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1GDR 2014
B. Ramstein, IPN Orsay
Perspectives of recent HADES experiments with a pion beam
16/12/2014, GDR annual meeting, Ecole Polytechnique
B. Ramstein
B. Ramstein 2
Outline
GDR 2014
Introduction: General motivations of HADES experiments
Results from NN reactions with HADES Role of baryonic resonances in dilepton emission
Perspectives of HADES measurements with the GSI pion beam ( data taking in summer 2014)
Conclusions
Present explanation of dilepton spectra at ultra-relativistic energies (NA60, STAR, PHENICS)
Dileptons: a probe of in-medium vector meson modifications:
Rapp and Wambach EPJA 6 (1999) 415Rapp, Chanfray and Wambach NPA 617, (1997) 472
« in-medium broadening »
In-medium spectral function depends on NN* coupling main players: N(1520), N(1720), (1910)
Source of mesons at 1-2 AGeVNN NR NN
N R N
Dominant 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
GDR 2014 B. Ramstein 3
4
The Collaboration
SIS
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 4
GDR 2014 B. Ramstein
HADES strategy:
e+e- , strangeness, charged hadron production
Nuclear matter studies: A+A,p+A, π-+A
Elementary reactions p+p, quasi-free np, π-+p
5
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: ~ 50 kHz
Momentum measurementMagnet: ∫Bdl = 0.1- 0.34 Tm MDC: 24 Mini Drift ChambersLeptons: x~ 140 per cell, p/p ~ 1-2 %
HADES 2nd generation dilepton spectrometer
GDR 2014 B. Ramstein 5
M/M ~ 2% at peak
Electromagnetic Calorimeter for experiments with SIS 100/FAIR
SIS
Larger plane of drfit chambers built at IPNO
Exclusive analysis : ppppe+e- at 1.25 GeV
6
p
p2
e+
D+p
p1
q2=M2inv(e+e-)=M2
* e-
First measurement ! Dalitz decay branching ratio in agreement with QED value (4.2 10 -5) BR= 4.42 10-5 20% ( syst.) 9% (stat)
• Supported by the analysis of 1 production channels PhD T. Liu Orsay 2010 HADES collab: E.P.J. A48 (2012) 74 • on-going Partial Wave Analysis (collab. With Bonn-Gatchina)
ppe+e-X E=2.2 GeV, 3.5 GeV
GDR 2014 B. Ramstein 7
E=2.2 GeVE=3.5 GeV
Comparison to cocktail of point-like dilepton sources• Direct production of / • Dalitz decay of resonance (point-like)
Effect of electromagnetic form factors / Coupling of to baryonic resonances ?
Hades data, PRC85 054005 (2012)
Hades data, EPJA48 (2012) 64
Exclusive analysis G. Agakishiev et al. Eur.Phys.J. A50 (2014) 8
From NN to πN reactions
GDR 2014 B. Ramstein 8
J. Weil, H. van Hees and U. Mosel, EPJA 48, 111 (2012)GiBUU transport model
ρ is modified in elementary collisions, due to coupling to baryonic resonances
Strong constraints for medium effects interpretation
Advantages of -pne+e- : interaction better known fixed mass of the resonance in s channel much larger acceptance for exclusive channels
electromagnetic -pne+e-
hadronic -p p--, n+--, p0--
N-1
N*/
pp 3.5 GeV
e+
e-
RN
B. Ramstein 9
Pion beam experiments
GSI pion beam momentum 0.6 < p <1.5 GeV/cUnique facility in world at present able to bring new pion beam data
All what we know about N* couplings to ρN, π, N is based on the analysis of 240000 events (bubble chamber < 1980)
ωη
114 kevents
72 kevents
SAID, data base, CNS, GWU http://gwdac.phys.gwu.edu
1.4 2.1.6 1.8 s (GeV)
GDR 2014 B. Ramstein 10
Pion beam experiments
2 Double-Sided Silicon sensors100 x100mm2, 300μm thick2 x128 channels
Pion beam tracker:
Diamond detectors
Two beam periods at GSI in summer 2014 in beam sharing mode Restricted program due to limitations on
• Beam time: last operation period before SIS100 integration (FAIR)• Pion flux: up to 120000/s (radiation safety limit)
Beam optics calculation: responsibility IPNO
Pion beam: in-medium strangeness production
GDR 2014 B. Ramstein 11
target K0_S K+ K- Λ ϕ
W 102k 100k 4.2k 92k 213
C 129.5k 99.7k 6.9k 78.6k 398
φ production
Very premiminary
1st data set: π-+A p=1.7 GeV/c
Interest of IRFU to include strangeness in INCL cascade calculations
main goal= strangeness production
GDR 2014 B. Ramstein 12
Pion beam: ρNN(1520) couplings2nd data set: energy scan in π - + p around N(1520)
Main goal: determine precisely the ρNN(1520) couplings by measuring -p -p, -p -
+n, -p -0p ® crucial to constrain the predictions of in-medium modifications of the ρ meson
spectral function® fundamental interest: structure of N(1520)
GDR 2014
V. Shklyar Hades symposium, Seillac 2011
Controversial results with Manley PWA analysis:
Bonn-Gatchina PWA analysis
ρ contribution factor 10 lower
dominated by Δπ contribution
π-pπ+π p
π-pπ+π p
Quality of pion beam data : di-pion production
GDR 2014 B. Ramstein 13
π+π- and π0π- production : • energy scan : 5 points around N(1520) s= 1.441-1.556 GeV/c2 • > 500 000 events/point corresponding to π - + p π+π- n • complementary to π0π0 production measured by Cristal Ball PWA (including also photoproduction data) to extract N(1520) coupling to ρN and
π+π- production
(CH)n
CVery premiminary
Pion beam:dielectron channels
GDR 2014 14
Controversial yield predictions:Highly dependent on ρNN* couplings andρ/ω interference
• B. Kaempfer , A Titov , R.Reznik NPA 721(2003)583 M.F.M. Lutz , B. Friman, M. Soyeur Nuclear Physics A 713 (2003) 97–118
• VDM electromagnetic form factors: M. Zetenyi and G. Wolf, Phys.Rev. C86 (2012) 065209
• Resonance model: J.Weil • Sensitivity of Mee distribution to to Δπ and ρN
contributions (Bonn-Gatchina predictions)
B. Ramstein
3rd data set: π - + p n e+e- at s=1.49 GeV close to N(1520) pole mass and below η threshold
Main goal : Time-Like electromagnetic structure of N-N(1520) transition/ coupling to ρ meson
e+
e-
RN
Pion beam : quality of di-electron channels
GDR 2014 B. Ramstein 15
Dielectrons from (CH)n target
Mee>0.12 GeV/c2
Very preliminaryContribution of C under the neutron peak
~25% , can be easily subtracted® selection of about 300 evts π - + p ne+e-
Mee>140 MeV/c2
π - + p Xe+e-
n
On-going analysis : Electron ID, Combinatorial Background subtraction,…. F. Scozzi, PhD (IPNOrsay, TU Darmstadt)
Conclusion
GDR 2014 B. Ramstein 16
HADES results (focus on pp/pn reactions) selective study of e+e- production from Dalitz decay of baryonic resonances sensitivity to Baryonic resonances Time-Like electromagnetic structure/coupling to ρN Indispensable complement for in medium studies
Recent pion beam experiment Very promising data: strangeness, π+π-, e+e- expected precise determination of N(1520) coupling to ρN Continuation at SIS18 in 2017-2018 ?
HADES at FAIR : pp, pA with an ECAL
Thank you
GDR 2014 B. Ramstein 17
Hubert Kuc (codirection IPNO/UJ Kracow) PhD defense Thursday 18 December,
Salle des conseils IPN Orsay,14h30
« Di-pion and di-electron production in quasi-free np reactions with HADES »
Baryon Resonance electromagnetic Dalitz decays
GDR 2014 B. Ramstein 18
QED: point-like R-* vertexM. Zetenyi et al. PRC 67, 044002 (2003).
extended Vector Dominance ModelM. I. Krivoruchenko et al. Ann. Phys. 296, 299 (2002).
Covariant model (bare quark core + meson cloud) G. Ramalho and T. Pena, Phys.Rev. D85 (2012) 113014
π+π -
Fixed « Δ » mass
p+p 3.5 GeVp+p 3.5 GeV
19
Motivations of -pne+e- experiments with HADES
e+
e-
RN
r r
N-1
N(1520)
+ ...
Time-Like electromagnetic form factors
e+
n
e--
* - R
q2 > 0variable
p
e+
e-e-
*
-
R
p
Space-Like electromagnetic form factors
q2 <0 fixed
studied at JLab/CLAS
Inverse pion electroproduction
p
unique chance to study the Time-Like electromagnetic structure of N*(1520) to constrain the in-medium modifications of the ρ meson spectral function
-pne+e- below ρ/ω production threshold at s=1.52 GeV/c2
“off-shell ρ production”
GDR 2014 B. Ramstein 19
Subtraction of long-lived sources
The meson in hot and dense hadronic matter from SIS18 to SPS
Source of mesons
Source of mesons at 1-2 AGeV
NN NR NNN R N
Source of mesons
Dominant source of mesons at ultra relativistic
energies+-
Depends on RN coupling
20Coupling of ρ to baryonic resonances can be studied in NN collisions at 1-2 GeV
mass shift excluded !
Arnaldi et al., PRL 100,022302 (2008)
agreement with in-medium ρ mesonbroadening
G. Agakishiev et al. Phys.Rev. C84 (2011) 014902
Dilepton excess over long-lived sources
In +In 158 GeV/u
GDR 2014B. Ramstein
GDR 2014B. Ramstein 21
πN Nπ π : Existing data
SAID, data base, CNS, GWU http://gwdac.phys.gwu.edu
7.3 kevents
114 kevents
72 kevents
69 kevents
15
30
30
15
pπ- π0
nπ+ π-
nπ+π+
pπ+π0
1.4 2.
W (GeV)
1.6 1.8• More recent data (TRIUMF,LAMPF,BNL) do not cover the region between 1.32 and 1.9 GeV high statistics differential distributions are needed22
Resonance excitation in 2 channel
s
N(1440,1710) +(1910) N(1535) +(1620) N(1720) +(1600) N(1520) +(1700) N(1680) +(1905) N(1675) +(1925)
• s =1.5 dominance of
resonance channels
D13(1520) & P11(1440)
Predictions:
2014: B-G (A.Sarantsev) K-matrix approach constraints from N, N
- p RN,(I=0)N, (I=1)N
+ non resonant contributions