Transcript Medium Effects in Two-Pion Production in Proton

Two-Pion Production
on the Nucleon and in Nuclei
Erice 2007
Heinz Clement

pp production in NN collisions
in „vacuum“




in medium



Tp< 1 GeV: s and Roper
Tp> 1 GeV: DD
Bound nuclear final states: ABC effect and DD
comparison to ( g,pp ) and ( p, pp )
summary
gN, pN, …  NN collisions

Nucleon Resonances

s-channel production
↔
associate production
↔
virtual p, s, ...
↔
NN and Nd collisions
( if 2-body decay)


excitation by g, p, ...
NN system

only measurements on d
p and pp Production
@ CELSIUS and COSY

D
test case
N*(1440)
investigate by s excitation

excitations in the NN system

NN excitations in Nuclei
D (1232)
excitation
in single-pion production
D excitation in pN → NNp
pp → ppp0
@ 893 MeV
 GD = 100 MeV
pn → ppp@ 893 MeV
Roper Resonance
*
N (1440)

pN and gN:
Roper´s resonance
 a resonance without seeing it


New generation of measurements:

the „narrow“ Roper
Roper´s pN Resonance
How to excite the Roper?

N
→ N* (1440)
I( Jp ): ½( ½ )+ → ½( ½ )+

scalar-isoscalar excitation: s
or
 isovector excitation: p, g (M1), …
with spinflip preferred

Where to see?

gN
photo absorption
 gp → p p0p0


Where is the Roper?
Morsch and Zupranski, PRC 61, 024002 (1999)
D
D13(1520) …
Where to see?

D
2. resonance region D13(1520) …
3. resonance region F15(1680) …
pN scattering:
I=3/2

Where is the
Roper?
I=1/2
I=1/2, 3/2
PDG 2006
p- p total cross section
Where is
the
Roper?
SAID data base
pN partial wave analysis

Partial wave amplitudes

Argand plot
SAID nucl-th/0605082
imag
real
Re A
imag
real
here is theRoper :
SAID:
Mpole = 1357 MeV
Gpole = 160 MeV
Bonn (Sarantsev et al.):
pN + gN
1371 (2)
184 (20)
New Generation of Experiments
visualizing a „narrow“ Roper (?)

a p → a X @ 4.2 GeV
(Saturne)

J/y → N N* and N N*
(BES)

pp → npp+ @ 1.1 and 1.3 GeV (WASA)
New Generation of Experiments:
1. a p → a X (Saclay)
G 190 MeV
G 400 MeV
 scalar-isoscalar
probe a
however:
Hirenzaki et al., PRC 53, 277 (1996)
 interfering
background
from projectile
excitation
Morsch et al., PRL 69, 1336 (1992) and PRC 61, 024002 (1999)
New Generation of Experiments:
2. J/y → N N* and N N* (BES)
n pp- and pp+ n events  I= 1/2 N* excitations only
Roper M=1358(6,16) MeV
G=179(26,50) MeV
Ablikim et al., PRL 97 (2006) 062001
hep-ex/0405030
3. pp → npp+
(WASA)
Mpp+
D
 Tp = 1.1 GeV
Tp = 1.3 GeV
Data prefer Roper values:
M  1355 MeV
G 140 MeV
(nucl-ex/0612015)
Mnp+
Roper
Dalitz plots MC
pp → npp+ @ 1.3 GeV

D++ and D+


only Roper
D++ , D+, Roper
Mnp+ 2
Mpp+ 2
Dalitz Plots pp → npp+ @ 1.3 GeV
( not corrected)

data

MC
(„through detector“)
Mnp+ 2
Mpp+ 2
Decay of Roper

decay channels:
BR(1440)
PDG 2006
BR(1371)
Bonn 2007 (Sarantsev et al.)
0.61 (2)
0.39 (5)
0.18 (2)

N* → Np
0.55 – 0.75
N* → Npp
0.30 – 0.40
→ Dp → Npp
0.20 – 0.30
→ Nr → N(pp)I=L=1 < 0.08
→ Ns → N(pp)I=L=0
0.05 – 0.10

N* → Dp / N* → Ns :
0.9 (2)




0.21 (3)
2–6
PRC 67 ( 2003 ) 052202 (Pätzold et al)

N* → Npp: look in pp → pp* → pppp :
1.0 (1)
pp production
DD
Status quo
ante:
Roper
chiral
dynamics
experimental
and theoretical
situation
← ← CELSIUS → →
← polarized COSY → →
pp Production:

Energy
dependence
of total cross
section
pp → ppp0p0
Valencia
DD
N*→Ns
Roper
N*→Dp
WASA
PROMICE/WASA
bubble chamber data
Angular distributions
cos Qpcm
cos Qpcm
775 MeV
900 MeV
1000 MeV
1100 MeV
1000 MeV
1100 MeV
1300 MeV
1200 MeV
1300 MeV
1200 MeV
775 MeV
900 MeV
Invariant Mass distributions
M p0 p0
Mpp0
775 MeV
900 MeV
1000 MeV
1100 MeV
1200 MeV
1300 MeV
775 MeV
900 MeV
1000 MeV
1100 MeV
1200 MeV
1300 MeV
threshold region:
p+pRoper
excitation and
decay
( conventional analysis )
d
PRC 67 ( 2003 ) 052202
“s“
D
N*
N*
jkkjm
mmm
mmlllll
llllllllll
Branching Ratio @ pole: 1440 1350 MeV
N*→Dp / N*→Ns =
PDG
3.4 (3)
4 (2)
0.6 (1)
<)
d
<)
CELSIUS-WASA
pp → ppp0p0
Tp = 775 MeV
Tp = 900 MeV
Ipp = 0
See talk Tatiana Skorodko
∙∙∙∙∙∙∙∙

Npp
dominantly N → Ns !
N* →
( nucl-ex/0612015)
BR(Dp/Ns) = 1 : 2
―—— BR(Dp/Ns) = 1 : 8
Ipp = 0 + 1
Ipp = 0
Conclusions (1)

Roper Resonance historically:

Originally found in pN phase shifts of P11 partial
wave

Interpretation as a Breit-Wigner resonance in pN
 M  1440 MeV, G  400 MeV
Conclusions (2)

Roper resonance now:







SAID pN partial wave analysis:
Bonn (Sarantsev et al) pN + gN
M
1357
1371(2)
G (MeV)
160
184(20)
Explicitly seen in:
ap →aX
J/y → n ppp p → p np+
1390
1358
1355
190 (?)
160
140
Roper decay N* → N pp

pp → NNpp
 dominantly N* → N s
Conclusions (3)

Scalar-isoscalar probes (s exchange) see „narrow“
monopole excitation at very low excitation energy :
breathing mode @ w  400 MeV !
i.e. only 100 MeV above D, the lowest excited state
alternative approach close to threshold:
inclusion of dynamic s by pp rescattering
M.M.Kaskulov
et al.,
MESON2004,
Int. J. Mod.
Phys. A20
(2005) 674
Phys. Rev. C70
(2004) 014002
and 057001
☺ pp rescattering  pp phase shifts
☺ no explicit Roper resonance !
☺ only 1 parameter  fixed by absolute
scale of cross section
dynamic s , no explicit Roper
Tp = 750 MeV
phase space
calculation
without free
parameter
Conclusions on vacuum reaction

close to threshold: p+p- data consistent with dynamic s
( pp rescattering ) - however,
fails at higher energies ( no D, no Roper )

Tp < 1 GeV : Roper excitation and decay
resonance parameters – partly in good agreement
with most recent results from other experiments

Tp > 1 GeV: dominant configuration ( DD ) 0+ ?
present theoretical calculations do not give a good
description of data
pp Production in Nuclei

medium effects of the pp system

nuclei as isospin filter:
pp – system
0 0

pp → pp pp
pn → d pp
 pd → 3He pp:
 dd → 4He pp:

I = 0, 1, 2
0, 1
0, 1
0
}
ABC effect
Inclusive Measurements on Nuclei
(unresolved nuclear final states)
Lutz et al., NPA542, 521(1992)

Medium modifications of hadrons by



conventional processes ( e.g. D - h ) ?
partial chiral restoration ?
s chiral partner of p ?
Low-mass Mpp enhancement observed
in measurements on nuclei :



( p-, p+ p- )
( p-, p0 p0 )
( g , p0 p0 )
CHAOS @ TRIUMF
Crystal Ball @ BNL
TAPS @ MAMI
}
isoscalar effect
p+ A → p+p- X
p+ A → p+p+ X´
CHAOS
Mpp spectra
phase space
in CHAOS
acceptance
Double Ratio
Y ( MppA )
A 
Cpp
s TA
Y ( MppN )
s TN
Valencia group calculation
Phase space
Crystal Ball: p- A → p0p0 X
g A → p0 p+ / - X
g A → p0 p0 X
TAPS: g A → pp X
Valencia
group
calculation
Phase space
Comparison of CHAOS, CB and
TAPS results
Ratio
C/D
Pb / C
CHAOS
TAPS
Exclusive Measurements on Nuclei
(bound nuclear final states)


ABC – Effect:
low-mass enhancement in Mpp spectra
in scalar-isoscalar channel

excitation of the DD system
Missing mass [ GeV/c2 ]
.3 .4
| |
ABC effect
.5
|
→
(Abashian, Both, Crowe )

Inclusive measurements:
pd → 3He X
Abashian et al.
Berkeley
Banaigs et al.
Saclay

low-mass enhancement !
Q = 0.3 deg
NP B67 (1973)1
pd = 3.14 GeV/c

Tp = 893 MeV
First exclusive measurement: @ CELSIUS-WASA
p d → 3He pp @ Tp = 895
Mpp
MeV
M3He p
(DD)conventional
p0p0
(I=0)
ABC
+ -
pp
( I = 0, 1 )
(DD)int
Phys. Lett. B637,
223 (2006)
Angular Distribution of Isoscalar Low-Mass
Enhancement ?
Phys. Lett. B637,
223 (2006)
Mp0p0
cos
(
p 0p 0
Qp 0
)
scalar – isoscalar !
First exclusive measurement: @ CELSIUS-WASA
p d → d p0p0 + pspectator
Mpp
Tp = 1.04 GeV
Mdp
(DD)conventional
ABC
Tp = 1.36 GeV
(DD)int
Proc. MESON 06,
Int. J. Mod. Phys.
A22 (2007) 617
Quasifree pn → dp0p0 (bin T

Angular distributions:
p
= 1.0 – 1.04 GeV)
overall cms
pp
p
d
p
beam
d
pp subsystem (Jackson frame)
p
p
beam
with cut on ABC peak
Energy Dependence of ABC
(this work)
(JINR, DESY)
pn → d* → DD → d pp
(DD)conventional
pp → d p+p0 (no ABC effect)
control reaction
pp → dp+p0 @ 1.1 GeV


I = 1 channel  no ABC !
despite DD excitation
p0p0 Enhancement Gallery
pn → d p0p0
@ 1.0 GeV
pd → 3He p0p0
@ 0.9 GeV
dd → 4He p0p0
ABC largest
→ p0p0
enhancement
huge ?
heavier
nuclei ??
CELSIUS-WASA measurements
WASA@COSY proposal:
exclusive measurements
at several energies
Summary on pp Production in Nuclei
 inclusive measurements:
p A → X pp
g A → X pp
}
isoscalar low-mass enhancement in Mpp
increasing with increasing A
 exclusive measurements:
A B → C pp

ABC effect:
scalar-isoscalar low-mass enhancement in Mpp
increasing with increasing A
• correlated with the excitation of a DD system !
• specific configuration ( I = 0, Jp = 1+ or 3+) in pn system ?
supported by BMBF, DFG ( Europ. Graduate School ), COSY-FFE and Landesforschungsschwerpunkt Baden-Württemberg