Motivation for studies of pion induced Motivation for studies of pion induced dilepton productiondilepton production

Motivation for pion experiments (perspective from 2001):

•Subthreshold / production amplitudes in NVN a)Key measurement for in-medium / mass modification?

b) unique tool to study Vector Meson coupling to baryon resonances

• Vector mesons production off nucleus

Spectral function of meson

GeVm

mimM

77.0

)()(

VacuumVacuum::

one example

W. Peters et.al. NPA 632(1998)109:

Nuclear matterNuclear matter: additional terms : additional terms

+

N-1

N(1520)

+ ...

(1232)

N-1

dominant role of baryons (also for SPS) ! dominant role of baryons (also for SPS) ! important for future CBM important for future CBM

2222 )]([)](Re[

)(2)(

MImMmM

MImMA

even at high T int. with baryons is dominant !

•Direct -N Interactions (‘Rhosobars’)

In medium vector meson properties and N scattering

..)4)( VN

N

V

VT

m

mVN

T forward scattering amplitude

)0(12),()(2

)(

VNCM

CMV

Vnp ImTsq

qMs

•low density theorem

•Optical and detailed balance theorem

B.Friman N.PhysA610(1996)

R. Rapp and J.Wambach

In medium properties are related to elementary TVN !

Resonance contribution at vector mass region- off shell contributions?URQMD: arXiv:0811.4073v2: resonance model HSD : arXiv:0712.0635v2

Resonance contribution at vector mass region- off shell contributions?

• data seems to favour smaller VM contribution at the pole

p-n puzzle? pp vs “quasi-free” pn @ 1.25

Model Calculations:a) NN-bremsstrahlung Kaptari & Kämpfer (K&K)

b) , yield constraint by data. Dalitz decay Krivoruchenko et al. Phys. Rev. D 65 (2001) 017502 + VMD form-factor (Q. Wan and F. Iachello, Int. J. Mod. Phys. A 20 (2005) 1846)

• pn data are not (yet) described by calculations !off –shell contribution with strong isospin depend.?

Vector meson production in πN

2

3

2

1|

3

1

2

1

2

1|

3

2

2

1

2

1|11|

I=1/2 (N*) I=3/2()

1. π- + p n e+e- reactions in Isospin space

2

3

2

1|

3

2

2

1

2

1|

3

1

2

1

2

1|01|

+ n : exit channel + n : exit channel

2

1

2

1|

2

1

2

1|00|

I=1 isovector I=1 isoscalar

TVN π- + n

= TI=0() +TI=1() • different resonance probed via /

2. π+ + n : π- + p rotated in Isospin space around Y by 1800

TVN π+ +n

= TI=0() - TI=1() • opposite sign of iso-vector part (-1)I

• access to vector-meson Baryon interaction !

Meson and resonanse Meson and resonanse production with pion beamsproduction with pion beams

Eth

resh

[GeV

]

Mx [GeV/c2]

/

pp->ppX

-p->Xn

Meson production thresholds

/

• direct resonance excitation: second, third res. region • strong off-shell contribution for production D13(1520) partial wave analysis of Nππ channel. What about ? D. M. Manley et al.Phys. Rev. D 30(1984) 904

• p>0.5 GeV/c weak contribution from (1232) (1232)->Ne+e- small !!

N,

M. Effenberger et al. PHYS. REV. C 60(1999) 044614

p~1.3 GeV/c

1.21 1.52 1.68

s

2

224

2*2 |

)()(|

||||

mimmm

Tf

mimmm

Tf

mee

enep npnp

VDM model: f/ decay couplings

2011.06.0

2036.07.6

GeVfkeVee

GeVfkeVee

Relative phase of Tp->()N determines interference pattern

/ production in --n n reactionsreactions

Exclusive: --p ->ep ->e++ee- - nn

++n ->en ->e++ee- - p (via p (via +++d)? +d)?

T/ amplitudes in N (/) N reactions

• Coupled channels calculations(N, N, N, ,…)

- opposite sign of T/ :

destructive interferences in π- p and positive in +n

• Large influence of I=1/2 below threshold: S11(1535) and D13(1520)

TV

N

- p (/) n +n (/) p M.F.M. Lutz , B. Froman, M. Sayuer . / Nuclear Physics A 713 (2003) 97–118

/ interference yield in --n (published-n (published-2003)2003)

--n n e e++ee- - n n ++p p ee++ee- - p p M.F.M. Lutz , B. Friman, M. Sayuer Nuclear Physics A 713 (2003) 97–118

/ interference: different models M.F.M. Lutz , B. Friman, M. Sayuer Nuclear Physics A 713 (2003) 97–118

B. Kaempfer , A Titov , R.Reznik Nucl. Phys. A721(2003)583

A.Titov, B.KaempferEPJA 12(2001)217

• quantitatively same picture but differs in details:

resonance contributions(i.e D15(1520) not important)

coupling strengths (quark model vs coupled chann.)

• Virtual photon angular distributions in CM sensitive to res.contributions

me+e-=0.6 GeV

• Becondary beams (C+Be, N+Be,..): 1.Primary beam intensity ? (~0.5*SCL) ~ 6.5*1010 N2 ions/cycle reached in tests (2005) 2.duty factor (fast ramping of SIS magnets)?3.extraction efficiency (~0.85) ?

• Pion Beam profile at the target

• Pion momentum p/p =4% : in beam detectors X1/X2 and Y3 (start) is necessary for pion mometum determination (p/p =0.1% )

pion beams @GSIpion beams @GSI

see Bjoern & Jurek talks

Proton & pion beams @GSIProton & pion beams @GSI Intensity of pions/spill : expectations for SCL and 100% exctraction efficiency

0.6 < p <1.5 GeV/c operation region

• reached (2005 with N2 beam-0.5 SCL): 1.8*106/spill (4 sec long- 4 sec spill off ) @ p= 1.3 GeV/c • fast ramping of SIS magnets : 1.5-2 increase in duty factor possible ?

Beam focus at the target position Beam focus at the target position

LH2 Target: entrance part diamter 15 mm LH2 cell diameter 25 mmd=2*1023 atoms/cm2

25mm

Bunch mark: production in -p reactions

large cross sections AND kinematically complete measurement !

Reaction rates

total rates : LH2 at top Iπ =0.5*106/sec and reac =80 mb

e+e- @ 1.3 GeV ( = 2.5mb * 7.2 * 10-5 =180 nb) rec. in HADES :

Yield per day (24 day)= R*0.5(DAQ)*0.7(DF machine)=54/day

(~ 10/day measured for pp run)

cGeVpmbnptot

/3.1@5.2

cGeVpmbXpp ptot /5.3@4.0 measured in 2006 !

sscm

atR /110*8*/10*5.0*10*2 36

223

sEffAccscm

atR /110*8.1)1.0(**/10*5.0*10*2 36

223

/ interference yield in --n (in times n (in times when HADES proposal was prepared-when HADES proposal was prepared-

2001)2001)

Optimal energy

@ s=1.55GeV

80 nb

// production in production in -- N reactions N reactions

- p n

•Me+,e- >0.5 GeV dominated by and e+e- decays

• Note: very small ->Ne+e- !

- n - , - n n - is subthreshold !

•Me+,e- >0.5 GeV dominated by ->e+e-

F37(1930), D35(1950) with I3/2= -1/2

important for π-A reactions !

(see Elena’s talk)

E.Bratkovskaya Phys.Rev.C60(1999)Ekin= 1.3 GeV (s=1.89)

Simulations HADES proposal-2001

e+e- missing mass

e+e- missing mass:

- + n e+e- n + X •selection of /

•suppression:

->e+e-, 0 0, ….

cocktail 4 cocktail HADES acc

e+e- miss. Mass

Landolt-Boernstein, New Series I / 12b

PLUTO simulation’sPLUTO simulation’s(HADES proposal 2003)(HADES proposal 2003)

8o nb:~20 day

180 nb:~50 day

missing mass cut on nutron !

e+e-suppressed!

Omega production in Omega production in AA

pe+e-< 300 MeV/c

-p boundn e+e-n

„at rest”:

mass modifications in 0

e+

e-

208Pb-

HADES

W.Schoen et al.

Acta Phys.PolB27(1996)2959

M.Effenberger et al. Nucl-th/9901039

• in‘99 spectacular effects predicted…

Measured: +A (CBTAPS/CLAS)

incident photon energy range E = 900 – 2200 MeV

Preliminary

V.Metag priv. comm.

• no mass shift • in-medium broadenning: transparency measurement

~ absorption =vabs 90 MeV !

() =217 14

pe+e- >0.8 GeV/c

arXiv:0707.2324v3

0

CLAS

Theory’2008: Sensitivity to an in-medium mass shift

E= 1500 – 2200 MeV

for E= 1500 – 2200 MeV effect only observable for extremely hard cut on ω momentum:

E= 900 – 1200 MeV

• possible mass shift observable near threshold even without cut on ω momentum c/MeV150p

Gi-BUU simulations: K. Gallmeister et al. Prog. Part. Nucl. Phys. 61 (2008) 283

3 scenarios:1.) no in-medium modification2.) broadening3.) broadening and mass shift

Any chance for HADES?Any chance for HADES?HADES proposal 2006HSD: calculations (E. Bratkovskaya, D. Mishra)

experiment exp. rates:

25 day at 1.3 GeV/c and maximal luminosity

p+Nb @ 3.5 GeV/c rates:

expected 40/daymeasured 10/day

1.17 GeV

3.5 GeV

Vector mesons / at SIS

p+p at 3.5 GeV

PRELIMINARY

2005

40Ar+ 38KCl 1.75 AGeVp+ 92Nb 3.5 GeV

20072008“on-line spectrum!”

• Data are available! • No quick answer to the question on in-medium / spectral function ! • Only comprehensive analysis (in progress) of the pp/p+A/and A+A can give answer

resonance contribution?

Conclusions (to be work-out during this meeting)

• π- p (π+ n ) reactions below threshold – sensitive tool to study baryon-vector meson dynamics :

1. relevant for in-medium properties (SIS/18/300->SPS)

2. separation of vector/isovector em.current (intereference pattern)

• πA reactions –probe for in-medium vector meson properties and low momentum

+ see other contributions (Madaleine , Laura, Elena, Gyuri,…)

• Experiments: very challenging !!!

beam intensity, in-beam pion tracking, broad focus->large background

Di-electrons from Di-electrons from --AA reactions reactions

- Pb @ Ekin= 1.3 GeV

R-> R->

E.Bratkovskaya et.al. Phys.Rev.C60(1999)

No mass modifications

R-> and mass modifications

Final result depend on unknown elementary cross sections !!