Transcript Slide 1

Recent HADES results
P. Salabura
M. Smoluchowski Institute of Physcis
Jagiellonian University
HADES 2010-2013 results
• e+e- production in p+p, p+A @ 3.5 GeV
Vector meson and  in (cold) nuclear matter
Baryon Resonance decays
• e+e- production in HI collisions: status of Au+Au data
e+e- sources at SIS18 energies
excitation function !
e+e-
, 
Ne+e-
 
Me+e->M0
~2
1
2
3
4
5
DLS: PRC57 (1998)1867
e+e- 
HADES PRC85 (2012) 054005
° e+e-
isospin effects Ebeam < 2 AGeV
Ebeam (GeV)
• Me+e- < 0.15 GeV/c2 dominated by 0 Dalitz
• 0.15 < Me+e- < 0.55 GeV/c2 : Resonance (, N*)Ne+e- (Dalitz decays)
NN-bremmstrahlung, and  e+e- decays !
• M > 0.55 GeV/c2 : Resonance (, N* ) Dalitz decays + /
Understanding of Baryon Sources is essential for HADES physics
3
Inclusive e+e- production in
pp @ 2.2 and 3.5 GeV
2.2 GeV
HADES PRC85 (2012) 054005
•
3. 5 GeV
HADES EPJA 48 (2012) 64
Unexplained yield excess above exp. cocktail below VM pole
• At 3.5 GeV :
 0 Dalitz decay fixed by data
 and resonance (, N* ) not easy to isolate ! higher resonances?
 / fixed to some extent by exclusive pp data (hadronic channels) and clear  peak
e+e- pT distributions
p+p @ 3.5 GeV
sensitive to / contributions !
p+p vs p+Nb @ 3.5 GeV
data: HADES PLB715 (2012) 304
„fast” pe+e->0.8 GeV/c
„fast” pe+e-< 0.8 GeV/c
Nuclear modification factor
pp data scaled by
„Apart” scaling
• large acceptance at small Me+e- and p (<1 GeV/c) ( first measurement at low p !)
• for slow e+e- : excess emerges above pp reference ,  peak less pronounced
Rapidity distributions pp vs pNb @ 3.5 GeV
p+Nb:clear shift towards target rapidity for M>M
e+e- excess in p+Nb : low pe+e„slow” (p<0.8 GeV/c) pairs
„excess over pp reference”
Rpa vs momentum
Me+e
RpA (vs p) – increase at small momenta : largest for the „-region”
BUT NOT for  peak   absorption (observed also by CBTAPS and CLAS in (+A) ) !

clear excess in p+A below VM pole 
- secondary reactions : +N   (1720,..)(N* (1520),..) NNe+e- (see J. Weil talk)
or/and in medium  modification ? first the p+p reference must be understood !
0 /  production in p+Nb @ 3.5 GeV with
conversion method
HADES (2013) arXiv:1305.3118
mT scaling of light mesons
Total detection probability 10-6 -10-7 !
Similar analysis
for p+p in progress!
0/ pT distribution/yields compared to
transport
EXP (4):
0

e+e- sources in pp @ 3.5 GeV
J.Weil:
EPJA48 (2012)111
E. Bratkovskaya et. al.:
arXiv:1301.0786v1
•
Many uncertainties: inclusive cross sections , ,  , / (fixed now by HADES)
pe+e- transition (Dalitz decay); rates, em. Transition Form-Factors
 - spectral function !
Ne+e- Dalitz decay
QCD
QED
„point-like”   N e- e +
• exact field theory calculation
• 3 independent amplitudes:
e.g. Electric, Magnetic and Coulomb
d (Δ  Ne  e - )
 f
dq 2


electromagnetic form factors
GM(q2),GE(q2),GC(q2)
2

q
2
2
2  2 2
m Δ, q  G M q  3 G E q  2 m 2
Δ

 
 


G q  
2
2
C

GM
(N)
Exp=3.00.05 Exp=0.660.06
Wolf, Nucl.Phys. A517
(1990) 615
GM=3.0
0.22
Ernst, Phys.Rev C 58,
447 (1998)
GM=3.0
1.03
Krivoruchenko
Phys.Rev.D 65 (2001),
017502
GM(0)=3.0
0.65
Zetenyi and Wolf,
Heavy Ion Phys. 17
(2003) 27.
GM(0)=3.0
0.65
I.G. Aznauryan andV.D. Burkert,
Prog. Part. Nucl. Phys.67 (2012)
Jones and Scadron convention
„pion cloud”
e+
„quark core”
q
qq
e-
spin flip
« Photon point » : q2=0
GM(0)=3, GE(0)=GC(0)~0
N e+e- : two component (pion cloud+quark core) models


2

q
d (Δ  Ne e )
2
 2
 f m ,q 2  G M q 2  3 G E q 2 
2
2
Δ
dq
2 mΔ



-
Iachello, Wan: implemented for HADES by
I. Froehlich et. EPJA 45, 401 (2010)
cloud/core ~ 0.99/0.01
 
 
G q 
2
C
2





M. Pena, G. Ramahlo
PRD85 (2012) 113014
cloud/core ~ 0.44/0.56
M=1.8
QED
QED
M=1.5
M=1.23
Mee [GeV/c2]
• pion cloud /core contribution affects strongly Q2 dependence of eTFF  VDM
T. Pena - higher resonances in work..
Higher resonances..
QED: point-like R-* vertex
extended VDM:
Resonance model
M. Zetenyi et al. PRC 67, 044002 (2003)
constraints from R->N
M. I. Krivoruchenko et al.
Ann. Phys. 296, 299 (2002).
GiBUU, UrQMD, BUU,HSD ..
example:J. Weil EPJA 48(2012)111
„factorization”
eTFF (Mee)
Baryon resonaces in [email protected] GeV
Goal: Study 3 connected exclusive channels:
• pppp0 and pppn+ to fix R (,N*) cross sections
• Convert Rpe+e- and check in pp pp e+e-
• Resonance model: production amplitude is given by incoherent sum
of Resonance contributions, isospin relations
Starting point: S. Teis R parametrization (S. Teis et al., Z. Phys. A356, 421 (1997).) , take 4* resonances +
empirical angular distributions (strong forward-backward peaking)
d
A
(M R )  (M )
dt
t
BR(Rpe+e-) : „QED” point-like R-* vertex
M. Zetenyi and Gy. Wolf., Heavy Ion Phys. 17 (2003) 27.
For the overlaping resonances only one
resonance with largest BR(N) selected
One pion production
A.Dybczak phd Kraków (2013)
pn+
• Acceptance
corrected spectra
• ++ (1232) dominates !
excelent description of -line
shape („Moniz” FF)
pp0
• +(1232),
N*(1440),N*(1520),..
P.Salabura
exclusive / production in pp @ 3.5 GeV
K.Teilab phd Frankfur (2011)
 =
N* (1535) fixed from  Dalitz plot
=
N* (1535) ->p BR(42%)
N*(1535) = 1520.15 [mb]
Results for ppe+e- channel
„QED” : point like RN* vertex
• Significant contribution from higher (than ) mass resonances
• Addtional strength below VM pole needed – off shell  meson coupling !
– extended interaction vertex
• low mass resonances : (1232), N(1440), N(1520) ?
eVDM and (1232) eTFF
eTFF from
Iachello, Wan
• large ambiguities related to the
resonance selection
saturates the
yield- no place
left for other
resonances
Comparison to other parametrizations
comparison to S. Teis
comparison to UrQMD:
S. Bass Prog.Part.Nucl.Phys. 41 (1998) 225-370
J. Weil et al. EPJA 48(2012)111
Resonances with
BR(N)
RNNe+eResonance XS and RN BR from UrQMD
Resonance XS and RN BR from GiBUU
e+e- from HI collisions
e+e- pairs from Ar+KCl @ 1.756
Cocktail with „freeze-out” comp.
 component subtracted
data PRC84(2001)014902
 first ->e+e- observation at SIS18 energies
 first evidence for „true” excess above NN and light CC systems
 Excess yield scales with system size ~ Apart1.4  multistep processes?
let’s see Au+Au !
Au+Au May’2012
• New RPC detector (180 << 450 )
• New DAQ and read-out – 10 kHz data taking rate
Strangeness reconstruction
Lepton ID and purity
Single lepton purity
PID: Multi-Variante Analysis
electrons
Vertex reconstruction
hadrons
Conference
Summary
 Precise e+e- data collected for pp/pNb @ 3.5 GeV
evidences for interesting physics („excess” below VM pole)
 Intepretation is challanging !
- pp reference net (yet) well understood
exclusive ppe+e-, pp0 , pn+ show that off-shell -R coupling
in R-> pe+e- is very important
-  inclusive production is possible with conversion technique !
IT IS IMPORTANT REFERENCE system for HADES at FAIR
 HADES made succefull Au+Au @1.23 GeV campaign
• single track and resonance (hadron) reconstruction shows great data
quality
• e+e- spectra are very close to be produced
The HADES collaboration
13 Institutions
Technical Proposal
accepted 1995
First experiments 2001
 Cracow (Univ.), Poland
 Darmstadt (GSI), Germany
 Dresden (FZD), Germany
 Dubna (JINR), Russia
 Frankfurt (Univ.), Germany
SIS
 Giessen (Univ.), Germany
 München (TUM), Germany
 Moscow (ITEP,RAS), Russia
 Nicosia (Univ.), Cyprus
 Orsay (IPN), France
 Rez (CAS, NPI), Czech Rep.
 Sant. de Compostela (Univ.), Spain
GSI

23.01.2009
P.Salabura
LIP, Portugal
28
Study of hadron properties in dense
baryonic matter
• The case of Large B and moderate T :
L. McLerran, R.D. Pisarski 2007
interesting region in phase diagramme with a large
discovery potential
 not probed experimentally by means of rare
penetrating probes
Probes:

experiment: chemical freeze-out
HADES
sensitive probe of extended baryon structure
RHIC, BES
Na61
-medium modifications ?
Begun et. al. arXiv:1208.410
CBM
Fair
dielectrons :
 meson in medium properies
 Multistrange baryons: -(1321), 
Strategy:
Systematic measurements
in p +p, p+A and A+A at 2- 8 AGeV
VDM
Resonance properties UrQMD
S. Bass Prog.Part.Nucl.Phys. 41 (1998) 225-370
23.01.2009
P.Salabura
Conference
Baryon resonance structure
Space-Like el.Transition Form Factors
e-
q2 <0
*
e-
Time-Like el.Transition Form Factors : Dalitz decays
n
-

p
R
p
0
p
q2 >
* e+
R
0
e--
studied at JLab/CLAS/MAMI,..
pion electroproduction
R
e-pe-N 
Time Like
domain : q2 >0
q2
e+
, ,
Dalitz Decays: poorly known !
Dalitz decays , e+e- NNe+e-
0
*
Vector Dominance Model
 directly related to :
Space Like
domain
q2 <0
N
e-
e+e- from C+C collisions and NN
 contribution subtracted
ratio CC/NN
baryons

NN=1/2(np+pp) –reference- and C+C normalized to the individual N(0 )=1/2(N(+) + N(-))
e+e- subtracted („long lived” source) - cross section known from other exp.( TAPS)

C+C data (1 and 2 AGeV !) reproduced (within 20%) by NN reference up to 0.45 GeV/c2
– no room (within error bars) for in-medium effects
data: HADES PLB690 (2010)118 PRL98(2007) 052302
cocktail: „long lived sources”-freeze out
Excess scaling with Apart/Ebeam
TAPS -
C+C
Ca+Ca
HADES, DLS e+e-
• Baryonic sources : (1232) ~10-20%, N(1535,..)- 1-2%, N–N bremsstr..
excitation function similar in shape to pions
Quasi free p+n reaction with deutron
X
d
spectator model
p
pt
pspec
n
• average pn distance ~ 3 fm
• total cross section reduced by ~8%
(p shadowing + meson absorption)
momentum
in deuteron
rest frame
Ek=1.25 AGeV
Quasi-free pn reactions in d+p collisions
X=, , .. spectator model
p
d
pt
pspec
n
spectator on-shell
CELSIUS: PRC58(1998)2667
Ed=0.76 GeV
COSY-TOF EPJA29(2006) 353
Ep=1.35 GeV
Spectator model at work (Q<100 MeV)
d+p -> ps ppCOSY-TOF
p+d -> ps d
EPJ. A 29, (2006) 353
ANKE PRL 97 (2006) 142301
p+d -> ps pn 
COSY11, SATURNE, CELSIUS
P. Moskal, nucl–ex/0110001 and
P. Moskal PRC79(2009) 015208
pspectator momentum
MC
( NN pot)
• overall good agreement with spec. model
p+d -> ns pp
exclusive channel: np.npe+eExclusive (e+e-) - one proton e+e- in HADES
ppe+enpe+e-
• excess in np reaction visible also in
exclusive channels (note: no  contribution! )
• missing mass spectra reproduced by
simulation
npnpe+eMe+e- >M0
ppppe+eMe+e- >M0
Inclusive e+e- (n+p)QF vs pp
calculations: R. Shyam and U. Mosel Phys. Rev. C
82:062201, 2010 data: HADES PLB690 (2010)118
• excess np. over pp !
R. Shyam and U. Mosel Phys. Rev. C 82:062201, 2010
due to eFF of charged pion
charge pion exchange & pion eFormFactor
pion eTFF :
W. Weise, G. Brown, M. Rho
NPA 474(1986)669
p
n
π+
π-
n
ρ
p
p
e+
π0
e-
π0
p
p
ρ
e+
e-
p
e+e- in p+p @ 1.25 GeV
inclusive
Main source: pe+e- Dalitz decay
 production not possible – below threshold
p
p
GM (q2)
VMD
p

+
p
*
e+
Time Like (q2 >0)
 (J=3/2) ->N (J=1/2) * transition:
Calculations: Vector Meson Dominance Krivoruchenko et al. PRD 65 (2001) 017502
G. Ramalho and T. Pena arxiv: 1205.2575v1 (2012)
F. Dohrmann et al., Eur. Phys. J. A 45, 401 (2010)
HADES: PLB690 (2010)118
• 0 ,  fixed by 1 pion exclusive production : HADES
EPJA48(2012) 74
BR (Ne+e-)  4*10-5 agrees with model predictions.
G(q2 ) dependence not very essential at this low energy..
„Emissivity” of baryonic matter
Dense matter : 3*B ~ 0.5/fm3
30% baryon resonances 33
Vacumm
pions (T~ 80 MeV)
RNe+ee+
e+
e+
e-
q
qq
e-
q
q eqq
q q
pion
cloud
q
q q
q
q q
qq
e+
q
q q
qq
e-
q
q q
q
q q
q
q q
How does the radiation from
overlaping baryons looks like?
Transparency ratio in „cold matter”
• „disapearance of meson in nuclear matter”
 AVX
TA 
A   N VX
Glauber Picture;
CabreraNPA733(2004)130
 A   d d 3r ( r )
d N
d
Production
 ISI (not for ), Pauliblocking, Fermi-motion,
secondary processes,
shadowing ….
 normalization to C to

 
q
r' r  l 
|q |

1
exp(  dl Im 
q0
'
(
q
,

(
r
))) P( r  r ' )
medium
Absorption
FSI of decay products
in-medium width
coll ( q)  
Im  ( q)

absent for e+e-