Dubna, November 2003Joachim Stroth Hadron Structure in Dense Nuclear Matter Vector mesons Di-electron spectroscopy in heavy ion collisions The HADES spectrometer

Dubna, November 2003 Joachim Stroth

Hadron Structure in Dense Nuclear Matter

Vector mesons

Di-electron spectroscopy in heavy ion collisions

The HADES spectrometer ...

... and the future of di-electron spectroscopy

Summary


A photon ...

e

e

q

q

*


.... hadronizes via Vector Meson Dominance

e

e

* 0


Di-electron Spectroscopy in Heavy Ion Collisions

p

n

++

K

p

Penetrating probes: information from the early stage low branching ratio, O (10-5)

e+

e-


Nuclear matter under extreme conditions

DATA: Fit of statistical model to measured abundances in the final state

P. Braun-Munzinger, J. Stachel et al.


Reasons for Medium Modifications

Meson self energy in medium• many more degrees of

freedom (spreading)

Broadening !?

Dynamical mass generation by spontaneous Chiral Symmetry breaking

– mq 10 MeV (current quark mass)

– mu,d mp,n / 3 300 MeV(constituent quark mass)

mass shift !?


Time dependence of the Chiral Condensate

B. Friman et al.: Eur. Phys. J. (1998)

Method: quark-gluon string model (Toneev at al. NP A519(1990)463c)


Modification of meson spectral function through coupling to resonances

Nuclear Physics A, Volume 632, 9 March 1998, W. Peters, M. Post, H. Lenske, S. Leupold and U. Mosel

Modification of the -Meson spectral function depends on....

relative momentum to the medium

the density of the surrounding medium

normal

nuclear ground state density

twice


Di-electrons measured with DLS at Berkeley

• Daten: R.J. Porter et al.: PRL 79(97)1229 • Modell: E.L. Bratkovskaya et al.: NP A634(98)168,

BUU, Spektralfunktionen im Vakuum

DLS


Extended Vector Meson Dominance

Still experimental data in the low mass region above the theoretical expectation

Shekhter et al., PRC 68 (2003)


Bratislava (SAS, PI), Catania (INFN - LNS), Cracow (Univ.), Darmstadt,(GSI),

Dresden (FZR), Dubna (JINR, LHE), Frankfurt (Univ.),Giessen (Univ.),

Milano (INFN, Univ.), Moscow (ITEP, INR, MEPhI), Munich (Tech. Univ.),

Nicosia (Univ.), Orsay (IPN),Rez (CAS, NPI), Sant. de Compostela (Univ.),

Valencia (Univ.)


High acceptance dielectron spectrometer HADES

GeometrySix sectors form a hexagonal frustum:

inin, , pair acceptance

Tracking Superconducting toroid (6 coils)

– Bmax = 0.7 T,

– Bending power 0.34 Tm

MDC (multiwire drift chamber)– Low mass design– four planes of small cell (cmdrift

chamber.

Lepton identification & trigger RICH

– Radiator: C4F10

– Spherical mirror– Photon Detector: CsI photo cathode

META (TOF & Pre-Shower)– TOF plastic scintillators– Lead Shower detector

• LVL2 trigger on Electrons – Fast (~200 s)– Highly selective

(suppression up to1/100)



Omega production in A

Selective measurement of medium modification ant nuclear ground state density

uncertainties in calculations (interferences, el. form-factors, res N*,)

needs data from

e+

e-

208Pb-

HADES

W.Schoen et al.

Acta Phys.PolB27(1996)2959

M.Effenberger et al. Nucl-th/9901039

neenp

XeeN


The current experimental program of HADES

11/2002:11/2002: Commissioning (12C+12C)

– 36 M events

– no outer drift chambers

11/2002: 11/2002: Production run (12C+12C)

– 200 M events, 44 % LVL2 triggered

– 4 Sectors with outer tracking(4/2)

10/2003:10/2003: Commissioning (p+lH2)

– 6 Sectors with outer tracking (6/4)

02/2004:02/2004: Production run (p+lH2)


Electron identification using the RICH

• hadron contamination < 2%• p/ separation for p < 1000 MeV/c

C+C, 2AGeV

p*q [MeV/c]

v/c

Tracking+TOF

q*p [MeV/c]

v/c


Tracking with the drift chambers and more

FE electronics

threshold

t1

t2

drift cell


Pairs from C+C @2 AGeV

Nov02(60% of data) CB

Me+e- [MeV/c2]

Cou

nts

/10

MeV

CB combinatorial background

! no close pair rejection

NNNCB 2

signalCB

ee0 Preliminary


Nov02

Preliminary

Nov01

Nov02 data scaled down by 10

0e+e-

Me+e- [MeV/c2]

Nov02 C+C @2 AGeVC

ou

nts

/MeV

shapes of the inv. mass distributions are consistent

50k pairs in Nov02 (60% of data)

Nov02: 4 sectors equipped with outer MDC

Not acceptance corrected


Signal pairs from C+C

Me+e- [MeV/c2]

dN

/dM

[1/

MeV

]

Me+e- [MeV/c2]

CB subtracted but not acceptance corrected !

normalized by number of LVL1 triggers

different magnetic field settings for 1AGeV

1 AGeV 2 AGeV

Preliminary


Nuclear matter at the highest densities

The futureCompressed Baryonic Matter

Experiment


Di-electron spectroscopy at the future facility

Radiation hard Silicon pixel/strip detectors

magnet

1 m


Electrons from Dalitz (pt vs y) HADES at SIS HADES at SIS 100100

e+ e-

1

0

1

00 3 0 3

e+ e-

0 3 0 3

2 GeV/u 8 GeV/u

• particle multiplicity higher in forward region • pion acceptance by 20-30% lower at 8 GeV/u than at

2 GeV/u• single lepton (from eta Dalitz) acceptance by 10-20%

lower• dilepton acceptance by 20% lower

C+C


Feasibility study : e+ e- with CBMwith CBM

CBM experimental concept:

Electron identification after tracking!

Background from conversion dominatese+e- vertex cuts is essential:

SNR 3 in 1 M eventsstudy ongoing, tracking needed


Summary

Dielectrons are ideal probes for the dense phase of nuclear matter.

Creation and propagation well understood (QED).

• High penetrability

• The disadvantage of small branching ratios can partly be compensated by using

state of the art micro electronics

First results of the HADES spectrometer are arriving

• Conduct systematic investigation of heavy collisions up to 2 GeV/u

• Complemented by a series of experiments using proton and pion beams

The future accelerator facility will provide ideal conditions to create nuclear matter

at the highest densities

• HADES can cover beam energies up to 8 GeV/u

• Conceptually new technique for dielectron spectroscopy with CBM

Documents

Dubna, November 2003Joachim Stroth Hadron Structure in Dense Nuclear Matter Vector mesons Di-electron spectroscopy in heavy ion collisions The HADES spectrometer