Rivet analyses

Measurement of the b-quark production cross-section in 7 and 13 TeV pp collisions

Experiment: LHCB (LHC)

Inspire ID: 1504058

Status: VALIDATED

Authors: - Gino Daniels - Lars Kolk - Julian Boelhauve

References: - Phys.Rev.Lett. 118 (2017) 5, 052002 - Phys.Rev.Lett. 119 (2017) 16, 169901 (erratum) - DOI:10.1103/PhysRevLett.118.052002 - DOI:10.1103/PhysRevLett.119.169901 (erratum) - arXiv: 1612.05140

Beams: p+ p+

Beam energies: (3500.0, 3500.0); (6500.0, 6500.0)GeV

Run details: - Minimum-bias proton-proton interactions at 7 or 13 TeV centre-of-mass energy.

Measurements of the cross section for producing b quarks in the reaction $pp \to b\overline{b}X$ are reported in 7 and 13 TeV collisions at the LHC as a function of the pseudorapidity η in the range 2 < η < 5 covered by the acceptance of the LHCb experiment. The measurements are done using semileptonic decays of b-flavored hadrons decaying into a ground-state charmed hadron in association with a muon. The cross sections in the covered η range are 72.0 ± 0.3 ± 6.8 and 154.3 ± 1.5 ± 14.3 μb for 7 and 13 TeV. The ratio is 2.14 ± 0.02 ± 0.13, where the quoted uncertainties are statistical and systematic, respectively. The agreement with theoretical expectation is good at 7 TeV, but differs somewhat at 13 TeV. The measured ratio of cross sections is larger at lower η than the model prediction.

Source code:LHCB_2016_I1504058.cc

// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

  /// @brief b-quark production in 7 and 13 TeV pp collisions
  class LHCB_2016_I1504058 : public Analysis {

  public:
    RIVET_DEFAULT_ANALYSIS_CTOR(LHCB_2016_I1504058);

    void init() {
      // Check energy of input file and book corresponding histogram
      if (isCompatibleWithSqrtS(7000 * GeV))  _sqs = 0;
      else if (isCompatibleWithSqrtS(13000 * GeV))  _sqs = 1;
      if (_sqs < 0 && !merging()) {
        throw BeamError("Invalid beam energy for " + name() + "\n");
      }
      book(_b_quark_hist[0], 1, 1, 1);
      book(_b_quark_hist[1], 2, 1, 1);
      // Select pseudorapidity range
      declare(UnstableParticles(Cuts::absetaIn(2.0, 5.0)), "UPs");
    }

    void analyze(const Event &ev) {
      // Apply UnstableParticles projection to get entire decay chain of every particle
      const UnstableParticles &unst_parts = apply<UnstableParticles>(ev, "UPs");
      for (const Particle &part : unst_parts.particles()) {
        // Select beauty hadrons
        if (!(PID::isBottomHadron(part.pid())))
          continue;

        // Skip bottomonia (excluded from definition) and Bc+ meson (ignored in
        // measurement)
        if ((PID::isQuarkonium(part.pid())) || (part.abspid() == PID::BCPLUS))
          continue;

        // Veto beauty hadrons w/ beauty hadron child (pick only children)
        if (part.isLastWith(hasBottom)) continue;

        // Double sample size by taking absolute value and then scale by 0.5 due to LHCb
        // being one-sided
        double eta = part.abseta();

        // Scale again by 0.5 to get mean of beauty quarks and antiquarks
        _b_quark_hist[_sqs]->fill(eta, 0.25);
      }
    }

    void finalize() {
      // Compute scale factor with inelastic cross-section from input file and sum of
      // weights (corresponds to number of events in input file) and do not modify it
      // for using symmetric LHCb phase space as taken into account by histogram count
      scale(_b_quark_hist, crossSection() / microbarn / sumOfWeights());

      // compute ratio of b quark productions at 13 and 7 TeV (during merge)
      if (_b_quark_hist[0]->effNumEntries() != 0. && _b_quark_hist[1]->effNumEntries() != 0.) {
        Estimate1DPtr tmp;
        book(tmp, 3, 1, 1);
        divide(_b_quark_hist[1], _b_quark_hist[0], tmp);
      }
    }

    Histo1DPtr _b_quark_hist[2];
    int _sqs = -1;
  };

  RIVET_DECLARE_PLUGIN(LHCB_2016_I1504058);
}