The multiplicity dependence of electron production from heavy-flavour hadron decays as a function of transverse momentum was measured in p-Pb collisions at
s
NN
= 5
.
02 TeV using the ALICE detector ...at the LHC. The measurement was performed in the centre-of-mass rapidity interval
−
1
.
07
< y
cms
<
0
.
14 and transverse momentum interval 2
< p
T
<
16 GeV
/c
. The multiplicity dependence of the production of electrons from heavy-flavour hadron decays was studied by comparing the
p
T
spectra measured for different multiplicity classes with those measured in pp collisions (
Q
pPb
) and in peripheral p-Pb collisions (
Q
cp
). The
Q
pPb
results obtained are consistent with unity within uncertainties in the measured
p
T
interval and event classes. This indicates that heavy-flavour decay electron production is consistent with binary scaling and independent of the geometry of the collision system. Additionally, the results suggest that cold nuclear matter effects are negligible within uncertainties, in the production of heavy-flavour decay electrons at midrapidity in p-Pb collisions.
A
bstract
The production of charm jets in proton-proton collisions at a center-of-mass energy of
s
=
7
TeV was measured with the ALICE detector at the CERN Large Hadron Collider. The measurement is ...based on a data sample corresponding to a total integrated luminosity of 6
.
23 nb
−1
, collected using a minimum-bias trigger. Charm jets are identified by the presence of a D
0
meson among their constituents. The D
0
mesons are reconstructed from their hadronic decay D
0
→K
−
π
+
. The D
0
-meson tagged jets are reconstructed using tracks of charged particles (track-based jets) with the anti-
k
T
algorithm in the jet transverse momentum range
5
<
p
T
,
jet
ch
<
30 GeV
/c
and pseudorapidity |
η
jet
|
<
0
.
5. The fraction of charged jets containing a D
0
-meson increases with
p
T
,
jet
ch
from 0
.
042 ± 0
.
004 (stat) ± 0
.
006 (syst) to 0
.
080 ± 0
.
009 (stat) ± 0
.
008 (syst). The distribution of D
0
-meson tagged jets as a function of the jet momentum fraction carried by the D
0
meson in the direction of the jet axis
z
∥
ch
is reported for two ranges of jet transverse momenta,
5
<
p
T
,
jet
ch
<
15 GeV
/c
and
15
<
p
T
,
jet
ch
<
30 GeV
/c
in the intervals
0.2
<
z
‖
ch
<
1.0
and
0.4
<
z
‖
ch
<
1.0
, respectively. The data are compared with results from Monte Carlo event generators (PYTHIA 6, PYTHIA 8 and Herwig 7) and with a Next-to-Leading-Order perturbative Quantum Chromodynamics calculation, obtained with the POWHEG method and interfaced with PYTHIA 6 for the generation of the parton shower, fragmentation, hadronisation and underlying event.
The interaction of K– with protons is characterised by the presence of several coupled channels, systems like $\overline{K}$0 n and πΣ with a similar mass and the same quantum numbers as the K–p ...state. The strengths of these couplings to the K–p system are of crucial importance for the understanding of the nature of the Λ(1405) resonance and of the attractive K–p strong interaction. In this article, we present measurements of the K–p correlation functions in relative momentum space obtained in pp collisions at $\sqrt{s}$=13 Te, in p–Pb collisions at $\sqrt{s_{NN}}$= 5.02 Te, and (semi)peripheral Pb–Pb collisions at $\sqrt{s_{NN}}$= 5.02 Te. The emitting source size, composed of a core radius anchored to the K+p correlation and of a resonance halo specific to each particle pair, varies between 1 and 2 fm in these collision systems. The strength and the effects of the $\overline{K}$0n and πΣ inelastic channels on the measured K–p correlation function are investigated in the different colliding systems by comparing the data with state-of-the-art models of chiral potentials. A novel approach to determine the conversion weights ω, necessary to quantify the amount of produced inelastic channels in the correlation function, is presented. In this method, particle yields are estimated from thermal model predictions, and their kinematic distribution from blast-wave fits to measured data. The comparison of chiral potentials to the measured K–p interaction indicates that, while the πΣ –K–p dynamics is well reproduced by the model, the coupling to the $\overline{K}$0n channel in the model is currently underestimated.
A
bstract
The inclusive production of the
ψ
(2S) charmonium state was studied as a function of centrality in p-Pb collisions at the nucleon-nucleon center of mass energy
s
N
N
=
5.02
TeV at the CERN ...LHC. The measurement was performed with the ALICE detector in the center of mass rapidity ranges −4
.
46
< y
cms
<
−2
.
96 and 2
.
03
< y
cms
<
3
.
53, down to zero transverse momentum, by reconstructing the
ψ
(2S) decay to a muon pair. The
ψ
(2S) production cross section σ
ψ
(2S)
is presented as a function of the collision centrality, which is estimated through the energy deposited in forward rapidity calorimeters. The relative strength of nuclear effects on the
ψ
(2S) and on the corresponding 1S charmonium state J/
ψ
is then studied by means of the double ratio of cross sections σ
ψ
(2S)
/
σ
J/
ψ
pPb
/
σ
ψ
(2S)
/
σ
J/
ψ
pp
between p-Pb and pp collisions, and by the values of the nuclear modification factors for the two charmonium states. The results show a large suppression of
ψ
(2S) production relative to the J/
ψ
at backward (negative) rapidity, corresponding to the flight direction of the Pb-nucleus, while at forward (positive) rapidity the suppressions of the two states are comparable. Finally, comparisons to results from lower energy experiments and to available theoretical models are presented.
Measurements of the elliptic flow coefficient relative to the collision plane defined by the spectator neutrons v2 {$Ψ_{SP}$} in collisions of Pb ions at center-of-mass energy per nucleon–nucleon ...pair $\sqrt{s_{NN}}=$ 2.76 TeV and Xe ions at $\sqrt{s_{NN}}=$ 5.44 TeV are reported. The results are presented for charged particles produced at midrapidity as a function of centrality and transverse momentum for the 5–70% and 0.2–6 GeV/c ranges, respectively. The ratio between v2 {$Ψ_{SP}$} and the elliptic flow coefficient relative to the participant plane v2 {4}, estimated using four-particle correlations, deviates by up to 20% from unity depending on centrality. This observation differs strongly from the magnitude of the corresponding eccentricity ratios predicted by the TRENTo and the elliptic power models of initial state fluctuations that are tuned to describe the participant plane anisotropies. The differences can be interpreted as a decorrelation of the neutron spectator plane and the reaction plane because of fragmentation of the remnants from the colliding nuclei, which points to an incompleteness of current models describing the initial state fluctuations. A significant transverse momentum dependence of the ratio v2 {$Ψ_{SP}$} /v2 {4} is observed in all but the most central collisions, which may help to understand whether momentum anisotropies at low and intermediate transverse momentum have a common origin in initial state fluctuations. The ratios of v2 {$Ψ_{SP}$} and v2 {4} to the corresponding initial state eccentricities for Xe–Xe and Pb–Pb collisions at similar initial entropy density show a difference of (7.0 ± 0.9)% with an additional variation of +1.8% when including RHIC data in the TRENTo parameter extraction. These observations provide new experimental constraints for viscous effects in the hydrodynamic modeling of the expanding quark–gluon plasma produced in heavy-ion collisions at the LHC.
Measurements of event-by-event fluctuations of charged-particle multiplicities in Pb–Pb collisions at
s
NN
=
2.76 TeV using the ALICE detector at the CERN Large Hadron Collider (LHC) are presented ...in the pseudorapidity range
|
η
|
<
0.8
and transverse momentum
0.2
<
p
T
<
2.0
GeV/
c
. The amplitude of the fluctuations is expressed in terms of the variance normalized by the mean of the multiplicity distribution. The
η
and
p
T
dependences of the fluctuations and their evolution with respect to collision centrality are investigated. The multiplicity fluctuations tend to decrease from peripheral to central collisions. The results are compared to those obtained from HIJING and AMPT Monte Carlo event generators as well as to experimental data at lower collision energies. Additionally, the measured multiplicity fluctuations are discussed in the context of the isothermal compressibility of the high-density strongly-interacting system formed in central Pb–Pb collisions.
Two-particle angular correlations between unidentified charged trigger and associated particles are measured by the ALICE detector in p–Pb collisions at a nucleon–nucleon centre-of-mass energy of ...5.02 TeV. The transverse-momentum range 0.7<pT,assoc<pT,trig<5.0 GeV/c is examined, to include correlations induced by jets originating from low momentum-transfer scatterings (minijets). The correlations expressed as associated yield per trigger particle are obtained in the pseudorapidity range |η|<0.9. The near-side long-range pseudorapidity correlations observed in high-multiplicity p–Pb collisions are subtracted from both near-side short-range and away-side correlations in order to remove the non-jet-like components. The yields in the jet-like peaks are found to be invariant with event multiplicity with the exception of events with low multiplicity. This invariance is consistent with the particles being produced via the incoherent fragmentation of multiple parton–parton scatterings, while the yield related to the previously observed ridge structures is not jet-related. The number of uncorrelated sources of particle production is found to increase linearly with multiplicity, suggesting no saturation of the number of multi-parton interactions even in the highest multiplicity p–Pb collisions. Further, the number scales only in the intermediate multiplicity region with the number of binary nucleon–nucleon collisions estimated with a Glauber Monte-Carlo simulation.
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