Processing and Interconnections of Finely Segmented Semiconductor Pixel Detectors for Applications in Particle Physics and Photon Detection

Radiation hardness is in the focus of the development of particle tracking and photon imaging detector installations. Semiconductor detectors, widely used in particle physics experiments, have turned into capacitive-coupled (AC-coupled) detectors from the originally developed conductively coupled (DC-coupled) detectors. This is due to the superior isolation of radiation-induced leakage current in AC-coupled detectors. However, some modern detector systems, such as the tracking detectors in the CERN LHC CMS or ATLAS experiments, are still DC-coupled. This originates from the difficulty of implementing AC coupling on very small pixel detector areas. In this report, we describe our advances in the detector processing technology. The first topic is the applications of the atomic layer deposition processing technology, which enables the very high densities of capacitance and resistance that are needed when the dimensions of the physical segmentation of pixel detectors need to be scaled down. The second topic is the flip-chip/bump-bonding interconnection technology, which is necessary in order to manufacture pixel detector modules on a large scale with a more than 99% yield of noise-free and faultless pixels and detector channels.Peer reviewe

Measurement of electrons from beauty-hadron decays in p-Pb collisions at √sNN=5.02 TeV and Pb-Pb collisions at √sNN=2.76 TeV

The production of beauty hadrons was measured via semi-leptonic decays at mid-rapidity with the ALICE detector at the LHC in the transverse momentum interval 1 <PT <8 GeV/c in minimum-bias p-Pb collisions at root(NN)-N-S = 5.02 TeV and in 1.3 <PT <8 GeV/c in the 20% most central Pb-Pb collisions at root(NN)-N-S = 2.76 TeV. The pp reference spectra at root s = 5.02 TeV and root s = 2.76 TeV, needed for the calculation of the nuclear modification factors RpPb and R-PbPb, were obtained by a pQCD-driven scaling of the cross section of electrons from beauty-hadron decays measured at root s = 7 TeV. In the PT interval 3 <PT <8 GeV/c, a suppression of the yield of electrons from beauty-hadron decays is observed in Pb-Pb compared to pp collisions. Towards lower PT, the R-PbPb values increase with large systematic uncertainties. The R-ppb is consistent with unity within systematic uncertainties and is well described by theoretical calculations that include cold nuclear matter effects in p-Pb collisions. The measured R-pPb and these calculations indicate that cold nuclear matter effects are small at high transverse momentum also in Pb-Pb collisions. Therefore, the observed reduction of R-PbPb below unity at high PT may be ascribed to an effect of the hot and dense medium formed in Pb-Pb collisions.Peer reviewe

Evolution of the longitudinal and azimuthal structure of the near-side jet peak in Pb-Pb collisions at root s(NN)=2.76 TeV

In two-particle angular correlation measurements, jets give rise to a near-side peak, formed by particles associated to a higher-p(T) trigger particle. Measurements of these correlations as a function of pseudorapidity (Delta eta) and azimuthal (Delta phi) differences are used to extract the centrality and p(T) dependence of the shape of the near-side peak in the p(T) range 1 <p(T) <8 GeV/c in Pb-Pb and pp collisions at root s(NN) = 2.76 TeV. A combined fit of the near-side peak and long-range correlations is applied to the data and the peak shape is quantified by the variance of the distributions. While the width of the peak in the Delta phi direction is almost independent of centrality, a significant broadening in the Delta eta direction is found from peripheral to central collisions. This feature is prominent for the low-p(T) region and vanishes above 4 GeV/c. The widths measured in peripheral collisions are equal to those in pp collisions in the Delta phi direction and above 3 GeV/c in the Delta eta direction. Furthermore, for the 10% most central collisions and 1 <p(T, assoc) <2 GeV/c, 1 <p(T,trig) <3 GeV/c, a departure from a Gaussian shape is found: a depletion develops around the center of the peak. The results are compared to A Multi-Phase Transport (AMPT) model simulation as well as other theoretical calculations indicating that the broadening and the development of the depletion are connected to the strength of radial and longitudinal flow.Peer reviewe

W and Z boson production in p-Pb collisions at TeV root s(NN)=5.02 TeV

The W and Z boson production was measured via the muonic decay channel in proton-lead collisions at root s(NN) = 5.02 TeV at the Large Hadron Collider with the ALICE detector. The measurement covers backward (4.46 10 GeV/c are determined. The results are compared to theoretical calculations both with and without including the nuclear modification of the parton distribution functions. The W-boson production is also studied as a function of the collision centrality: the cross section of muons from W-boson decays is found to scale with the average number of binary nucleon-nucleon collisions within uncertainties.Peer reviewe

Production of pi(0) and eta mesons up to high transverse momentum in pp collisions at 2.76 TeV

Correction: DOI:10.1140/epjc/s10052-017-5144-7The invariant differential cross sections for inclusive pi(0) and eta mesons at midrapidity were measured in pp collisions at root s = 2.76 TeV for transverse momenta 0.4 <pT <40 GeV/c and 0.6 <pT <20 GeV/c, respectively, using the ALICE detector. This large range in pT was achieved by combining various analysis techniques and different triggers involving the electromagnetic calorimeter (EMCal). In particular, a newsingle-cluster, shower-shape based method was developed for the identification of high-pT neutral pions, which exploits that the showers originating from their decay photons overlap in the EMCal. Above 4 GeV/c, the measured cross sections are found to exhibit a similar power-law behavior with an exponent of about 6.3. Next-to-leading-order perturbative QCD calculations differ from the measured cross sections by about 30% for the pi(0), and between 30-50% for the. meson, while generator-level simulations with PYTHIA 8.2 describe the data to better than 10-30%, except at pT <1 GeV/c. The new data can therefore be used to further improve the theoretical description of pi(0) and eta meson production.Peer reviewe

Two-pion femtoscopy in p-Pb collisions at root(NN)-N-S=5.02 TeV

We report the results of the femtoscopic analysis of pairs of identical pions measured in p-Pb collisions at root(NN)-N-S = 5.02 TeV. Femtoscopic radii are determined as a function of event multiplicity and pair momentum in three spatial dimensions. As in the pp collision system, the analysis is complicated by the presence of sizable background correlation structures in addition to the femtoscopic signal. The radii increase with event multiplicity and decrease with pair transverse momentum. When taken at comparable multiplicity, the radii measured in p-Pb collisions, at high multiplicity and low pair transverse momentum, are 10%-20% higher than those observed in pp collisions but below those observed in A-A collisions. The results are compared to hydrodynamic predictions at large event multiplicity as well as discussed in the context of calculations based on gluon saturation.Peer reviewe

K*(892)(0) and phi(1020)meson production at high transverse momentum in pp and Pb-Pb collisions at root sNN=2.76 TeV

The production of K*(892)(0) and phi(1020) mesons in proton-proton (pp) and lead-lead (Pb-Pb) collisions at root sNN = 2.76 TeV has been analyzed using a high luminosity data sample accumulated in 2011 with the ALICE detector at the Large Hadron Collider (LHC). Transverse momentum (p(T)) spectra have been measured for K*(892)(0) and phi(1020) mesons via their hadronic decay channels for p(T) up to 20 GeV/c. The measurements in pp collisions have been compared to model calculations and used to determine the nuclear modification factor and particle ratios. The K*(892)(0)/K ratio exhibits significant reduction from pp to central Pb-Pb collisions, consistent with the suppression of the K*( 892)(0) yield at low pT due to rescattering of its decay products in the hadronic phase. In central Pb-Pb collisions the pT dependent phi(1020)/p and K*(892)0/p ratios show an enhancement over pp collisions for pT approximate to 3 GeV/c, consistent with previous observations of strong radial flow. At high pT, particle ratios in Pb-Pb collisions are similar to those measured in pp collisions. In central Pb-Pb collisions, the production of K*(892)(0) and phi(1020) mesons is suppressed for p(T) > 8 GeV/c. This suppression is similar to that of charged pions, kaons, and protons, indicating that the suppression does not depend on particle mass or flavor in the light quark sector.Peer reviewe

Inclusive J/psi production at mid-rapidity in pp collisions at root s=5.02 TeV

Inclusive J/psi production is studied in minimum-bias proton-proton collisions at a centre-of-mass energy of root s = 5.02 TeV by ALICE at the CERN LHC. The measurement is performed at mid-rapidity (vertical bar y vertical bar and are extracted and compared with results obtained at other collision energies.Peer reviewe

Insight into particle production mechanisms via angular correlations of identified particles in pp collisions at root s=7 TeV

This article has an erratum: Doi: 10.1140/epjc/s10052-019-7398-8Two-particle angular correlations were measured in pp collisions at root s = 7 TeV for pions, kaons, protons, and lambdas, for all particle/anti-particle combinations in the pair. Data for mesons exhibit an expected peak dominated by effects associated with mini-jets and are well reproduced by general purpose Monte Carlo generators. However, for baryon-baryon and anti-baryon-anti-baryon pairs, where both particles have the same baryon number, a near-side anti-correlation structure is observed instead of a peak. This effect is interpreted in the context of baryon production mechanisms in the fragmentation process. It currently presents a challenge to Monte Carlo models and its origin remains an open question.Peer reviewe

Centrality dependence of the pseudorapidity density distribution for charged particles in Pb-Pb collisions at root s(NN)=5.02 TeV

We present the charged-particle pseudorapidity density in Pb-Pb collisions at root s(NN) = 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 21 400 +/- 1 300, while for the most peripheral (80-90%) we find 230 +/- 38. This corresponds to an increase of (27 +/- 4)% over the results at root s(NN) = 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. (C) 2017 The Author(s). Published by Elsevier B.V.Peer reviewe