Precision measurement of the mass difference between light nuclei and anti-nuclei with the ALICE experiment at the LHC

Con questo lavoro è stata effettuata una misura della differenza $\Delta \mu = \Delta (m / |z|)$ fra il rapporto massa su carica del deutone (d) e dell'anti-deutone (${\rm \overline{d}}$), e del nucleo di ${\rm ^{3}He}$ e di anti-${\rm ^{3}He}$ con l'esperimento ALICE ad LHC in collisioni Pb--Pb a un'energia nel centro di massa per coppia di nucleoni $\sqrt{s_{\rm NN}}=2.76~{\rm TeV}$. Le misure sono pari a ${\Delta \mu}_{\rm{d\bar{d}}}/{\mu}_{\rm{d}} = [0.9 \pm 0.5 (\rm{stat.}) \pm 1.4 (\rm{syst.})] \times 10^{-4}$ e ${\Delta \mu}_{\rm{^{3}He ^{3}\overline{He}}}/{\mu}_{\rm{^{3}He}} = [-1.2 \pm 0.9 (\rm{stat.}) \pm 1.0 (\rm{syst.})] \times 10^{-3}$. Combinando questi risultati con le misure esistenti delle masse dei (anti-)nucleoni, sono state estratte le corrispondenti differenze di energia di legame ${\Delta \varepsilon}_{\rm{d\bar{d}}}/{\varepsilon}_{\rm{d}} = -0.04 \pm 0.05(\rm{stat.}) \pm 0.12(\rm{syst.})$ e ${\Delta \varepsilon}_{\rm{^{3}He ^{3}\overline{He}}}/{\varepsilon}_{\rm{^{3}He}} = 0.24 \pm 0.16(\rm{stat.}) \pm 0.18(\rm{syst.})$. I risultati verificano, con una precisione senza precedenti, l'invarianza CPT nel settore dei nuclei leggeri.With this work a measurement of the difference $\Delta \mu = \Delta (m / |z|)$ between the mass-over-charge ratio of deuteron (d) and anti-deuteron (${\rm \overline{d}}$), and ${\rm ^{3}He}$ and ${\rm ^{3}\overline{He}}$ nuclei, carried out with the ALICE experiment in Pb--Pb collisions at a centre-of-mass energy per nucleon pair $\sqrt{s_{\rm NN}}=~2.76~\rm{TeV}$ has been performed. The measurement yields ${\Delta \mu}_{\rm{d\bar{d}}}/{\mu}_{\rm{d}} = [0.9 \pm 0.5 (\rm{stat.}) \pm 1.4 (\rm{syst.})] \times 10^{-4}$ and ${\Delta \mu}_{\rm{^{3}He ^{3}\overline{He}}}/{\mu}_{\rm{^{3}He}} = [-1.2 \pm 0.9 (\rm{stat.}) \pm 1.0 (\rm{syst.})] \times 10^{-3}$. Combining these results with existing measurements of the masses of the (anti-)nucleons, the relative binding energy differences are extracted, ${\Delta \varepsilon}_{\rm{d\bar{d}}}/{\varepsilon}_{\rm{d}} = -0.04 \pm 0.05(\rm{stat.}) \pm 0.12(\rm{syst.})$ and ${\Delta \varepsilon}_{\rm{^{3}He ^{3}\overline{He}}}/{\varepsilon}_{\rm{^{3}He}} = 0.24 \pm 0.16(\rm{stat.}) \pm 0.18(\rm{syst.})$. These results test, to an unprecedented precision, the CPT invariance in the sector of light nuclei

Characterisation of analogue Monolithic Active Pixel Sensor test structures implemented in a 65 nm CMOS imaging process

Analogue test structures were fabricated using the Tower Partners Semiconductor Co. CMOS 65 nm ISC process. The purpose was to characterise and qualify this process and to optimise the sensor for the next generation of Monolithic Active Pixels Sensors for high-energy physics. The technology was explored in several variants which differed by: doping levels, pixel geometries and pixel pitches (10-25 $\mu$m). These variants have been tested following exposure to varying levels of irradiation up to 3 MGy and $10^{16}$ 1 MeV n$_\text{eq}$ cm$^{-2}$. Here the results from prototypes that feature direct analogue output of a 4$\times$4 pixel matrix are reported, allowing the systematic and detailed study of charge collection properties. Measurements were taken both using $^{55}$Fe X-ray sources and in beam tests using minimum ionizing particles. The results not only demonstrate the feasibility of using this technology for particle detection but also serve as a reference for future applications and optimisations

Azimuthal anisotropy of charged jet production in root s(NN)=2.76 TeV Pb-Pb collisions

We present measurements of the azimuthal dependence of charged jet production in central and semi-central root s(NN) = 2.76 TeV Pb-Pb collisions with respect to the second harmonic event plane, quantified as nu(ch)(2) (jet). Jet finding is performed employing the anti-k(T) algorithm with a resolution parameter R = 0.2 using charged tracks from the ALICE tracking system. The contribution of the azimuthal anisotropy of the underlying event is taken into account event-by-event. The remaining (statistical) region-to-region fluctuations are removed on an ensemble basis by unfolding the jet spectra for different event plane orientations independently. Significant non-zero nu(ch)(2) (jet) is observed in semi-central collisions (30-50% centrality) for 20 <p(T)(ch) (jet) <90 GeV/c. The azimuthal dependence of the charged jet production is similar to the dependence observed for jets comprising both charged and neutral fragments, and compatible with measurements of the nu(2) of single charged particles at high p(T). Good agreement between the data and predictions from JEWEL, an event generator simulating parton shower evolution in the presence of a dense QCD medium, is found in semi-central collisions. (C) 2015 CERN for the benefit of the ALICE Collaboration. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).Peer reviewe

Forward-central two-particle correlations in p-Pb collisions at root s(NN)=5.02 TeV

Two-particle angular correlations between trigger particles in the forward pseudorapidity range (2.5 2GeV/c. (C) 2015 CERN for the benefit of the ALICE Collaboration. Published by Elsevier B. V.Peer reviewe

Event-shape engineering for inclusive spectra and elliptic flow in Pb-Pb collisions at root(NN)-N-S=2.76 TeV

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Production of He-4 and (4) in Pb-Pb collisions at root(NN)-N-S=2.76 TeV at the LHC

Results on the production of He-4 and (4) nuclei in Pb-Pb collisions at root(NN)-N-S = 2.76 TeV in the rapidity range vertical bar y vertical bar <1, using the ALICE detector, are presented in this paper. The rapidity densities corresponding to 0-10% central events are found to be dN/dy4(He) = (0.8 +/- 0.4 (stat) +/- 0.3 (syst)) x 10(-6) and dN/dy4 = (1.1 +/- 0.4 (stat) +/- 0.2 (syst)) x 10(-6), respectively. This is in agreement with the statistical thermal model expectation assuming the same chemical freeze-out temperature (T-chem = 156 MeV) as for light hadrons. The measured ratio of (4)/He-4 is 1.4 +/- 0.8 (stat) +/- 0.5 (syst). (C) 2018 Published by Elsevier B.V.Peer reviewe

Elliptic flow of muons from heavy-flavour hadron decays at forward rapidity in Pb-Pb collisions at root s(NN)=2.76TeV

The elliptic flow, v(2), of muons from heavy-flavour hadron decays at forward rapidity (2.5 <y <4) is measured in Pb-Pb collisions at root s(NN)= 2.76TeVwith the ALICE detector at the LHC. The scalar product, two- and four-particle Q cumulants and Lee-Yang zeros methods are used. The dependence of the v(2) of muons from heavy-flavour hadron decays on the collision centrality, in the range 0-40%, and on transverse momentum, p(T), is studied in the interval 3 <p(T)<10 GeV/c. A positive v(2) is observed with the scalar product and two-particle Q cumulants in semi-central collisions (10-20% and 20-40% centrality classes) for the p(T) interval from 3 to about 5GeV/c with a significance larger than 3 sigma, based on the combination of statistical and systematic uncertainties. The v(2) magnitude tends to decrease towards more central collisions and with increasing pT. It becomes compatible with zero in the interval 6 <p(T)<10 GeV/c. The results are compared to models describing the interaction of heavy quarks and open heavy-flavour hadrons with the high-density medium formed in high-energy heavy-ion collisions. (C) 2015 CERN for the benefit of the ALICE Collaboration. Published by Elsevier B.V.Peer reviewe

Pseudorapidity and transverse-momentum distributions of charged particles in proton-proton collisions at root s=13 TeV

The pseudorapidity (eta) and transverse-momentum (p(T)) distributions of charged particles produced in proton-proton collisions are measured at the centre-of-mass energy root s = 13 TeV. The pseudorapidity distribution in vertical bar eta vertical bar <1.8 is reported for inelastic events and for events with at least one charged particle in vertical bar eta vertical bar <1. The pseudorapidity density of charged particles produced in the pseudorapidity region vertical bar eta vertical bar <0.5 is 5.31 +/- 0.18 and 6.46 +/- 0.19 for the two event classes, respectively. The transverse-momentum distribution of charged particles is measured in the range 0.15 <p(T) <20 GeV/c and vertical bar eta vertical bar <0.8 for events with at least one charged particle in vertical bar eta vertical bar <1. The evolution of the transverse momentum spectra of charged particles is also investigated as a function of event multiplicity. The results are compared with calculations from PYTHIA and EPOS Monte Carlo generators. (C) 2015 CERN for the benefit of the ALICE Collaboration. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).Peer reviewe

Centrality evolution of the charged-particle pseudorapidity density over a broad pseudorapidity range in Pb-Pb collisions at root s(NN)=2.76TeV

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