A low-noise CMOS pixel direct charge sensor, Topmetal-II

We report the design and characterization of a CMOS pixel direct charge sensor, Topmetal-II-, fabricated in a standard 0.35um CMOS Integrated Circuit process. The sensor utilizes exposed metal patches on top of each pixel to directly collect charge. Each pixel contains a low-noise charge-sensitive preamplifier to establish the analog signal and a discriminator with tunable threshold to generate hits. The analog signal from each pixel is accessible through time-shared multiplexing over the entire array. Hits are read out digitally through a column-based priority logic structure. Tests show that the sensor achieved a <15e- analog noise and a 200e- minimum threshold for digital readout per pixel. The sensor is capable of detecting both electrons and ions drifting in gas. These characteristics enable its use as the charge readout device in future Time Projection Chambers without gaseous gain mechanism, which has unique advantages in low background and low rate-density experiments

Measuring KS0K± interactions using Pb–Pb collisions at √sNN=2.76 TeV

We present the first ever measurements of femtoscopic correlations between the K0 S and K± particles. The analysis was performed on the data from Pb–Pb collisions at √sNN = 2.76 TeV measured by the ALICE experiment. The observed femtoscopic correlations are consistent with final-state interactions proceeding via the a0(980) resonance. The extracted kaon source radius and correlation strength parameters for K0 SK− are found to be equal within the experimental uncertainties to those for K0 SK+. Comparing the results of the present study with those from published identical-kaon femtoscopic studies by ALICE, mass and coupling parameters for the a0 resonance are tested. Our results are also compatible with the interpretation of the a0 having a tetraquark structure instead of that of a diquar

Measurement of D-meson production at mid-rapidity in pp collisions at s=7{\sqrt{s}=7} TeV

The production cross sections for prompt charmed mesons $\mathrm{D^0}$ , $\mathrm{D^+}$ , $\mathrm{D^{*+}}$ and $\mathrm{D_s^+}$ were measured at mid-rapidity in proton–proton collisions at a centre-of-mass energy $\sqrt{s}=7~{\mathrm {TeV}}$ with the ALICE detector at the Large Hadron Collider (LHC). D mesons were reconstructed from their decays $\mathrm{D}^0 \rightarrow \mathrm{K}^-\pi ^+$ , $\mathrm{D}^+\rightarrow \mathrm{K}^-\pi ^+\pi ^+$ , $\mathrm{D}^{*+} \rightarrow \mathrm{D}^0 \pi ^+$ , $\mathrm{D_s^{+}\rightarrow \phi \pi ^+\rightarrow K^-K^+\pi ^+}$ , and their charge conjugates.With respect to previous measurements in the same rapidity region, the coverage in transverse momentum ( $p_\mathrm{T}$ ) is extended and the uncertainties are reduced by a factor of about two. The accuracy on the estimated total $\mathrm{c}{\overline{\mathrm{c}}}$ production cross section is likewise improved. The measured $p_\mathrm{T}$ -differential cross sections are compared with the results of three perturbative QCD calculations

Centrality dependence of the pseudorapidity density distribution for charged particles in Pb-Pb collisions at sNN=5.02\sqrt{s_{\rm NN}}=5.02 TeV

We present the charged-particle pseudorapidity density in Pb–Pb collisions at sNN=5.02 TeV in centrality classes measured by ALICE. The measurement covers a wide pseudorapidity range from −3.5 to 5, which is sufficient for reliable estimates of the total number of charged particles produced in the collisions. For the most central (0–5%) collisions we find 21400±1300 , while for the most peripheral (80–90%) we find 230±38 . This corresponds to an increase of (27±4)% over the results at sNN=2.76 TeV previously reported by ALICE. The energy dependence of the total number of charged particles produced in heavy-ion collisions is found to obey a modified power-law like behaviour. The charged-particle pseudorapidity density of the most central collisions is compared to model calculations — none of which fully describes the measured distribution. We also present an estimate of the rapidity density of charged particles. The width of that distribution is found to exhibit a remarkable proportionality to the beam rapidity, independent of the collision energy from the top SPS to LHC energies

First measurement of jet mass in Pb-Pb and p-Pb collisions at the LHC

This letter presents the first measurement of jet mass in Pb–Pb and p–Pb collisions at sNN=2.76 TeV and sNN=5.02 TeV, respectively. Both the jet energy and the jet mass are expected to be sensitive to jet quenching in the hot Quantum Chromodynamics (QCD) matter created in nuclear collisions at collider energies. Jets are reconstructed from charged particles using the anti- kT jet algorithm and resolution parameter R=0.4 . The jets are measured in the pseudorapidity range |ηjet|<0.5 and in three intervals of transverse momentum between 60 GeV/ c and 120 GeV/ c . The measurement of the jet mass in central Pb–Pb collisions is compared to the jet mass as measured in p–Pb reference collisions, to vacuum event generators, and to models including jet quenching. It is observed that the jet mass in central Pb–Pb collisions is consistent within uncertainties with p–Pb reference measurements. Furthermore, the measured jet mass in Pb–Pb collisions is not reproduced by the quenching models considered in this letter and is found to be consistent with PYTHIA expectations within systematic uncertainties.This letter presents the first measurement of jet mass in Pb-Pb and p-Pb collisions at $\sqrt{s_{\rm NN}}$ = 2.76 TeV and 5.02 TeV, respectively. Both the jet energy and the jet mass are expected to be sensitive to jet quenching in the hot Quantum Chromodynamics (QCD) matter created in nuclear collisions at collider energies. Jets are reconstructed from charged particles using the anti-$k_{\rm T}$ jet algorithm and resolution parameter $R = 0.4$. The jets are measured in the pseudorapidity range $|\eta_{\rm{jet}}|<0.5$ and in three intervals of transverse momentum between 60 GeV/$c$ and 120 GeV/$c$. The measurement of the jet mass in central Pb-Pb collisions is compared to the jet mass as measured in p-Pb reference collisions, to vacuum event generators, and to models including jet quenching. It is observed that the jet mass in central Pb-Pb collisions is consistent within uncertainties with p-Pb reference measurements. Furthermore, the measured jet mass in Pb-Pb collisions is not reproduced by the quenching models considered in this letter and is found to be consistent with PYTHIA expectations within systematic uncertainties

Energy dependence of forward-rapidity J/ψ and ψ(2S) production in pp collisions at the LHC

We present results on transverse momentum (pT) and rapidity (y) differential production cross sections, mean transverse momentum and mean transverse momentum square of inclusive J/ψ and ψ(2S) at forward rapidity (2.5 15 GeV/c the non-prompt contribution reaches up to 50% of the total charmonium yield