rivet is hosted by Hepforge, IPPP Durham

Rivet analyses reference

ATLAS_2014_I1282441

The differential production cross section of the $\phi(1020)$ meson in $\sqrt{s}=7$ TeV $pp$ collisions measured with the ATLAS detector
Experiment: ATLAS (LHC)
Inspire ID: 1282441
Status: VALIDATED
Authors:
  • Tim Martin
  • Kiran Joshi
References:
  • arXiv: 1402.6162
  • Eur.Phys.J. C74 (2014) no.7, 2895
Beams: p+ p+
Beam energies: (3500.0, 3500.0) GeV
Run details:
  • Run minimum bias events

A measurement is presented of the $\phi \rightarrow K^+K^-$ production cross section at $\sqrt{s}$ = 7 TeV using pp collision data corresponding to an integrated luminosity of 383 $\mu$b$^{-1}$ collected with the ATLAS experiment at the LHC. Selection of $\phi(1020)$ mesons is based on the identification of charged kaons by their energy loss in the pixel detector. The differential cross section is measured as a function of the transverse momentum, $pT,\phi$, and rapidity, $y_\phi$, of the $\phi(1020)$ meson in the fiducial region 500 < $pT,\phi$ < 1200 MeV, |$y_\phi$| < 0.8, kaon $pT,K$ > 230 MeV and kaon momentum $p_K$ < 800 MeV. The integrated $\phi(1020)$ production cross section in this fiducial range is measured to be $\sigma_{\phi \rightarrow K^+K^-}$ = 570 \pm 8 (stat) \pm 66 (syst) \pm 20 (lumi) $\mu$b.

Source code: ATLAS_2014_I1282441.cc
 1// -*- C++ -*-
 2#include "Rivet/Analysis.hh"
 3#include "Rivet/Projections/FinalState.hh"
 4#include "Rivet/Projections/UnstableParticles.hh"
 5#include "Rivet/Projections/IdentifiedFinalState.hh"
 6
 7namespace Rivet {
 8
 9
10  class ATLAS_2014_I1282441 : public Analysis {
11  public:
12
13    ATLAS_2014_I1282441()
14      : Analysis("ATLAS_2014_I1282441")
15    { }
16
17
18    void init() {
19
20      // Use a large eta range such that we can discriminate on y
21      /// @todo Convert to use a y-cut directly
22      UnstableParticles ufs(Cuts::abseta < 10 && Cuts::pT > 500*MeV);
23      IdentifiedFinalState phis(ufs);
24      phis.acceptIdPair(PID::PHI);
25      declare(phis, "Phis");
26
27      IdentifiedFinalState kpms(Cuts::abseta < 2.0 && Cuts::pT > 230*MeV);
28      kpms.acceptIdPair(PID::KPLUS);
29      declare(kpms, "Kpms");
30
31      book(_h_phi_pT       ,1,1,1);
32      book(_h_phi_rapidity ,2,1,1);
33    }
34
35
36    void analyze(const Event& event) {
37      const Particles& ks_all = apply<IdentifiedFinalState>(event, "Kpms").particles();
38      Particles kp, km;
39      for (const Particle& p : ks_all) {
40        if (!p.hasAncestor(PID::PHI)) { MSG_DEBUG("-- K not from phi."); continue; }
41        if (p.p3().mod() > 800*MeV) { MSG_DEBUG("-- p K too high."); continue; }
42        (p.charge() > 0 ? kp : km).push_back(p);
43      }
44
45      const Particles& phis_all = apply<FinalState>(event, "Phis").particles();
46      Particles phis;
47      /// @todo Use particles(Cuts&) instead
48      for (const Particle& p : phis_all) {
49        if ( p.absrap() > 0.8 ) { MSG_DEBUG("-- phi Y too high."); continue; }
50        if ( p.pT() > 1.2*GeV ) { MSG_DEBUG("-- phi pT too high."); continue; }
51        phis.push_back(p);
52      }
53
54      // Find Phi -> KK decays through matching of the kinematics
55      if (!kp.empty() && !km.empty() && !phis.empty()) {
56        MSG_DEBUG("Numbers of particles:  #phi=" << phis.size() << ", #K+=" << kp.size() << ", #K-=" << km.size());
57        for (size_t ip = 0; ip < phis.size(); ++ip) {
58          const Particle& phi = phis[ip];
59          for (size_t ikm = 0; ikm < km.size(); ++ikm) {
60            for (size_t ikp = 0; ikp < kp.size(); ++ikp) {
61              const FourMomentum mom = kp[ikp].mom() + km[ikm].mom();
62              if ( fuzzyEquals(mom.mass(), phi.mass(), 1e-5) ) {
63                MSG_DEBUG("Accepted combinatoric: phi#:" << ip << " K+#:" << ikp << " K-#:" << ikm);
64                _h_phi_rapidity->fill(phi.absrap());
65                _h_phi_pT->fill(phi.pT()/MeV);
66              } else {
67                MSG_DEBUG("Rejected combinatoric: phi#:" << ip << " K+#:" << ikp << " K-#:" << ikm << " Mass difference is " << mom.mass()-phi.mass());
68              }
69            }
70          }
71        }
72      }
73
74    }
75
76
77    void finalize() {
78      scale(_h_phi_rapidity, crossSection()/millibarn/sumOfWeights());
79      scale(_h_phi_pT, crossSection()/microbarn/sumOfWeights());
80    }
81
82
83  private:
84
85    Histo1DPtr _h_phi_rapidity, _h_phi_pT;
86
87  };
88
89
90  RIVET_DECLARE_PLUGIN(ATLAS_2014_I1282441);
91
92}