Abstract:
The total charm-quark production cross section per unit of rapidity
$$\textrm{d}\sigma ({{\textrm{c}}\overline{\textrm{c}}})/\textrm{d}y$$
d
σ
(
c
c
¯
)
/
d
y
, and the fragmentation fractions of charm quarks to different charm-hadron species
$$f(\textrm{c}\rightarrow {\textrm{h}}_{\textrm{c}})$$
f
(
c
→
h
c
)
, are measured for the first time in p–Pb collisions at
$$\sqrt{s_\textrm{NN}} = 5.02~\text {Te}\hspace{-1.00006pt}\textrm{V} $$
s
NN
=
5.02
Te
V
at midrapidity (
$$-0.96
-
0.96
<
y
<
0.04
in the centre-of-mass frame) using data collected by ALICE at the CERN LHC. The results are obtained based on all the available measurements of prompt production of ground-state charm-hadron species:
$$\textrm{D}^{0}$$
D
0
,
$$\textrm{D}^{+}$$
D
+
,
$$\textrm{D}_\textrm{s}^{+}$$
D
s
+
, and
$$\mathrm {J/\psi }$$
J
/
ψ
mesons, and
$$\Lambda _\textrm{c}^{+}$$
Λ
c
+
and
$$\Xi _\textrm{c}^{0}$$
Ξ
c
0
baryons. The resulting cross section is
$$ \textrm{d}\sigma ({{\textrm{c}}\overline{\textrm{c}}})/\textrm{d}y =219.6 \pm 6.3\;(\mathrm {stat.}) {\;}_{-11.8}^{+10.5}\;(\mathrm {syst.}) {\;}_{-2.9}^{+8.3}\;(\mathrm {extr.})\pm 5.4\;(\textrm{BR})\pm 4.6\;(\mathrm {lumi.}) \pm 19.5\;(\text {rapidity shape})+15.0\;(\Omega _\textrm{c}^{0})\;\textrm{mb} $$
d
σ
(
c
c
¯
)
/
d
y
=
219.6
±
6.3
(
stat
.
)
-
11.8
+
10.5
(
syst
.
)
-
2.9
+
8.3
(
extr
.
)
±
5.4
(
BR
)
±
4.6
(
lumi
.
)
±
19.5
(
rapidity shape
)
+
15.0
(
Ω
c
0
)
mb
, which is consistent with a binary scaling of pQCD calculations from pp collisions. The measured fragmentation fractions are compatible with those measured in pp collisions at
$$\sqrt{s} = 5.02$$
s
=
5.02
and 13 TeV, showing an increase in the relative production rates of charm baryons with respect to charm mesons in pp and p–Pb collisions compared with
$$\mathrm {e^{+}e^{-}}$$
e
+
e
-
and
$$\mathrm {e^{-}p}$$
e
-
p
collisions. The
$$p_\textrm{T}$$
p
T
-integrated nuclear modification factor of charm quarks,
$$R_\textrm{pPb}({\textrm{c}}\overline{\textrm{c}})= 0.91 \pm 0.04\;\mathrm{(stat.)} ^{+0.08}_{-0.09}\;\mathrm{(syst.)} ^{+0.05}_{-0.03}\;\mathrm{(extr.)} \pm 0.03\;\mathrm{(lumi.)}$$
R
pPb
(
c
c
¯
)
=
0.91
±
0.04
(
stat
.
)
-
0.09
+
0.08
(
syst
.
)
-
0.03
+
0.05
(
extr
.
)
±
0.03
(
lumi
.
)
, is found to be consistent with unity and with theoretical predictions including nuclear modifications of the parton distribution functions.
