Invariant differential yields of deuterons and antideuterons in pp collisions at √ s = 0.9, 2.76 and 7 TeV and the yields of tritons, 3He nuclei, and their antinuclei at √ s = 7 TeV have been ...measured with the ALICE detector at the CERN Large Hadron Collider. The measurements cover a wide transverse momentum ( p T ) range in the rapidity interval |y|<0.5 , extending both the energy and the pT reach of previous measurements up to 3 GeV/ c for A=2 and 6 GeV/ c for A=3. The coalescence parameters of (anti)deuterons and 3¯¯¯¯ He nuclei exhibit an increasing trend with pT and are found to be compatible with measurements in pA collisions at low pT and lower energies. The integrated yields decrease by a factor of about 1000 for each increase of the mass number with one (anti)nucleon. Furthermore, the deuteron-to-proton ratio is reported as a function of the average charged particle multiplicity at different center-of-mass energies.
The production of the ρ(770)0 meson has been measured at midrapidity (|y|<0.5) in pp and centrality differential Pb-Pb collisions at √sNN= 2.76 TeV with the ALICE detector at the Large Hadron ...Collider. The particles have been reconstructed in the ρ(770)0→π+π− decay channel in the transverse-momentum (pT) range 0.5–11 GeV/c. A centrality-dependent suppression of the ratio of the integrated yields 2ρ(770)0/(π++π−) is observed. The ratio decreases by ∼40% from pp to central Pb-Pb collisions. A study of the pT-differential 2ρ(770)0/(π++π−) ratio reveals that the suppression occurs at low transverse momenta, pT<2 GeV/c. At higher momentum, particle ratios measured in heavy-ion and pp collisions are consistent. The observed suppression is very similar to that previously measured for the K∗(892)0/K ratio and is consistent with EPOS3 predictions that may imply that rescattering in the hadronic phase is a dominant mechanism for the observed suppression.
The production of K∗(892)0 and ϕ(1020) mesons in proton–proton (pp) and lead–lead (Pb–Pb) collisions at √sNN = 5.02 TeV has been measured using the ALICE detector at the Large Hadron Collider (LHC). ...The transverse momentum (pT) distributions of K∗(892)0 and ϕ(1020) mesons have been measured at midrapidity (|y|<0.5) up to pT= 20 GeV/c in inelastic pp collisions and for several Pb–Pb collision centralities. The collision centrality and collision energy dependence of the average transverse momenta agree with the radial flow scenario observed with stable hadrons, showing that the effect is stronger for more central collisions and higher collision energies. The K*0/K ratio is found to be suppressed in Pb–Pb collisions relative to pp collisions: this indicates a loss of the measured K∗(892)0 signal due to rescattering of its decay products in the hadronic phase. In contrast, for the longer-lived ϕ(1020) mesons, no such suppression is observed. The nuclear modification factors (RAA) of K∗(892)0 and ϕ(1020) mesons are calculated using pp reference spectra at the same collision energy. In central Pb–Pb collisions for pT > 8 GeV/c, the RAA values of K∗(892)0 and ϕ(1020) are below unity and observed to be similar to those of pions, kaons, and (anti)protons. The RAA values at high pT (>8 GeV/c) for K∗(892)0 and ϕ(1020) mesons are in agreement within uncertainties for √sNN= 5.02 and 2.76 TeV.
Neutral pion and
η
meson invariant differential yields were measured in non-single diffractive p–Pb collisions at
s
NN
= 5.02 TeV with the ALICE experiment at the CERN LHC. The analysis combines ...results from three complementary photon measurements, utilizing the PHOS and EMCal calorimeters and the Photon Conversion Method. The invariant differential yields of
π
0
and
η
meson inclusive production are measured near mid-rapidity in a broad transverse momentum range of
0.3
<
p
T
<
20
GeV
/
c
and
0.7
<
p
T
<
20
GeV
/
c
, respectively. The measured
η
/
π
0
ratio increases with
p
T
and saturates for
p
T
> 4
GeV
/
c
at
0.483
±
0
.
015
stat
±
0
.
015
sys
. A deviation from
m
T
scaling is observed for
p
T
<
2
GeV
/
c
. The measured
η
/
π
0
ratio is consistent with previous measurements from proton-nucleus and pp collisions over the full
p
T
range. The measured
η
/
π
0
ratio at high
p
T
also agrees within uncertainties with measurements from nucleus–nucleus collisions. The
π
0
and
η
yields in p–Pb relative to the scaled pp interpolated reference,
R
pPb
, are presented for
0.3
<
p
T
<
20
GeV
/
c
and
0.7
<
p
T
<
20
GeV
/
c
, respectively. The results are compared with theoretical model calculations. The values of
R
pPb
are consistent with unity for transverse momenta above 2
GeV
/
c
. These results support the interpretation that the suppressed yield of neutral mesons measured in Pb–Pb collisions at LHC energies is due to parton energy loss in the hot QCD medium.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The PANDA spectrometer will be built at the FAIR facility at Darmstadt (Germany) to perform accurate tests of the strong interaction through pp and pA annihilation studies. The charged particle ...tracking at PANDA will be done using both solid state and gaseous detectors. Among the latter, two straw tube detector systems will be built 1, The cylindrical, central straw tube tracker features a high spatial and momentum resolution for a wide range of particle momenta from about 8 GeV/c down to a few 100 MeV/c, together with particle identification in the momentum region below about 1 GeV/c by measuring the specific energy-loss, A new technique, based on self-supporting straw double layers with intrinsic wire tension developed for the COSY-TOF straw tracker 2, has been adopted for the PANDA trackers. The development of the readout electronics for the straw tubes is ongoing. Prototypes have been produced and used to instrument straw tube modules that have been tested with cosmic rays and proton beams. Design issues of the PANDA straw tubes, together with the results of the prototype tests are presented.
The correlations between event-by-event fluctuations of anisotropic flow harmonic amplitudes have been measured in Pb-Pb collisions at √sNN=2.76 TeV with the ALICE detector at the Large Hadron ...Collider. The results are reported in terms of multiparticle correlation observables dubbed symmetric cumulants. These observables are robust against biases originating from nonflow effects. The centrality dependence of correlations between the higher order harmonics (the quadrangular v4 and pentagonal v5 flow) and the lower order harmonics (the elliptic v2 and triangular v3 flow) is presented. The transverse momentum dependences of correlations between v3 and v2 and between v4 and v2 are also reported. The results are compared to calculations from viscous hydrodynamics and a multiphase transport (AMPT) model calculations. The comparisons to viscous hydrodynamic models demonstrate that the different order harmonic correlations respond differently to the initial conditions and the temperature dependence of the ratio of shear viscosity to entropy density (η/s). A small average value of η/s is favored independent of the specific choice of initial conditions in the models. The calculations with the AMPT initial conditions yield results closest to the measurements. Correlations among the magnitudes of v2, v3, and v4 show moderate pT dependence in midcentral collisions. This might be an indication of possible viscous corrections to the equilibrium distribution at hadronic freeze-out, which might help to understand the possible contribution of bulk viscosity in the hadronic phase of the system. Together with existing measurements of individual flow harmonics, the presented results provide further constraints on the initial conditions and the transport properties of the system produced in heavy-ion collisions.
Angular correlations between heavy-flavor decay electrons and charged particles at midrapidity (|η| < 0.8) are measured in p-Pb collisions at √sNN = 5.02 TeV. The analysis is carried out for the ...0%–20% (high) and 60%–100% (low) multiplicity ranges. The jet contribution in the correlation distribution from high-multiplicity events is removed by subtracting the distribution from low-multiplicity events. An azimuthal modulation remains after removing the jet contribution, similar to previous observations in two-particle angular correlation measurements for light-flavor hadrons. A Fourier decomposition of the modulation results in a positive second-order coefficient (v2) for heavy-flavor decay electrons in the transverse momentum interval 1.5 < p T < 4 GeV/c in high-multiplicity events, with a significance larger than 5σ. The results are compared with those of charged particles at midrapidity and those of inclusive muons at forward rapidity. The v2 measurement of open heavy-flavor particles at midrapidity in small collision systems could provide crucial information to help interpret the anisotropies observed in such systems.
A
bstract
Systematic studies of charge-dependent two- and three-particle correlations in Pb-Pb collisions at
s
NN
= 2.76 and 5.02 TeV used to probe the Chiral Magnetic Effect (CME) are presented. ...These measurements are performed for charged particles in the pseudorapidity (
η
) and transverse momentum (
p
T
) ranges |
η
|
<
0
.
8 and 0
.
2
< p
T
<
5 GeV/
c
. A significant charge-dependent signal that becomes more pronounced for peripheral collisions is reported for the CME-sensitive correlators
γ
1, 1
= 〈cos(
φ
α
+
φ
β
− 2Ψ
2
)〉 and
γ
1, − 3
= 〈cos(
φ
α
− 3
φ
β
+ 2Ψ
2
)〉. The results are used to estimate the contribution of background effects, associated with local charge conservation coupled to anisotropic flow modulations, to measurements of the CME. A blast-wave parametrisation that incorporates local charge conservation tuned to reproduce the centrality dependent background effects is not able to fully describe the measured
γ
1
,
1
. Finally, the charge and centrality dependence of mixed-harmonics three-particle correlations, of the form
γ
1, 2
= 〈cos(
φ
α
+ 2
φ
β
− 3Ψ
3
)〉, which are insensitive to the CME signal, verify again that background contributions dominate the measurement of
γ
1
,
1
.
The most precise measurements to date of the $^{3}_{Λ}$H lifetime τ and Λ separation energy BΛ are obtained using the data sample of Pb–Pb collisions at $\sqrt{s_{NN}}$ = 5.02 TeV collected by ALICE ...at the LHC. The $^{3}_{Λ}$H is reconstructed via its charged two-body mesonic decay channel ($^{3}_{Λ}$H → 3He + π– and the charge-conjugate process). The measured values τ = 253 ± 11 (stat.) ± 6(syst.) ps and BΛ = 102 ± 63 (stat.) ± 67 (syst.) keV are compatible with predictions from effective field theories and confirm that the $^{3}_{Λ}$H structure is consistent with a weakly-bound system.
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