overview on pentaquarks · 4 summary and outlook biplab dey overview on pentaquarks june 6 th, 2017...

Overview on Pentaquarks

Biplab Dey

(on behalf of the LHCb collaboration)

FPCP'17, Prague

Biplab Dey Overview on Pentaquarks June 6th , 2017 1 / 23

Outline

1 Introduction: Θ+(1540) to the LHCb Pentaquarks

2 Details of the angular analysis: Λ0b→ J/ψpK−

3 Further prospects: LHCb and JLab

4 Summary and outlook


Introduction: Θ+(1540) to the LHCb Pentaquarks

Outline







Pentaquarks in old K̄N partial-wave analyses

PDG1976

PDG1992

K+ scattering data on deuteronfrom LBL (PRD 2 (1970) 2599)

Re-analysed in 2003 (nucl-th/0405024).m(K+n) ∼ 1540 MeV shows abump. S = +1 Pentaquark?


https://journals.aps.org/prd/abstract/10.1103/PhysRevD.2.2599

https://arxiv.org/abs/nucl-th/0405024


The second wave: the Θ+(1540) saga

1997: Polyakov et al.(hep-ph/9703373) chiral-soliton model predicts a 12

+

narrow Γ ∼ 15 MeV uudds Θ+ state around MΘ+ ∼ 1530 MeV.

LEPS 2002m(K+n) spectra 2002: LEPS (hep-ex/0301020) reports 1st

experimental evidence of Θ+ in γ(n)→ K−K+(X )

2002-2004: Flurry of both positive and negativeresults from pretty much every HEP experiment.

2004: PDG includes Θ+(1540) in summary tables.

2006: negative results from CLAS (hep-ex/0510061)high-statistics (dedicated run) exclusiveγp → K 0

s [K+n] �nally settles the issue.

2006: PDG omits Θ+(1540) in summary tables. JLAB/CLAS 2006


https://arxiv.org/abs/hep-ph/9703373

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.91.012002



�Would-be� 5-quark states I: Λ(1405)

uds state in the quark model, but can be uudsu as well.

Decays almost completely to Σπ, but lineshape is not a Breit-Wigner.

Occurs �just� below the NK threshold (P ∼ −1 MeV).

Dalitz (Annals Phys. 8 (1959)) found itas �resonance-like� solutions for K−p → Σπscattering at imaginary K− momentum.

Widely surmised in the chiral-unitarycommunity to be dynamically generatedNK state with two poles.

``Resonance-like’’


http://www.sciencedirect.com/science/article/pii/0003491659900648

https://arxiv.org/abs/1602.08852


�Would-be� 5-quark states II: [φp]

Bound [φp] state with uudss̄, is a goodcandidate for a Pentaquark.

Both LEPS (nucl-ex/0506015) and CLAS(1403.2110) see a localized bump at√s ∼ 2.1 GeV in photoproduction.

Unexpected, since Pomeron exchangedominates.

CLAS γp → [φp]:

Lebed (1510.01412) claims that a rapidlyseparating colored diquark-antitriquark[su][sud ] pair explains the structure.

Similar models proposed for other exoticstates.

[sq]

[s(ud)]

1510.01412


https://arxiv.org/abs/nucl-ex/0506015


https://arxiv.org/pdf/1510.01412.pdf




Third wave: LHCb finds Pentaquarks!

2015: LHCb con�rms presenceof two hidden charm exotic[J/ψp] states, Pc(4380)+ andPc(4450)+ in Λ0

b→ J/ψpK−.

(PRL 115, 072001)

Three critical factors here:

Pc(4380)

3/2-, 9σ

Pc(4450)

5/2+, 12σ

1_ Exotics in the double heavy [cc̄] system.

2_ Not just a �bump hunt�. Detailed amplitude analysis of the full decaychain required to elucidate the signi�cance.

3_ The LHCb detector is perfectly tuned to detect this topology. Themother Λ0

bsignal is very clean (∼ 26000 yield in Run I).


http://arxiv.org/abs/1507.03414


LHCb consolidates the P+c observation I

Λ0b→ J/ψpK− data can't be explained as re�ections of Λ∗ → pK−

states in the m(J/ψp)2-m(pK )2 Dalitz plane.(PRL 117, 082002)

Model-independent approach: detailed knowledge of Λ∗J spectra notrequired.

Λ* moments model from Data (no fit)

9σ deviationwrt Data

LHCb




LHCb consolidates the P+c observation II

Cabibbo suppressed Λ0b→ J/ψpπ− consistent with exotic contrib. at

3.1σ (PRL 117, 082003)

Yield is ∼ 1885 andB(Λ0

b→ J/ψpπ−)

B(Λ0b→ J/ψpK−)

≈ 8%

Pc(4450)-

Pc(4380)+

Pc(4450)+

Z(4200)-

N*-only



Details of the angular analysis: Λ0b

→ J/ψ pK−

Outline







→ J/ψ pK−

Λ0b→ J/ψpK− angular analysis I (PRL 115, 072001)

Employs the helicity formalism for building up sequential decays.

Λ∗ decay chain:Λ0

b→ J/ψ (→ µ+µ−)Λ∗(→ pK−)

5 angles {θΛ0

b

, θK , φK , θψ, φψ}and m(pK )

ΛΛ

μ

μ

μ

μ

ψ

ppKKθ θ φ

θ

*

+

−

+

−K − −

ψ Λ

Λ

b

*ψ *

φ = 0

Λ

Λ

φ μψ*

Λ

b

lab frame

rest frame0

0

rest frame

∗

x

z

b

Λ

rest frame

P+c decay chain:

Λ0

b→ P+

c (→ J/ψ (→ µ+µ−)p)K−

6 angles{θPc

Λ0

b

, φPc , φPcψ , θPc , φ

Pcµ , θ

Pcψ , φψ}

K

μ

Λ

−

ΛΛψ *

Λ

−

−*

lab

θΛcPPc

ψ ppψ

b

φ −πφ −π

φ −πcP

b rest frameψ rest frame

Pc rest frame

frame

b

θPc

Pc

PcψP

μμ

+μ

μ+

θψ

c

−

A helicity coupling and Wigner D-matrix element at each node.




→ J/ψ pK−

Λ0b→ J/ψpK− angular analysis II (PRL 115, 072001)

Three additional phenomenological kinematic terms:

Lineshapes: mpK (Λ∗),mJ/ψ p(P

+c )-dependent relativistic Breit-Wigner

(rBW) propagators for each resonance R.Blatt-Weisskopf form-factor: orbital angular momentum barrier term(q/mR)LR barrier term, where q is the breakup-momentum.

Fit projections including only Λ∗ states:

m(pK)

Λ*-only``extended’’

fix

ed

to

PD

G

m(J/ψ p)




→ J/ψ pK−

Λ0b→ J/ψpK− angular analysis III (PRL 115, 072001)

m(pK ) slices:

m(pK)<1.55

m(pK)∈ [1.70,2]

m(J/ψ p)

Pc(4450)

Pc(4380)

Best solution is w/ two new P+c states

(3/2−, 5/2+). (3/2+, 5/2−) is also possible.

Phase-motion extracted in 6 m(J/ψp) bins.

Re A

-0.35 -0.3 -0.25 -0.2 -0.15 -0.1 -0.05 0 0.05 0.1 0.1

-0.35

-0.3

-0.25

-0.2

-0.15

-0.1

-0.05

0

0.05

0.1

0.15

LHCb

(4450)cP

(a)

15 -0.1 -0.05 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35

(4380)cP

(b)

Pc Re APc

Im A

P c




→ J/ψ pK−

What next in Λ0b→ J/ψpK−: JPAC model fits

Poorly understood m(pK ) spectrum biggest systematic uncertainty

Coupled-channel KN spectrum from JPAC (1510.07065):

Treats re-scattering among Σπ, KN, Λπ, Λππ, ...Partial waves (res. + non-res.) instead of resonant rBW.K -matrix formalism: better unitarity than rBW.

K -matrix poles are not thesame as the single rBWresonances.

Extends only tillm(pK ) ∼ 2.17 GeV. Needfurther extrapolation till2.5 GeV.


http://www.indiana.edu/~jpac/



→ J/ψ pK−

What next in Λ0b→ J/ψpK−: covariant amps.

Three disadvantages of the helicity formalism:

Kinematical Lorentz boost factors not included.The (qR/mR)LR barrier terms are phenomenological. Not exact.For sequential decays with multiple paths the additional rotations canquickly become unmanageable.

Covariant amplitudes solve all three in one go

Covariant by construction. See Anisovich et al. (hep-ph/0407211).Covariant orbital ang. mom. tensors carry the exact ∼ qLR dependence.Single spin-quantization axes for all states.

The di�erence due to the kinematic factors can be substantial in theentire Dalitz plane.

Separate covariant amplitudes being developed by the JPAC group.

Uses so-called CGLN amplitudes instead of orbital tensors.


https://arxiv.org/abs/hep-ph/0407211

Further prospects: LHCb and JLab

Outline







Further Pentaquark searches at LHCb

Searches for new decay modes of the observed P−c 's

Λ0b→ χc{1,2}pK (NEW! 1704.07900)

Λ0b→ Λ+

c D0(∗)

K

Searches for new production modes of the observed P−c 's

Λ0b→ J/ψpK ∗−

{Υ,Bs} → J/ψppΞ−b → J/ψpK−K−

Inclusive J/ψp

Searches for new Pentaquark multiplets

Ξ−b → J/ψΛK− (1701.05274)B0

(s) → J/ψpp (1306.4489)

Λ0b→ J/ψΛφ

Λ0b→ Σ++

c h+π−π−h−, h ∈ {π,K}






Observation of Λ0b→ χc{1,2}pK

− (NEW! 1704.07900)

From Gao et al. (1507.04950):Pc(4450)+ occurs just above the[χc1p] threshold.[mP+

c (4450) −mχc1 −mp

]∼ 0.9 MeV

Kinematic re-scattering?

Phase-motion accountable:

Theory fitTheory fit

LHCb P

c

+(4450) data

Proposal: true resonance should peak in [χc1p] in Λ0b→ χc1pK

−





Observation of Λ0b→ χc{1,2}pK

− (NEW! 1704.07900)

New LHCb Λ0b→ χc{1,2}pK

− �rst observation analysis (Run I).

χc{1,2} → J/ψγ, as in B0 → χc{1,2}K∗ (1305.6511) replacing π → p.

Final Λ0bmass �ts with J/ψ and χc1 mass-constrained in kinematic �t:

Λb→J/ψ pK

control mode29815 ± 178

Small breakup mom. allows precise meas. of Λ0bmass from the χc1 �t

m(Λ0b) = 5619.44± 0.28(stat)± 0.26(sys)





Observation of Λ0b→ χc{1,2}pK (NEW! 1704.07900)

Bkgd. subtracted χcJ masses(no χc1 mass-constraint): B(Λ0

b→ χc2pK )

B(Λ0b→ χc1pK )

= 1.02± 0.11

Somewhat unexpected, given LHCbhas measured (1305.6511)

B(B0 → χc2K∗)

B(B0 → χc1K ∗)= 0.17± 0.05

m(χc1p) and m(pK ) spectra investigated, but need more data.

With Run I+II (2015/16), O(1000) χc1 expected.

Amplitude analysis will be possible where the radiative photon makesthe analysis di�erent from Λ0

b→ J/ψpK .





Observation of Ξ−b → J/ψΛK− ( 1701.05274)

Oset et al. (1510.01803):Pc(4450)+ is a meson-baryon�molecule� in the unitary approach.

Predicts a strange partner, P−cs , atmR ∼ 4650 MeV and ΓR ∼ 10 MeV.

Should be visible in Ξ−b → J/ψΛK−

Similar topology as in Λ0b→ J/ψpK ,

replacing u-quark by an s-quark.

arXiv:1510.01803

Pcs

(4650)-

LHCb analysis: �rst observation using entire Run I dataset.





Observation of Ξ−b → J/ψΛK− ( 1701.05274)

Separate analyses for Λ decaysinside (LL) or outside (DD) theVertex Detector

Λ0b→ J/ψΛ used as control mode.

Where f{Ξb,Λ0

b} are the

b → {Ξb, Λ0b} fragmentation

fractions:

99±12

209±17

fΞb

fΛ0

b

B(Ξ−b → J/ψΛK−)

B(Λ0b→ J/ψΛ)

= 0.0419± 0.0029(stat)± 0.0014(sys)

Expect angular analysis after full Run 2 (2018).




Study of B0(s) → J/ψpp ( 1306.4489 )

Restricted phase-space: m(J/ψp) < 4341(4429) MeV, for B0(Bs)

Ground state P−c states can show up in this mode.

Clean signature at LHCb: two protons + J/ψ . Rare due toCabibbo/OZI/phase-space suppressions:

b

W + ¿

d

Bd0

cc

d

d

uu

uu

J /ψ

p

p

b

W + ¿

s

Bs0

cc

d

d

uu

uu

J /ψ

p

p

LHCb 1/fb (2011 dataset) analysis(1306.4489): no observation but U.L.:

B(B0 → J/ψpp < 6.0× 10−7) @95%CL

B(Bs → J/ψpp < 5.3× 10−6) @95%CL

Run I + 2(2015/16) analysis ongoing.

99±12

209±17

Bs

,2.8σB01/fb





Photoproducing Pentaquarks at JLab

Direct photoproduction of γp → P+c → J/ψp natural extension of φp

production from the light s-quark to the heavy c-quark sector.

12-GeV upgrade of the CEBAF accelerator well suited to search forthese at JLab (CLAS12 and GlueX detectors).

Proposals: Kubarovsky (1508.00888), Wang (1508.00339), Karliner (1508.01496).

Wang, 1508.00339

old SLAC/Cornell data

(Assumes B(P+c → J/ψp) ∼ 100%)

Main �background� will be di�ractivePomeron exchange

Access to the P+c lineshapes (consistent

with a rBW?)

P+c → J/ψN∗ → J/ψp(π0)? (hard at

LHCb)

Molecular-model, Karliner (1508.01496):P+c (4450) should couple to ΣcD̄

∗.







Summary and outlook

Outline






Summary and outlook

Summary and outlook

�Everything not forbidden is compulsory�

LHCb's 2015 Pentaquark discovery shows (again) that heavy quarksystems are favorable toward exotics.

Detailed angular analysis played a critical role.

Nature of these states: meson-baryon molecule? diquark-antitriquark?rescattering? true 5-quark state?

LHCb: advance the Λb → J/ψp{K−, π−} angular analyses with betterΛ∗ (N∗) models and covariant amplitudes.

LHCb: large program to hunt for new multiplets/production/decaymodes. Post Run II, expect ∼ ×5 statistics than Run I.

JLab: photoproduction in GlueX/CLAS12 could be the �rst validation.

Theorists: let us know if you have interesting modes we can look at.


overview on pentaquarks · 4 summary and outlook biplab dey overview on pentaquarks june 6 th, 2017...

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