On the Rise of the Proton Structure Function F2_2 Towards Low x

A measurement of the derivative (d ln F_2 / d lnx)_(Q^2)= -lambda(x,Q^2) of the proton structure function F_2 is presented in the low x domain of deeply inelastic positron-proton scattering. For 5*10^(-5)=1.5 GeV^2, lambda(x,Q^2) is found to be independent of x and to increase linearly with ln(Q^2)

The ATLAS level-1 trigger: Status of the system and first results from cosmic-ray data

The ATLAS detector at CERN's Large Hadron Collider (LHC) will be exposed to proton proton collisions from beams crossing at 40 MHz. At the design luminosity of 1034 cm(-2) s(-1) there are on average 23 collisions per bunch crossing. A three-level trigger system will select potentially interesting events in order to reduce the readout rate to about 200 Hz. The first trigger level is implemented in custom-built electronics and makes an initial fast selection based on detector data of coarse granularity. It has to reduce the rate by a factor of 104 to less than 100 kHz. The other two consecutive trigger levels are in software and run on PC farms. We present an overview of the first-level trigger system and report on the current installation status. Moreover, we show analysis results of cosmic-ray data recorded in situ at the ATLAS experimental site with final or close-to-final hardware. (C) 2007 Elsevier B.V. All rights reserved. RI Perrino, Roberto/B-4633-2010; Kurashige, Hisaya/H-4916-2012; Veneziano, Stefano/J-1610-2012; spagnolo, stefania/A-6359-201

Search for single top quark production in ep collisions at HERA.

A search for single top quark production is performed in collisions at HERA. The search exploits data corresponding to an integrated luminosity of 118.3 pb-1. A model for the anomalous production of top quarks in a flavour changing neutral current process involving a coupling is investigated. Decays of top quarks into a b quark and a W boson are considered in the leptonic and the hadronic decay channels of the W. Both a cut-based analysis and a multivariate likelihood analysis are performed to discriminate anomalous top quark production from Standard Model background processes. In the leptonic channel, 5 events are found while 1.31 0.22 events are expected from the Standard Model background. In the hadronic channel, no excess above the expectation for Standard Model processes is found. These observations lead to a cross section at . Alternatively, assuming that the observed events are due to a statistical fluctuation, upper limits of 0.55 pb on the anomalous top production cross section and of 0.27 on the coupling are established at the 95% confidence level

Measurement of anti-deutron production and a search for heavy stable charged particles at HERA.

The cross section for anti-deuteron photoproduction is measured at HERA at a mean centre-of-mass energy of GeV in the range 0.2 < p T /M < 0.7 and |y| < 0.4, where M, p T and y are the mass, transverse momentum and rapidity of the anti-deuteron in the HERA laboratory frame, respectively. The numbers of anti-deuterons per event are found to be similar in photoproduction to those in central proton-proton collisions at the CERN ISR but much lower than those in central Au-Au collisions at RHIC. The coalescence parameter B 2, which characterizes the likelihood of anti-deuteron production, is measured in photoproduction to be , which is much higher than in Au-Au collisions at a similar nucleon-nucleon centre-of-mass energy. No significant production of particles heavier than deuterons is observed and upper limits are set on the photoproduction cross sections for such particles