Measurement of the forward energy flow in pp collisions at $\sqrt{s}=7\ \mbox{TeV}$
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Regular Article - Experimental Physics
Measurement of the √ forward energy flow in pp collisions at s = 7 TeV The LHCb Collaboration CERN, 1211 Geneva 23, Switzerland
Received: 21 December 2012 / Revised: 22 March 2013 / Published online: 17 May 2013 © CERN for the benefit of the LHCb collaboration 2013. This article is published with open access at Springerlink.com
√ Abstract The energy flow created in pp collisions at s = 7 TeV is studied within the pseudorapidity range 1.9 < η < 4.9 with data collected by the LHCb experiment. The measurements are performed for inclusive minimum-bias interactions, hard scattering processes and events with an enhanced or suppressed diffractive contribution. The results are compared to predictions given by P YTHIA-based and cosmic-ray event generators, which provide different models of soft hadronic interactions.
1 Introduction In Quantum Chromodynamics (QCD), the final state of an inelastic hadron-hadron collision can be described by contributions from hard and soft scattering occurring between the constituents of the hadrons, initial- and final-state (gluon) radiation and the fragmentation of the initially coloured partonic final state into colour-neutral hadrons. The soft component of a collision is called the underlying event. Its precise theoretical description remains a challenge, while the dynamics of hard scattering processes is well described by perturbative QCD. One source of the underlying event activity is multi-parton interactions (MPI). These arise mainly in the region of a very low parton momentum fraction, where parton densities are high so that the probability of more than a single parton-parton interaction per hadron-hadron collision is large. MPI effects become increasingly important at LHC collision energies, where inelastic interactions between very soft partons are sufficiently energetic to contribute to final state particle production [1]. MPI phenomena can be probed by measuring in the centre-of-mass system the amount of energy created in inelastic hadron-hadron interactions at large values of the pseudorapidity η = − ln[tan(θ/2)], with θ being the polar angle of particles with respect to the beam axis. The energy e-mail:
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flow is expected to be directly sensitive to the amount of parton radiation and MPI [2]. For a particular pseudorapidity interval with width η, the total energy flow, which is normalised to the number of inelastic pp interactions Nint , is defined as Npart,η 1 1 1 dEtotal = Ei,η , (1) Nint dη η Nint i=1
where Npart,η is the total number of stable particles and Ei,η is the energy of the individual particles. In this study, the energy flow is measured in pp collisions √ at s = 7 TeV within the pseudorapidity range 1.9 < η < 4.9. This extends the previous measurements that have been made in p p¯ [3] and ep collisions [4] to larger pseudorapidity values and higher centre-of-mass energies, and complements the studies performed by the CMS and ATLAS collaborations [5, 6]. Experimental results are compare
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