Studying hadron properties in baryonic matter with HADES „Nuclear matter at High densities”...

Studying hadron properties in baryonic matter with HADES

„Nuclear matter at High densities” Hirschegg 18-25.01.2009

P. Salabura

Jagiellonian University/GSI for the HADES collaboration

23.01.2009 P.Salabura

Study of hadron properties in dense and hot nuclear matter

Dense matter Freeze-outA+A @ 1-2 AGeV

HADES case:

Probes:

dielectrons penetrating probes-direct access

to in medium hadron masses : vector mesons

(/e+e-)

strangeness production (, K , ) EOS(see

C.Sturm talk), K-N potentials

Strategy: Systematic spectroscopy in proton, pion and heavy ion induced reactions

TC~170 MeV

mB

HADES @ SIS

Nucleus te

mp

erat

ure

Quark Matter

Hadron Resonance Gas

DLS @ Bevelac

CERES, NA60 (SPS)

T

940 MeVbaryon chemical potential

thermal freeze out

chemical freeze out

KEK,JLAB, TAPS

PHENIX (RHIC)

CBM/FAIR

Goal: learn about properties of dense matter in collision zone• new forms of matter ? • properties of hadrons in matter

e+ e-e+ e-

1

Gross properties of the baryonic matter (from transport models)


freeze-out

Au+Au

1-2 AGeV : moderate densities but long system life time

Baryonic matter: • /N = 1-3, T< 80 MeV, ~12-14 fm/c

nucleons, baryonic resonances (~30%) 33 mesons(π0)~10% “resonance matter”

• abundances reach maximum at ~2-3B

• long lived sources π0/ decay outside fireball

• short lived resonances / (c1.3 fm/c) –absorption (NNN or NNπ)!

• dielectron emission over full history of coll….

„ALL – freeze-out”= in-medium

• Sub-threshold production of heavy mesons : Multi-step processes (K-) , Resonance decays ,N*N/

• for dielectrons x BR ~10-4 !

S.Vogel et al. (URQMD) arXiv:0710.4463v2

E.Bratkovskaya W. Cassing (HSD)

2

Pair excess in URHIC collisions


• D. Adamova, et al., subm. to PLB, nucl-ex/0611022

• large pair excess over yield from the “freeze-out”Main source (not for RHIC !) π+π-e+e-(+-)

in-medium spectral functions

What about baryon rich matter?(pion densities 5-6 lower as compared to SPS!)

sNN=17.4 GeV

submitted to Phys. Lett.B

arXiv: 0802.0050

3


Pair excess at low energies?

low mass (0.14<Mee< 0.6 GeV/c2) pair excess @ 1AGeV ("DLS" puzzle")

Calculation: E.L.Bratkovskaya et al.Phys. Lett. B445 (1999) 265

Calculation: Ernst et al.Phys. Rev. C58 (1998) 447

1 AGeV

Calculation: C. Fuchs et al. Phys. Rev. C68 (2003) 014904

DLS Data: R.J. Porter et al.: Phys.Rev.Lett. 79 (1997) 1229

Status before HADES era:

no explanation for pair excess in light and medium HI systems!

4

Side View

START

FW

5

High Acceptance Di-Electron Spectrometer

Beams from SIS18: pions, protons, nuclei

Spectrometer with high invariant mass resolution (2% at / mass) and powerful PID capabilities : p/π/K/e

Versatile detector for rear particle decays :

• dielectrons (e+,e-)

• strangeness: , K,0 ,

GeometryFull azimuth, polar angles 18 - 85 e+e- pair acceptance 0.35~ 80.000 channels, segmented solid or LH2 targets

1 m


6

Experimental campaigns

p+p

1.25 GeV (2006)

2.2 GeV (2002)

3.5 GeV (2007)

d+p

C+C

2.0 AGeV (2002)

1.0 AGeV (2004)

1.25 GeV (2007)Ar+KCl

1.75 GeV (2005)

p+Nb

3.5 GeV (2008)

p+p

„Anomalous” excess of e+e- pairsin 0.15 < Mee < 0.5 GeV/c2

NN-Bremsstrahlungand Dalitz decays

vector mesons / in-medium

p+p

Resonance (,N*) production Form-factors and studies of / Dalitz decays (helicity angles)

Strangeness: , K±,0, production in HI


N+N

N

()

re+

e-

e +e -

N

e+

e-

e+

e-

7

Cocktail A („background”) “long-lived sources at freeze-out” π0 → e+ e- , η → e+ e- Dalitz ω → e+e- (direct) , ω →e+e- π0 (dalitz)π0/ yield fixed by measurement(TAPS)

Cocktail B: Cocktail A + Δ + ρ = “short-lived” resonances Δ → e+ e- N (Dalitz decay) N(Δ) =3/2 N( π0) – fixed to „freeze-out” abund.

ρ → e+e- (direct)

Definition of „pair excess”

cocktail: thermal source PLUTO event generator I. Froehlich et al.,arXiv:0708.2382 Excess – pair yield above A

-> medium AND first chance coll.



Inclusive e+e- from C+C collisions A. Agakichiev Phys.Rev. Lett 98(2007) 052302 A. Agakichiev Phys. Lett. B 663 (2008) 43

NNN

2

10

NORMALIZATION: N± from the same data sample

(M

ee)

~9

% a

t Me

e~0

.8 G

eV

/c2

syst. error (27%)syst. error (21%)

8


Beam energy dependence of the excess

Y

Y

Y

YYF excexc

1

• enhancement scales like pions !

• Baryon resonance decays? N-N bremsstrahlung?

F(2.0) = 1.9 ± 0.2(stat) ± 0.3(sys) ± 0.3( sys)F(1.0) = 6.8 ± 0.6(stat) ± 1.3(sys) ± 2.0( sys)

TAPS collab.

Z.Phys. A 359 (1997) 65 Phys.Rev. C 56 (1997)

R2920

9


N-N Bremsstrahlung

E.L. Bratkovskaya and W. Cassing arXiv:0712.0635v1

NN ("quasielastic")-non resonant

• Strong + electromagnetic process (OBE models)

1

2

e+

e- + =

resonant -baryon resonances ()

1

2

+

collection of results from E.L Bratkovskaya & W. Cassing: Nucl.Phys A 807, 214 (2008).

• bremsstrahlung OBE calculations:

Kaptari & Kämpfer, NPA 764 (2006) 338:

K&K OBE calculation:

pn bremsstrahlung 4 larger

(simplified picture!)

10


Comparison with up-to-date HSD

0.0 0.2 0.4 0.6 0.810-8

10-7

10-6

10-5

10-4

10-3

10-2

0.0 0.2 0.4 0.6 0.810-8

10-7

10-6

10-5

10-4

10-3

10-2

HADES

HSD: Dalitz Dalitz Dalitz Dalitz Brems. NN Brems. N All

C+C, 1.0 A GeVno medium effects

1/N

dN

/dM

[1

/GeV

/c2 ]

HSD: Dalitz Dalitz Dalitz Dalitz Brems. NN Brems. N All

M [GeV/c2]

HADES

C+C, 1.0 A GeVin-medium effects: CB+DM

1/N

dN

/dM

[1

/GeV

/c2 ]

M [GeV/c²]

HSD: E.L. Bratkovskaya and W. Cassing Nucl.Phys A 807, 214 (2008).

New treatment of Bremsstrahlung: L.P. Kaptari and B. Kämpfer, Nucl.Phys. A 764 (2006) 338

DLS Data: R.J. Porter et al. Phys.Rev.Lett. 79 (1997) 1229

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

10-3

10-2

10-1

100

101

102

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

10-3

10-2

10-1

100

101

102

Brems. NN Brems. N All

DLS

Dalitz Dalitz Dalitz Dalitz

C+C, 1.04 A GeVin-medium effects: CB+DM

d/d

M

[b/

(GeV

c2 )]

M [GeV/c2]

Brems. NN Brems. N All

DLS

Dalitz Dalitz Dalitz Dalitz

C+C, 1.04 A GeVno medium effects

d/d

M

[b/

(GeV

c2 )]

M [GeV/c²]Does Δ and Bremsstrahlung explain excess? verification in NN collisions is needed

11

Reference reaction: dielectrons from pp and “quasi-free” pn @ 1.25 AGeV


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 described by calculations !

12

13

C+C @ 1 AGeV – pp & pn @ 1.25 GeV

• Dielectron spectrum from C+C given as superposition of NN collisions !

no indications for in-medium effects ! (at least for C+C)

• What about larger systems ?

spectra normalized to 0

yield in C+C and NN

Absolute scale:

• C+C @ 1 AGeV<M>/Apart = 0.056 ± 0.007

• N+N @ 1.25 (A)GeV

<MNN >/Apart 0.093

but for N+N @ 1.00 (A)GeV

<MNN >/Apart 0.06


Ar+Kcl @ 1.75 AGeV

15

centrality : <b>LVL1 = 3.5 fm Number of participating nucl. <Apart> 38.5 ±4

Thermal source model Transport (HSD) N =3/2 N

0 for propagation in matter accounted

estimate of at freeze-out (much larger yield) mT scaling NN bremsstrahlung : not important

at this energy

PRELIMINARY

E.L. Bratkovskaya and W. Cassing Nucl.Phys A 807, 214 (2008).


Excess vs beam energy and system size

15

• Excess scales with (Apart) , >1 (~2)

multistep processes?

NN->N, ->N, N->

Resonance radiation is the dominant source

of e+e- yield!

PRELIMINARY

• Apart dependence need more studies :

Au+Au @ 1 AGeV vs C+C @ 1AGeV (2010)

Ni+Ni @ 1.93 AGeV – dilepton mass

dependence

inclusive meson production (TAPS data)(min. bias)

e+e- pair excessHADES DLS

ArkCl <Apart> = 19 vs. CC <Apart> = 6



Vector mesons in medium

16

Vector mesons in medium


Na60: R. Arnaldi et al., PRL 96 (2006) 162302

calculations: H. van Heesand R. Rapp, PRL 99 (2006) 102301, R. Rapp, J. WambachEPJA 6 (1999) 415

CERES D. Adamova et al. nucl-ex/0611022

• SPS energies: broadening due to interactions with hadronic medium (baryons are more important !)

• What is the situation at lower energies?

• No unique evidence for in medium modifications from p+A or +A reactions (CLAS/KEK/CBTAPS)

17

Vector mesons / at SIS

p+p at 3.5 GeV

PRELIMINARY

h

Dr

2005

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

w

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 full

picture

resonance contribution?

What is K-N potential ?


• K+ potential seems to be slightly repulsive-> confirmed also by K0 pt distributions)• Precise data on K- /K0 flow can be provided byFOPI , HADES (2009,2010)

18

K- Production at SIS energies

NNNNKNNKNN

K- Production in HI reactions

Similar scaling of K+ and K- Mesons as a function of Apart

correlated production via strangeness-exchange

or Strangeness Exchange? belived to be dominant (KAOS data)

NK

NKNN

non-resonant resonant (->K+K- )

• important to clarify for prediction of in-medium effects on K± production ( rates, flow phenomena)

NNNKNKN

sub-threshold in NN (Ethreshold 2.6 GeV) !

secondary reactions (in-medium)

B.Kampfer et. al Phys. G: Nucl. Part. Phys. 28 (2002) 2133–2136, 2035-2040

23.01.2009 19P.Salabura

K+ K- , differential production rates


• for the first time measured in the same (large) acceptance

• /K- =0.340.13 ~17% K- comes from !… but there is also non-resonant part!

MeV884)( yTB

M =1017,8 ± 0.9 MeV/c2

= 6.2 MeV/c2

20

K-/ ratio


Statistical model K. Redlich, H. Oeschler-priv.comm

• For NN at threshold /K- = 1.02±0.1 ANKE coll. PHYS. REV. C 77, 015204 (2008)

• /K- in Ar+KCl is ~ 3 smaller -> more K- thanks to medium (i.e strangeness exchange)

• …but reactions of the type NN->NN and NN->NNK+K- (non-resonat) is important,too !

• Agreement with Kaon systematics

21

23.01.2009 P.Salabura 22

Outlook: future exp.Upgrade RPC, DAQ, MDC1, EM Calorimeter (for SIS100)2008/9/10

Hades goes to FAIR ( 8 AGeV)> 2013 (SIS100)

2011

p + N, p + A resonance (, N*) radiative decays, strangeness

2010

Ni + Ni @ Au+Au dielectrons (/), strangeness (K-K+)2009-2011

SIS18

increase of Mul(/) by 2 orders of magnitue !!

CBM

HADES


Outlook and summary:Radiation from nuclear matter at 1-2 AGeV :• at low energy ( 1 AGeV) first chance NN colisions are important source of pairs

(pn- bremsstrahlung? strong isospin effect pp vs pn!)• small systems (i.e C+C) can be described by superposition of NN collisions• for larger systems (i.e Ar+KCl) and larger energies strong contribution from „resonance

matter”” () visible with non-linear Apart dependence

• In medium masses• strong (broadenning) modification of meson spectral function at SPS energies• vector mesons observed for a first time at SIS/Bevalac energy regime• / region measured with good precision – possibility to search for in-medium

modifications of v.m. spectral functions• K- in medium mass accessible only via indirect observables (flow,rates)- reaction

mechanism must be known accurately (strangeness exchange)

• Outlook >2009 - HI collisions (Au+Au/Ni+Ni) at SIS18 and pion physics

>2012 - HADES at FAIR

Conference

23.01.2009 P.Salabura 26

The Collaboration

GSI

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


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