The CBM experiment at the upcoming FAIR accelerator aims to create highest baryon densities in nucleus-nucleus collisions and to explore the properties of super-dense nuclear matter. Event rates of ...10 MHz are needed for high-statistics measurements of rare probes, while event selection requires complex global triggers like secondary vertex search. To meet these demands, the CBM experiment uses self-triggered detector front-ends and a data push readout architecture. The First-level Event Selector (FLES) is the central physics selection system in CBM. It receives all hits and performs online event selection on the 1 TByte/s input data stream. The event selection process requires high-throughput event building and full event reconstruction using fast, vectorized track reconstruction algorithms. The current FLES architecture foresees a scalable high-performance computer. To achieve the high throughput and computation efficiency, all available computing devices will have to be used, in particular FPGAs at the first stages of the system and heterogeneous many-core architectures such as CPUs for efficient track reconstruction. A high-throughput network infrastructure and flow control in the system are other key aspects. In this paper, we present the foreseen architecture of the First-level Event Selector.
The study of (anti-)deuteron production in pp collisions has proven to be a powerful tool to investigate the formation mechanism of loosely bound states in high-energy hadronic collisions. In this ...paper the production of
(anti-)deuterons
is studied as a function of the charged particle multiplicity in inelastic pp collisions at
s
=
13
TeV using the ALICE experiment. Thanks to the large number of accumulated minimum bias events, it has been possible to measure (anti-)deuteron production in pp collisions up to the same charged particle multiplicity (
d
N
ch
/
d
η
∼
26
) as measured in p–Pb collisions at similar centre-of-mass energies. Within the uncertainties, the deuteron yield in pp collisions resembles the one in p–Pb interactions, suggesting a common formation mechanism behind the production of light nuclei in hadronic interactions. In this context the measurements are compared with the expectations of coalescence and statistical hadronisation models (SHM).
A
bstract
A measurement of the inclusive b-jet production cross section is presented in pp and p-Pb collisions at
s
NN
= 5
.
02 TeV, using data collected with the ALICE detector at the LHC. The jets ...were reconstructed in the central rapidity region
|η| <
0
.
5 from charged particles using the anti-
k
T
algorithm with resolution parameter
R
= 0
.
4. Identification of b jets exploits the long lifetime of b hadrons, using the properties of secondary vertices and impact parameter distributions. The
p
T
-differential inclusive production cross section of b jets, as well as the corresponding inclusive b-jet fraction, are reported for pp and p-Pb collisions in the jet transverse momentum range 10
≤ p
T
,
ch jet
≤
100 GeV/
c
, together with the nuclear modification factor,
R
pPb
b
−
jet
. The analysis thus extends the lower
p
T
limit of b-jet measurements at the LHC. The nuclear modification factor is found to be consistent with unity, indicating that the production of b jets in p-Pb at
s
NN
= 5
.
02 TeV is not affected by cold nuclear matter effects within the current precision. The measurements are well reproduced by POWHEG NLO pQCD calculations with PYTHIA fragmentation.
The measurement of the azimuthal-correlation function of prompt D mesons with charged particles in pp collisions at
s
=
5.02
TeV
and p–Pb collisions at
s
NN
=
5.02
TeV
with the ALICE detector at the ...LHC is reported. The
D
0
,
D
+
, and
D
∗
+
mesons, together with their charge conjugates, were reconstructed at midrapidity in the transverse momentum interval
3
<
p
T
<
24
GeV
/
c
and correlated with charged particles having
p
T
>
0.3
GeV
/
c
and pseudorapidity
|
η
|
<
0.8
. The properties of the correlation peaks appearing in the near- and away-side regions (for
Δ
φ
≈
0
and
Δ
φ
≈
π
, respectively) were extracted via a fit to the azimuthal correlation functions. The shape of the correlation functions and the near- and away-side peak features are found to be consistent in pp and p–Pb collisions, showing no modifications due to nuclear effects within uncertainties. The results are compared with predictions from Monte Carlo simulations performed with the PYTHIA, POWHEG+PYTHIA, HERWIG, and EPOS 3 event generators.
A
bstract
Inclusive
ψ
(2S) production is measured in p-Pb collisions at the centre-of-mass energy per nucleon-nucleon pair
s
NN
= 8
.
16 TeV, using the ALICE detector at the CERN LHC. The production ...of
ψ
(2S) is studied at forward (2
.
03
< y
cms
<
3
.
53) and backward (
−
4
.
46
< y
cms
< −
2
.
96) centre-of-mass rapidity and for transverse momentum
p
T
<
12 GeV/
c
via the decay to muon pairs. In this paper, we report the integrated as well as the
y
cms
- and
p
T
-differential inclusive production cross sections. Nuclear effects on
ψ
(2S) production are studied via the determination of the nuclear modification factor that shows a strong suppression at both forward and backward centre-of-mass rapidities. Comparisons with corresponding results for inclusive J/
ψ
show a similar suppression for the two states at forward rapidity (p-going direction), but a stronger suppression for
ψ
(2S) at backward rapidity (Pb-going direction). As a function of
p
T
, no clear dependence of the nuclear modification factor is found. The relative size of nuclear effects on
ψ
(2S) production compared to J/
ψ
is also studied via the double ratio of production cross sections
σ
ψ
(2S)
/σ
J
/ψ
pPb
/
σ
ψ
(2S)
/σ
J
/ψ
pp
between p-Pb and pp collisions. The results are compared with theoretical models that include various effects related to the initial and final state of the collision system and also with previous measurements at
s
NN
= 5
.
02 TeV.
The production of the
Λ
(1520) baryonic resonance has been measured at midrapidity in inelastic pp collisions at
s
=
7
TeV
and in p–Pb collisions at
s
NN
=
5.02
TeV
for non-single diffractive events ...and in multiplicity classes. The resonance is reconstructed through its hadronic decay channel
Λ
(1520)
→
pK
-
and the charge conjugate with the ALICE detector. The integrated yields and mean transverse momenta are calculated from the measured transverse momentum distributions in pp and p–Pb collisions. The mean transverse momenta follow mass ordering as previously observed for other hyperons in the same collision systems. A Blast-Wave function constrained by other light hadrons (
π
, K,
K
S
0
, p,
Λ
) describes the shape of the
Λ
(1520) transverse momentum distribution up to
3.5
GeV
/
c
in p–Pb collisions. In the framework of this model, this observation suggests that the
Λ
(1520) resonance participates in the same collective radial flow as other light hadrons. The ratio of the yield of
Λ
(
1520
)
to the yield of the ground state particle
Λ
remains constant as a function of charged-particle multiplicity, suggesting that there is no net effect of the hadronic phase in p–Pb collisions on the
Λ
(1520) yield.
A
bstract
The
p
T
-differential non-linear flow modes,
v
4
,
22
,
v
5
,
32
,
v
6
,
33
and
v
6
,
222
for
π
±
, K
±
,
K
S
0
, p +
p
¯
, Λ +
Λ
¯
and
ϕ
-meson have been measured for the first time at
s
...NN
= 5
.
02 TeV in Pb-Pb collisions with the ALICE detector at the Large Hadron Collider. The results were obtained with a multi-particle technique, correlating the identified hadrons with reference charged particles from a different pseudorapidity region. These non-linear observables probe the contribution from the second and third order initial spatial anisotropy coefficients to higher flow harmonics. All the characteristic features observed in previous
p
T
-differential anisotropic flow measurements for various particle species are also present in the non-linear flow modes, i.e. increase of magnitude with increasing centrality percentile, mass ordering at low
p
T
and particle type grouping in the intermediate
p
T
range. Hydrodynamical calculations (iEBE-VISHNU) that use different initial conditions and values of shear and bulk viscosity to entropy density ratios are confronted with the data at low transverse momenta. These calculations exhibit a better agreement with the anisotropic flow coefficients than the non-linear flow modes. These observations indicate that non-linear flow modes can provide additional discriminatory power in the study of initial conditions as well as new stringent constraints to hydrodynamical calculations.
A
bstract
The production of prompt D
0
, D
+
, and D
*+
mesons was measured at midrapidity (|
y
|
<
0.5) in Pb–Pb collisions at the centre-of-mass energy per nucleon–nucleon pair
s
NN
= 5
.
02 TeV ...with the ALICE detector at the LHC. The D mesons were reconstructed via their hadronic decay channels and their production yields were measured in central (0–10%) and semicentral (30–50%) collisions. The measurement was performed up to a transverse momentum (
p
T
) of 36 or 50 GeV/c depending on the D meson species and the centrality interval. For the first time in Pb–Pb collisions at the LHC, the yield of D
0
mesons was measured down to
p
T
= 0, which allowed a model-independent determination of the
p
T
-integrated yield per unit of rapidity (d
N/
d
y
). A maximum suppression by a factor 5 and 2.5 was observed with the nuclear modification factor (
R
AA
) of prompt D mesons at
p
T
= 6–8 GeV/c for the 0–10% and 30–50% centrality classes, respectively. The D-meson
R
AA is compared with that of charged pions, charged hadrons, and J
/ψ
mesons as well as with theoretical predictions. The analysis of the agreement between the measured
R
AA
, elliptic (
v
2
) and triangular (
v
3
) flow, and the model predictions allowed us to constrain the charm spatial diffusion coefficient
D
s
. Furthermore the comparison of
R
AA
and
v
2
with different implementations of the same models provides an important insight into the role of radiative energy loss as well as charm quark recombination in the hadronisation mechanisms.
The production of
π
±
,
K
±
,
K
S
0
,
K
∗
(
892
)
0
,
p
,
ϕ
(
1020
)
,
Λ
,
Ξ
-
,
Ω
-
, and their antiparticles was measured in inelastic proton–proton (pp) collisions at a center-of-mass energy of
s
...= 13 TeV at midrapidity (
|
y
|
<
0.5
) as a function of transverse momentum (
p
T
) using the ALICE detector at the CERN LHC. Furthermore, the single-particle
p
T
distributions of
K
S
0
,
Λ
, and
Λ
¯
in inelastic pp collisions at
s
=
7
TeV are reported here for the first time. The
p
T
distributions are studied at midrapidity within the transverse momentum range
0
≤
p
T
≤
20
GeV/
c
, depending on the particle species. The
p
T
spectra, integrated yields, and particle yield ratios are discussed as a function of collision energy and compared with measurements at lower
s
and with results from various general-purpose QCD-inspired Monte Carlo models. A hardening of the spectra at high
p
T
with increasing collision energy is observed, which is similar for all particle species under study. The transverse mass and
x
T
≡
2
p
T
/
s
scaling properties of hadron production are also studied. As the collision energy increases from
s
= 7–13 TeV, the yields of non- and single-strange hadrons normalized to the pion yields remain approximately constant as a function of
s
, while ratios for multi-strange hadrons indicate enhancements. The
p
T
-differential cross sections of
π
±
,
K
±
and
p
(
p
¯
) are compared with next-to-leading order perturbative QCD calculations, which are found to overestimate the cross sections for
π
±
and
p
(
p
¯
) at high
p
T
.
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