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Paper   IPM / Particles / 12141
School of Particles and Accelerator
  Title:   Forward Energy Flow, Central Charged-Particle Multiplicities, and Pseudorapidity Gaps in W and Z Boson Events from pp Collisions at sqrt(s) = 7 TeV
  Author(s): 
1.  Hessamadin Arfaei
2.  Hamed Bakhshiansohi
3.  Seyed Mohsen Etesami
4.  Ali Fahim
5.  Majid Hashemi
6.  Hoda Hesari
7.  Abideh Jafari
8.  Mohsen Khakzad
9.  A Mohammadi
10.  Mojtaba Mohammadi Najafabadi
11.  Saeid Paktinat
12.  Batool Safarzadeh
13.  Maryam Zeinali
  Status:   Published
  Journal: Eur. Phys. J. C
  No.:  1839
  Vol.:  72
  Year:  2011
  Supported by:  IPM
  Abstract:
A study of forward energy flow and central charged-particle multiplicity in events with W and Z bosons decaying into leptons is presented. The analysis uses a sample of 7 TeV pp collisions, corresponding to an integrated luminosity of 36 pb-1, recorded by the CMS experiment at the LHC. The observed forward energy depositions, their correlations, and the central charged-particle multiplicities are not well described by the available non-diffractive soft-hadron production models. A study of about 300 events with no significant energy deposited in one of the forward calorimeters, corresponding to a pseudorapidity gap of at least 1.9 units, is also presented. An indication for a diffractive component in these events comes from the observation that the majority of the charged leptons from the W(Z) decays are found in the hemisphere opposite to the gap. When fitting the signed lepton pseudorapidity distribution of these events with predicted distributions from an admixture of diffractive (POMPYT)and non-diffractive (PYTHIA) Monte Carlo simulations, the diffractive component is determined to be (50.0+-9.3 (stat.)+-5.2 (syst.))

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