We present spectra of charged hadrons from Au+Au and d+Au collisions at sqrts(NN)=200 GeV measured with the BRAHMS experiment at RHIC. The spectra for different collision centralities are compared to ...spectra from p+(-)p collisions at the same energy scaled by the number of binary collisions. The resulting ratios (nuclear modification factors) for central Au+Au collisions at eta=0 and eta=2.2 evidence a strong suppression in the high p(T) region (>2 GeV/c). In contrast, the d+Au nuclear modification factor (at eta=0) exhibits an enhancement of the high p(T) yields. These measurements indicate a high energy loss of the high p(T) particles in the medium created in the central Au+Au collisions. The lack of suppression in d+Au collisions makes it unlikely that initial state effects can explain the suppression in the central Au+Au collisions.
Invariant pT spectra and rapidity densities covering a large rapidity range (−0.1<y<3.5) are presented for π± and K± mesons from central Au + Au collisions at sNN=62.4 GeV. The mid-rapidity yields of ...meson particles relative to their anti-particles are found to be close to unity (π−/π+∼1, K−/K+∼0.85) while the anti-proton to proton ratio is p¯/p∼0.49. The rapidity dependence of the π−/π+ ratio is consistent with a small increase towards forward rapidities while the K−/K+ and p¯/p ratios show a steep decrease to ∼0.3 for kaons and 0.022 for protons at y∼3. It is observed that the kaon production relative to its own anti-particle as well as to pion production in wide rapidity and energy ranges shows an apparent universal behavior consistent with the baryo-chemical potential, as deduced from the p¯/p ratio, being the driving parameter.
Invariant p sub()Tspectra and rapidity densities covering a large rapidity range (-0.1<y<3.5) are presented for pi super(+/-) and K super(+/-) mesons from central Au + Au collisions at MathML ...equation. The mid-rapidity yields of meson particles relative to their anti-particles are found to be close to unity (pi super(-)/pi super(+)not, vert, similar1, K super(-)/K super(+)not, vert, similar0.85) while the anti-proton to proton ratio is MathML equation. The rapidity dependence of the pi super(-)/pi super(+) ratio is consistent with a small increase towards forward rapidities while the K super(-)/K super(+) and MathML equation ratios show a steep decrease to not, vert, similar0.3 for kaons and 0.022 for protons at ynot, vert, similar3. It is observed that the kaon production relative to its own anti-particle as well as to pion production in wide rapidity and energy ranges shows an apparent universal behavior consistent with the baryo-chemical potential, as deduced from the MathML equation ratio, being the driving parameter.
The proton-to-pion ratios measured in the BRAHMS experiment for
Au
+
Au
and
p
+
p
collisions at
s
N
N
=
62.4
and 200 GeV are presented as a function of transverse momentum and collision centrality at ...selected pseudorapidities in the range of 0–3.8. A strong pseudorapidity dependence of these ratios is observed. We also compare the magnitude and
p
T
-dependence of the
p
/
π
+
ratios measured in
Au
+
Au
collisions at
s
N
N
=
200
GeV
and
η
≈
2.2
with the same ratio measured at
s
N
N
=
62.4
GeV
and
η
=
0
. The great similarity found between these ratios throughout the whole
p
T
range (up to
2.2
GeV
/
c
) is consistent with particle ratios in
A
+
A
collisions being described with grand-canonical distributions characterized by the baryo-chemical potential
μ
B
. At the collision energy of 62.4 GeV, we have observed a unique point in pseudorapidity,
η
=
3.2
, where the
p
/
π
+
ratio is independent of the collision system size in a wide
p
T
-range of
0.3
⩽
p
T
⩽
1.8
GeV
/
c
.
We present spectra of charged pions and protons in 0–10% central Au+Au collisions at sNN=200 GeV at mid-rapidity (y=0) and forward pseudorapidity (η=2.2) measured with the BRAHMS experiment at RHIC. ...The spectra are compared to spectra from p+p collisions at the same energy scaled by the number of binary collisions. The resulting nuclear modification factors for central Au+Au collisions at both y=0 and η=2.2 exhibit suppression for charged pions but not for (anti-) protons at intermediate pT. The p¯/π− ratios have been measured up to pT∼3 GeV/c at the two rapidities and the results indicate that a significant fraction of the charged hadrons produced at intermediate pT range are (anti-) protons at both mid-rapidity and η=2.2.
PDF
