ALICE is the heavy-ion experiment at the CERN Large Hadron Collider. The experiment continuously took data during the first physics campaign of the machine from fall 2009 until early 2013, using proton and lead-ion beams. In this paper we describe the running environment and the data handling procedures, and discuss the performance of the ALICE detectors and analysis methods for various physics observables.

/pdf/performance-of-the-alice-experiment-at-the-cern-lhc-3v531yoy85.pdf

Performance of the ALICE experiment at the CERN LHC

Results are presented on hyperon and antihyperon production in Pb–Pb, pPb and pBe collisions at 158 GeV/c per nucleon. Λ, Ξ and Ω yields have been measured at central rapidity and medium transverse momentum as functions of the centrality of the collision. Comparing the yields in Pb–Pb to those in pBe interactions, strangeness enhancement is observed. The enhancement increases with the centrality and with the strangeness content of the hyperons, reaching a factor of about 20 for the Ω in the central Pb–Pb collisions.

Enhancement of hyperon production at central rapidity in 158-A-GeV/c Pb-Pb collisions

The innovation in monolithic and hybrid semiconductor ‘micropattern’ or ‘reactive’ pixel detectors for tracking in particle physics was actually to fit logic and pulse processing electronics with μW power on a pixel area of less than 0.04 mm 2 , retaining the characteristics of a traditional nuclear amplifier chain. The ns timing precision in conjunction with local memory and logic operations allowed event selection at >10 MHz rates with unambiguous track reconstruction even at particle multiplicities >10 cm −2 . The noise in a channel was ∼100 e − rms and enabled binary operation with random noise ‘hits’ at a level 75 μm ×500 μm down to 34 μm ×125 μm have been used by different teams. In binary mode a tracking precision from 6 to 14 μm was obtained, and using analog interpolation one came close to 1 μm . Earlier work, still based on charge integrating imaging circuits, provided a starting point. Two systems each with more than 1 million sensor + readout channels have been built, for WA97-NA57 and for the Delphi very forward tracker. The use of 0.5 μm and 0.25 μm CMOS and enclosed geometry for the transistors in the pixel readout chips resulted in radiation hardness of ∼2 Mrad , respectively, >30 Mrad .

Semiconductor micropattern pixel detectors: a review of the beginnings

Autoradiography is a widely used technique for imaging trace quantities of radioactivity within biological samples, conventionally using photographic film. This method produces images with high spatial resolution, but it suffers from very low sensitivity and poor dynamic range. Digital autoradiography systems with greatly improved sensitivity and linearity are commercially available, but the spatial resolution is usually much less than that achieved using film. We report here the design, construction and characterization of a novel digital autoradiography system based on scientific-grade charged coupled devices (CCDs). Images of x-ray and β emissions from radionuclides commonly used in autoradiography show that the system can perform high-speed quantitative imaging with a spatial resolution of ~30 µm. Using a frame by frame acquisition method the dynamic range is shown to be at least three orders of magnitude. The absolute detection efficiency is comparable to the best of the currently available digital systems. CCD images of 125I and 14C radioisotope distributions in tissue samples are superior to the equivalent film images and have been acquired in 1-10% of the time.

http://iopscience.iop.org/article/10.1088/0031-9155/45/7/322/pdf

The performance of a CCD digital autoradiography imaging system.

In this paper, we describe the circuit we propose for pixel applications. In particular, we present the different parts of the analog cell, which includes a charge pre-amplifier using PJFET, bipolar and MOS transistors. The pre-amplifier incorporates a new DC feedback circuit which eases tunability, enhances stability and makes the pre-amplifier less sensitive to leakage current. The first stage is followed by a low offset bipolar-based comparator, in which special attention has been paid to reducing threshold spread. We also present experimental results on cell-to-cell mismatch and time walk, which are crucial parameters for realizing an accurate and reliable pixel detector.

Pixel analog cells prototypes for ATLAS in DMILL technology

We have constructed and tested silicon pixel detector arrays of 96 × 378 (36 288) sensor elements with 75 μm × 500 μm area. The low-noise signal processing circuit associated with each element occupies an identical area on a bump-bonded readout chip. The pixel cell response for ionizing particles is binary with an adjustable threshold between 4000 e − and 15 000 e − . Single chips, the array of 6 ladders and a double array have been characterized in particle test beams and in the Omega experiment WA97 at CERN. The two arrays together, staggered by ∼ 4 mm cover hermetically a 53 mm × 55 mm area with 72 576 pixels. The proportion of properly functioning pixels was 98% in the first 36 k pixel array and 80% in the second one. The ∼ 1% “always-on” pixels could be masked electronically. After masking the rate of “spurious noise hits” was −8 of the identified particle hits while with beam off no hits at all were recorded With a beam trigger most events consisted of a single cluster with a single hit. At the 8000 e − threshold an efficiency > 99% was measured. Tracks were reconstructed with a precision of 22 μm. The proportion of double hits (∼ 11%) depends only slightly on threshold and detector bias voltage, and for these double hits a precision of 10 μm on the particle position was obtained.

/pdf/first-operation-of-a-72-k-element-hybrid-silicon-1e8m78gbu6.pdf

First operation of a 72 k element hybrid silicon micropattern pixel detector array

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First operation of a 72 k element hybrid silicon micropattern pixel detector array