Baryonic B decays from BABARRencontres de Moriond QCD 2012

Oliver Grünberg(University of Rostock)

—on behalf of the BABAR collaboration

March 12th, 2012

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Content

Analysed decay channels

B− → Σ++c pπ−π−

B0 → Λ+c ppp

The BABAR experimentunderlying dataset : NBB = 429 fb−1 · 1.1 nb ≈ 471 · 106BB

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1. Physics motivation

What we knowlarge mass of the B mesons allows a wide spectrum of baryonic decays

(6.8± 0.6)% of all B mesons have baryons in the final state 1

(4.5± 1.2)% of all B mesons have a Λ+c in the final state 2

only 1/5 of all exclusive baryonic B decays have been measured

What we would like to knowWhich baryonic B decays have a large branching fraction?

Which influencing factors enhance baryon production in B decays?

I size of phase spaceI resonant substructures

1 Z. Phys. C 56 p. 1-6: “Measurement of inclusive baryon production in B meson decays”, ARGUS (1992)

2 Phys. Rev. D 75 (2007) 012003 “Incl. Λ+c Prod. in e+e− Annih. at

√s = 10.54 GeV and in Υ (4S) Decays”, BABAR (2007)

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1. Physics motivation

Influence from the size of phase space

Consider B− → Λ+c Λ−c K− vs. B− → Λ+

c pπ−

small influence from weak decay since |Vcs| ≈ |Vud|

Main difference: size of phase space

PS(B− → Λ+c Λ−c K−)

PS(B− → Λ+c pπ−)

≈ 167

butB(B− → Λ+

c Λ−c K−)B(B− → Λ+

c pπ−)≈ 3

1

|212

|m10 12 14 16 18 20 22 24 26 28

|2 13

|m

6

8

10

12

14

16

18

20

-π p +cΛ → -B

- K-

cΛ +cΛ → -B

→ Strong matrix element dominatesphase space suppressionBi

Bj= Γi

Γj∼ |Mi|2|Mj |2 ·

PSi

PSj

→ αS ∼ 1log(q2) : small phase space fa-

vors formation of quarks to baryons ?

→ B(B0 → Λ+c ppp) vs.

B(B0 → Λ+c pπ

+π−)?

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1. Physics motivation

B(B → Λ+c p+ n(π)) benefit a lot from resonant subchannels

B(B− → Λ+c pπ

−)resonant

B(B0 → Λ+c pπ−)

≥ 50% ,B(B0 → Λ+

c pπ+π−)resonant

B(B0 → Λ+c pπ+π−)

≈ 43%

)πn(0 1 2 3 4

PDG

BR

-510

-410

-310

-210

)π + n(p +cΛ →

0B

)π + n(p +cΛ → -B

Upper Limit @ CL = 90 %

→ B [n(π)] grows from n(π) = 0 to n(π) = 35 / 14

2. Study of the decay B− → Σ++c pπ−π−

Reconstruction of B− → Σ++c pπ−π− in the subchannel

Σ++c → Λ+

c π+, Λ+

c → p K− π+

signal extraction in ∆E∗ = E∗B −√s/2 with selection in:

I mpK−π+ within range m(Λ+c )fit ± 2.8 · σ(Λ+

c )fit

I mES∗ =

√(√s/2)2 − ~p∗

2

B within range mES(B−)fit ± 3.3 · σ(B−)fit

E [GeV]∆-0.1 -0.05 0 0.05 0.1

Eve

nts

/ 15

MeV

0

50

100

150

200

250

300

350

400

Data

/dof = 7/11)2χFit (preliminaryBaBar

each slice of ∆E was fitted inm(Λ+

c π+) to reject background

(B− → Λ+c pπ

+π−π−

nonresonant)

NSig = 787± 43

ε = (11.3± 0.2)%

B(B− → Σ++c pπ−π−) = (2.98± 0.16(stat) ± 0.15(syst) ± 0.77Λc) · 10−4

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2. Study of the decay B− → Σ++c pπ−π−

Invariant mass spectrum of Σ++c π−

efficiency corrected

]2) [GeV/c-π++cΣm(

2.55 2.6 2.65 2.7 2.75 2.8 2.85 2.9 2.95 3

2W

eigh

ted

even

ts /

5 M

eV/c

0

50

100

150

200

250

300

350

400

450

500(2595)cΛ (2625)cΛ (2765)cΛ (2880)cΛ (2940)cΛ

E signal band∆

E sideband∆preliminaryBaBar

Data suggest resonant subchannel B− → Λc(2593)+pπ−

no significant signal for other Λ+c resonances

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2. Study of the decay B− → Σ++c pπ−π−

Invariant mass spectrum of p π−

background subtracted

efficiency corrected

]2) [GeV/c-πpm(1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6

Wei

ghte

d ev

ents

/ 50

MeV

0

200

400

600

800

1000

1200

14004-body phase space MC

Weighted data

- -(1232)∆ - -(1620)∆

preliminaryBaBar

Excess in range 1.2 < m(pπ−) < 1.7 GeV/c2 may be due toresonances ∆(1232)−−,∆(1600)−−,∆(1620)−−

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2. Study of the decay B− → Σ++c pπ−π−

Invariant mass spectrum of Σ++c π− π−

background subtracted

efficiency corrected

]2) [GeV/c-π-π++cΣm(

2.8 3 3.2 3.4 3.6 3.8 4 4.2 4.4

2W

eigh

ted

Eve

nts

/ 50

MeV

/c

0

100

200

300

400

500

600

700

800

900

1000

4-body phase space MC

Weighted data

preliminaryBaBar

Unexplained structures around 3.250 GeV/c2 and 4.200 GeV/c2

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3. Search for the decay B0 → Λ+c ppp

Reconstruction of B0 → Λ+c ppp in the subchannel Λ+

c → p K− π+

signal extraction in ∆E vs. mES with selection of mpK−π+

within range m(Λ+c )fit ± 2.8 · σ(Λ+

c )fit

Choice of ∆E:mES signal window in signal MC

]2 [GeV/cESm5.2 5.21 5.22 5.23 5.24 5.25 5.26 5.27 5.28 5.29 5.3

E [

GeV

]∆

-0.1

-0.05

0

0.05

0.1

preliminaryBaBar

2 events in data

ε = (3.66± 0.03)%

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3. Search for the decay B0 → Λ+c ppp

Calculation of an upper limit with the two events that are found:

no reliable background estimation from mES and mpK−π+ sidebands andMC

Conservative upper limit:

I NSig = 2I NBg = 0

Bayesian and frequentist upper limit are identical

B(B0 → Λ+c ppp) ·

B(Λ+c → pK−π+)

5 %< 6.2 · 10−6 @ CL = 90%

⇑PDG value

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4. Conclusions and interpretation

B− → Σ++c pπ−π−

Branching fraction

B(B− → Σ++c pπ−π−) = (2.98± 0.16(stat) ± 0.15(syst) ± 0.77Λc

) · 10−4

Suggestion for B− → Λc(2593)pπ−

Unexplained structures around m(Σ++c π−π−) = 3.250 GeV/c2 and

m(Σ++c π−π−) = 4.200 GeV/c2

for comparison:

I B(B− → Σ0cpπ

+π−) = (4.4± 1.7) · 10−4 (1)I B(B− → Λ+

c pπ+π−π−) = (2.3± 0.7) · 10−3 (1)

Large fraction of resonant decays including a ΣcB(B− → Σ0

cpπ+π−) + B(B− → Σ++

c pπ−π−)B(B− → Λ+

c pπ+π−π−)≈ 31%

(1) Phys. Rev. D 66 (2002) 091101R “Measurement of Exclusive B Decays to Final States Containing a Charmed Baryon”12 / 14

4. Conclusions and interpretation

B0 → Λ+c ppp

Conservative upper limit

B(B0 → Λ+c ppp) ·

B(Λ+c → pK−π+)

5 %< 6.2 · 10−6 @ CL = 90%

for comparison:

B(B0 → Λ+c pπ

+π−) = (1.12± 0.32) · 10−3 (1)

Phase space of B0 → Λ+c ppp may be too small to favor baryonisation

(1) Phys. Rev. D 75 (2007) 011101R "Study of the Charmed Baryonic Decays B0 → Σ++c p π− and B0 → Σ0

cp π+ "

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Thanks for your attention!

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B− → Σ++c pπ−π−

Systematic errors

Source of error Relative error

BB counting 1.1%

Signal events 4.0%

Tracking 2.4%

Efficiency 1.8%pPδ2 5.1%

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B− → Σ++c pπ−π−

]2) [GeV/c-π-π++cΣm(

2.8 3 3.2 3.4 3.6 3.8 4 4.2 4.4

2W

eigh

ted

even

ts /

50 M

eV/c

0

200

400

600

800preliminaryBaBar

/dof = 5.1/162χ

2 6) MeV/c± = (108 Γ

2 20) MeV/c±=(3245 µ

Signal: Breit-WignerBackground: 2-body phasespace with m1 = m(Σ++

c ) and m2 = 2 ·m(π−)

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