1. Dilepton production in 1-2 AGeV energy range:
Recent results from the HADES experiment at GSI.
Béatrice Ramstein
and
Thierry Hennino, Tingting Liu, Malgorzata Sudol
Institut de Physique Nucléaire d’Orsay, France
Picture of Piasky, of HADES

2. Outline Introduction:
motivations of HADES experiments : dilepton production in Heavy_ion and elementary reactions
short status on medium effects
Inclusive e+e- production in heavy-ion reactions C+C, Ar+KCl
pp and dp reactions:
inclusive/exclusive dilepton channels, hadronic channels
Perspectives:
Heavy-ion reactions
HADES upgrade  FAIR
pion induced reactions
Conclusions
To be updated

3. Motivations of the HADES experiment
Exploring the phase diagram of
hadronic matter…..
AGS
SPS
RHIC
QGP
hadrons
SIS-100
SIS-300
SIS-18
CBM G7
HADES
KEK,JLAB,TAPS
Na60
E/A=1-2 AGeV
/o ~ 1-3, T < 100 MeV
N/Apart ≈ 10%
….. using dilepton emission:
rare but undistorted probe
D’où vient cette figure ?

4. A faithful probe of the hot and dense phase: the dilepton pair decay of vector mesons
R(A=100) 5.5 fm e+
Dilepton spectroscopy gives access
to vector meson spectral function e-
and are undistorted by strong interactions
V e+e- JP=1-
Meson
Mass
(MeV/c2) G ct
(fm)
Main decay
e+e- BR r
768
152
1.3
p+ p-
4.4 x 10-5 w
782
8.43
23.4
p+ p- p0
7.2 x 10-5 f
1019
4.43
44.4
K+ K-
3.1 x 10-4

5. Interest of vector meson study
r, w
V l+l- JP=1-
direct coupling to *
Vector Dominance Model (Sakurai 1969): coupling of a real (or virtual) photon to any electromagnetic hadronic current is mediated by a vector meson
Sensitivity of vector meson mass to Chiral Symmetry Restoration g* e+ e-
on-shell g* e+ e- N
r, w
electromagnetic
elastic or transition
form factor
off-shell

6. “melting of quark condensate “
Chiral symmetry restoration in medium
In the limit of massless u,d quarks, exact symmetry of the QCD lagrangian,
but not of QCD vacuum and excited states
(spontaneous breaking of chiral symmetry)
≠ 0
g,p-,p - beams
SIS 18
SIS 200
T [MeV]
300
LHC
RHIC
SPS
“melting of quark condensate “
Klimt, Lutz , Weise, Phys.Lett.B249 (1990) 386
SIS100
,-,p beams -
Verfier autre ref chez Djalali
But the quark condensate is not an observable !
models are needed to relate <qq> to hadron masses -

7. Medium modifications (I):
1st scenario: « dropping mass »
Scaling inspired by chiral effective models:
Brown-Rho PRL66(1991) 2720
QCD sum rules :
Hatsuda and Lee PRC46 (1992) 34 , Kwon et al. PRC78 (2008)
Quark meson coupling (QMC):
Saito et al. PRC55 (1997) 2637
15%
K. Saito et.al
Phys.Rev.C55(1997)2637

8. Medium modifications (II):
schematic summary !
see e.g. Rapp and Wambach for a recent review I
2nd scenario: « in-medium broadening »
Spectral functions of the mesons in the medium: coupling to resonances + r
N-1
N(1520)
+ ...
D(1232) 
Memes types d’effet sont attendus en fonction de la tp
Hadronic many-body approach
Rapp and Wambach EPJA 6 (1999) 415
Rapp, Chanfray and Wambach NPA 617, (1997) 472

9. Results from ultra-relativistic heavy-ion reactions
CERES / CERN
Pb (158 AGeV) +Au
Na60 / CERN
In (158 AGeV) + In
AGS
SPS
RHIC
QGP
hadrons
SIS-100
SIS-18
Na60
CBM 
CBM 
HADES
KEK,JLAB,TAPS G7
Adamova et al. PLB 666 (2008) 425
Rapp and Wambach calc. with modified 
spectral function
Mettre les references, same calculation in both cases
Arnaldi et al., PRL 100, (2008)
Broadening of  spectral function
is favoured, no mass shift
+ Helios/CERN+Na50/CERN
Phenix/RHIC (on-going analysis),

10. Results at =0, small T G7/CLAS/Jlab + A p+Cu E=12 GeV QGP hadrons
AGS
SPS
RHIC
QGP
hadrons
SIS-100
SIS-300
SIS-18
CBM G7
HADES
KEK,JLAB,TAPS
Na60
Re-analysis of CBELSA/TAPS results:
° in A reactions at E= GeV
Kotulla et al. PRL 100, (2008)
No effect on  meson
 + A E = GeV
CB normalization essential !

11. From C. Djalali, Hadron2009

12. DLS Results for /o ~ 1-3, T < 100 MeV (Heavy-ion collisions E/A=1-2 AGeV)
pp/pd, Ca+Ca, C+C 1.04 AGeV
mass resolution : 10-20%
30-40% systematical error
Data: R.J. Porter et al.: PRL 79(97)1229
Model: E.L. Bratkovskaya et al.: NP A634(98)168, BUU, vacuum spectral function
DLS puzzle
Strong dilepton enhancement over hadronic cocktails
not explained even by in-medium mass shifts and  broadening
Bevalac
( )
Na60
QGP
SPS
SIS-100
SIS-300
CBM
RHIC
AGS
SIS-18
Bevalac
HADES
DLS
hadrons
KEK,JLAB,TAPS G7

13. Specificity of 1-2 A GeV energy range
N/Apart ≈ 10%
long life time of the dense system
(up to 15 fm/c)  ~ 1.3 fm/c,  ω~ 23 fm/c
dominance of  resonance
resonance matter (33)
15 fm/c
UrQMD calculations Au+Au 1 AGeV
r/r0 
n,p
r/r0
r/r0
1-2 GeV 
Very imp. Rle for HI dynamics and pion production but it has also a very direct role on dilepton production due to the delta Dalitz decay. Mettre figure plus recente de resonance
change to more recent transport model
tot   
N-1

14. Role of resonances in dilepton production at 1-2 AGeV
° Dalitz decay: °  e+e- (BR ~ 1.2 %)
R  N° ,  (1232) , N (1440)…
 Dalitz decay:   e+e- (BR ~ 0.6 %)
N(1535)  p
/ω vector meson production
N(1520)  /ω N , ….. /ω  e+e-
Dalitz decay of baryonic resonances:
Both are linked through
electromagnetic form factors
(1232)  Ne+e- (BR ~ )
not measured !
Faessler et al. RQMD
+ NN Bremsstrahlung NN  NN*
 e+e-

15. 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
Orsay (IPN), France
Rez (CAS, NPI), Czech Rep.
Sant. de Compostela (Univ.), Spain
Valencia (Univ.), Spain
Coimbra (Univ.), LIP, Portugal
The HADES detector is installed on the GSI facility, but HADES is a european collaboration. Actually 150 persons working in about 156institutions all over Europe. 15” tot 45”
GSI
SIS

16. HADES 2nd generation dilepton spectrometer Side View FW  < 7°
START
Acceptance: Full azimuth, polar angles 18o - 85o
Pair acceptance  0.35
Particle identification:
RICH, Time Of Flight, Pre-Shower (pad chambers & lead converter) ( also MDC (K))
Trigger:
1st Level: charged particle multiplicity (~10 kHz)
2nd Level: single electron trigger (~2.5 kHz)
Momentum measurement
Magnet: ∫Bdl = Tm
MDC: 24 Mini Drift Chambers
Leptons: x~ 140  per cell, p/p ~ 1-2 %
M/M ~ 2% at  peak FW
 < 7°
Consists of 6 sectors, Regarder slide de Gosia. Pair acceptance de DLS?
1’10 tot 8’10

17. IPN team IPN contribution 4th plane of drift chambers
Jean-Louis Boyard (retired 2008)
Jean-Claude Jourdain (retired 2001)
Thierry Hennino
Tingting Liu (PhD)
Emilie Morinière (PhD 2008)
Béatrice Ramstein
Michèle Roy-Stephan (retired 2006)
Malgorzata Sudol (part-time post-doc)
…+Jacques Van de Wiele (phenomenology)
4th plane of drift chambers
drift cell (14x10 mm2)
active area 3.5 m2
R&D détecteurs,
J. Pouthas, P. Rosier
6 drift chambers constructed at IPN

18. HADES subdetectors Magnet Coils PreShower TOF MDC I RICH LH2 target
(IPN)
TOF

19. Lepton Identification with HADES
Drift Chamber:
Track reconstruction
RICH pattern
Pre-Shower condition e- + + +
momentum % velocity
momentum ∙ charge
C+C 2 AGeV

20. HADES experimental program
2001/2
C + C 2 AGeV
understand dilepton spectrum/test transport models in simple case: low to very low medium effects
+ check of DLS
2004
C + C 1 AGeV
2004
p + p 2.2 GeV
exclusive ppe+e- (°,)
Validation of detector performance (pp elastic)
° and  Dalitz decays (helicity distribution),
“free” cocktail
ω line shape and cocktail (,,,,,
strangeness
p + p 3.5 GeV
2007
pion production
 Dalitz decay first measurement
p + p 1.25 GeV
exclusive ppe+e- (°,)
2006
medium effects on dielectron spectra,
Ar + KCl 1.75 AGeV
2005
d + p 1.25 AGeV
Reference for medium effects, strangeness
p+Nb 3.5 GeV
2008
pn Bremsstrahlung /  Dalitz decay
Add animations
HADES upgrade

21. results from Heavy Ion reactions ….

22. Dielectron DATA analysis:
normalization to 0 (Nπo = ½ (Nπ- + Nπ+))
Comb. Background (CB) subtraction
Mee < 150 MeV/c2 Like-sign pairs
Mee > 150 MeV/c2 event mixing
Signal: ~ counts
Me+e- ≥ 150 MeV/c2: ~ 646 counts
Efficiency correction
45’’ Same method apllied for each system. Now we are ready for the comparison to DLS data tot 8’55
Measured rates span over 5 orders of magnitude
Systematic errors:
20% efficiency correction
10% combinatorial background
15% 0 normalization
22% - 27% Total

23. NN Bremsstrahlung and the DLS puzzle
1997: transport models failed to explain DiLeptonSpectrometer (Berkeley) data
2007: DLS and HADES agree and are compatible with new transport model
calculations G.Agakichiev et al. Phys. Lett. B 663,43 (2008)
Calculation: E.L.Bratkovskaya et al.
Nucl. Phys. A634 (1998) 168
DLS
HADES
M [GeV/c²]
Hadron String Dynamics
E. Bratkovskaya and W.Cassing, nucl-th/
DLS
M [GeV/c²]
Revenir sur le Bremsstrahlung au niveau de pp/pn
new (contradictory) treatments of Bremsstrahlung:
R. Shyam & U.Mosel, PRC67 (2003)
L.P. Kaptari, B. Kämpfer, NPA 764 (2006) 338

24. NN Bremsstrahlung and  Dalitz decay
NN  NN* NNe+e-
  Ne+e- (BR from QED = not measured )
nucleon graphs
 graphs
Mee(GeV/c2)
q2 = M*2 > 0 N
N, 
Quantum
interference
Time-Like electromagnetic form factors
two recent full quantum mechanical
One Boson Exchange calculations:
1) R. Shyam & U. Mosel, PRC 79 (2009) 03520
2) L.P. Kaptari, B. Kämpfer, NPA 764 (2006) 338
1’30
 pp dominated by  graphs
 nucleon graphs (Bremsstrahlung) larger in pn than in pp collisions
 Yields differ in the two models by factors 3-4
HSD model uses enhanced yield for NN bremsstrahlung, according to K&K OBE model

25. DLS puzzle solved by new calculation of NN Bremsstrahlung ?
Maybe, but a lot of contradictory calculations are pretty good too ….
RQMD: E.Santini et al
BUU Barz et al.
C+C 2 AGeV
UrQMD Bleicher et al.
IQMD Thomere et al.
 Dalitz pn
HADES data:
Phys Rev. Lett 98 , (2007)
pn Bremsstrahlung and Delta Dalitz decay
are important issues for understanding
intermediate mass dilepton yield

26. HSD transport code prediction
E.L. Bratkovskaya, W. Cassing, Nucl.Phys.A 807 (2008)
pp -> ppω
HSD
OBE
Inclusive /ω cross-sections not known
 important ingredient of transport model calculations
 can be measured in pp reactions
Quel type d’effet de milieu?

27. First results from HI reactions ….
…..call for study of elementary processes
 Dalitz decay : pp E=1.25 GeV
NN Bremsstrahlung: dp (pn) E=1.25 AGeV
°,  production pp E= 2.2 GeV
/ω production: pp E=3.5 GeV
E<  production threshold
( 0.5–7)
2 m
7 m
Forward Wall
HADES
spectator proton
deuteron
beam
Specific instrumental tools:
LH2 target, proton/deuteron beams, Forward Wall

28. pp elastic scattering  tracking, efficiencies, resolutions
hadronic channels
pp elastic scattering  tracking, efficiencies, resolutions
pppp°, pppp  consistency of hadronic and leptonic reconstructions
pppn+, pppp°, pppp  pp+-0
check of resonance model ( dilepton cocktail)
pp pppp+-0 (on-going analysis)

29. exclusive pion production channels measured by HADES
absolute normalisation
from elastic scattering
Very good agreement
with resonance model
Teis et al. ZPA 356(1997) refinements
in both isospin channels
Consistent picture at
E=1.25 GeV and 2.2 GeV
important check for dilepton analysis
(° and resonances are dilepton sources !)
T. Liu PhD Orsay
arXiv: [nucl-ex]

30.  and  production : acceptance corrected results
 production: 1 exchange
 decay: cos2
Neutron angular
distribution in CM
+ angular dist.
in (+ ,p) ref. frame p n
D++ qn
preliminary p+
D++
preliminary
qp+ p
Total cross sections compared to systematics
pppp
preliminary
Erreur sur sec. Eff eta
preliminary
preliminary
T. Liu PhD Orsay arXiv: [nucl-ex]

31. inclusive e+e- analysis at E=1.25 GeV/ nucleon

32. Results for pp reaction at 1.25 GeV
PLUTO ROOT-based event generator I. Fröhlich et al, arxiv: [nucl-ex]
I. Fröhlich et al,arxiv: [nucl-ex]
resonance model: Teis et al. Zeit. Phys.A356(1997) refinements
° Dalitz decay  ° = 4.5 mb
branching ratio ° → e+e- 1.2 %
 Dalitz decay : =3/2  ° = 6.75 mb
branching ratio  → Ne+e- (QED : )
Time-like N-  transition electromagnetic form factors
subm. to PRL
[nucl-ex]
Iachello and Wan
0.6m2
GM(q2) D+ p e+
e-- *
q2 = M2inv(e+e-) = M*2 > 0
GM(0)~3
Faire une animation, enelver OBE
Resonance model results:
° Dalitz
Dalitz)+ effect of Iachello FF

33. Quasi-free « pn » dilepton spectra
Comparison to resonance model
° Dalitz decay  ° = 8.6 mb
branching ratio ° →e+e- 1.2 %
 Dalitz decay : =3/2  ° = 12.9 mb
New features with respect to pp reactions:
participant neutron Fermi momentum
( Paris potential)
 contribution (due to Fermi motion)
subm. to PRL
[nucl-ex]
 Dalitz
° Dalitz
 Dalitz (BR ~ ) + +
effect of Iachello FF
Ne mettre queresonance model
Additionnal sources with respect to pp?
NN Bremsstrahlung is absent !!
 Check with full One Boson Exchange calculations

34. pp/pn reactions at 1.25 GeV:
Comparison to simulations with OBE differential cross sections :
R. Shyam & U.Mosel, PRC67 (2003)
L.P. Kaptari, B. Kämpfer, NPA 764 (2006) 338
Kaptari & Kämpfer
Shyam & Mosel
Faire une animation, mettre seulement OBE
pp OK with Shyam & Mosel
overestimated by K&K
 critical test for models
HADES np data: a new puzzle ??

35. pp allows to dicriminate
pp/pn reactions at 1.25 GeV: transport model calculations
pp allows to dicriminate
among models
HADES np data:
a new puzzle ??
Faire une animation, mettre seulement OBE
HSD: E.Bratkovskaya et al.NPA 807(2008)214
IQMD: J. Aichelin et al.

36. Towards a consistent description of dilepton spectra from different systems
C+C 2 A GeV
p+p 1.25 GeV
Refinement of HSD model
the vector-meson production via the LUND string has been reduced in order to mach pp exp. data better
- the isospin dependence for the channels NN-> V+NN and pi+N-> V+N have been improved
Ar+KCl 1.75 A GeV
C+C 1 A GeV
quasi-free n+p 1.25 GeV
preliminary
need for description of both HI and elementary collisions with same set of parameters
Not yet fully achieved ! 36

37. N+N dilepton spectra as a reference for A+A
η contributions subtracted !
yield normalized to M(π0)
preliminary
preliminary x3
Beam energy does not matter for masses below 480 MeV/c2  
N-1
« experimental » indication
for emission from the dense phase
resonance propagation 37

38. exclusive ppppe+e- analysis E=1.25 GeV

39. exclusive analysis : ppppe+e- at 1.25 GeV using pe+e- events (i)
pppe+e-X missing mass MX
Selection of ppppe+e- channel is efficient mp
simulation
HADES
data
MX(GeV/c2)
Mee>140 MeV/c2
preliminary
W. Przygoda’s analysis
B.Ramstein Hadron 2009 proceedings
Dilepton mass distribution
in very good agreement with
° and  Dalitz decay
consistent with inclusive dilepton analysis
pp p+ppe+e-
ppp+pp°ppe+e-
200 events
for Me+e- > 140 MeV/c2
preliminary
0.2

40. exclusive analysis (ii) ppppe+e- at 1.25 GeV
reconstructed by (p,e+,e-)
Mee>140 MeV/c2
No acceptance corrections !
preliminary
(p,e+,e-) invariant mass (GeV/c2)
2 indistinguishible protons
(p1,e+,e-) p p2 e+ D+
q2=M2inv(e+e-)=M2* 1 e-
(p2,e+,e-)
acceptance corrected
simulation of
 production + Dalitz decay
(cf hadronic channels)
cos(CMpe+e-)
preliminary
dominance of ppp + p pe+e-
room for pp Bremsstrahlung contribution?

41. exclusive analysis ppppe+e- at 1.25 GeV: helicities
 Dalitz decay: +  p g* pe+e-:
only transverse g*
(if Coulomb interaction is neglected)
helicity angle    * N e+ e-
Helicity distributions *  e+e-
d/dΩe~ 1+cos2
True helicity from pe+e- events:
* in  ref. frame
acceptance corrected
fit 1+B cos2
B=1.110.32
cos
preliminary
First measurement of  Dalitz decay!
Dalitz decay branching ratio in agreement
with QED value ( ) within ~20%
Helicity consistent with 1+cos2

42. Inclusive e+e- in pp reaction at 3.5 GeV
/ meson production
Inclusive cross sections measurements
Meson production mechanisms
Reference to the pA and AA reactions

43. Vector mesons / at SIS
p+p at 3.5 GeV p+ 92Nb 3.5 GeV Ar+ 38KCl AGeV
preliminary
2008
“on-line spectrum!” w
preliminary h D
Very preliminary r
sM(w)  15 MeV/c2
Inclusive pp X cross-section
Input for transport models
First observations of  production at SIS energies
possibility of check of p+A results from KEK & CBTAPS/CLAS 43

44. Cocktail simulation for pp E=3.5 GeV
 production through  resonance =3/2 °
 production
from one pion exchange model
, ,  phase space production
particle decays
relativistic BW with mass dependent width
cross sections
πo : 15  4 mb
η :  0.03 mb
ω :  0.07 mb
ρ :  0.08 mb
preliminary
A. Rustamov et al. Hadron 2009
Distr. Ang. De prod. du omega ? Eta cross-section reasonable? Regarder les ref de l’expose d’Anar

45. On-shell/off-shell  production: cocktail subtracted data :
p+p E=3.5 GeV
After subtraction of °,  and 
remaining contributions:
and baryonic resonance
PLUTO: phase space
HSD: LUND string Model
UrQMD: production through resonance
preliminary
Off-shell  production through
resonances
Mettre schéma de R-> VDM. UrQMD quelle equipe ?
 meson production needs improvement
in transport models
Analysis: A. Rustamov (GSI)

46. Future plans HADES upgrade CBM HADES
Resistive Plate Chambers , 120 << channels, t85 ps
New DAQ electronics ~20kHz LVL1
New MDCI
Ag+Ag at 1.65 AGeV and Au+Au at 1.25AGeV,
Pion beams 2012
move to SIS100 (FAIR), E ~ 8 AGeV
experiments at SIS100 (FAIR) cca
CBM
8 – 45 GeV/u
Regarder CBM
HADES
2 – 8 GeV/u

47. Perspectives of pion beam experiments

48. Motivations of N experiments with HADES
Well-known interactions
Exclusive channels - p   n
Special interest of / subthreshold production (sqrt(s)=1.72 GeV)
Strangeness production  (1405), and K
M. Lutz , B. Friman, M. Soyeur
Nuclear Physics A 713 (2003) 97–118
p- p → e+e-n
sqrt(s)=1.65 GeV
Pluto r w
E =0.66 GeV
p=0.80 GeV/c
total
spectacular destructive interference of /ω production
linked to coupling to baryon resonances (S11, S31, D13, D33)
electromagnetic structure of resonances
importance for A, AA dilepton spectra
See also predictions by Titov & Kämpfer EPJA12 (2001) 217

49. Motivations of dilepton spectroscopy in A experiments
New HSD calculations
HSD: preliminary
strong medium effects are predicted
HSD’09 =>
similar to W. Cassing, Y.S. Golubeva, A.S. Iljinov, L.A. Kondratyuk, Phys. Lett. B 396 (1997) 26

50. Conclusions: HADES experiments
Inclusive spectra in pp/pn and heavy-ion reactions:
critical tests for transport models
a consistent description of dilepton production in all systems is needed !! ↓
Prerequisite to medium effect investigations
Ar+KCl
future Ag+Ag and Au+Au reactions
Not mentionned: very fruitful strangeness production program:
« Deep sub-threshold - production in Ar+KCl reactions at 1.76 AGeV » PRL 103 (2009)
«  decay: a relevant source for K- production at SIS energies »
Specificity of elementary reactions:
Sensitivity to time-like electromagnetic form factors of nucleon and resonances
Selectivity on dilepton sources (  Dalitz decay,  Dalitz decay,  production,…)
Very new ppppe+e- exclusive analysis !
First measurement of  Dalitz decay
helicity distributions to be investigated in dp and heavy-ion reactions
perspectives of pion beam experiments ( 2011)

51. MERCI

52. Pion beam experiments with HADES
Dilepton spectroscopy in A AND N induced experiments
GSI pion beams
p~ GeV/c
second resonance region
expected intensities 106/s
acceptance p/p =8%
1.21
1.52
1.68 s
Technical problems:
Beam intensity / profile
Beam detectors (momentum
reconstruction and anti-halo)

53. Future HI experiments in HADES
- statistics corresponding to 4 week of the experiment
- 30% most central events
- multiplicities taken from HSD, for omega and phi adjusted by ArKCl experiment
expected rates:
GeV/c
omega: /day /day
rho: /day /day
phi: /day /day

54. Experimental tests of Quasi-Free (p,n):
Spectator tagging is under control
p momentum
in d reference frame
- QF simulation
Note: absolute normalization!
M < 140 MeV/c2
M > 140 MeV/c2
Scaling factor for massive pairs
d/dp
- QF simulation

55. pp  pp e+ e-  at 2.2 GeV: an “easier case” exclusive reconstruction p°,h  ge+e-
ppe+e- detected
+ miss.mass cut 
Comparison with resonance model
Teis et al, ZPA356 (97) 421
D1232 
N1440
N1535
D1600
acceptance corrections
p/h  g g*  ge+e-
Helicity distributions g*  e+e-
d/dΩe~ 1+cos2
nice check of QED predictions 55

56. Analysis steps : one example
Forward Wall (np selection):
1. Mult > 0
2. search for particle with
1.6 GeV < p < 2.6 GeV
(e+,e-) pair cuts:
1. track and ring quality
2. identification
3. background rejection cuts
4. openangle > 9°.
Combinatorial background: like sign pairs
efficiency corrections:
preliminary
Note:
~1500 pairs above °
Nice S/B ratio
normalisation by elastic scattering measurement
(syst.error ~ 30 %)

57. Forward Wall
Scintillator hodoscope located 7 meters downstream the target
7.1 deg
Information from the Wall:
Time of flight
Coordinate of the fired cell
TAT ~ dE/dx
FW acceptance to spectator protons
92%
89%

58. Strangeness production with HADES the  (1405) case
4 particles detected
pp 3.5 GeV
p,K+ missing mass
missing ° 
  (1405) mass

59. DiLepton Spectrometer data (Berkeley
Shekter et al. RQMD
E. Bratkovskaya and W. Cassing nucl-th:

60. p+A @ 12 GeV KEK-PS E325 2/dof =1.8 2/dof =2.3 CB subtracted
M. Naruki Phys.Rev.Lett 96 (2006)
CB subtracted
Data described (both nuclei) assumming / mass modification m*=m0( /0)
fit supports  * consistent with the vacuum for /
46 / 61%  decays inside nucleus and 5/9 %  only: (for C/Cu respectively)!
/=0.7±0.2
/=0.9±0.2
CB shape from mixed event but w.o absolute normalization (fit parameter)!
Fit, excluding excess region, gives / <0.15 (Cu) and <0.32(C) with CL of 95% ! In contrast to other pp data /~1
2/dof =2.3
2/dof =1.8

61. HADES and DLS Phase Space Coverage
mid-rapidity
HADES
DLS
Method for HADES/DLS comparison:
HADES yield extrapolated to full phase space.
DLS acceptance filter applied
50’’ However, a direct comparison is not possible, since the acceptance are different. 9’45 61

62. Dalitz decay : sensitivity to Iachello’s N- transition form factorsp e-
q2 = M2inv(e+e-) = M*2 > 0 *
Dalitz decay
+ → pe+e-
Dalitz decay
branching ratio
BR ~
M=1232 MeV/c2
M=1480 MeV/c2
(Eth=1.25 GeV)
M=1830 MeV/c2
GM=3.0
GM(q2) Iachello
(Eth=2.2 GeV)
d/dM
Mee(GeV/c2)
two component Iachello model = « VDM like »
Wan & Iachello, int. J. Mod. Phys. A 20(2005) 1846
0.6m2
GM(q2)
45’ 6’30