Overview on Pentaquarks · 4 Summary and outlook Biplab Dey Overview on Pentaquarks June 6 th, 2017...
Transcript of 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
Biplab Dey Overview on Pentaquarks June 6th , 2017 2 / 23
Introduction: Θ+(1540) to the LHCb Pentaquarks
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
Biplab Dey Overview on Pentaquarks June 6th , 2017 2 / 23
Introduction: Θ+(1540) to the LHCb Pentaquarks
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?
Biplab Dey Overview on Pentaquarks June 6th , 2017 3 / 23
Introduction: Θ+(1540) to the LHCb Pentaquarks
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
Biplab Dey Overview on Pentaquarks June 6th , 2017 4 / 23
Introduction: Θ+(1540) to the LHCb Pentaquarks
�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’’
Biplab Dey Overview on Pentaquarks June 6th , 2017 5 / 23
Introduction: Θ+(1540) to the LHCb Pentaquarks
�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
Biplab Dey Overview on Pentaquarks June 6th , 2017 6 / 23
Introduction: Θ+(1540) to the LHCb Pentaquarks
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).
Biplab Dey Overview on Pentaquarks June 6th , 2017 7 / 23
Introduction: Θ+(1540) to the LHCb Pentaquarks
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
Biplab Dey Overview on Pentaquarks June 6th , 2017 8 / 23
Introduction: Θ+(1540) to the LHCb Pentaquarks
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
Biplab Dey Overview on Pentaquarks June 6th , 2017 9 / 23
Details of the angular analysis: Λ0b
→ J/ψ pK−
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
Biplab Dey Overview on Pentaquarks June 6th , 2017 9 / 23
Details of the angular analysis: Λ0b
→ 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.
Biplab Dey Overview on Pentaquarks June 6th , 2017 10 / 23
Details of the angular analysis: Λ0b
→ 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)
Biplab Dey Overview on Pentaquarks June 6th , 2017 11 / 23
Details of the angular analysis: Λ0b
→ 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
Biplab Dey Overview on Pentaquarks June 6th , 2017 12 / 23
Details of the angular analysis: Λ0b
→ 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.
Biplab Dey Overview on Pentaquarks June 6th , 2017 13 / 23
Details of the angular analysis: Λ0b
→ 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.
Biplab Dey Overview on Pentaquarks June 6th , 2017 14 / 23
Further prospects: LHCb and JLab
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
Biplab Dey Overview on Pentaquarks June 6th , 2017 14 / 23
Further prospects: LHCb and JLab
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}
Biplab Dey Overview on Pentaquarks June 6th , 2017 15 / 23
Further prospects: LHCb and JLab
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
−
Biplab Dey Overview on Pentaquarks June 6th , 2017 16 / 23
Further prospects: LHCb and JLab
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)
Biplab Dey Overview on Pentaquarks June 6th , 2017 17 / 23
Further prospects: LHCb and JLab
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 .
Biplab Dey Overview on Pentaquarks June 6th , 2017 18 / 23
Further prospects: LHCb and JLab
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.
Biplab Dey Overview on Pentaquarks June 6th , 2017 19 / 23
Further prospects: LHCb and JLab
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).
Biplab Dey Overview on Pentaquarks June 6th , 2017 20 / 23
Further prospects: LHCb and JLab
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
Biplab Dey Overview on Pentaquarks June 6th , 2017 21 / 23
Further prospects: LHCb and JLab
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
∗.
Biplab Dey Overview on Pentaquarks June 6th , 2017 22 / 23
Summary and outlook
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
Biplab Dey Overview on Pentaquarks June 6th , 2017 22 / 23
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.
Biplab Dey Overview on Pentaquarks June 6th , 2017 23 / 23