First proton-proton collisions at the LHC as observed with the ALICE detector: measurement of the charged-particle pseudorapidity density at root s=900 GeV

On 23rd November 2009, during the early commissioning of the CERN Large Hadron Collider (LHC), two counter-rotating proton bunches were circulated for the first time concurrently in the machine, at the LHC injection energy of 450 GeV per beam. Although the proton intensity was very low, with only one pilot bunch per beam, and no systematic attempt was made to optimize the collision optics, all LHC experiments reported a number of collision candidates. In the ALICE experiment, the collision region was centred very well in both the longitudinal and transverse directions and 284 events were recorded in coincidence with the two passing proton bunches. The events were immediately reconstructed and analyzed both online and offline. We have used these events to measure the pseudorapidity density of charged primary particles in the central region. In the range vertical bar eta vertical bar S collider. They also illustrate the excellent functioning and rapid progress of the LHC accelerator, and of both the hardware and software of the ALICE experiment, in this early start-up phase

Multilevel Reality, Mechanistic Explanations, and Intertheoretic Reductions

In this paper I argue that the question of interlevel explanations runs against the old and thorny problem of the intertheoretical reductions. In order to find a clue as to the solution of this last problem, I shall distinguish, though only provisionally and ideal-typically, between two sorts of intertheoretical or interlevel relations, a weak and a strong one. This distinction, somewhat like a masonry falsework, will be at least in a sense removed, because both types of reduction cannot exist in their pure form. They are only idealised forms of reduction, ideal types between which we find an indefinite number of intermediate forms of actual reductions. In both cases, relating multiple perspectives to one another to better understand the subject-matter under investigation requires constructing a new, wider or deeper perspective. And in both cases, the question of interlevel explanatory reductions, just as that of intertheoretical ones, cannot be answered abstractly, by purely philosophical considerations, but only with reference to, and in accordance with, the practice of scientists and the history of science. This is true not only for physical, but also for biological theories, as I shall briefly illustrate by two examples taken from biology (the protein folding field and today\u2019s debate about cancer research)