Chitrasen Jena

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Measurement of D-meson production in p–Pb collisions
with the ALICE detector
Chitrasen Jena (for the ALICE Collaboration)∗
School of Physical Sciences, National Institute of Science Education and Research, Jatni - 752050, India
Introduction
Heavy quarks such as charm and beauty are
produced in the initial stage of collisions via
hard parton scattering processes. They propa-
gate through the strongly-interacting medium
created in high-energy heavy-ion collisions
and are expected to lose energy via both elas-
tic [1] and inelastic [2] processes. The result-
ing modification of the transverse momentum
spectra of heavy flavours in heavy-ion colli-
sions with respect to pp collisions is a sen-
sitive probe for the medium properties. A
complete understanding of the results from
heavy-ion collisions requires the study of cold
nuclear matter (CNM) effects such as mod-
ification of the parton distribution functions
in the nucleus and momentum broadening
due to parton scattering in the nucleus [3].
These nuclear effects can be studied by mea-
suring heavy-flavour production in proton-
nucleus collisions, where an extended hot and
dense strongly-interacting medium is not ex-
pected to form.
D-meson reconstruction
D mesons are reconstructed in ALICE
through their hadronic decays: D0 → K−π+,
D+ → K−π+π+, D∗+ → D0π+ and D+s →
φπ+ → K+K−π+. The analysis strategy is
based on an invariant mass analysis of fully re-
constructed decay topologies originating from
secondary vertices, which are typically dis-
placed by few hundred micrometers from the
primary vertex. The topological reconstruc-
tion of the decays allows for an efficient rejec-
tion of the combinatorial background from un-
correlated tracks. In order to further suppress
∗Electronic address: cjena@niser.ac.in
)c (GeV/
T
p
0 5 10 15 20 25
/G
e
V
)
c
b
 
µ
) 
(
y
d
T
p
/(
d
σ
2
d
1
10
210
310
410
ALICE
=5.02 TeV
NN
sp-Pb,   
<0.04
cms
y-0.96<
 3.2% norm. unc. not shown±
BR syst. unc. not shown
0
D
+
D
 5× 
*+
D
+
sD
ALI−PUB−79352
FIG. 1: pT-differential inclusive production cross
section of prompt D0, D+, D∗+, and D+s mesons
in p–Pb collisions at
√
sNN = 5.02 TeV [4].
the combinatorial background, particle identi-
fication (PID) on the D-meson decay products
is employed using the information of specific
energy loss in the Time Projection Chamber
(TPC) and the time-of-flight measured with
the Time Of Flight (TOF) detector. Details
of the analysis procedure in p–Pb collisions are
reported in [4].
Results and Discussion
Figure 1 shows the pT-differential produc-
tion cross sections of prompt D0, D+, D∗+,
D+s mesons [4] and Fig. 2 presents the y-
differential production cross section of prompt
D0 for 2 < pT < 5 GeV/c, 5 < pT < 8 GeV/c
and 8 < pT < 16 GeV/c in p–Pb collisions at√
sNN = 5.02 TeV. The measurement is per-
formed in the rapidity interval −0.96 < y <
0.04 in the centre-of-mass system. Within the
current statistical and systematic uncertain-
ties, no evidence of a dependence of the pro-
Proceedings of the DAE-BRNS Symp. on Nucl. Phys. 60 (2015) 724
Available online at www.sympnp.org/proceedings
cms
y
-1.5 -1 -0.5 0 0.5
 c
)
-1
b
 G
e
V
µ
d
y
 (
T
 /
 d
p
σ
2
d
10
210
310
410
<5 GeV/c
T
2<p
<8 GeV/c
T
5<p
<16 GeV/c
T
8<p
Systematic uncert.
from Data
from B feed-down subtr.
 3.4%) and BR syst. unc. not shown±Normalization (
=5.02 TeV
NN
sp-Pb, 
 meson0D
Pbp
(MNR+EPS09)pA R×(FONLL) dy
σd ×A 
ALI−DER−61952
FIG. 2: y-differential production cross section of
prompt D0 mesons in p–Pb collisions for three dif-
ferent pT intervals, compared with theoretical cal-
culations.
duction cross section on rapidity is observed.
The measured pT-, y-differential cross sections
are compatible with predictions obtained by
scaling the y-differential cross section calcu-
lated for pp collisions with FONLL by the Pb
mass number and on the basis of the MNR
calculation with EPS09 nuclear parton distri-
bution function parametrization.
In order to disentangle the initial-state and
final-state effects in heavy-ion collisions, a sen-
sitive observable is the nuclear modification
factor (RpPb), defined as
RpPb(pT) =
dσpPb/dpT
A× (dσpp/dpT)
, (1)
where dσpPb/dpT is the pT-differential cross
section in p–Pb collisions, dσpp/dpT is the
pT-differential cross section in pp collisions at
the same centre-of-mass energy, and A is the
mass number of the Pb nucleus. Figure 3
shows the average RpPb of D mesons as a
function of pT in p–Pb collisions at
√
sNN =
5.02 TeV, compared to the average RAA of
prompt D mesons in central (0–20%) and
semi-peripheral (40–80%) Pb–Pb collisions at√
sNN = 2.76 TeV [5]. The nuclear modifica-
tion factor, RpPb, is close to unity within un-
)c (GeV/
T
p
0 5 10 15 20 25
N
u
c
le
a
r 
m
o
d
if
ic
a
ti
o
n
 f
a
c
to
r
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
=5.02 TeVNNsp-Pb, 
<0.04
cms
y-0.96<
=2.76 TeVNNsPb-Pb, 
|<0.5
cms
y|
centrality 0-20%
centrality 40-80%
ALICE
*+
, D
+
, D
0
Average D
ALI−PUB−79458
FIG. 3: Average RpPb of D
0, D+ and D∗+ mesons
as a function of pT in p–Pb collisions at
√
sNN =
5.02 TeV compared to D-meson RAA in central
(0–20%) and in semi-peripheral (40–80%) Pb-Pb
collisions at
√
sNN = 2.76 TeV [4].
certainties, indicating that cold nuclear mat-
ter effects are small for pT & 3 GeV/c. There
is a clear suppression in Pb–Pb collisions com-
pared with p–Pb collisions for pT & 3 GeV/c,
which indicates that final-state effects, such
as partonic energy loss in the medium, play
a far more dominant role in the suppression
of D-meson production at higher pT than cold
nuclear matter effects.
Acknowledgments
CJ acknowledges financial support from
XII plan project: Experimental High Energy
Physics Program at NISER (Sub-Project-
ALICE).
References
[1] M.H. Thoma and M. Gyulassy, Nucl.
Phys. B 351, 491 (1991).
[2] M. Gyulassy and M. Plumer, Phys. Lett.
B 243, 432 (1990).
[3] R. Vogt, arXiv:1508.01286 [hep-ph].
[4] B. Abelevet al. (ALICE Collaboration),
Phys. Rev. Lett. 113, 232301 (2014) and
references therein.
[5] B. Abelevet al. (ALICE Collaboration)
JHEP 1209, 112 (2012).
Proceedings of the DAE-BRNS Symp. on Nucl. Phys. 60 (2015) 725
Available online at www.sympnp.org/proceedings


Measurement of D-meson production in p-Pb collisions with the ALICE detector

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Measurement of D-meson production in p-Pb collisions with the ALICE detector

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