Investigation of diffractive processes with the CMS detector: New results
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EMENTARY PARTICLES AND FIELDS Theory
Investigation of Diffractive Processes with the CMS Detector: New Results R. A. Ryutin* Institute for High Energy Physics, Protvino, Moscow oblast, 142284 Russia Received March 3, 2010
Abstract—An experiment aimed at studying leading neutrons at LHC with the aid of the CMS detectors is proposed. Data of this experiments can be used to extract cross sections for π + p and π + π + scattering. Numerical estimates are presented for the proposed measurements. DOI: 10.1134/S1063778810110207
1. INTRODUCTION On the basis of a phenomenological analysis, one can state that diffractive processes are responsible for a significant part of total cross sections at energies in excess of several TeV units. For LHC, the respective predicted values range between 15 and 25%. Single diffraction (SD), double diffraction (DD), and central diffraction (CD) are dominant diffractive processes. As is well known, gaps in the rapidity distribution of particles and small (not greater than 10%) longitudinal losses of momenta of colliding hadrons are among the main signatures of diffractive processes. There is a diffractive-physics working group in the CMS Collaboration. The main processes studied by this group include (i) jet production (p + p → N ∗ + jjX, where N ∗ is a proton or hadron-dissociation products, jj stands for jets, and “+” denotes rapidity gaps) and W -boson production (p + p → N ∗ + W (→ μν)X) studied in hard single diffraction [1, 2] in order to measure diffraction structure functions and corrections associated with rescattering; (ii) exclusive lepton production [3] (p + p → p + l+ l− + p through γγ → l+ l− and γp → Υ → l+ l− ) studied in order to measure the luminosity and to perform detector calibrations; and (iii) inclusive jet production p + p → j + X and forward-jet (so-called Mueller– Navelet jets) production p + p → j1 + j2 studied in order to test perturbative QCD, to obtain constraints on parton distributions, and to verify the Balitsky– Fadin–Kuraev–Lipatov (BFKL) evolution [4]. The exclusive-central-diffraction (ECD) process p + p → p + Mc + p, where Mc is a central system, plays a particularly important role. Calculations of the cross sections for this process can be found in [5–10]. The advantages of the ECD process are *
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known to include (i) a clear-cut signature consisting in the presence of two final-state protons, a central system whose decay products are recorded by the CMS detectors, and two rapidity gaps; (ii) a large value of the signal-to-background ratio owing to the exclusive character of the process; (iii) a high resolution in the mass of the central system and the possibility of employing the missing-mass method; and (iv) the possibility of performing a spin-parity analysis in the azimuthal distribution of final-state protons [7]. However, there is a flaw: ECD cross sections are small, which requires a long-term accumulation of statistics. The presence of a large number of pileup events at high luminosities, which are required for a fast accumulati
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