Yongseok Oh

Spectrum and Production of

Strange Baryons

8/24/09 HEP Seminar

KISTI, Aug, 2009 2

OverviewOverview

Nuclear & Hadron Physics

Structure of hadrons Effective theories and models for QCD Mechanisms of particle production

Relativistic heavy ion physics Matter at extreme conditions New state of matter

Rare Isotopic Accelerator Structure of atomic nuclei Nucleosynthesis

Missing resonance problem

Spectrum of baryons containing strange quark(s)

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Hadron physicsHadron physics

Structure of hadronsStructure of hadrons

Have we discovered enough hadrons?

1. To understand hadron spectroscopy

2. To understand QCD in low energy scale

3. To understand the response of hadrons to the probe

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Heavy ion physicsHeavy ion physics

1. To understand Early universe, Neutron stars..

2. To understand QCD in non-perturbative domain

3. To understand generation of mass, confinement of quarks, its relation symmetries

Hadrons under extreme conditionsHadrons under extreme conditions

New state of matter?

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How do we study hadrons & nuclei?How do we study hadrons & nuclei?

JLab RHIC SPring-8

GSI

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New & future acceleratorsNew & future accelerators

LHC

GSI (upgrade)

JLab (upgrade)

J-PARC

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Particle zoo (mesons)Particle zoo (mesons) mesons: flavor: 3 3 1 8qq Ä = Å

0PJ -= 1PJ -=

Pseudoscalar mesons Vector mesons

And meson resonances (excited states)

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Particle zoo (baryons)Particle zoo (baryons)

baryons: flavor: 3 3 3 1 8 8 10qqq Ä Ä = Å Å Å

1

2PJ

+

=3

2PJ

+

=

And baryon resonances (excited states: orbital angular momentum)

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Flavor SU(4)Flavor SU(4)

mesons baryons

Other exotic hadrons

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Missing resonance problemMissing resonance problem

Particle Data Group: ~ 100 mesons and ~ 80 baryons

(about 20 nucleon and resonances)

Quark model vs Experiment

Many particles are missing in PDG.

Failure of quark model? Quark model predictions for N* N

Search for resonances in other reactions!

, , etcN VN KYg ®

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Dynamical coupled-channel analysisDynamical coupled-channel analysis

Hadron Production data

, , , etceN N N NNg p

Dynamical reaction model + Amplitude analysis

N* parameters QCD

Hadron models+ QCD sum rules

+ Lattice QCD

Information on hadron structure

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Vector meson photoproductionVector meson photoproduction0p V pg ®

meson pomeronFour ground vector mesons(, , , K*)

Four ground vector mesons(, , , K*)

Searching for missing resonances

Photoproduction of YO et al, PRC58, PRL79

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meson photoproductionmeson photoproduction

Major background: pion exchange

YO et al, PRC63, PRC66

Pomeron exch.

pion exch. + N*

with N*

without N*

Dominant N*: N(1910) with 3/2 : missing resonance, N(1960) with 3/2 : D13(2080) in PDG

Differential cross sectionTotal cross section

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meson photoproductionmeson photoproduction

Cross sections are not enough. Spin asymmetries are needed.Cross sections are not enough. Spin asymmetries are needed.

* *

,

~ , asym. ~i i i ji i j

d H H H Hs å å

with N*

without N*without N*

with N*

JLab: first data coming soon

Parity asymmetry Double asymmetryBT d d

Cd d

s s

s s ¯

¯

-=

+1 11, 1 0,02

N U

N U

d dP

d ds

s sr r

s s -

-= = -

+

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*(1350) production*(1350) productionYO et al, PRC77

Role of nucleon & resonances in Role of nucleon & resonances in 0 (1385)p Kg +® S

Total cross section

Without N*/* With N*/*

3(2095)

2N

-

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* production* production

Predictions for LEPS (SPring8):Predictions for LEPS (SPring8): (1385)n Kg + -® S

Differential cross section Photon beam asymmetry

beam

d d

d d

s ss s

¯

¯

-S =

+

predictions

YO et al, PRC77

data: LEPS (2008)

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Hadron modelsHadron models

Quark-based models (relativistic) quark model (with effective potential) Diquark model Nambu—Jona-Lasinio model (chiral symmetry) Bag models 1/Nc expansion

Effective theories Chiral perturbation theory Heavy quark effective theory

QCD sum rules

Skyrme soliton model

and so on…

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What do we know about X baryons Strangeness -2 baryons: qss (q: light u/d quark) Baryon number = 1, isospin = 1/2 If flavor SU(3) symmetry is exact for the classification of all particles, then we have N(X*)

= N(N*) + N(D*) Currently, only a dozen of X baryons have been identified so far.

(cf. more than 20 N*s & more than 20 D*s)

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XX in PDG in PDG

What do we know about X baryons?

Particle Data Group (2006): 11 X’s

Parity: not directlymeasured

States whose JP is known

Cf. Spin of W-= 3/2

was confirmedby BaBar

PRL 97 (2006)

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What do we know about X baryons Strangeness -2 baryons: qss (q: light u/d quark) Baryon number = 1, isospin = 1/2 If flavor SU(3) symmetry is exact for the classification of all particles, then we have N(X)

= N(N*) + N(D*) Currently, only a dozen of X have been identified so far.

(cf. more than 20 N*s & more than 20 D*s) Only X(1318) and X(1530) have four-star status Only three states with known spin-parity Even the quantum numbers of most X resonances are still to be identified Practically, no important information for the X resonances.

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Baryon structure from X spectroscopy

Properties of S=-1 resonances(through the study on production mechanisms)

Exotic particles (penta-quarks & tetra-quarks)(purely exotic, not cryptoexotic)

New particles (perhaps an S=-4 dibaryon?)

What can we learn from X?

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Characters of the Characters of the XX hyperons hyperons

Narrow widths: G(X*)/G(N* or D*) ~ 1/10 for pionic decays G is proportioanl to (# of light valence quarks)2 Riska, EPJA 17 (2003)

Decay Gexp

(MeV)Ratioexp (# of light valence quark)2

DNp 120 12 9

S*Sp 40 4 4

X*Xp 10 1 1

Decuplet octet + p

from J. Price

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XX baryons in Experiments baryons in Experiments

Good Things Small decay widths

Narrow peaks Identifiable in a missing mass plot, e.g.,

missing mass Mc(K+K+) in + p K+ + K+ + X,invariant mass of decay products such as X p L

Background is less complicated. (+ p K+ + K+ + X* K+ + K+ + p + Xgs)

Isospin ½ (cf. nucleonic resonances have N* & D*; =1/2 and 3/2)(baryons with one strange quark: L & S hyperons)

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Bad Things Mostly processes through Kp reactions or the S-hyperon induced reactions were used.

(initial state has S=-1) No current activity in X physics with hadron beams

They can only be produced via indirect processes from the nucleon. (initial state has S=0) In the case of photon-nucleon reaction, we have at least three-body final state. The current CLAS data indicate that the production cross section is less than 20 nb at

low energies. (cf. KL or KS photoproduction have cross sections of order of a few mb).

Other technical difficulties

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PDG saysPDG says

Particle Data Group (2006)

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WA89 (CERN-SPS)WA89 (CERN-SPS)

S--nucleus collisions

EPJC, 11 (1999)

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Exotic Exotic XX(1860) or (1860) or (1860)(1860)

Isospin-3/2 state: therefore, penta-quark exotic

Report from NA49 in pp collision PRL 92 (2004) but never be confirmed by other experiments with higher statistics, e.g. WA89

PRC 70 (2004)

NA49 WA89

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Earlier experimentsEarlier experiments

WA89 results (hep-ex/0406077)

1530 1690 1860(?)

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Recent activityRecent activity

CLAS at JLab: initiated a Cascade physics programphotoproduction processes: p KKX

PRC 71 (2005)

nucl-ex/0702027

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More on CLAS dataMore on CLAS data

Invariant mass distributionin the Xp channel

Also cross sections for X photoproduction

X(1530)X(1620) &

X(1690) ?

Need higher statistics !

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Possible Questions Possible Questions

What is the third lowest state following X(1320) and X(1530)? X(1620) vs X(1690)

Does X(1620) exist?

Spin-Parity of the excited states?

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3. 3. XX baryons in theories baryons in theories

Review on the works before 1975Samlos, Goldberg & Meadows, Rev. Mod. Phys. 46 (1974) 49 Classify the states as octet or decuplet

(depending on the spin-parity, use Gell-man—Okubo mass rel.)(recent work along this line; Guzey & Polyakov, hep-ph/0512355)

What is the third state following X(1320) and X(1530)?

Quantum numbers? Couplings & decay channels

Most model builders have not considered X spectrum or the structure of X resonances seriously, except the lowest X’s of octet and decuplet. Most model gives (almost) correct values for X(1320) & X(1530). But the predictions on the higher states are quite different.

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Nonrelativistic Quark ModelNonrelativistic Quark Model

Chao, Isgur, Karl, PRD 23 (1981)

from S. Capstick

X(1690)*** has JP=1/2+ ?

The first negative parity state appears at ~1800 MeV.

Decay widths are not fully calculated by limiting the final state. (but indicates narrow widths)

Relativistic quark model ?The 3rd lowest state

at 1695 MeV?

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Relativistic Quark ModelRelativistic Quark Model

Capstick & Isgur PRD 34 (1986)

NRQM

RQM

The 3rd lowest state?

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One-boson-exchange modelOne-boson-exchange model

Glozman & Riska, Phys. Rep. 268 (1996)

Exchange of octet pseudoscalar mesons.First order perturbation calculation around harmonic oscillator spectrum.

Negative parity state seems to have lower mass: but no clear separation between +ve and –ve parity states

Strong decay widths are not calculated.

The 3rd lowest state?

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Comparison of NRQM & OBEComparison of NRQM & OBE

The two models show very different X hyperon spectrum.

The predictions on the candidate for X(1690) are different.

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Large NLarge Ncc (constituent quark model) (constituent quark model)

Expand the mass operator by 1/Nc expansion

Basically O(3) X SU(6) quark model

Mass formula (e.g. 70-plet: L=1, p=-1)

Fit the coefficients to the known particle masses and then predict.

11 3

0 1

ˆ ˆn n n n

n m

c d

M O B

from J.L. Goity

Where is X(1690)?

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The 3rd lowest state?

Schat, Scoccola, Goity, PRL 88 (2002) and other groups

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Quark-based modelsQuark-based models

The third state Expt. X(1620)*, X(1690)***, spin-parity unknown NRQM: 1695 MeV with 1/2+ RQM: 1755 MeV with 1/2- OBE: 1758 MeV with 1/2- or 3/2- Large Nc: 1780 MeV with 1/2-

Algebraic model: 1727 MeV with 1/2+

Highly model-dependent: expt. should judge The predicted masses are higher than 1690 MeV (except NRQM) How to describe X(1690)? The presence of X(1620) is puzzling, if it exists. Cf. similar problems in quark models: L(1405)

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QCD sum rulesQCD sum rules

Mass splitting between 1/2+ and1/2- baryons. Jido & Oka, hep-ph/9611322

Interpolating field (with a parameter t)

X(1/2+) = 1320 MeV and X(1/2-) = 1630 MeV. So, X(1690) would be X(1/2-).

Sum rules for 1/2+, 1/2-, and 3/2-. F.X. Lee & X. Liu, PRD 66 (2002) Three-parameter calculation (similar interpolating field)

X(1/2+) = 1320 MeV, X(1/2-) = 1550 MeV, X(3/2-) = 1840 MeV (exp. 1820 MeV)

X(1820) is well reproduced, but where is X(1690)?

5 5( ) ( ) ( ) ( ) ( ) ( )abc a b c a b cJ s x Cd x s x t s x C d x s x

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Lattice calculationLattice calculation

Quenched approx. Level cross-over in the physical region?Results for 1/2+ and 1/2- states

1/2-

1/2+

F.X. Lee et al., NPB(PS) 119 (2003)

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Lattice calculationLattice calculation

Quenched approx. (variational method)

The first excited state seems to have -ve parity at 1780 MeV. (two states are nearly degenerate)Bern-Graz-Regensburg Coll., PRD 74 (2006)

X with J = 1/2

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Skyrme modelsSkyrme models

Baryons are topological solitons in the nonlinear meson field theory.

In SU(2)F, it gives N and D.

Extension to SU(3) Is SU(3) a good symmetry for baryon structure?

SU(3) collective rotation (Chemtob, Prasalowicz, …) Ms ~ Mq perturbative treatment for symmetry breakers

Exact diagonalization (Yabu, Ando, …) Ms > Mq diagonalize the total Hamiltonian

Bound state approach (Callan, Klebanov, …) Ms >> Mq different treatment for isospin and strangeness

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Bound state approachBound state approach

bound Kaon

SU(3) is badly broken

Treat light flavors and strangenesson the different footing

= SU(2) + K/K*

Soliton provides background potentialwhich traps K/K* (or heavy) meson

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Bound state approachBound state approach

N, D: almost SU(2) object

Hyperons: bound states ofthe soliton and K/K*

Anomaly terms(i) Push up the S = +1 state

to the continuum no bound state

(ii) Pull down the S = -1 statebelow the threshold bound state

Heavy quark baryons:bound states of the soliton

and heavy meson (D/D*, B/B*)

Heavy vector mesons(i) Should be treated

explicitly(ii) Gives the correct heavy

quark symmetry of theresulting baryon spectrum degenerate S and S*

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Bound state approachBound state approach

Renders two bound states with negative strangeness P-wave; lowest state S-wave: first excited state

After quantization P-wave L(1116) +ve parity hyperon S-wave L(1405) -ve parity hyperon

Mass formula

( ) ( ) ( ) ( ) ( ) ( ){

( ) ( ) ( ) ( )

1 1 2 2

1 21 2 1 2 1 1 1 2 2 2

1 2 1 21 2

11 1 1 1

2

1 1 12 2

sol

m m

m m

M M n n

I I c c J J c c c J J c c c J J

c c c cJ J J J I I R J J

I

w w= + +

+ + + + + - + + - +

ü+ - ïïé ù+ + - + - + + - ýë û ïïþ

ur ur urg

270 MeV energy difference

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PDGPDG

26 S’s18 L’s11 X’s 4 W’s

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Hyperon spectrum (expt)Hyperon spectrum (expt)

289 MeV

290 MeV

285 MeV positive parity

negative parity

parity undetermined

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Mass spectrumMass spectrum

YO, PRD 75

Nearly equal spacingsbetween particles of same spin

and of opposite parity(~300 MeV)

Mass differencesL(1/2)=L(1/2-)-L(1/2+): 289

S(1/2): 311, S(3/2): 278X(3/2): 290, 300

W(3/2): 284, 304, 322, W(1/2): 303

Spin-parity not known

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Mass spectrumMass spectrumYO, PRD 75

Recently confirmed by COSYPRL 96 (2006)

JP of (1690) is ½-BABAR: PRD 78 (2008)

NRQM predicts ½+

Unique prediction of this model.Most of the quark-based models fail

to describe these two states simultaneously.

,PJ nY

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Mass spectrumMass spectrum

Two X(1/2-) states One kaon in P-wave and one kaon in S-wave J = Js + Jm (Jm = J1 + J2)

Js : soliton spin (=1/2), J1(J2): spin of the P(S)-wave kaon (=1/2)

Jm = 0 or 1 both of them can lead to J=1/2 Two J=1/2 states and one J=3/2 state

In this model, it is natural to have two 1/2- states and their masses are 1616 MeV & 1658 MeV!

Cf. unitary extension of chiral perturbation theory Ramos, Oset, Bennhold PRL 89 (2002)

1/2- state at 1606 MeV Garcia-Recio, Lutz, Nieves, PLB 582 (2004)

X(1620) & X(1690): 1/2- states

Clearly different from the quark models

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OutlookOutlook

Recent studies on hadron structure Spectrum of strange baryons Production mechanism of baryons

Programs for studying hadron structure Full coupled-channel dynamical model

A lot of precise data from JLab, Spring-8 etc Combined analysis of meson production (YO et al., 2008) JLab-EBAC Cascade physics program Excited Cascade particles & other exotic states like di-Cascade

Soliton model in holographic QCD Borromean hadrons?

(, n, n) three-body system is bound,while neither (, n) nor (n, n) are bound.