Experimental and theoretical backgrounds for generation of

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19th International IUPAP Conference on Few
-
Body Problems in Physics

31.08
-

05.09.2009
-

University of Bonn / Germany


Experimental and theoretical
backgrounds for generation of
dibaryons

in NN and 3N
interactions





V.I. Kukulin

Institute of Nuclear Physics

Moscow State University

CONTENT


1.

Hard problems with 2
π
-
exchange and scalar force.


2.

Dibaryon mechanism for scalar field generation in
Roper resonance and in NN system.


3.

Experimental evidence: two
-
pion and two
-
gamma
production in nuclear collisions.


4.
New three
-
body force based on dibaryon mechanism.
Nonconventional picture for nuclei.


5.
New electro
-
magnetic currents and the deuteron
structure at high momentum transfer.


6.

Conclusion.




Problems with scalar NN force at intermediate
distances

“We show that the highly dominant configuration is


|s
4
p
2
[42]
O

[51]
FS



due to its specific flavour
-
spin symmetry. Using the
Born
-
Oppenheimer approximation we find
a strong effective repulsion
at zero separation between nucleons

in both
3
S
1

and
1
S
0

channels. The
symmetry structure of the highly dominant configuration implies the
existence of a node in the S
-
wave relative motion wave function at short
distances. The amplitude of the oscillation of the wave function at short
range will be however strongly suppressed.”



“The main outcome is that V
NN
(R=0) is highly repulsive in both
3
S
1

and
1
S
0

channels, the height being
0.830

GeV

in the former case and
1.356

GeV

in the latter one.”


“Thus it is the GBE interaction which brings about 1
GeV

repulsion,
consistent with the previous discussion.”

Short
-

and intermediate
-
range nuclear force in quark
models


Here we will focus mainly on the symmetry aspects rather than details of quark
dynamics.


So, the mixed symmetry
6
q
-
configuration |s
4
p
2
[
42
]
x
> is strongly dominating
over the fully symmetric one |s
6
[
6
]
x
> as:

W([
42
]):W([
6
])=
8
:
1
(for two non
-
interacting nucleons)



It was proved (Y.Yamauchi, A.Buchmann, A.Faessler; I.T.Obukhovsky,
O.Kusainov; M.Oka, K.Yazaki and many others) that this dominating mixed
-
symmetry configuration is preserved also for any reasonable
qq

interaction
model.

The nucleon
-
nucleon phase shifts found with
GBE
-
and OGE
-
models for q
-
q force

OGE
qq
force

GBE
qq
force

NN potential extracted from Lattice QCD

Short
-

and intermediate
-
range nuclear force


At
r
NN
>1.2
-
1.4 fm the NN interaction is mediated by
π

and 2
π
-
exchange
(i.e. Yukawa picture). However when
r
NN
<
1.2

fm

(i.e. at intermediate and
short ranges) two nucleons overlapped and the whole picture of
interaction is dictated by quark dynamics.

The
dibaryon mechanism for scalar field
generation in Roper resonance and NN system

Expansion of the total dibaryon propagator into
Δ
+
Δ
,N+R etc. loops in Dyson equation.



The phase shifts

of NN scattering

in dibaryon model

The phase shifts of NN scattering in low
partial waves

References


Dibaryon

(dressed bag) model for NN interaction:

1.
Nucl
. Phys. A
689
,
327
c (
2001
).

2.
Phys. At.
Nucl
.
64
,
1667
(
2001
).

3.
J. Phys. G
27
,
1851
(
2001
).

4.
Int. J. Mod. Phys. E
11
,
1
(
2002
).

5.
AIP Conf. Proceeds.
892
,
485
(
2007
).


Relativistic generalization of
dibaryon

model:

1.
Phys. At.
Nucl
.
68
,
1511
(
2004
).

2.
Ann. Phys.
320
,
71
(
2005
).

Interpretation in terms of the 2

ω
-
excited
string.

See A. Faessler, V.I. Kukulin and M.A.Shikhalev, Ann. Phys.
320

(2005) 71.

The dibaryon model prediction for the two
-
pion
production via σ
-
meson in the Roper resonance decay
and at p+n or p+p collisions





Roper resonance now:


M


⡍敖(



SAID


partial wave analysis
:
1357 160


Bonn
(Sarantsev et al)


丠⬠


ㄳ㜱
(
2

ㄸ1
(

)



Explicitly seen

in:




p →

X
1390 190
(?)



J/


→ n p



1358 160


p p → p n



1355 140


Roper decay N
*

→ N



pp → NN




dominantly

N
*

→ N



Scalar
-
isoscalar probes (


exchange) see „narrow“
monopole excitation at very low excitation energy :


breathing mode @





㐰〠
Me ℠


Summary about Roper
-
resonance characteristics

Various mechanisms for the 2
π
-

meson
generation from the dressed intermediate
dibaryon

III. Experimental evidence

3.1. Early evidences for dibaryon production in pp
collisions.

3.2. New observation for the
σ
-
channel in Roper
decay (
T. Scorodko et al., Progr. Part. Nucl. Phys.
61,168 (2008)
).

3.3. ABC
-
puzzle (historically).

3.4. Exclusive (WASA
-

PROMICE) measurements for
the ABC
-
puzzle: p+d →
3
He +2
π
, p+d → d(
π π
) +p,
p+n → d +(
π π
)
0

etc. (
M.Bashkanov et al., Progr.
Part. Nucl. Phys. 61,168 (2008)
).

3.5.
γγ
-
correlations in p+p, p+C and d+C
intermediate
-
energy collisions in GeV region.

ABC effect


Inclusive measurements:


pd

3
He X




Abashian et al. Berkeley




Banaigs et al. Saclay






low
-
mass enhancement !



Missing mass [ GeV/c
2

]


.3 .4 .5 →


| | |


= 0.3 deg

p
d

= 3.14 GeV/c



T
p
= 893 MeV


(
A
bashian,
B
oth,
C
rowe )


NP B
67
(
1973
)
1

First exclusive measurement: @ CELSIUS
-
WASA


p d


d





⬠p
spectator

M


M
d


T
p

= 1.04 GeV

ABC

(

)
int

(

)
conventional

Proc. MESON
06, Int. J. Mod.
Phys. A22
(2007) 617

T
p

= 1.36 GeV

Energy Dependence of ABC

pn → d
*




→ d


(this work)


(JINR, DESY)



conventional

pp → d





(no ABC effect)


M. Bashkanov et al., Phys. Rev. Lett. 102, 052301 (2009)

Angular Distribution of Isoscalar Low
-
Mass
Enhancement ?

M





scalar


isoscalar !

Phys. Lett. B637,


223
(2006)

Direct experimental evidence for the
s
-
channel
dibaryon induced
σ
-
meson production

The spike around 2
π
-
threshold turns out to be very stable against
cuts. E.g., increase of the threshold E
γ
= 50 MeV to E
γ
= 100 MeV
has no significant effect on this intermediate spike.

Moreover, the model which incorporates very well the
γγ

events
and M

γγ


from
π
0

and
η

production gives practically no events in
the intermediate area with M

γγ

~300


400 MeV! Also from MC
simulation of
π
+
π
-

production we do not get any contributions in
the M

γγ


spectrum.


Then the experimentalists (CELSIUS
-
WASA) conlude:



Since none of these simulated processes is able to account for
the structure observed near the
ππ

threshold and also detailed
and comprehensive tests of detector performance and event
structures have
not given
any hint for an artifact, we are led to
consider seriously the possibility that
the observed structure
(at M

γγ

~300


400 MeV)
is real and might be due to the process pp


pp
σ



pp
γγ
,
in particular also since pp


pp
π
+
π
-

and pp


pp
π
0
π
0

reactions are dominated by
σ

production.“






The new
γγ
-
data with large
statistics

In these nice experiments done at the Dubna
Nuclotron machine the authors analyzed the
γγ
-
spectra from pC and dC collisions at
5.5
GeV/c (for
protons) and
1.7
-
3.8
GeV/c per nucleon (for
deuterons).

To be published
in Phys. Rev. C
(
2009
).

γγ
-
yield from dC collisions at E=2.75 GeV/cA

γγ
-
yield from pC collisions at E=
5.5
GeV/c


Production of two
γ
-
quanta
according to dibaryon model

New three
-
body forces in DBM and
the properties of
3
N system

The dibaryon model leads inevitably to
appearance of new scalar and spin
-
orbit
three
-
body forces which may modify the
whole nuclear dynamics.


J. Phys. G
30
,
287
,
309
, (
2004
);

Phys. At. Nucl.
68
,
1511
(
2005
).

New dibaryon induced
3
N force

Two
-
proton density in
3
He (solid line) and two
-
neutron density in
3
H for dibaryon model vs two
-
proton density in
3
He for Bonn NN
potential (triangles).

s
-
channel (new)

t
-
channel (conventional)





New

s
-
channel meson
-
exchange

currents.

t
-
channel currents
vs

s
-
channel current

valid at long distances valid at intermediate and short distances

Meson
-
exchange currents (continued)



References:

1.
Bled Workshop in Physics,
7
,
33
(
2006
).

2.
Phys. Rev. C
74
,
064005
(
2006
).

3.
Phys. Rev. C
77
,
041001
(
2008
).

There are also some
new

terms in
s
-
channel:

All these new currents will be manifested

at sufficiently high
q
2

The structure function B(Q
2
) for elastic e
-
d scattering.

See V.I. Kukulin, I.T. Obukhovsky, P. Grabmayr, and A. Faessler, Phys. Rev
. C
74
,
064005
(
2006
).

Conclusions

1.
The deficiency of scalar fields in OBE
-

and constituent quark
models gives a very strong evidence in favour of existence of
σ
-
dressed intermediate dibaryons
in which the scalar field is
generated in the string deexcitation process.

2.
New experimental data of Tübingen and Dubna groups on
2
π

and
2
γ

production in nuclear collisions confirm very nicely the dibaryon
mechanism for NN interaction.

3.
The dibaryon model for nuclear force leads to numerous
implications for nuclear physics


main of them is an appearance
of a new non
-
nucleonic (i.e. the dressed dibaryon) components in
nuclear wave functions with probability ≥
10
%.

4.
In turn, these new components leads to new e.
-
m. currents, new
powerful
3
N force, existence of new Coulomb effects, revision of
CSB effects, appearance of cumulative processes in hadronic
scattering off nuclei, etc.

Charge symmetry breaking effects
in DBM

Two alternative values of the
nn

scattering length are assumed:

a
1
nn
=
-
18.7
fm and a
2
nn
=
-
16.3
fm.


The first value has been extracted from the previous analysis of

experiments
d
(
π
-
γ
)
nn

reaction and is used in all current

NN potential models, while the second value a
2
nn
=
-
16.3
fm
has been derived from numerous three
-
body breakup
experiments
n+d



nnp

done for the last three decades.

CSB effect means the difference between a
nn

and “pure
nuclear” a
pp

values, i.e. a
pp

value corrected for the Coulomb
pp interaction: a
pp
exp

=
-

8.72
fm (with Coulomb interaction).

In the conventional in the NN potential models (like CD Bonn,
Nijmegen etc.)

a
pp
CC

(CD Bonn) =
-

17.3 fm


while in the DBM

a
pp
CC

(DBM) =
-

16.57 fm


(i)
This means that
a
pp
CC


is strongly model
-
dependent.

(ii) If to assume
a
nn

=
-

16.3 fm extracted from
nd


nnp

breakup experiments the CSB effects in
dibaryon

model
are rather small !! In conventional potential models the
CSB effects are much stronger !!



Solution for
Δ
E
C
-
problem:
Δ
E
C

= E
B
(
3
He)
-
E
B
(
3
H)

Δ
E
C
exp
=
760
keV while the modern
Δ
E
C
theor
=
640
keV .
The difference in
Δ
E
C
120
keV is explained now mainly
by CSB effects.


New three
-
body Coulomb force in DBM
approach.

V
coul
(
ρ
) is the Coulomb force between the charged
dibaryon (Z
D

= +
1
in
3
He) and the external proton. This
force has been ignored in all previous few
-
nucleon
models.

The explanation of the
Δ
E
C

puzzle is reached within the conventional NN
potential model (AV
18
+ UIX) only with a
nn

=
-

18.7
fm. However, this value
is in contradiction with a
nn

=
-

16.3
fm extracted from nd breakup.



The circular polarization P
γ
of
γ
-
quantum

in the n+p → d+
γ

reaction.



The
γ
-
induced polarization P’
y

of the neutron measured in
the d(
γ
, n)p reaction at polar
angles

=
45
,
90
and
135
o
.