Rivet analyses referenceATLAS_2012_I1091481Azimuthal ordering of charged hadronsExperiment: ATLAS (LHC) Inspire ID: 1091481 Status: VALIDATED Authors:
Beam energies: (450.0, 450.0); (3500.0, 3500.0) GeV Run details:
Measurement of the ordering of charged hadrons in the azimuthal angle relative to the beam axis at the Large Hadron Collider (LHC). A spectral analysis of correlations between longitudinal and transverse components of the momentum of the charged hadrons is performed. Data were recorded with the ATLAS detector at centre-of-mass energies of $\sqrt{s} = 900 \text{GeV}$ and $\sqrt{s} = 7 \text{TeV}$. The correlations measured in a phase space region dominated by low-$p_\perp$ particles are not well described by conventional models of hadron production. The measured spectra show features consistent with the fragmentation of a QCD string represented by a helix-like ordered gluon chain. Source code: ATLAS_2012_I1091481.cc 1// -*- C++ -*-
2#include "Rivet/Analysis.hh"
3#include "Rivet/Projections/ChargedFinalState.hh"
4
5namespace Rivet {
6
7
8 class ATLAS_2012_I1091481 : public Analysis {
9 public:
10
11 /// Constructor
12 RIVET_DEFAULT_ANALYSIS_CTOR(ATLAS_2012_I1091481);
13
14 /// Book histograms and initialise projections before the run
15 void init() {
16
17 ChargedFinalState cfs100(Cuts::abseta < 2.5 && Cuts::pT > 0.1*GeV);
18 declare(cfs100,"CFS100");
19 ChargedFinalState cfs500(Cuts::abseta < 2.5 && Cuts::pT > 0.5*GeV);
20 declare(cfs500,"CFS500");
21
22 for (double eVal : allowedEnergies()) {
23 const string en = toString(int(eVal));
24 if (isCompatibleWithSqrtS(eVal)) _sqs = en;
25 size_t ih = bool(en == "7000") + 1;
26
27 book(_h[en+"E_10_100"], ih, 1, 1);
28 book(_h[en+"E_1_100"], ih, 1, 2);
29 book(_h[en+"E_10_500"], ih, 1, 3);
30
31 book(_h[en+"eta_10_100"], ih, 2, 1);
32 book(_h[en+"eta_1_100"], ih, 2, 2);
33 book(_h[en+"eta_10_500"], ih, 2, 3);
34
35 book(_c[en+"inclusive"], "_norm_inclusive_"+en);
36 book(_c[en+"lowPt"], "_norm_lowPt_"+en);
37 book(_c[en+"pt500"], "_norm_pt500_"+en);
38 }
39 if (_sqs == "" && !merging()) {
40 throw BeamError("Invalid beam energy for " + name() + "\n");
41 }
42 }
43
44
45 // Recalculate particle energy assuming pion mass
46 double getPionEnergy(const Particle& p) {
47 double m_pi = 0.1396*GeV;
48 double p2 = p.p3().mod2()/(GeV*GeV);
49 return sqrt(sqr(m_pi) + p2);
50 }
51
52
53 // S_eta core for one event
54 //
55 // -1 + 1/Nch * |sum_j^Nch exp[i*(xi eta_j - Phi_j)]|^2
56 //
57 double getSeta(const Particles& part, double xi) {
58 std::complex<double> c_eta (0.0, 0.0);
59 for (const Particle& p : part) {
60 double eta = p.eta();
61 double phi = p.phi();
62 double arg = xi*eta-phi;
63 std::complex<double> temp(cos(arg), sin(arg));
64 c_eta += temp;
65 }
66 return std::norm(c_eta)/part.size() - 1.0;
67 }
68
69
70 // S_E core for one event
71 //
72 // -1 + 1/Nch * |sum_j^Nch exp[i*(omega X_j - Phi_j)]|^2
73 //
74 double getSE(const Particles& part, double omega) {
75 double Xj = 0.0;
76 std::complex<double> c_E (0.0, 0.0);
77 for (unsigned int i=0; i < part.size(); ++i) {
78 Xj += 0.5*getPionEnergy(part[i]);
79 double phi = part[i].phi();
80 double arg = omega*Xj - phi;
81 std::complex<double> temp(cos(arg), sin(arg));
82 c_E += temp;
83 Xj += 0.5*getPionEnergy(part[i]);
84 }
85 return std::norm(c_E)/part.size() - 1.0;
86 }
87
88
89 // Convenient fill function
90 void fillS(Histo1DPtr h, const Particles& part, bool SE=true) {
91 // Loop over bins, take bin centers as parameter values
92 // @todo use barchart()
93 for (auto& b : h->bins()) {
94 double x = b.xMid();
95 double width = b.xWidth();
96 double y;
97 if (SE) y = getSE(part, x);
98 else y = getSeta(part, x);
99 h->fill(x, y * width);
100 }
101 }
102
103
104 /// Perform the per-event analysis
105 void analyze(const Event& event) {
106 // Charged fs
107 const ChargedFinalState& cfs100 = apply<ChargedFinalState>(event, "CFS100");
108 const Particles part100 = cfs100.particles(cmpMomByEta);
109 const ChargedFinalState& cfs500 = apply<ChargedFinalState>(event, "CFS500");
110 const Particles& part500 = cfs500.particles(cmpMomByEta);
111
112 // Veto event if the most inclusive phase space has less than 10 particles and the max pT is > 10 GeV
113 if (part100.size() < 11) vetoEvent;
114 double ptmax = cfs100.particlesByPt()[0].pT()/GeV;
115 if (ptmax > 10.0) vetoEvent;
116
117 // Fill the pt>100, pTmax<10 GeV histos
118 fillS(_h["E_10_100"], part100, true);
119 fillS(_h["eta_10_100"], part100, false);
120 _c[_sqs+"inclusive"]->fill();
121
122 // Fill the pt>100, pTmax<1 GeV histos
123 if (ptmax < 1.0) {
124 fillS(_h["E_1_100"], part100, true);
125 fillS(_h["eta_1_100"], part100, false);
126 _c[_sqs+"lowPt"]->fill();
127 }
128
129 // Fill the pt>500, pTmax<10 GeV histos
130 if (part500.size() > 10) {
131 fillS(_h["E_10_500"], part500, true );
132 fillS(_h["eta_10_500"], part500, false);
133 _c[_sqs+"pt500"]->fill();
134 }
135 }
136
137 /// Normalise histograms etc., after the run
138 void finalize() {
139 // The scaling takes the multiple fills per event into account
140 for (double eVal : allowedEnergies()) {
141 const string en = toString(int(eVal));
142
143 scale(_h[en+"E_10_100"], 1.0/ *_c[en+"inclusive"]);
144 scale(_h[en+ "E_1_100"], 1.0/ *_c[en+"lowPt"]);
145 scale(_h[en+"E_10_500"], 1.0/ *_c[en+"pt500"]);
146
147 scale(_h[en+"eta_10_100"], 1.0/ *_c[en+"inclusive"]);
148 scale(_h[en+ "eta_1_100"], 1.0/ *_c[en+"lowPt"]);
149 scale(_h[en+"eta_10_500"], 1.0/ *_c[en+"pt500"]);
150 }
151 }
152
153
154 private:
155
156 map<string,Histo1DPtr> _h;
157 map<string,CounterPtr> _c;
158
159 string _sqs = "";
160 };
161
162
163 RIVET_DECLARE_PLUGIN(ATLAS_2012_I1091481);
164
165}
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