180716-fpcp-baryon.pdf - cern indico

Jul. 16, 2018Recent Results with Charm Baryons

S. Nishida FPCP 2018 @ Hyderabad

1

Shohei Nishida

Recent Results with Charm Baryons

FPCP 2018 @ Hyderabad

Juｌ. 16, 2018

KEK



2

Contents

• Introduction

• Absolute Branching Fraction of c+

✓ c+ → 0K+, (1530)0K+

✓ c+ → + X

• c →

• c+ → p+−

• Observation of c(2930)

• Hadronic Decay of c

• Excited c

• Doubly Charmed Baryon cc++

• Production Rate of Baryons.

• Summary

Belle II during construction



3

Charmed Baryons

• Charmed baryons consist of one heavy charm

quark and two light (u, d, s) quarks.

• Large mass difference provides a natural way to

classify these states using HQET (i.e. simpler than

other baryons).

• Production mechanism

✓ Charm production e+e− → cc at e+e− colliders,

prompt charm production at hadron collider.

✓ Through decays from B, Bs, b …..

c

qq

• Doubly charmed baryons

not well studied.



4

Charmed Baryons

Many decays of c

Observation of c(2930)

Decay of c

Observations

of c*

Study of cc



5

Experiments

BaBar @ PEP-II

e+e− : ~10.6 GeV ((4S))

(e+e− → cc) = 1.3 nb

Lpeak = 1×1034 cm−2 s−1

Belle @ KEKB

e+e− : ~10.6 GeV ((4S))

(e+e− → cc) = 1.3 nb

Lpeak = 2×1034 cm−2 s−1

BESIII @ BEPC II

e+e− : 2-4.6 GeV

(e+e− → cc) = 3 nb

Lpeak = 1×1033 cm−2 s−1

LHCb @ LHC

pp : 7-13 TeV

(cc) = 1.4-2.6 mb

Lpeak = 4×1032 cm−2 s−1

(luminosity leveling)



6

Absolute Branching Fraction of c

• BESIII accumulated 567 pb−1 of data at 4.599 GeV

✓ 26 MeV above c+c

− threshold: e+e− → c+c

−

• Absolute branching fraction can be measured by tagging one c.

✓ B(c+ → e+ e) = (3.63±0.38±0.20)% [PRL115, 221805 (2015)]

✓ B(c+ → pK−+) = (5.84±0.27±0.23)% [PRL116, 052001(2016)]

• 1.0 ×105 c+c

− produced.

• 12 c modes for single tag.

✓ depends on analyses.

• ~ 104 events tagged.

Also useful to study mode with neutrons:

c+ → − (→n−) ++0

[PLB772 (2017) 388]First observation.



7

c+ → 0K+, (1530)0K+

[arXiv:1803.04299]• c+ → 0K+ and (1530)0K+

• Pick up a kaon and measure the

missing mass.

• Only possible at clean environment.

0(1530)0

B(c+ → 0K+)

= (5.90±0.86±0.39)×10−3

B(c+ → (1530)0K+)

= (5.02±0.99±0.31)×10−3

• More precise than past relative

measurements.



8

c+ → + X

[arXiv:1803.05706]• Measurement of c+ → + X

• Single tag with c− → pKS, pK+−

• Select events with .

pKSpK+−

Sum of exclusive modes with is (24.5±2.1)%

(PDG) i.e. still more unmeasured modes with .

B(c+ → + X) = (38.2 ±0.8)%

+2.8−2.2

ACP(c+ → + X) = (2.1 ±1.4)%+7.0

−6.6



9

c →

• Provide information - scattering length.

✓ Useful information on the study of (1405).

• Analysis

✓ c+ → ++−, 0+0, +00

➢ Not c+ → −++ (− → n−).

✓ + → p0, 0 → 0, 0 → p−

✓ Signal is extracted in model independent

way using binned Dalitz distribution.

✓ B.F. relative to c+ → pK−+ is measured.

c → 711 fb−1

c+ → pK−+ efficiency

M(K)2

M(pK)2

0.18

0

[arXiv:1802.03421]

B(c+ → pK−+) =

(6.84±0.24 )% [Belle, PRL113, 042002(2014)]

(5.84±0.27±0.23)% [BESIII, PRL116, 052001(2016)]

(6.35±0.33)% [PDG]

+0.21−0.27



10

c →

c+ → ++−

M(+−)2

M(

+

−)2 0.05

0

c+ → +00

M(+0)2

M(

0

0)2

0.018

0

[arXiv:1802.03421]efficiency efficiency



11

c →

[arXiv:1802.03421]

B(c+ → pK−+) = (6.35±0.33)%

Efficiency corrected yields

Branching fractions

• First measurement of the branching ratio of c+ → +00

• Significant improvement in measurement of c+ → ++−, 0+0



12

c+ → p+−

• c+ → p+− : FCNC process.

• With the short distance effect, B.F. ~ O(10−9).

• Long distance (tree-level) effect: B.F. < O(10−6).

• New Physics may enhance the signal.

• Previous measurement < 4.4 × 10−5 by BaBar.

non-resonant

region

region

Measurement by LHCb with 3.0 fb−1.

[PRD97, 091101(R) (2018)]

• Divided into 3 M(+−) regions.

• c+ → p as a normalization mode.

(normal

-ization)

B(c+ → p+−) < 7.7×10−8

B(c+ → p) = (9.4±3.2±1.0±2.0)×10−4

(fourth error is from relevant B.F.)

• Improved the measurement.

• Demonstrate that rare decay of

charmed baryons can be studied.



13

Observation of c(2930)0

• Babar found some indication of c(2930)0 in

B− → K−c+c

−. with 210 fb−1.

✓ Bump in K−c+ distribution.

• The same decay can be used to study for

charmonium-like state like Y(4660)

(i.e. B → K−Y(4660) → K−c+c

− ).

• Belle performed the study with 711 fb−1.

[PRD77, 031101(R)]

210 fb−1

• B− → K−c+c

− with

c+ → p K−+, pKS, +, pKS+−, +−+.

(E is correlated with Mbc)



14


M(K−c+) distribution

Nothing seen in M(c+c

−) distribution

[EPJ C78, 252 (2018)]

• Observation of c(2930)0 with > 5.

• M(c(2930)0) = 2928.9±3.0 MeV

• (c(2930)0) = 19.5±8.4 MeV

• B(B− → c(2930)0c−) B(c(2930) 0 → K−c

+) = (1.73±0.45±0.21) × 10−4

+0.9−12.0

+5.9−7.9



15

Evidence for c(2930)+

[arXiv:1806.09182] • Same analysis with neutral B0 → KSc+c

−.

• Signal excess found in M(KSc) distribution.

• Evidence of c(2930)+ with 3.9.

• M(c(2930)+) = 2942.3±4.4±1.6 MeV

• (c(2930)+) = 14.8±8.8±7.1 MeV

• B(B0 → c(2930)+c−) B(c(2930)+ → K0c

+)

= (2.28±0.49±0.29) × 10−4



16

Hadronic Decay of c

• c has less information on its hadronic decay, compared to other

charmed baryons; Belle measured following decays.

• Normalization mode but no absolute branching fraction measured: −+

• Previously observed by CLEO [PRL86, 3730 (2001)], and BaBar [PRL99, 062001 (2007)] :

−+0, −++−, −K−++, 0K−+

• Previously observed by Fermilab E687 only [PLB338, 106 (1994)] :

+K−K−+ (more than −+ : 42 evt. v.s. 10 evt at E687)

• Modes not observed: −K0+, 0K0, K0K0

−+

• Belle analysis using 980 fb−1.

• Sub-decay modes: − → K−, − → −, 0 → 0,

+ → p0 , → p−



17

Hadronic Decay of c

−+0 −++−

−K−++ 0K−+

−KS0+ 0KS

0

0KS0KS

0+K−K−+

[PRD97,

032001(2018)]



18

Hadronic Decay of c

[PRD97, 032001(2018)]

−+0

−K−++

0K−+



19

Hadronic Decay of c

First measurement!

• +K−K−+ not found, while E687 observed 42.5±8.8 events

• B(Yc → Y++−) / B(Yc → Y+) >> 1 for other charmed baryons, but

B(c → ++−) / B(c → +) << 1

First measurement of

intermediate resonance

[PRD97, 032001(2018)]



20

Excited c

• c0 (ccs) : J=1/2

• Spectrum not known: only c(2770)0 →c (J=3/2) was observed.

• c*0 →c00 violates isospin.

• LHCb searched for the excited c0* using c

+K− final state.3.3 fb−1

[PRL 118, 182001(2017)]

• c+ is reconstructed

with pK−+.

• Five narrow c (3000/3050/3066/3090/3119)

are observed.

✓ = 1 9 MeV

• Wide ( ~ 60 MeV) enhancement at 3188 GeV.

3000

3050

3090

3066

31883119



21

Excited c

• Belle also measured c*0 → c+K− .

• c+ is reconstructed with −++, K−++, 0+,

0+−+, +K−+, KS+ and 0KS+.

980 fb−1

[arXiv:1805.09384,

accepted by PRL]

• c*0 width is fixed with the value from LHCb.

• All the c*0 except c(3119)0 are confirmed.

wrong sign

c+ sideband

c+

mass



22

Doubly Charmed Baryon cc++

• SELEX observed doubly charmed baryon cc+ in c

+K−+ and pD+K− at the mass

of 3518.7±1.7 MeV, with life time <33 fs. [PRL89, 112001 (2002), PLB628, 18 (2005)]

• The signal was not observed by FOCUS, BaBar, Belle and LHCb.

• Recently LHCb observed cc++ in c

+K−++ final state at the mass of 3621.40

±0.78 MeV [PRL119 (2017) 112001].

• Mass difference of ~100 MeV between cc+ and cc

++ is too large for isodoublets.

• Measurement of lifetime of cc++.

cc+ → c

+K−+ cc+ → c

+K−+

[PRD74, 011103 (2006)] [PRL97, 162001 (2006)]



23

Doubly Charmed Baryon cc++

1.7 fb−1• Measure life time of cc

++ → c+K−++.

• Control mode b0 → c

+−+−.

[arXiv:1806.02744]

(before decay time acceptance correction)

• Measure life time of cc++ → c

+K−++.

• Control mode b0 → c

+−+−.

• First measurement of the life time of cc++.

• cc+ life time is 3-4 times shorter → (cc

+) ~ 60-90 fs

(cc++) = 0.256 ±0.014 [ps]+0.024

−0.022Consistency between

SELEX cc+ and LHCb

cc++ ?



24

Production Rate of Baryons

[PRD97, 072005 (2018)]Inclusive production cross section from e+e−

hyperon charmed baryons

c

c

• (production rate) / (2J+1) exp(−m)

✓ Reproduced by relativistic string fragmentation model

• Factor 3 difference between c and c is seen (not in hyperons), which indicates

the di-quark structure of these charmed baryons.



25

Summary

• New measurements of c+ branching fraction

✓ c+ → 0K+, (1530)0K+, c

+ → + X at BESIII

✓ c → at Belle

✓ c+ → p+− at LHCb

• Observation of c(2930)0 and evidence for c(2930)+ in B → Kc+c

− at Belle.

• Hadronic Decay of at c Belle

• New excited c observed at LHCb were confirmed at Belle.

• Lifetime of doubly charmed baryon cc++.

• Production rate of Baryons.

• There will be more analyses from data at e+e− experiments and LHCb.

• Once Belle II start taking data, more results on charmed baryons are expected.



26

Backup



27


[EPJ C78, 252 (2018)]

• Clear correlation can be seen between E and Mbc.

• No correlation between MB and Mbc



29

Excited c

[PRL 118, 182001(2017)]



30

ACP in c+ → pK+K−, p+−

• Several years ago, LHCb reported large CP violation

in Singly Cabibbo-Suppressed (SCS) D decays:

ACP = ACP(D→K+K−) − ACP(D→+−)

• Although this anomaly itself disappeared later, one

can do the same measurement in other SCS decays.

• LHCb performed the ACP measurement

with c+ → pK+K− and p+− .

✓ Reconstruct as a part of b0 → c

+−X decay

chain (to utilize long life of b0).

ACP(D→K+K−) − ACP(D→+−)

2014?

pK+K− p+−

1.6×105 events~2.5×104 events

3 fb−1

[JHEP03 (2018) 182]



31

ACP in c+ → pK+K−, p+−

Background-suppressed Dalitz plot

c+ → pK+K− c

+ → p+−

to maximize cancelation, some phase

space dependent weight is applied (wgt)



32

c+ → pK+K−, p+−

[JHEP 03 (2018) 043]

180716-fpcp-baryon.pdf - cern indico

Documents