Transcript Diapositive 1

Electromagnetic structure of Time-Like
baryonic transitions in pion induced reactions
HADES experiments at GSI.
B. Ramstein, IPN Orsay
R
N
ECT, Trento, 20/05/2013

1
B. Ramstein

e-
e+
Outline
 Introduction:
General context of HADES experiments
In-medium modifications of vector mesons
Link to Time-Like elctromagnetic structure of baryonic transitions
Results from pp reactions with HADES
Sensitivity to Time-Like electromagnetic structure of baryonic transitions
 Perspectives of HADES measurements with the GSI pion beam
-p ne+e- below ω threshold
Time-Like electromagnetic transition form factors
-p -p, -p -+n, -p -0p and kaon production
PWA  baryonic resonance parameters
(2014)
 Conclusions
2
B. Ramstein
Trento, 20/05/2013
Motivations of the HADES experiment
Exploring the phase diagram of
hadronic matter…..
E/A=1-2 AGeV
 /o ~ 1-3, T < 100 MeV
 N/Apart ≈ 10%
Na60
LHC
SPS
QGP
CERES
SIS-100
SIS-300
RHIC
AGS
hadrons
DLS
….. using dilepton emission:
rare but undistorted probe
CBM
DLS
SIS-18 HADES
KEK,JLAB,TAPS
G7
e+
e-
Trento, 22/02/2013
B. Ramstein
3
In-medium vector meson modifications:
see e.g. Leupold ,Metag,Mosel Int. J. of Mod. Phys. E19 (2010) 147 for a recent review
« in-medium broadening »
N*


+ ...
N-1
Rapp and Wambach EPJA 6 (1999) 415
Rapp, Chanfray and Wambach NPA 617, (1997) 472
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B. Ramstein
In-medium spectral function
depends on  NN* coupling
4
The  meson in hot and dense hadronic matter from
SIS18 to SPS
Source of  mesons
Source of  mesons at 1-2 AGeV
NN NR NN
N R N

Depends on
RN coupling
5
Source of  mesons
Source of  mesons at
ultra relativistic energies
+- 
Coupling of ρ to baryonic resonances can be studied in NN and N collisions at 1-2 GeV
Relation to electromagnetic
structure of baryons
Dalitz decay of baryonic resonances
RNe+e

R
e+
ρ meson production and decay
R

eelectromagnetic
elastic or transition
form factors

N
Vector Meson Dominance Model
N
e+
e-
Coupling constants
q2=M2inv(e+e-)=M2* >0
q2  0 : « Time like « region
electromagnetic form factors are unknown !
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6
Baryonic transition electromagnetic form factors in spaceLike region
Baryonic electromagnetic form factors
are measured for q20
Magnetic form factor for
γ*p(1232)
e+
eq2=M2* <0
Data: Mainz, Jlab
*
+
p
I.G. Aznauryan,V.D. Burkert Prog. Part. Nucl. Phys. 67, 1 (2012)
Helicity amplitudes for γ*pN(1520) D13 compared to quark models
No measurement at q2 > 0  use models fitted on space like data
7
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Two-component quark model
B’
B’
B
B
 unified description of baryonic form factors
 analytical derivation of form factor starting
from wave functions
V= , , 
Iachello &Wan ,Phys. Rev. C 69, 055204 (2004)
Wan & Iachello, int. J. Mod. Phys. A20(2005) 1846
Emilie Moriniere PHD, Orsay
F. Dorhmann et al , EPJA 45,401(2001)
 N- transition: 4 parameters fitted on
 elastic nucleon FF (SL+TL)
 SL N- transition GM
 analytical continuation to Time-Like region
GMN-/3GD
GN-M(q2)
Space-like
8
B. Ramstein
Time-like
0.6m2
Trento, 20/05/2013
Bare quark+meson cloud model for N- transition em form factor
G.Ramalho and T. Pena Phys. ReV. D85,113014 (2012)
Coupling to the bare quarks Coupling to the meson cloud
Bare quark contributiion
m2 
Full model
0.6m2
Space Like
Time Like
Extension to Time-Like region
 exists for elastic nucleon
form factors
( to be measured with PANDA)
 In progress for higher resonances
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9
Hades « strategy » : 2013 status
 Study dilepton emission in dense and hot matter (cf. DLS/Berkeley)
A+A reactions in the 1-2 AGeV energy range
C+C, Ar+KCl, Au+Au (2012)
 cold matter at normal nuclear density p+Nb 3.5 GeV
(cf KEK, Jlab, CBELSA/TAPS)
 Elementary collisions pp, dp and in future -p
•
reference to heavy-ion spectra
•
understand dilepton production mechanism (exclusive channels)
• dilepton emission is probing time-like electromagnetic structure of hadronic transitions!
 Simultaneous measurements of hadronic channels (pp NN, pp NN)
Cross-checks on known channels, detailed information on baryonic resonance production
 …. strangeness measurement program: K- , K0,, (1385), (1405) to be
investigated also in -p and -A
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10
The Collaboration

Catania (INFN - LNS), Italy
 Cracow (Univ.), Poland
Darmstadt (GSI), Germany
Dresden (FZD), Germany
Dubna (JINR), Russia
Frankfurt (Univ.), Germany
Giessen (Univ.), Germany
Milano (INFN, Univ.), Italy
München (TUM), Germany
Moscow (ITEP,MEPhI,RAS), Russia
Nicosia (Univ.), Cyprus
GSI
Orsay (IPN), France
Rez (CAS, NPI), Czech Rep.
SIS
Sant. de Compostela (Univ.), Spain
 Valencia (Univ.), Spain

Trento,
20/05/2013
IPN Orsay, 17/10/2011
Coimbra (Univ.), LIP, Portugal
B. Ramstein
Béatrice Ramstein
11
11
HADES
2nd generation dilepton
spectrometer
Side View
Acceptance: Full azimuth, polar angles 18o - 85o
Pair acceptance  0.35
Particle identification:
RICH, Time Of Flight, Pre-Shower (pad
Upgrade ( (2010)
chambers & lead converter)
also MDC (K))
New DAQ ~20 kHz
Trigger:
 new MDCs for plane 1
1st Level: charged
RPCparticle
θ <45°multiplicity (~10 kHz)
FW
 < 7°
START
2nd Level: single electron trigger (~2.5 kHz)
Momentum measurement
Magnet: ∫Bdl = 0.1- 0.34 Tm
MDC: 24 Mini Drift Chambers
Leptons: x~ 140  per cell, p/p ~ 1-2 %
M/M ~ 2% at  peak
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12
Sensitivity to Time-Like Electromagnetic
transitions in pp reactions
ppppe+e- 1.25 GeV  resonance Dalitz decay
2.2 and 3.5 GeV higher lying resonances
Dilepton production in pp reaction at 1.25 GeV
HADES: Phys.Lett.B690 (2010)118
 below  threshold
 only 2 dilepton sources
 ° Dalitz decay ° =4.5 mb
branching ratio ° → e+e- 1.2 %
  Dalitz decay :
branching ratio  → Ne+e- (QED :4.2 10-5)
 non resonant contribution expected to be
small
Time-like N-  transition electromagnetic
form factors G (q2)
M
Resonance model results:
° Dalitz
 Dalitz)+ effect of Iachello FF
0.6m2
Wan and Iachello Int. J Mod. Phys. A20 (2005) 1846
G. Ramalho and T. Pena arxiv: 1205.2575v1 (2012)
Béatrice Ramstein
14
Exclusive analysis : ppppe+e- at 1.25 GeV
using pe+e- events
Good agreement with
acceptance corrected
In HADES acceptance
simulation of
 production + Dalitz decay
(cf hadronic channels)
Exclusive channels confirm the dominance of  Dalitz decay
p
p
p1
+
 First measurement of  Dalitz decay!
p2 Dalitz decay branching ratio in agreement with QED value
(4.2 10 -5)
e+
cos(CMpe+e-)
(p,e+,e-) invariant mass (GeV/c2)
q2=M2inv(e+e-)=M2*
e-
Helicity distributions *  e+ed/dΩe~ 1+cos2
e
cos
Trento, 20/05/2013
N
*

W. Przygoda’s analysis
Cracow
e+
15
Non-resonant contributions in NNNNe+eOBE models
R. Shyam & U. Mosel, PRC 79 (2009) 03520
L.P. Kaptari, B. Kämpfer, NPA 764 (2006) 338
HADES data: Phys.Lett.B690 (2010)118
meson exchange currents
Pion form factor
N
N
n
p
n
p
|
Half-off-shell electromagnetic nucleon form factors
In the unphysical region (cf PANDA ) p p → e+ e- π0
p d → e+ e- π0 n
|
• sensitivity to hadronic electromagnetic structure
• much better agreement with data with  em
form factor !
On-going analysis:
 pionic channels
 exclusive pnpne+eB. Ramstein
with  em
FF
16
ppe+e-X E=2.2 GeV,3.5 GeV
Comparison to cocktail of dilepton sources
•Direct production of /
•Dalitz decay of  resonance (point-like)
E=2.2 GeV
E=3.5 GeV
Hades collab.,
EPJA48 (2012) 64
Hades collab.,
PRC85 054005 (2012)
Effect of electromagnetic form factors / Coupling of  to baryonic resonances ?
Trento, 20/05/2013
B. Ramstein
17
Exclusive ppppe+e- channel at 3.5 GeV
 Cross sections and angular distributions for baryonic resonances from hadronic
channel analysis
 Direct production of ,, with cross sections from hadronic analysis
(of / +-0) and = 1/2
 Constant form factors (taken at q2=0) M. Zetenyi and G. Wolf Heavy Ion Phys. 17 (2003)
27
ppe+ e-
ppe+ e-
ω
R

ρ

R
ω
A. Dybczak, Cracow
Additional information from exclusive channels
Missing yield related to light baryonic resonances (N(1520) ,..)
Transport model calculations for inclusive e+e- production in pp
“ electromagnetic form factor approach”:
“ρ production approach”:
NR couplings
VDM
pp 3.5 GeV
Courtesy of JanusWeil
Hades data, Eur.Phys.J. A48 (2012) 64
N- Form Factor: G.Ramalho and T. Pena Phys. ReV. D85,113014 (2012)
 mass distribution strongly modified in NN collisions
Same origin as in-medium effects
N*/
(coupling to baryonic resonances)


 large uncertainties: production
cross sections of baryonic resonances, ρNN* couplings
N-1 
 beam experiment
19
B. Ramstein
ρ
N(1520)
J.Weil, H. van Hees and U. Mosel, EPJA 48, 111 (2012)
N(1620)
N(1720)
Project of pion beam experiments with
HADES
pion momentum 0.6 < p <1.5 GeV/c
I ~ 106/s
s
1.21
20
B. Ramstein
1.52 1.68
η
ω
Trento, 20/05/2013
Pion beam experiments with HADES: an « old » idea
• Belongs since the very beginning to the HADES experimental program
Dilepton spectroscopy in  induced experiments
+A
• Cold nuclear matter studies, medium effects on /ω mesons
Strangeness production (K+,K-,K0S,ϕ) in +A
+N
•
Reference for +A studies,
•
Exclusive channels  - p  n e+e- studies of ρ/ω production
•
Special interest of subthreshold
production
(coupling to baryonic resonances)
Below
threshold
One pion, two pions and kaon production from an energy scan in -p
reactions
HADES 2013 program with pion beams
Based on HADES results
Constraints of beam time at GSI
21
B. Ramstein
Trento, 20/05/2013
Motivations of N experiments with HADES:
Dilepton channels
 well-known production mechanism
 fixed resonance mass MR=sqrt(s)
 exclusive  - p  n e+e- channels ( contribution can be rejected )
Time-Like electromagnetic form factors
Space-Like electromagnetic form factors
n
e+
q2 <0 fixed
R
Inverse pion electroproduction
* e+
p
*
p
q2 > 0
variable
R
e-
-
e--
p
R
N


e+
e-
More direct access to Time-Like em
transition form factors than in pp
Trento, 20/05/2013
B. Ramstein
studied at JLab/CLAS
Vector Dominance Model
 / coupling
N(1520)


+
...
N-1
22
/ production in N reactions
B. Kaempfer , A Titov , R.Reznik Nucl. Phys.
A721(2003)583
A. Titov, B.Kaempfer EPJA 12(2001)217
quark models
or derived from
Branching ratios
M.F.M. Lutz , B. Friman, M. Sayuer
Nuclear Physics A 713 (2003) 97–118
hadronic coupled channel
models fitted to γpρ/ω p and
-pρ/ω n data
Coupling constants
-pρn
R
N(1535)
N(1680)
N
e+
ρ/ω
smaller amplitudes
D13(1520) has a larger contribution
e-
N(1440)
-pωn
Mee=0.6 GeV/c2
N(1535)
N(1440)
Common result:
sensitivity of subthreshold production
to coupling to baryonic resonances
important interference effects
expected between I=0 (ω)
and I=1 (ρ) channels
N(1680)
N(1675)
B. Ramstein, IPN Orsay
23
/ interference: different models
A. Titov, B.Kaempfer EPJA 12(2001)217
M.F.M. Lutz , B. Friman, M. Sayuer
Nuclear Physics A 713 (2003) 97–118
γ* angular distributions
in CM sensitive to res.contributions
Almost total cancellation of ρ and ω amplitudes !
R
N
 e+
e-
B. Ramstein, IPN Orsay
Data (ee invariant mass and
angular distributions)
needed to fix coupling of
baryonic resonances to ρ/ω
mesons
24
Electromagnetic form factors approach
 M. Zetenyi and G.Wolf, Phys.Rev. C86 (2012) 065209
 ρ production is embedded in the em form factor
R
R
u channel
s channel
+ Born term
+ ρ meson exchange
adjustment to pion photoproduction cross sections of
• RN couplings (within the range allowed by the radiative decay widths)
γp+n
25
B. Ramstein
π-p ne+e-
Further studies needed:
Inclusion of ω contribution
Too large cross sections for
ρ production
Trento, 20/05/2013
Simulations using the resonance model
H.Kuc (Orsay/Cracow)
R
N
Dalitz decays
  e+
e-
Form factors:
« photon-point » M. Zetenyi, Gy.Wolf, nuclth0202047
Missing mass selection
after missing mass cut
-pe+e- n
p=0.8 GeV/c
s=1.55 GeV/c
26
Missing 2mass
(GeV/c)
M
(GeV/c
)
ee
B. Ramstein
Mee (GeV/c2)
π-p ne+e-: count rate estimates
P=0.8 GeV/c (below  threshold)
Resonance
model
Evts/week
M>0.14
GeV/c2
970
Titov et al.
~3000
H.Kuc
incoherent sum
(M. Soyeur)
Coherent sum
(M. Soyeur)
~100
π-p ne+e- with HADES
Measurement of e+e- invariant mass spectra
and angular distributions (cf results
from pp reactions)
 unique chance for a direct access to Time-like
electromagnetic form factors
27
Resonance model
M. Lutz
et al.
M.F.M. Lutz , B. Friman, M. Soyeur
Nuclear Physics A 713 (2003) 97–118
R
N
  e+
e-
πNππN: present status
All what we know about N*
couplings to ρN, π, N is due to
Manley, Arndt, Goradia, Teplitz PRD 30
(1984) 904.
based on the analysis of 240000
events (bubble chamber < 1980)
 Complete existing very precise photoproduction data
 Improve knowledge of baryonic resonances, MR, (N*Nπ), (N*Nππ)
 Dynamical models are now available  a new combined PWA analysis of all pion and
photoproduction channels will be possible.
 Important for baryonic structure issues (Constituent Quark Models, Lattice QCD)
28
B. Ramstein
Trento, 20/05/2013
Some open issues for πNππN and πNπN measurements
N(1520) D13 state
Manley et al. strong N(1520)2
BR(ρN)~20%
Coupled channel Giessen / Manley
N(1440) P11
Branching ratios to πΔ and (π π)s N need to
be checked
N(1710) P11
 Important coupled channel effects
 With BR(ρN)~20%, cross sections
are not reproduced
 need for differential cross sections
Important for medium effects
 Existence contradictory
 Not seen in the latest PWA analysis
 BR(2π) =40 to 90 % (PDG 2010)
 N(1520) 
Trento, 20/05/2013
29
N-1
acceptance p/p =8%
Momentum measurement
needed
X,Y
det2
X,Y det1
Trigger on interactions
with the target, halo rejection
in beam, position sensitive detectors
• optimization of pion production yield (duty cycle, primary beam intensity)
• optimization of beam line acceptance and extension at the target
30
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Trento, 20/05/2013
Pion Beam tracking
L. Fabbietti’s group. Excellence Cluster Universe, Garching
10x10 cm2
2x128 channels
300  Si detector
Beam line optimization:
Orsay
p/p~0,1-0.3 %
x<1mm
Diamond start detector GSI
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31
Conclusion:
perspectives of pion beam experiments with HADES ( 2014)
• Strangeness production in -A at 1.7 GeV/c
• -pne+e- at 0.8 GeV/c
Elementary reactions are very important to control the interpretation of
medium effects (lesson from HADES dilepton experimental program )
Unique chance to study Time-Like electromagnetic structure of higher
lying resonances/coupling to ρ/ω mesons (complementary to pion
electroproduction)
• Energy scan of -p reactions : one pion, two pion and kaon production
Urgent need of new data for Partial Wave Analysis  baryonic resonance
properties
GSI pion beam is unique in world at present to provide these data
This should be exploited ,…. before HADES moves to FAIR
Trento, 20/05/2013
Béatrice Ramstein
32
Thank you
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B. Ramstein
33
Simulations for dilepton production below  threshold
Simple resonance model:
Dalitz decay of different baryonic
resonances with constant form factors
+ meson contribution
Efects of electromagnetic form factors ?
Important interference effects expected
between I=0 (ω) and I=1 (ρ) channels
Linked to coupling to baryonic resonances
H. Kuc PhD Orsay/Cracovie
P=0.8 GeV/c
after missing mass cut
-pe+e- n
Calculations based on hadronic couplings
M. Lutz, B. Friman, M. Soyeur, NPA 713 (2003) 9
Titov and Kämpfer EPJA 12 (2001) 217
Very new calculation based on VDM
transition form factors by Zetenyi and Wolf
arXiv:1208.5671v1 [nucl-th]
Mee(GeV/c2)
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34
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34
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35
two component model: fit of parameters to existing data
elastic nucleon form factors
4 parameters a2, , g8 ,v
N- magnetic transition form factors
2 additionnal parameters: a’,g10
best fit
a’/a= 1.27
g10/g8=1.28
GMN-/3GD
GMp/pFd
GEp /Fd
GMn /nFd
GE
( 
Fd Q 2 =
Trento, 20/05/2013
(1 
1

n
GMp
Time-Like
2
Q2
0.71
B. Ramstein
36
Towards a consistent description of dilepton
production in all systems
HSD: E. Bratkovskaya et al.
arXiv:1301.0786 [
pp also rather well described, problem remains with pn data
Still contradictory predictions (UrQMD)
modifications of spectral functions are small at SIS energies (except Au+Au ?)
But HADES data are useful to study the ρN(N*/) couplings (which are crucial
Trento,
20/05/2013
37 to models
for medium
effects) and B.
areRamstein
very efficient in putting constraints
Technical layout of HADES
HADES cave
HADES sector
inner MDC
Cryostat
RICH readout
Trento, 20/05/2013
B. Ramstein
Lecture III:
38
38
Studying cold nuclear matter in p+Nb at 3.5 GeV
G. Agakishiev et al., Phys.Lett. B715 (2012) 304-309
First measurement of lepton pairs with
pe+e- < 0.8 GeV/c radiated from cold matter
( not measured by CLAS, KEK-E325)
ω not modifed, but absorbed
clear excess in p+A below vector meson pole 
- secondary reactions +N  (1720,..)(N* (1520),..) NρNe+e- Electromagnetic Time-Like form factors ?
39
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Trento, 20/05/2013
 E.
Bratkovskaya (Frankfurt) New HSD calculations
• emphasizes interest of subthreshold production (via N(1520) resonance)
•Medium effects are predicted
-1
dN/dM [GeV ]
10
• accounting of the in-medium
-4

 + C, 1.4 GeV
10
-5
10
-6
10
-7
effects - a collisional broadening
and dropping mass of the vector
mesons (– leads to changes
of the final spectra:
HSD:
no medium effects
coll. broad.+ dropp. mass
0.4
0.6
0.8
1.0
2
M [GeV/c ]
-1
dN/dM [GeV ]
10
10
-4

 + Au, 1.4 GeV
- reduction of the  peaks
- enhancement of the dilepton
yield for 0.4<M<0.7 GeV
•effect is stronger for heavy
-5
nuclei
10
-6
10
-7
HSD:
no medium effects
coll. broad.+ dropp. mass
0.4
0.6
0.8
2
M [GeV/c ]
Beatrice Ramstein
1.0
HSD’09 =>
similar to W. Cassing, Y.S. Golubeva, A.S. Iljinov,
L.A. Kondratyuk, Phys. Lett. B 396 (1997) 26
Sesimbra, May 2009
40