GDR 20141 B. Ramstein, IPN Orsay Perspectives of recent HADES experiments with a pion beam 16/12/2014, GDR annual meeting, Ecole Polytechnique B. Ramstein

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


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


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


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)


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


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


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


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


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


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


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


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”


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

Documents

GDR 20141 B. Ramstein, IPN Orsay Perspectives of recent HADES experiments with a pion beam 16/12/2014, GDR annual meeting, Ecole Polytechnique B. Ramstein