The production of prompt D0, 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 $$ \sqrt{s_{\mathrm{NN}}} $$ 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 (pT) 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 D0 mesons was measured down to pT = 0, which allowed a model-independent determination of the pT-integrated yield per unit of rapidity (dN/dy). A maximum suppression by a factor 5 and 2.5 was observed with the nuclear modification factor (RAA) of prompt D mesons at pT = 6–8 GeV/c for the 0–10% and 30–50% centrality classes, respectively. The D-meson RAA 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 RAA, elliptic (v2) and triangular (v3) flow, and the model predictions allowed us to constrain the charm spatial diffusion coefficient Ds. Furthermore the comparison of RAA and v2 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 first measurement of the production of pions, kaons, (anti-)protons and $$\phi $$ ϕ mesons at midrapidity in Xe–Xe collisions at $$\sqrt{s_{\mathrm{NN}}} = 5.44~\text {TeV}$$ s NN = 5.44 TeV is presented. Transverse momentum ($$p_{\mathrm{T}}$$ p T ) spectra and $$p_{\mathrm{T}}$$ p T -integrated yields are extracted in several centrality intervals bridging from p–Pb to mid-central Pb–Pb collisions in terms of final-state multiplicity. The study of Xe–Xe and Pb–Pb collisions allows systems at similar charged-particle multiplicities but with different initial geometrical eccentricities to be investigated. A detailed comparison of the spectral shapes in the two systems reveals an opposite behaviour for radial and elliptic flow. In particular, this study shows that the radial flow does not depend on the colliding system when compared at similar charged-particle multiplicity. In terms of hadron chemistry, the previously observed smooth evolution of particle ratios with multiplicity from small to large collision systems is also found to hold in Xe–Xe. In addition, our results confirm that two remarkable features of particle production at LHC energies are also valid in the collision of medium-sized nuclei: the lower proton-to-pion ratio with respect to the thermal model expectations and the increase of the $$\phi $$ ϕ -to-pion ratio with increasing final-state multiplicity.
Proposed is a wide dynamic range CMOS image sensor (CIS) using the PD-storage dual capture (PDS-DC) method that can be applied to a 4-T active pixel sensor without any pixel modification. Dynamic range is increased by controlling the transfer gate during the integration time that is divided into two phases: long-exposure and short-exposure. The photon generated charges for both phases are stored in the photodiode (PD) while the excess charge is drained to VDD during the longexposure. This feature allows variable dynamic range adjustment by controlling the exposure time ratio and bias voltage that determines the well-capacity during the long-exposure. The prototype sensor is fabricated using 0.13 mm CIS process. The major advantage of the proposed PDS-DC is that it provides complete correlated double sampling. Measurement results demonstrate variable wide dynamic range feature. The effects of process variation are also presented.Introduction: The CMOS image sensor (CIS) is dominant in the image sensor market nowadays. However, the major drawback of the CIS is low dynamic range owing to low power supply voltage. The dynamic range of the CIS can be improved by circuit design technologies such as the logarithmic or linear-logarithmic pixel [1, 2] and multiple capture [3,4]. The logarithmic or linear-logarithmic pixel achieves a dynamic range of 100 dB or more by draining excess charge during the exposure through either an extra drain transistor, a transfer gate in the 4-transistor active pixel sensor (APS) or a biased reset transistor. However, they suffer from slow response, image lags, and high fixed pattern noise. The multiple-capture technique provides wide dynamic range without pixel modifications or a complex readout scheme. The major drawbacks of conventional multiple capture are multiple analogue-digital conversions (ADC), additional frame memories and image synthesis process either in the analogue or the digital domain. The floating diffusion (FD) storage dual-capture scheme is introduced in [4] to eliminate digital frame memories or an additional pixel storage capacitor by utilising FD as an in-pixel analogue storage. However, it has poor noise performance owing to incomplete correlated double sampling (CDS).In this Letter, we propose a dual capture scheme that uses the PD itself for charge storage and summation.
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