Pentaquark Searches at BaBar - Jefferson Lab · 17 Tetiana Berger-Hryn'ova Search for Nfor 5 +/Ξ...

Pentaquark Searchesat BaBar

Tetiana Berger-Hryn’ova, SLACFor the BaBar Collaboration

Tetiana Berger-Hryn'ova2

Outline

• Search for Θ+ in Electro- and Hadro-Production

• Inclusive Search for Strange-PentaquarkProduction in e+e- Annihilation

• Inclusive Search for anti-Charm Pentaquark Production in e+e- Annihilation

• Search for Θ*++(pK+) in B decay to the p�K+

final state


BaBar/PEP-II

BaBar DCH• 40 layers, axial and stereo wires.• Covers 92% of solid angle• δpt/pt ~ 0.5 -1.5 %• Particle ID up to 1.3 GeV/c

• PEP-II is an asymmetric e+e- collider with a CM energy of 10.58 GeV.

• Peak luminosity = 1.0 1034 cm-2s-1

• Integrated luminosity = ~310 fb-1

BaBar EMC• 6580 CsI(Tl) crystals• E resolution ~2 % at high E.

Cherenkov Angle(Kaon from D*+ → D0 π+ ,

D0 → K- π+ sample)

All Events

BaBar DIRC•Fused Silica Cherenkov radiator•Covers 80% of solid angle•Particle ID above 600 MeV/c

BaBar SVT• 5 layers of double-sided

Silicon strip sensors.


Search for Θ+ in Electro- & Hadro-Production


Electro- and Hadro-Production

Study Θ+→pKS0 production in

interactions with the material of the BABAR inner detector!• Hadroproduction: interactions

of hadrons produced in e+e-

annihilation with detector material• Electroproduction: off-beam e- and

e+ bent into beampipe (Be) in horizontal plane

Compare withBABAR

results

No signal in CLAS: ~6x more data!~40x more data!

Interaction Region

Evidence of Θ+ found in: • real/virtual photoproduction (*)• hadroproduction on hydrogenor nuclear target


Signal region (SR

Sideband (SB)SB

pKs0 reconstruction/Detector Material

Preliminary 233 fb-1 e+ e− data

p

KS0pKS

0

Vertexπ+

π−DOCA < 3 mmKS

0 FL > 2 mm

SVT


z profile e- side

Ta

TaBe

-0.2 < y < 0.7 cm

-3.1< x < -2.2 cm

Fe

e- e+

Detector Tomography with pKs0 Vertices

SVT support tube

DCH inner wall


SVT

beampipe


• Remove candidates with associated baryons (p,�,d,t)

• Look for other associated tracks

pKS0 Mass

Distribution

No Θ+ signal

SR

SB

Vertices from e-Be interaction (e-production)

pKS

0p,p,d,t;π±, K±

π+π−


Signal region (SR)

Sideband (SB)SB

KS0 Mass Distribution

No Θ+ signal

SR

SB

All vertices (e- and h-production)

M(KS0p)/GeV/c2


pK-Λ(1520)SR

SB

Association of π±, K± with (p, Ks0) Vtx

All vertices (same for e-Be with fewer events)

No Θ+ signal

removedK+*(892)

No Θ+ signal

SR

SB

events with p KS0 K−

SR-SB

Ksπ+K+*(892)

SR

SB

events with p KS0 π+

Prel

imin

ary

233

fb-1

e+e−

data


e-Be ElectroproductionHERMES (e+d→KS

0p + X)

M=1528±3 MeV~5σ

ZEUS (e-p→e-KS0p + X

M=1522±3 MeV~5σΣ*(1480)

Fit uses Σ*(1480) [PDG 1star]Possible acceptance loss in low mass region:(PID requires p(p) >4.1 GeV/c; p(KS

0)>3 GeV/c)

Preliminary233 fb-1 e+ e− data


e+e- InclusivePentaquark Searches


Ξ5- |dss(uu,dd)⟩

Ξ−π-

Overview

0

10

20

30

40

50

60

a)

Ent

ries

/ 7.

5 M

eV/c

2M(Ξπ) [GeV/c2]

-10

0

10

20

30

1.4 1.6 1.8 2 2.2 2.4 2.6 2.8

b)

• Exotic resonances: Θ+, seen by several and Ξ5

0,-- seen by one experiments.

• Fits into several models;10+8 multiplet of SU(3)f is favored.

• Production could be similar to baryons of same mass.

0

5

10

15

20

25

30

35

40

1.4 1.6 1.8 2 2.2 2.4

M(nK+) (GeV/c2)

Eve

nts

/ 20

MeV

/c2

05

10152025303540

1.5 2M(nK+) (GeV/c2)

Θ+ |ududs⟩

ΛK-, Σ0K- ΛK0S, Σ0K0

S

NA49

CLAS

ΛK+, Σ0K+

N5+ |uud(dd,ss)⟩N5

0 |udd(uu,ss)⟩

pK0S

ΛK0S, Σ0K0

S

Ξ5- - |sdsdu⟩ Ξ5

0 |uss(uu,dd)⟩ Ξ5+ |ususd⟩

Σ5+ |uus(dd,ss)⟩

Σ50 |uds(u�,d�,s�)⟩

Σ5- |dds(uu,ss)⟩

pK0S


Search for Θ+/Σ5+→ pKS

0

• Proton selection using dE/dx and Cherenkov, clean over wide momentum range.

• Use K0S → π+π−.

• 3x106 reconstructed decays

• Expected Resolution (HWHM) on Θ+ mass ~ 2 MeV (from MC)

• Can also look for Σ5+.

→ ~98K ΛC’s in data sample→ Resolution 5-7 MeV at ΛCmass

123 fb-1 PRL 95, 042002 (2005)

No Σ5+

×103

Can

dida

tes/

(2 M

eV/c

2 )Upper Limits of total cross section:

Θ++Θ- : for Γ=1(8)MeV ⇒171(363)fb


Search for Ξ50/--→ Ξ-π±

Λ

πΞ−

−πΞ

p+

−πΛ

−

IP

0

24,000 entries

8000 entries

No signal of Ξ50 / Ξ5

--

Mass resolution~8 MeV/c2 in Ξ5region (r.m.s)

• Geometrical selection of two displaced vertices• Good p and π selection (dE/dx, θc)• Select masses near the nominal Λ0 and Ξ- masses• Control signals: Ξ*0(1530) Ξ-π+, Ξc(2470) Ξ-π+

PR

L 95

, 042

002

(200

5)

U. L. on total cross section: Ξ5+++Ξ5

-- : for Γ=1(18)MeV ⇒ 25(36) fb


1.106 1.108 1.11 1.112 1.114 1.116 1.118 1.12 1.122 1.124 1.1260

2000

4000

6000

8000

10000 Λ

0.475 0.48 0.485 0.49 0.495 0.5 0.505 0.51 0.515 0.520

2000

4000

6000

8000

10000

K0S

Search for Ξ50/N5

0 → ΛK0S

0Λ

π−

π+

K0s

p+

π−

ΜΜppππ [GeV][GeV]

ΜΜππππ [GeV][GeV] 2.4 2.42 2.44 2.46 2.48 2.5 2.52 2.540

200

400

600

800

1000

NΞc ≈ 1100σ = 5.9 MeVΞC

0

(GeV)S0 KΛm

1.6 1.8 2 2.2 2.4 2.6 2.8 3

Entri

es p

er 2

MeV

0

200

400

600

800

1000 0cΞ

- p* < 3 GeV- p* > 3 GeV (scale 10)

05N

(GeV)S0 KΛm

1.7 1.75 1.8 1.85 1.9 1.95 2

En

trie

s p

er 2

MeV

0

200

400

600

800

1000

ΛK0S

123fb-1 hep-ex/0408064

No Ξ50 signal


(GeV)- KΛm1.6 1.8 2 2.2 2.4 2.6 2.8 3

En

trie

s p

er 2

MeV

0

1000

2000

3000

4000

5000

6000

7000

-Ω

- p* < 3 GeV

- p* > 3 GeV (scale 10)

ΛK−

(GeV)- KΛm1.7 1.75 1.8 1.85 1.9 1.95 2

En

trie

s p

er

1 M

eV

0

500

1000

1500

2000

2500

1.65 1.655 1.66 1.665 1.67 1.675 1.68 1.685 1.69 1.695 1.70

200

400

600

800

1000

1200

1400

1600

1800

Ω−

(GeV)+ KΛm1.5 2 2.5 3 3.5 4 4.5 5

Ent

ries

per

2 M

eV

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

20000

+cΛ

feed-down+cΛ

- p* < 3 GeV

- p* > 3 GeV (scale 10)

+5N

ΛK+

Search for N5+→ Λ K+, Ξ5

- → Λ K-

123 fb-1 hep-ex/0408064

(GeV)+ KΛm2.24 2.25 2.26 2.27 2.28 2.29 2.3 2.31 2.32 2.33 2.34

En

trie

s p

er

2 M

eV

0

50

100

150

200

250

300

= 615.7+cΛN

RMS = 5.3 MeVDATA

NΛc ≈ 600σ = 5.3 MeV

Λc+ Cabibbo-

Suppressed DecayNΩ ≈ 6300

σ = 3.0 MeV No Ξ5− signal


SearchSearch for for N5+/Ξ5

-→Σ0K±, Ξ50/N5

0→Σ0Ks0

00sKΣ

p*>3

GeV

1<p*

<2 G

eV

123 fb-1 hep-ex/0408064+Σ K0

No Ξ50/N5

0 signal

−Σ K0

No Ξ5- signalNo N5

+ signal


Results (e+e- Annihilations)• No signal for any

pentaquark state observed

• Assumptions– J=1/2– BF(Θ+ pKs

0)=25%– BF(Ξ5

-- Ξ-π+)=50%– BF for Ξ5

- and Ξ50 very

unclear– Intrinsic width 1-18 MeV/c2

• Limits on production times branching fraction 4-15x lower than production rates for conventional baryons

123 fb-1 PRL 95, 042002 (2005)


Θc0 Pentaquark Search

Θ+(udud�)

Ξ−−(sdsd�)Ξ+(usus�)

Θc0(udud�)

SU(4) 60-plet 15-pletC=+2

anti-15+ 6-pletC=+1

anti-6-pletC=-1

C

Y

I

anti-decupltet (10)+ octet (8)

C=0

(cdsd�)

(cdcd�)

D0→K-π+ mode only


After cuts~55k D*-

~4k bkgr

After cuts~73k D*-

~62k bkgr

D*-(�0→K+π−)

D*-(�0→K+π−π+π−)

Search for Θc0→pD*-(�0(K+π−,K+π−π+π−)π−)

BaBar Preliminary 123 fb-1 e+ e− data, see hep-ex/0510044 for details

with

pro

ton

requ

irem

ent

Expected Resolution (HWHM) on Θc mass ~ 3 MeV (from MC)

Reconstruct ~750k of D*-


Θ*++ Pentaquark Searchin B-decay


• Theory: Θ*++→ K+p mode dominant mΘ*++ = 1.6-1.7 GeV/c2 & ΓΘ*++= 37-66 MeV

• Not seen by CLAS, HERMES, SAPHIR, ZEUS• A hint from STAR? (at ~1.53GeV/c2, Γ~20MeV); isospin partner not seen

in BaBar inclusive search with ~3-10 times statistics

• In K+p scattering: no sign of Θ*++; constrains Γ(Θ*++)<15MeV

• Previous searches in B decays (idea: Phys.Lett.B, 587 62(2004))– By-product of the B±→p�K± analysis, very low background

– BaBar 81fb-1 [hep-ex/0408037]: B(B+→Θ*++�)×B(Θ*++→pK+)< 1.5×10-7 @ 90% CL for narrow state with m(Θ*++)=1.43-1.85 GeV/c2

– BELLE 140fb-1 [Phys Lett B 617(2005),141]: B(B+→Θ*++�)×B(Θ*++→pK+)< 0.9×10-7 @ 90% CL for narrow state at m(Θ*++)=1.71 GeV/c2 [search region: 1.6-1.8]

Current Statusuddd� uudd� uuud�

ddds uuus

usssdsssddss uuss

uuududdd

Θ*

Δ*

X1s

Ω*X2s


Analysis Overview• Data Samples

– 210 fb-1 on the ϒ(4S) resonance (232 M B± mesons)

• Isolate B±→p�K± final state, search for Θ*++ in mpK+

• Major Backgrounds:– Baryons from e+e-→q�, where q=u,d,s,c (suppress

topologically)– Allowed B decays: B± →XK±, X→p� (X=ηc,J/ψ,χc,ψ(2S))

u

�

ud

u�uB+

�

Θ*++

u

�

B+

�

u

�

uW+Θ*++u

d

e+ e-B decay

e+ e-

PRD 72, 051101(R) 2005

q�


ηc

J/ψ

ψ(2S)

B→ppK Dalitz Plot

p�K+ signal box 780 events: ~566±29 signal events ~ 202±5 combinatorial

background

Sideband: 1661 events

χc[0-2]

Θ*++ region

m p�

~mB

E* B

-E* B

expe

cted

B signal


Remove from UL calculation

Events with 2.85<mpp<3.15GeV/c2

Events with 2.85>mppGeV/c2 &mpp >3.15GeV/c2

Θ*++ Search(PRD 72, 051101(R) 2005)

For mpK+<3GeV/c2:σpK+ varies from 1-3MeV/c2

and εav=20.5±0.1%

assuming narrow (<1GeV) Θ*++ resonance!


Conclusions

• BaBar Pentaquark searches have yielded negative results• High statistics, excellent mass resolution:

– Hadro- and Electro-Production in Detector Material• No Θ+→pKs found

– Inclusive Search in e+e- Annihilations• No evidence found for eight members of strange anti-decuplet

and octet, and anti-charm Θc0

• Limits below expectation for baryons (factor 1-15) for Θ+, Ξ5--

• Low statistics/low background, excellent mass resolution:– No Θ*++ observed in B+→p�K+: limit set on product of BF

• Pentaquark Searches highlight potential for study of charmed and non-charmed Baryons at BaBar

Backup Slides


p and Ks0 Samples

lab. momentum of KS lab. momentum of p

Signalregion (SR)

Sideband(SB)

Sideband

S/B

flight length [cm]

Very good S/Bbehaviour withflight length

• Clean samples of selected p and Ks → π+π- candidates


Combine p or KS with identified π-- or K++

K*-(892)

Λ(1115)

π−−

π−−

π−−

Remove K*(892)

Κ++

SR

SR

SB

SB

SR

SB

SR-SB

No Θ+ Seen


Zeus Comparison


Upper Limits for Production Cross Section

UL @ 95% CL on production Xsection:

Γ= 1 Γ = 8 MeV

< 182.8 < 363.1 fb

< 5.4x10-5 < 10.7x10-5 per q� event

< 17.9x10-5 < 35.0x10-5 per ϒ(4S)

Sample Bin: 3.0 GeV < p* < 3.5 GeV

yield


Search for Θc0


Hints of a signal?

STAR

mpK+, GeV/c2

d-Au

STA

R P

relim

inar

y

Au-Au

Θ++?

Puzzle: BaBar didn’t observe the Θ*++ isovector partner Θ*+ in the search of pK0

S resonances

d-Au

Θ++?

From Volker D Burkert’s talk at LP05

pK+ and �K- d-Au at 200GeVcombinatorial & correlated pairs

Bkgr subtracted

Bkgr subtracted

Can

dida

tes/

(5M

eV/c

2 )

SuppressedZero!

×103


,||

,2)1cos3(||*

0

2*2 ,

∑∑

=

−=

i i

i Thri

pL

pLiB

θ

e+e-→q�Background Suppression

e+ e-

q�

e+ e-

B decay

(i = photons and tracks which are not part of the BppK) and

angles between the BppK thrust (momentum) and z axis

combined into Fisher Discriminant

SignalMCBackground

67%94%


mES ΔE Signal MC

mES, GeV/c2

Even

ts/3

MeV

/c2

Even

ts/1

0MeV

B reconstruction22

22

2 BiBiCM

ES pEppEm −⎟⎟⎠

⎞⎜⎜⎝

⎛⋅+=rr

ΔE, GeV

2EEΔE CM*

B −=

σΔE=16.7MeV

σmES=2.7MeV/c2

Off-resonance Data


B±→p�K± Signal Event Yield

Event estimate in the signal region for 1D fits to data: ΔE fit: 566±29 events && mES fit: 588±32 events

Expected Charmonium contribution: ~229±33

ΔE mES

5.276<mES<5.286GeV |ΔE|<29MeV

Pentaquark Searches at BaBar - Jefferson Lab · 17 Tetiana Berger-Hryn'ova Search for Nfor 5 +/Ξ...

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