N∗ and Δ∗ parity doublets in the baryon spectrum

Progress in Particle and Nuclear Physics PERGAMON

Progress in Particle and Nuclear Physics 50 (2003) 259-261 http://www.elsevier.comflocate/npe

N* and A* Parity Doublets in the Baryon Spectrum V. CREDI? fir

Helmhoirz-lrurilur

The N and 4 excitation total angular momentum Among others, structure

Srruhlen-

und Kemphysik,

spectrum

exhibits

ofBonn,

Urtiversify

states

of equal

but with opposite parity being ahnost degenerate

in mass.

it has been suggested

parity

doublets,

by L.Ya. Glozman

i.e.

Germany

that

the parity-doublet

may be due to efiective chiral restoration.

Study of baryon decay cascades with CB-TAPS The

IK excitation

gcncrate

wit,h

spectrum

equal total angular

in the A spcctrurn

parity

doublets,

momentum

and in the ‘4 spectrum.

Ag+(1820)

- A$-(1830).

observation

has recently

symmetry

displays

to the Wigncr-Weyl

It has been suggested

structure

representation

of the discus&

parity doublet

in the A spectrum

doubling

seems (nearly)

So far, existing of the whole baryon

states

of parity

symmet,ry,

of excited baryons

i.e one parity

doublet

J but opposite

This

mode of chiral

of highly-excited

energies.

In this cast:,

with the given parity

the available

spectroscopic

falling into a (l/2,1)

in t,hc nucleon

of the same spin being degenerate

with identical

are found.

[l, 21.

in the spectrum

It has even been shown that

the possibility

and

doublets

that arc compatible

tlc-

- A:-(1930)

from the Nambu-Golstone

observed

mass

can also be observed

arc A$-(1905)

in the limit of large excitation

of SIJ(2) 1, x sum

multiplcts.

baryons support

is striking:

approximately

The latter

examples

to a phase transition

that the parity-doublet

- the parity-chiral

the elect

parity.

are

mode in the upper part of the baryon spectrum

baryons should fall into representations

data for nonstrange

which

no clear indications

baryons may be due to effective chiral restoration

of the states

states

but. opposite Prominent

In the C spectrum; been related

i.e.

at ELSA

@ (1: l/2)

spectrum

and one

in mass (Tab. 1). In many cases;

parity often have very similar masses.

Parity

established

mass-formula spectrum

approaches

[3]. However,

for baryons a recently

have failed to present developed

a quite simple but very succesful mass formula for baryon resonances 0146-6410/03/$ see front matter 0 2003 Published PII: SOl46-6410(03)00018-8

by Elsevier

Science

BV.

a consistent

phenomcnological

picture

model derives

which can be interpreted

in terms

260

Phys. 50 (2003) 259-261

V Credk / Pros. Part. Nucl.

J=;

.S&+ (2100)(*)

Ni-

(2090)(r)

AS? (1910)

4;-

(1900)

.J = ;

X3’ (1900)

N;-

(2080)

a:.+ (1920)

hi-

(1940)(*)

‘.J= $

N!+ (2000)

N4- (2200)

a$+ (1905)

45.. (1930)

J=%

NI+ (1990)

N;-

(2190)

A;+ (1950)

4;-

(2200)(*)

J=;

NE+ (2220)

“;-

(2250)

A$+ (2300)

4;-

(2400)

s+-

(2600)

A++ (2420)

J z 12 .J = +2

? N 1;A (2700)

., = + L

?

?

?

?

a,.,

Table

Appearance

?

parity

4?+ (2750) (2950)

1 of high-mass

doublets

n spectrum.

?

of a static quark-diqusrk structure irl colour space [4]. Parity doublets

are dynamically

not evidcncc

states

multiplcts

chiral symmetry

restoration.

with defined intrinsic

4 states

with .1=1/Z,

degenerate.

According

to [4], high-mass

quark spins and orbital

angular

3/2 and 5/2 in Table 1: with positive

It is: however,

momenta.

parities,

L=2 and intrinsic In general, doublets

spin S=3/2

in the high-mass embracing

momenta.

Chiral

symmetry

of the two hypotheses

of different

is not restored

arc weakly attracted

[4]. Cohen and G&man

parity doublet.

il

rcsonanccs;

orbital

reveals

is weak, at most. The data are better

multiplets

arc: c,lcarly mass

(2200) form

with intrinsic

t.he first six

angular

these four momenlum

to .7=1/2,...,7/2.

comparison

spectrum

SL(6)

chiral partners

anticipate

coupling

a quantitative:

multiplets

that

seem to form a super-multiplct

and that

emphasize

&idcncc

described

J but the same intrinsic

in the high-mass

that

for parity

in terms of super-

orbital

antI spin’ angular

spectrum

but there

are indications

their m>LTsdifference

is smaller

than

that the scheme requires

the existence

one could

of a All/>-

a I\illlp+ at about 2500 MeV, of a 413,2- and a N,:j,2- at 2750 McV, and of three additional 2950 McV. Thr existcnc,c, of these states The CR-T.4PS full dynamical cascades

range.

of high-mass

The 47r acceptance guarantees proton

detector

thcrcfore,

is the ideal instrument,

to the ground

of the detector

a large efficiency

and ofT the neutron.

production

system

CB-EISA

to identify

state

data

prediction

via the: emission

states at,

restoration.

by observing

of single

pion and eta mesons.

with a good spatial

and cncrgy resolution

of many neutral from 2000/2001

states

and

final states over the

baryon statt!s up to 2.6 GcV/c2

of the type Y**(A**) + X*(4*) highly-excited

of chiral symmetry

to study various multi-photon

in combination

and selectivity

and decay cascades bc possible

is a compelling

It allows to identify highly-excited states

and do

into supcr-

For example.

and negative

less obvious that the A712~ ( 1950) and 47,2

resonances

created

are organiscd

The A7,2-1-(1950) has a mass which is very close to the other 3 positive-parity positive-parity

in N and

final states give strong

in photoproduction indications

for resonance

-+ p7r”7r”(p7r07/) are observed.

via the investigation

off the

of those cascades.

It will,

V Credi/

Prog.

Parr. Nucl.

Phys.

50 (2003)

259-261

References [l] L.Ya. Glwman, [2] M. Kirchbach,

Phys. L(%t,. B 475

(2000) 329.

Nucl. Phys. A 689 (2001) 157.

!3] S. Capstick

and W. Roberts,

Progress

in Particle

[4] E. Klempt,

A mass formula for baryon resonances,

and Nucl. Phys. 45 (2000) 241. Phys. Rev. C 66;(2002):058201

261