Enhanced production of low-mass electron-positron pairs in 40-AGeV Pb-Au collisions at the CERN SPS.
We report on first measurements of low-mass electron-positron pairs in Pb-Au collisions at the CERN SPS beam energy of 40 AGeV. The observed pair yield integrated over the range of invariant masses 0.2<m</=1 GeV/c(2) is enhanced over the expectation from neutral meson decays by a factor of 5.9+/-1.5(stat)+/-1.2(syst data)+/-1.8(syst meson decays), somewhat larger than previously observed at the higher energy of 158 AGeV. The results are discussed with reference to model calculations based on pi(+)pi(-)-->e(+)e(-) annihilation with a modified rho propagator. They may be linked to chiral symmetry restoration and support the notion that the in-medium modifications of the rho are more driven by baryon density than by temperature.
Adamová
D
D
NPI ASCR, Rez, Czech Republic.
Agakichiev
G
G
Appelshäuser
H
H
Belaga
V
V
Braun-Munzinger
P
P
Cherlin
A
A
Damjanović
S
S
Dietel
T
T
Dietrich
L
L
Drees
A
A
Esumi
S I
SI
Filimonov
K
K
Fomenko
K
K
Fraenkel
Z
Z
Garabatos
C
C
Glässel
P
P
Hering
G
G
Holeczek
J
J
Kushpil
V
V
Lenkeit
B
B
Maas
A
A
Marín
A
A
Milosević
J
J
Milov
A
A
Miśkowiec
D
D
Panebrattsev
Yu
Y
Petchenova
O
O
Petrácek
V
V
Pfeiffer
A
A
Rak
J
J
Ravinovich
I
I
Rehak
P
P
Richter
M
M
Sako
H
H
Schmitz
W
W
Sedykh
S
S
Seipp
W
W
Sharma
A
A
Shimansky
S
S
Slívová
J
J
Specht
H J
HJ
Stachel
J
J
Sumbera
M
M
Tilsner
H
H
Tserruya
I
I
Wessels
J P
JP
Wienold
T
T
Windelband
B
B
Wurm
J P
JP
Xie
W
W
Yurevich
S
S
Yurevich
V
V