector: high resolution 4π spectrometerwith particle identification capability
23

Belle Detector Performance
4π general purpose spectrometer with
●

●

●

●

●

●

high momentum resolution
σp/p = 0.3%@1GeV/cability to detect photons down
to 30 MeV
good photon energy resolution
σM = 5 MeV for π0→γγ
lepton identification capability
ε > 0.9, fake < 0.01
K/ π/ p separation capability
ε ~ 0.9, fake < 0.1
excellent B decay vertex reconstruction
σ(Δz) = 80μm!
24Belle Experiment Achievements●●●

originally designed and operated to test
SM mechansim for CP violation andmeasure time-dependent CP violationin the B system
run 1999 – 2010:
772M B meson pairs recorded
all its features led to many discoveries,
also beyond CP violationworld's highest luminosity in e+e- at Y(4S) region !
25

Event Selection and Decay Reconstruction: B± → χc1 π+π- K±●

analysis procedure: reconstruct B±
π+

K+
B+

e+

X?
e-

πχc1

у

e+ / μ+J/ψ
e- / μ-B-

26

Event Selection and Decay Reconstruction: B± → χc1 π+π- K±●

analysis procedure: reconstruct B±
π+

K+
B+

e+

X?
e-

●

selection cuts for intermediate particles:–

impact parameters: distance tointeraction point for charged tracks|dr| < 1.5 cm, |dz| < 5.0 cm

e+ / μ+–electron likelihood > 0.01

e- / μ-–muon likelihood > 0.1

πχc1

у
J/ψ

B-

●

●

dE/dx in CDC,
E/p ratio (E in ECL and p in CDC, SVD)
shower shape in ECL
number of Cherenkov photons in ACC
track penetration depth andhit scatter pattern in KLM
reconstructed hits in KLM compared to
extrapolation of CDC tracks

27

Event Selection and Decay Reconstruction: B± → χc1 π+π- K±●

analysis procedure: reconstruct B±
π+

K+
B+

e+

X?
e-

B-

●

selection cuts for intermediate particles:–

impact parameters: distance tointeraction point for charged tracks|dr| < 1.5 cm, |dz| < 5.0 cm

e+ / μ+–electron likelihood > 0.01

e- / μ-–muon likelihood > 0.1–

J/ψ window (nom. mass 3097 MeV):
2950/ 3030 MeV ≤ M(ee/μμ) ≤ 3130 MeV

πχc1

у
J/ψ

28

Event Selection and Decay Reconstruction: B± → χc1 π+π- K±●

analysis procedure: reconstruct B±
π+

K+
B+

e+

X?
e-

B-

●

selection cuts for intermediate particles:–

impact parameters: distance tointeraction point for charged tracks|dr| < 1.5 cm, |dz| < 5.0 cm

e+ / μ+–electron likelihood > 0.01

e- / μ-–muon likelihood > 0.1–

J/ψ window (nom. mass 3097 MeV):
2950/ 3030 MeV ≤ M(ee/μμ) ≤ 3130 MeV–

χc1 window (nom. mass 3511 MeV):
3467 MeV < M(J/ψ γ) < 3535 MeV–

perform mass-constrained fits for
J/ψ and χc1 candidates

πχc1

у
J/ψ

29

Event Selection and Decay Reconstruction: B± → χc1 π+π- K±●

analysis procedure: reconstruct B±
π+

K+
B+

e+

X?
e-

●

–

impact parameters: distance tointeraction point for charged tracks|dr| < 1.5 cm, |dz| < 5.0 cm

e+ / μ+–electron likelihood > 0.01

e- / μ-–muon likelihood > 0.1–

J/ψ window (nom. mass 3097 MeV):
2950/ 3030 MeV ≤ M(ee/μμ) ≤ 3130 MeV–

χc1 window (nom. mass 3511 MeV):
3467 MeV < M(J/ψ γ) < 3535 MeV–

perform mass-constrained fits for
J/ψ and χc1 candidates

πχc1

у
J/ψ

B-

●

selection cuts for intermediate particles:

kinematic variables in Υ(4s) rest frame:
beam-constrained mass Mbc anddifference to beam energy ΔE

30

Pion Selection
●

●

●

●

➔

small Q-value in X(3872) → χc1π+π- :3872 – (3511+140+140) ≈ 80 MeV
pions have very low transverse
momenta pT
results in curl up in CDC andpossible duplicated reconstruction
opening angle θopen between pion tracks:–~0° for same charge–~180° for opposite charge

compare pions in pairs, select the one
with smallest distance to interaction point

opposite charge

same charge
pT < 0.25 GeV|p(π1) − p(π2) | < 0.1 GeV

31B Candidate Reconstruction
signal MC

signal MC

32

B Candidate Reconstruction
ideally
peaks at 0nom. B mass
at 5.279 GeV

33

B Candidate Reconstruction
ideally
peaks at 0nom. B mass
at 5.279 GeV➔

signal window cut:–

|ΔE| < 0.02 GeV–

Mbc > 5.27 GeV

34

ΔE Distribution – Background Estimation●

B → J/ψ X MC sample for bkg study–●●

100x amount of data

signal is included in the MC sample
only peaking background comingfrom B± → χc2 π+π-K±–●

Mbc > 5.27 GeV
B → J/ψ X MC

shifted to negative ΔE region due toχc2's slightly higher mass, remember:all other backgrounds are smooth35

ΔE Distribution – Background Estimation●

B → J/ψ X MC sample for bkg study–●●

100x amount of data

signal is included in the MC sample
only peaking background comingfrom B± → χc2 π+π-K±–●

Mbc > 5.27 GeV
B → J/ψ X MC

shifted to negative ΔE region due toχc2's slightly higher mass, remember:Image Courtesy:
Vishal Bhardwaj

all other backgrounds are smooth36

ΔE Distribution – PDF and MC Expectation●●

unbinned maximum likelihood (UML) fit
to B → J/ψ X MC sample to findprobability density function (PDF)–

signal:sum of two Gaussians–

B± → χc2 π+π-K±:
sum of two Gaussians–

flat bkg:
1st order Chebyshev polynomial

Mbc > 5.27 GeV
B → J/ψ X MC

expected peak yield for the as yet unseen decay B± → χc1 π+π- K± : 1700 events–

assuming

decay dynamics
37

ΔE Distribution – Looking at Data
first observation of the decay of
B± → χc1π+π-K± with a signal peak yieldof 1597 ± 76 events

Mbc > 5.27 GeV
772M BB pairs

B± → χc2 π+π- K±●

comparing resolutions:σ(data) / σ(MC) = (1.18 ± 0.07)%➔

consistent within 10%
38

Reconstruction Efficiency Considerations
●

➔

●

➔

efficiency is changing as a functionof the invariant mass of χc1 π+πusing a reconstruction efficiency
weighted with the obtained signal yieldper χc1π+π- mass bin

efficiency correction estimated from
lepton and particle identification: 0.9622

signal MC
100 MeV bins

772M BB pairs
100 MeV bins

resultant reconstruction efficiency 12.90%

39

Branching Ratio of B± → χc1π+π-K±●

Nsig – 1597 ± 76●

Br(χc1 → J/ψγ) – (34.8 ± 1.5)%●

NBB – 772 x106●

Br(J/ψ →e+e-) – (5.94 ± 0.06)%●

Br(J/ψ →μ+μ-) – (5.93 ± 0.06)%●

systematic uncertainty – 5.10%●

εdet – 12.90%

40

The χc1 π+π- Invariant Mass Distribution●●

select B signal region to look
into M(χc1 π+π-)–|ΔE| < 0.02 GeV–

Mbc > 5.27 GeV

Mbc > 5.27 GeV
772M BB pairs

search for–a narrow resonance X(3872)
at 3872 MeV or–an as yet unseen charmoniumχc1(2P ) at 3920 MeV

41

M(χc1 π+π-) Distribution – Expected Background●●no peaking structure except fora ψ(2S) reflection at 4.1 GeV
ψ(2S) → J/ψ

π + π-

Mbc > 5.27 GeV|ΔE| < 0.02 GeV
B → J/ψ X MC

+γ
➔

➔

results in a fake χc1 !
but: region above 4.0 GeV is
not of interest for this analysis

42

M(χc1 π+π-) Distribution – Looking at Data

Mbc > 5.27 GeV|ΔE| < 0.02 GeV
772M BB pairs43M(χc1 π+π-) Distribution – Looking at Data

Mbc > 5.27 GeV|ΔE| < 0.02 GeV
772M BB pairs44

X(3872) → χc1 π+π●

➔

●

●

●

assuming B(X(3872) → χc1π+π−) tobe similar to B(X(3872) → J/ψπ+π−)roughly 15 events expected and seeing
X(3872) → χc1π+π− is within sensitivity reach

Mbc > 5.27 GeV|ΔE| < 0.02 GeV
772M BB pairs±3σ

not enough statistics for a conclusive fit
use approach of Feldman-Cousins
at 90% confidence level:
estimated signal events Nsig < 2.44
reconstruction efficiency εdet = 5.59%45

χc1(2P) → χc1 π+π●

●

➔

●

●

natural width estimated from otherχcJ(2P) states → 20 MeV
resolution estimated from MC studies(Gauss standard deviation) → 2 MeV

Mbc > 5.27 GeV|ΔE| < 0.02 GeV
772M BB pairs

fit with convolution of Gauss andBreit-Wigner → ( 12.2 ± 9.1 ) yieldconsidering 90% confidence level:
estimated signal events Nsig < 30.34
reconstruction efficiency εdet = 8.91%

46

Mbc > 5.27 GeV
772M BB pairs

Conclusion●●●

B± → χc1 π+π- K± unseen before this analysis
and important to pinpoint X(3872)'s structurevery interesting to look for:X(3872) or χc1(2P) decaying to χc1 π+πfirst observation of B± →χc1 π+π- K±
with (1597 ± 76) signal events from
772M BB pairs dataset–●

B± → χc2 π+πK±

X(3872)χc1(2P)

branching fraction 3.89 x 10-4

χc1 π+π- invariant mass spectrum:–

no statistically significant evidence for●

either X(3872): upper limit 1.4 x 10-6●

nor χc1(2P): upper limit 1.1 x 10-547

Backup48

Image Courtesy: Vishal Bhardwaj

49

Status on Exotic Hadrons●●

unexpected and still-fascinating X(3872)
has been joined by more than a dozen
other “XYZ” states that appear to lie
outside the quark model

charged states alligned according to best guessat quantum numbers of neutral charged partner

charmonium

charmonium(-like) states:–

X(3915), Y(3940), X(3940), X(4160)–

Y(4260), Y(4360), Y(4660)–

Z+(3900), Z+1(4050), Z+2(4250), Z+(4430)

50

Status on Exotic Hadrons●●●

unexpected and still-fascinating X(3872)
has been joined by more than a dozen
other “XYZ” states that appear to lie
outside the quark model

bottomonium

charmonium(-like) states:–

X(3915), Y(3940), X(3940), X(4160)–

Y(4260), Y(4360), Y(4660)–

Z+(3900), Z+1(4050), Z+2(4250), Z+(4430)

also, bottomonium(-like) states:–

Z+b(10610) and Z+b(10650) as
B(*)+B*0 molecule candidates–

equivalent to Y(4260) at 10.89 GeV?

51

Charmonium vs. Bottomonium – Status in PDG

52

53

X(3872) as Admixture

density of each component
differs as a function of the
distance r from the object's
center !

54

Belle Subdetectors●●

The Belle detector consists listed in order of radial distance from the interaction point of–a six-layer silicon vertex detector (SVD2),–

a ~50-layer central drift chamber (CDC),–

an array of ~1200 aerogel Cherenkov counters (ACC),–~130 time-of-flight scintillation counters (TOF),–

an electromagnetic calorimeter containing 8736 CsI(Tl) crystals (ECL),–

and the KLM detector.

All but the KLM are contained in a superconducting solenoid with a central magnetic
field of 1.5 T. The fourteen ~5-cm thick iron absorber plates of the KLM also serve as thesolenoid’s return yoke.

55

Systematic Uncertainties●

PDF – 2.96%: modeling and set parameters used for fitting distributions●

pion ID – 1.96%: Estimations are made based on a D* + → D0(K−π+)πslow process.

●lepton ID (e, μ) – 1.77%: J/ψ → e+e- (for EID) and e+e- → e+e-μ+μ- (for muID)●tracking – 1.71%: Track finding efficiency has been measured by the number of partiallyand fully reconstructed D* decays in D* → πD0, with D0 → ππKS and KS → π+π−. By
calculating the ratio of tracking efficiency in data and MC, the systematic uncertainty
associated with tracking has also been evaluated.

●

2ndary BF – 1.50%●

NBB – 1.37%: official number of Bs from Y(4S) recorded by Belle (771.581 ± 10.566) × 10 6●

kaon ID – 1.23%: see pion ID●●

π0 veto – 1.22%: obtaining the ratio of ∆E signal yield when using the cut, and without using
the cut, for data and Monte Carlo, and then dividing those in a double ratio, R(data/MC)
signal MC – 0.52%: limited MC sample of 0.5M events used to calculate efficiency➔

total: 5.10%

56

Electron Identification (EID)57

EID Efficiency●●●

One can also obtain the EID efficiency orinefficiency by comparing the J/ψ → e+eyield for the cases one or two electrons
are tagged, or the difference of the twocases.
The signal yield for single tagging andthe difference between single- anddouble-tagged events can be translated
to an (in)efficiency which is consistent
with the inefficiency that is predicted by
the MC.
The EID efficiency expected from thegeneric hadronic MC is consistent withthat for single electrons in real hadronic
data within 1%. The EID inefficiency isverified to be consistent between data
and MC within a 1.4% uncertainty.

58

EID Fake Rate for Pions and Kaons

●

●

●

●

Inclusive KS → π+π- decays are used as asource of charged pions to measure the
EID fake rate. No requirement is placedon the pion used to test the EID routines.
The overall agreement between data andMC is good in the pion fake rate case.
The fake rate for K± is examined using
the decay chain D*+→D0(→K-π+)π+. The
strategy for evaluating the fake rate is tocompare the signal yield of D0 with andwithout applying EID for the kaons.
Comparing events without EID andevents after applying EID and taking theratio, the fake rate for the kaons ismeasured to be comparable to the MC
prediction.

59

Muon Identification (MuID)●➔●

Muon identification begins with thereconstruction of a charged track in the
CDC with matching SVD hits, andcontinues with its extrapolation throughthe outer detectors to its stopping point
or its escape from the detector.
A track is considered to be within the
KLM acceptance if it crosses at least one
RPC layer; this requires at least 0:6
GeV/c of momentum.
A helical track, reconstructed in the CDC,
isrefined by a Kalman filter to determine
the helix parameters near the outermost
layer of CDC. The helix parameterization
is justified by the uniformity of thesolenoidal magnetic field within the
tracking volume and the small energy
loss of the track within the CDC.

●

Muon Likelihood: Two quantities areused to test the hypothesis that a
track is a muon rather than a hadron–

the difference between the measured
and expected range of the track–

the goodness of fit of the transverse
deviations of all hits associated withthe track (normalized by the numberof hits)

60

MuID Efficiency●●●

High-purity muons are obtained with thetwo photon reaction, e+e- → e+e-μ+μ- by
tagging one of the muons with a highmuon likelihood and then examining theother minimum-ionizing track in the event.
The contamination is predominantly frome+e- → τ+τ- where one τ decays
leptonically to give a tag muon and theother decays to πν to give a fake-muoncandidate, or from e+e- → e+e-ππX where
one of the pions is falsely tagged as amuon.
The systematic uncertainty is estimatedto be 2%, mainly from the residual hadroncontamination in the muon sample.
61

MuID Fake Rate for Pions and Kaons
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The majority of fake muons are punchthrough or decay-in-flight pions andkaons.
We measure the fake rate using thepions from KS → π+π- and the kaons from
D → Kπ where the D meson is identified
by observing the slow pion in D* → Dπslow.
A muon identification algorithm is usedthat uses the difference of muons fromhadrons in the range and the scatteringof the particles in the KLM.
Fake rates of pions are approximately
constant in the region p > 1.5 GeV/c.
Fake rates of kaons are approximately
constant in momentum above threshold.
62

X(3872) → χc1 π+π- – PDF and MC Expectation
Mbc > 5.27 GeV|ΔE| < 0.02 GeV

MC, normalized toexp. data statistics+ generated signal

if there are 15 eventsof X(3872) → χc1π+π-63

MC Study for χc1(2P)

σ = 2 MeV

64

The Belle2 Experiment●

Experimental Challenges–

10-20 times higher beam-related
backgrounds: Pile-up noise,
Radiation damage,–

10 times higher event rate: Seamlessdata acquisition system, High level
intelligent trigger–

Improved performance: Vertex
reconstruction, High particle ID
capability, Hermetic coverage.

65

The Belle2 ExperimentImage Courtesy: Ichiro Adachi (KEK)
Instr. for Colliding Beam Physics,
INSTR2014, Feb.24 - Mar.1, 2014

66

The Belle2 Experiment
●

●

●

●

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●

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currents x2
design luminosity of 8 x 1035 cm−2 s−1→ around 50 times as large as peak luminosity achieved by the KEKB collider
large crossing angle → low-emittance “nano-beam” collisions (10μm x 60nm)
vertex detector even closer to IP, 2 layers DEPFET pixel (14 & 22mm) sensors
and 4 layers of DSSD
CDC: larger radius and smaller cell size
Time-Of-Propagation (TOP) counters: ring-image of Cherenkov light cones in quartz radiator bars,
another ring-imaging Cherenkov counters with aerogel radiator in the forward end-cap
ECL with wide dynamic range → 20 MeV to 7 GeV, 2MHz wave-form sampling readout → morerobust against bkg, pure CsI crystals for end-cap → shorter time constant●

KLM modules will be replaced in the 2 innermost barrel layers and completely in the endcap●

Trigger rate 500Hz → 30kHz, Event size 40kB → 300kB(max)67