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Measurement of the forward charged particle pseudorapidity density in pp collisions at sqrt(s) = 8 TeV using a displaced interaction point

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 Publication date 2014
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The pseudorapidity density of charged particles dN(ch)/deta is measured by the TOTEM experiment in pp collisions at sqrt(s) = 8 TeV within the range 3.9 < eta < 4.7 and -6.95 < eta < -6.9. Data were collected in a low intensity LHC run with collisions occurring at a distance of 11.25 m from the nominal interaction point. The data sample is expected to include 96-97% of the inelastic proton-proton interactions. The measurement reported here considers charged particles with p_T > 0 MeV/c, produced in inelastic interactions with at least one charged particle in -7 < eta < -6 or 3.7 < eta <4.8 . The dN(ch)/deta has been found to decrease with |eta|, from 5.11 +- 0.73 at eta = 3.95 to 1.81 +- 0.56 at eta= - 6.925. Several MC generators are compared to the data and are found to be within the systematic uncertainty of the measurement.



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The TOTEM experiment has measured the charged particle pseudorapidity density dN_{ch}/deta in pp collisions at sqrt{s} = 7 TeV for 5.3<|eta|<6.4 in events with at least one charged particle with transverse momentum above 40 MeV/c in this pseudorapidity range. This extends the analogous measurement performed by the other LHC experiments to the previously unexplored forward eta region. The measurement refers to more than 99% of non-diffractive processes and to single and double diffractive processes with diffractive masses above ~3.4 GeV/c^2, corresponding to about 95% of the total inelastic cross-section. The dN_{ch}/deta has been found to decrease with |eta|, from 3.84 pm 0.01(stat) pm 0.37(syst) at |eta| = 5.375 to 2.38 pm 0.01(stat) pm 0.21(syst) at |eta| = 6.375. Several MC generators have been compared to data; none of them has been found to fully describe the measurement.
The charged particle production in proton-proton collisions is studied with the LHCb detector at a centre-of-mass energy of ${sqrt{s} =7}$TeV in different intervals of pseudorapidity $eta$. The charged particles are reconstructed close to the interaction region in the vertex detector, which provides high reconstruction efficiency in the $eta$ ranges $-2.5<eta<-2.0$ and $2.0<eta<4.5$. The data were taken with a minimum bias trigger, only requiring one or more reconstructed tracks in the vertex detector. By selecting an event sample with at least one track with a transverse momentum greater than 1 GeV/c a hard QCD subsample is investigated. Several event generators are compared with the data; none are able to describe fully the multiplicity distributions or the charged particle density distribution as a function of $eta$. In general, the models underestimate the charged particle production.
A measurement of the cross-section for $W to e u$ production in $pp$ collisions is presented using data corresponding to an integrated luminosity of $2,$fb$^{-1}$ collected by the LHCb experiment at a centre-of-mass energy of $sqrt{s}=8,$TeV. The electrons are required to have more than $20,$GeV of transverse momentum and to lie between 2.00 and 4.25 in pseudorapidity. The inclusive $W$ production cross-sections, where the $W$ decays to $e u$, are measured to be begin{equation*} sigma_{W^{+} to e^{+} u_{e}}=1124.4pm 2.1pm 21.5pm 11.2pm 13.0,mathrm{pb}, end{equation*} begin{equation*} sigma_{W^{-} to e^{-}bar{ u}_{e}}=,,,809.0pm 1.9pm 18.1pm,,,7.0pm phantom{0}9.4,mathrm{pb}, end{equation*} where the first uncertainties are statistical, the second are systematic, the third are due to the knowledge of the LHC beam energy and the fourth are due to the luminosity determination. Differential cross-sections as a function of the electron pseudorapidity are measured. The $W^{+}/W^{-}$ cross-section ratio and production charge asymmetry are also reported. Results are compared with theoretical predictions at next-to-next-to-leading order in perturbative quantum chromodynamics. Finally, in a precise test of lepton universality, the ratio of $W$ boson branching fractions is determined to be begin{equation*} mathcal{B}(W to e u)/mathcal{B}(W to mu u)=1.020pm 0.002pm 0.019, end{equation*} where the first uncertainty is statistical and the second is systematic.
166 - R. Aaij , B. Adeva , M. Adinolfi 2014
Charged particle multiplicities are studied in proton-proton collisions in the forward region at a centre-of-mass energy of $sqrt{s} = 7;$TeV with data collected by the LHCb detector. The forward spectrometer allows access to a kinematic range of $2.0<eta<4.8$ in pseudorapidity, momenta down to $2;$GeV/$c$ and transverse momenta down to $0.2;$GeV/$c$. The measurements are performed using minimum-bias events with at least one charged particle in the kinematic acceptance. The results are presented as functions of pseudorapidity and transverse momentum and are compared to predictions from several Monte Carlo event generators.
The energy flow created in pp collisions at sqrt(s)=7 TeV is studied within the pseudorapidity range 1.9<eta<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 PYTHIA-based and cosmic-ray event generators, which provide different models of soft hadronic interactions.
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