Rivet analyses
title: BESIII_2020_I1791570
Analysis of $J/\psi$, $\psi(2S)$ decays to $\Sigma^+\bar\Sigma^-$
Experiment: BESIII (BEPC)
Inspire ID: 1791570
Status: VALIDATED
Authors: - Peter Richardson
References: - Phys.Rev.Lett. 125 (2020) 5, 052004
Beams: e- e+
Beam energies: (1.6, 1.6); (1.8, 1.8)GeV
Run details: - e+e- > J/psi, psi 2s.
Analysis of the angular distribution of the baryons, and decay products, produced in $e^+e^-\to J/\psi, \psi(2S) \to \Sigma^+\bar\Sigma^-$. Gives information about the decay and is useful for testing correlations in hadron decays. N.B. The moment data is not corrected for efficiency/acceptance and should therefore only be used qualatively.
Source code:BESIII_2020_I1791570.cc
```c++ // -- C++ --
include "Rivet/Analysis.hh"
include "Rivet/Projections/Beam.hh"
include "Rivet/Projections/FinalState.hh"
include "Rivet/Projections/UnstableParticles.hh"
namespace Rivet {
/// @brief J/Psi, psi(2S) -> Sigma+ Sigmabar- class BESIII_2020_I1791570 : public Analysis { public:
/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2020_I1791570);
/// @name Analysis methods
/// @{
/// Book histograms and initialise projections before the run
void init() {
// Initialise and register projections
declare(Beam(), "Beams");
declare(UnstableParticles(), "UFS");
declare(FinalState(), "FS");
// Book histograms
size_t ih = 1;
for (double eVal : allowedEnergies()) {
const string en = toString(round(eVal / MeV));
if (isCompatibleWithSqrtS(eVal, 1e-3)) _sqs = en;
book(_h[en + "cThetaL"], "/TMP/cThetaL+" + en, 20, -1., 1.);
book(_h[en + "T1"], "/TMP/T1_" + en, 20, -1., 1.);
book(_h[en + "T2"], "/TMP/T2_" + en, 20, -1., 1.);
book(_h[en + "T3"], "/TMP/T3_" + en, 20, -1., 1.);
book(_h[en + "T4"], "/TMP/T4_" + en, 20, -1., 1.);
book(_h[en + "T5"], "/TMP/T5_" + en, 20, -1., 1.);
book(_h[en + "mu"], 1, 1, ih);
++ih;
}
raiseBeamErrorIf(_sqs.empty());
}
void findChildren(const Particle& p, map<long, int>& nRes, int& ncount) const {
for (const Particle& child : p.children()) {
if (child.children().empty()) {
nRes[child.pid()] -= 1;
--ncount;
}
else {
findChildren(child, nRes, ncount);
}
}
}
/// Perform the per-event analysis
void analyze(const Event& event) {
// get the axis, direction of incoming electron
const ParticlePair& beams = apply<Beam>(event, "Beams").beams();
Vector3 axis;
if (beams.first.pid() > 0)
axis = beams.first.mom().p3().unit();
else
axis = beams.second.mom().p3().unit();
// types of final state particles
const FinalState& fs = apply<FinalState>(event, "FS");
map<long, int> nCount;
int ntotal(0);
for (const Particle& p : fs.particles()) {
nCount[p.pid()] += 1;
++ntotal;
}
// loop over Sigma+ baryons
const UnstableParticles& ufs = apply<UnstableParticles>(event, "UFS");
Particle Sigma, SigBar;
bool matched(false);
for (const Particle& p : ufs.particles(Cuts::abspid == 3222)) {
if (p.children().empty()) continue;
map<long, int> nRes = nCount;
int ncount = ntotal;
findChildren(p, nRes, ncount);
matched = false;
// check for antiparticle
for (const Particle& p2 : ufs.particles(Cuts::pid == -p.pid())) {
if (p2.children().empty()) continue;
map<long, int> nRes2 = nRes;
int ncount2 = ncount;
findChildren(p2, nRes2, ncount2);
if (ncount2 == 0) {
matched = true;
for (const auto& val : nRes2) {
if (val.second != 0) {
matched = false;
break;
}
}
// fond baryon and antibaryon
if (matched) {
if (p.pid() > 0) {
Sigma = p;
SigBar = p2;
}
else {
Sigma = p2;
SigBar = p;
}
break;
}
}
}
if (matched) break;
}
if (!matched) vetoEvent;
// find proton
Particle proton;
matched = false;
for (const Particle& p : Sigma.children()) {
if (p.pid() == 2212) {
matched = true;
proton = p;
}
else if (p.pid() != 111) {
matched = false;
break;
}
}
if (!matched) vetoEvent;
// find antiproton
Particle pbar;
matched = false;
for (const Particle& p : SigBar.children()) {
if (p.pid() == -2212) {
matched = true;
pbar = p;
}
else if (p.pid() != 111) {
matched = false;
break;
}
}
if (!matched) vetoEvent;
// boost to the Sigma rest frame
LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(Sigma.mom().betaVec());
Vector3 e1z = Sigma.mom().p3().unit();
Vector3 e1y = e1z.cross(axis).unit();
Vector3 e1x = e1y.cross(e1z).unit();
Vector3 axis1 = boost1.transform(proton.mom()).p3().unit();
double n1x(e1x.dot(axis1)), n1y(e1y.dot(axis1)), n1z(e1z.dot(axis1));
// boost to the Sigma bar
LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(SigBar.mom().betaVec());
Vector3 axis2 = boost2.transform(pbar.mom()).p3().unit();
double n2x(e1x.dot(axis2)), n2y(e1y.dot(axis2)), n2z(e1z.dot(axis2));
double cosL = axis.dot(Sigma.mom().p3().unit());
double sinL = sqrt(1. - sqr(cosL));
double T1 = sqr(sinL) * n1x * n2x + sqr(cosL) * n1z * n2z;
double T2 = -sinL * cosL * (n1x * n2z + n1z * n2x);
double T3 = -sinL * cosL * n1y;
double T4 = -sinL * cosL * n2y;
double T5 = n1z * n2z - sqr(sinL) * n1y * n2y;
double mu = -(n1y - n2y);
_h[_sqs + "T1"]->fill(cosL, T1);
_h[_sqs + "T2"]->fill(cosL, T2);
_h[_sqs + "T3"]->fill(cosL, T3);
_h[_sqs + "T4"]->fill(cosL, T4);
_h[_sqs + "T5"]->fill(cosL, T5);
_h[_sqs + "mu"]->fill(cosL, mu);
_h[_sqs + "cThetaL"]->fill(cosL);
}
pair<double, pair<double, double>> calcAlpha0(const Histo1DPtr& hist) const {
if (hist->numEntries() == 0.) return make_pair(0., make_pair(0., 0.));
double d = 3. / (pow(hist->xMax(), 3) - pow(hist->xMin(), 3));
double c = 3. * (hist->xMax() - hist->xMin()) / (pow(hist->xMax(), 3) - pow(hist->xMin(), 3));
double sum1(0.), sum2(0.), sum3(0.), sum4(0.), sum5(0.);
for (const auto& bin : hist->bins()) {
double Oi = bin.sumW();
if (Oi == 0.) continue;
double a = d * (bin.xMax() - bin.xMin());
double b = d / 3. * (pow(bin.xMax(), 3) - pow(bin.xMin(), 3));
double Ei = bin.errW();
sum1 += a * Oi / sqr(Ei);
sum2 += b * Oi / sqr(Ei);
sum3 += sqr(a) / sqr(Ei);
sum4 += sqr(b) / sqr(Ei);
sum5 += a * b / sqr(Ei);
}
// calculate alpha
double alpha = (-c * sum1 + sqr(c) * sum2 + sum3 - c * sum5) / (sum1 - c * sum2 + c * sum4 - sum5);
// and error
double cc = -pow((sum3 + sqr(c) * sum4 - 2 * c * sum5), 3);
double bb = -2 * sqr(sum3 + sqr(c) * sum4 - 2 * c * sum5) * (sum1 - c * sum2 + c * sum4 - sum5);
double aa = sqr(sum1 - c * sum2 + c * sum4 - sum5)
* (-sum3 - sqr(c) * sum4 + sqr(sum1 - c * sum2 + c * sum4 - sum5) + 2 * c * sum5);
double dis = sqr(bb) - 4. * aa * cc;
if (dis > 0.) {
dis = sqrt(dis);
return make_pair(alpha, make_pair(0.5 * (-bb + dis) / aa, -0.5 * (-bb - dis) / aa));
}
else {
return make_pair(alpha, make_pair(0., 0.));
}
}
pair<double, double> calcCoeff(size_t imode, const Histo1DPtr& hist) const {
if (hist->numEntries() == 0.) return make_pair(0., 0.);
double sum1(0.), sum2(0.);
for (const auto& bin : hist->bins()) {
double Oi = bin.sumW();
if (Oi == 0.) continue;
double ai(0.), bi(0.);
if (imode == 0) {
bi = (pow(1. - sqr(bin.xMin()), 1.5) - pow(1. - sqr(bin.xMax()), 1.5)) / 3.;
}
else if (imode >= 2 && imode <= 4) {
bi = (pow(bin.xMin(), 3) * (-5. + 3. * sqr(bin.xMin()))
+ pow(bin.xMax(), 3) * (5. - 3. * sqr(bin.xMax())))
/ 15.;
}
else {
assert(false);
}
double Ei = bin.errW();
sum1 += sqr(bi / Ei);
sum2 += bi / sqr(Ei) * (Oi - ai);
}
return make_pair(sum2 / sum1, sqrt(1. / sum1));
}
/// Normalise histograms etc., after the run
void finalize() {
size_t ih = 1;
for (double eVal : allowedEnergies()) {
const string en = toString(round(eVal / MeV));
if (_h[en + "T1"]->numEntries() == 0) {
++ih;
continue;
}
const double sf = _h[en + "cThetaL"]->sumW();
normalize(_h[en + "cThetaL"]);
scale(_h[en + "T1"], 1.0 / sf);
scale(_h[en + "T2"], 1.0 / sf);
scale(_h[en + "T3"], 1.0 / sf);
scale(_h[en + "T4"], 1.0 / sf);
scale(_h[en + "T5"], 1.0 / sf);
scale(_h[en + "mu"], 2.0 / sf);
// calculate alpha0
pair<double, pair<double, double>> alpha0 = calcAlpha0(_h[en + "cThetaL"]);
Estimate0DPtr est;
book(est, 4, 1, ih);
est->set(alpha0.first, alpha0.second);
double s2 = -1. + sqr(alpha0.first);
double s3 = 3 + alpha0.first;
double s1 = sqr(s3);
// alpha- and alpha+ from proton data
pair<double, double> c_T2 = calcCoeff(2, _h[en + "T2"]);
pair<double, double> c_T3 = calcCoeff(3, _h[en + "T3"]);
pair<double, double> c_T4 = calcCoeff(4, _h[en + "T4"]);
double s4 = sqr(c_T2.first);
double s5 = sqr(c_T3.first);
double s6 = sqr(c_T4.first);
double disc = s1 * s5 * s6 * (-9. * s2 * s4 + 4. * s1 * s5 * s6);
if (disc >= 0.) {
disc = sqrt(disc);
double aM = -sqrt(-1. / s2 / s6 * (2. * s1 * s5 * s6 + disc));
double aP = c_T4.first / c_T3.first * aM;
double aM_P = (2 * (alpha0.first * c_T4.first * alpha0.second.first + c_T4.second * s2)
* (disc + 2 * s1 * s5 * s6)
- c_T4.first * s2
* (4 * s3 * c_T3.first * c_T4.first
* (c_T3.first * c_T4.first * alpha0.second.first
+ s3 * c_T4.first * c_T3.second + s3 * c_T3.first * c_T4.second)
+ (disc
* (-9 * s2 * s3 * c_T2.first * c_T3.first * c_T4.first * c_T2.second
+ 9
* ((1 - alpha0.first * (3 + 2 * alpha0.first)) * c_T3.first
* c_T4.first * alpha0.second.first
- s2 * s3 * c_T4.first * c_T3.second
- s2 * s3 * c_T3.first * c_T4.second)
* s4
+ 8
* (c_T3.first * c_T4.first * alpha0.second.first
+ s3 * c_T4.first * c_T3.second + s3 * c_T3.first * c_T4.second)
* s1 * s5 * s6))
/ (4 * pow(3 + alpha0.first, 3) * pow(c_T3.first, 3) * pow(c_T4.first, 3)
- 9 * s2 * s3 * c_T3.first * c_T4.first * s4)))
/ (2. * pow(c_T4.first, 3) * pow(s2, 2) * sqrt(-((disc + 2 * s1 * s5 * s6) / (s2 * s6))));
double aM_M = (2 * (alpha0.first * c_T4.first * alpha0.second.second + c_T4.second * s2)
* (disc + 2 * s1 * s5 * s6)
- c_T4.first * s2
* (4 * s3 * c_T3.first * c_T4.first
* (c_T3.first * c_T4.first * alpha0.second.second
+ s3 * c_T4.first * c_T3.second + s3 * c_T3.first * c_T4.second)
+ (disc
* (-9 * s2 * s3 * c_T2.first * c_T3.first * c_T4.first * c_T2.second
+ 9
* ((1 - alpha0.first * (3 + 2 * alpha0.first)) * c_T3.first
* c_T4.first * alpha0.second.second
- s2 * s3 * c_T4.first * c_T3.second
- s2 * s3 * c_T3.first * c_T4.second)
* s4
+ 8
* (c_T3.first * c_T4.first * alpha0.second.second
+ s3 * c_T4.first * c_T3.second + s3 * c_T3.first * c_T4.second)
* s1 * s5 * s6))
/ (4 * pow(3 + alpha0.first, 3) * pow(c_T3.first, 3) * pow(c_T4.first, 3)
- 9 * s2 * s3 * c_T3.first * c_T4.first * s4)))
/ (2. * pow(c_T4.first, 3) * pow(s2, 2) * sqrt(-((disc + 2 * s1 * s5 * s6) / (s2 * s6))));
double aP_M =
(c_T4.first * sqrt(-((disc + 2 * s1 * s5 * s6) / (s2 * s6)))
* (-2 * c_T3.second - (2 * alpha0.first * c_T3.first * alpha0.second.first) / s2
+ (c_T3.first
* (4 * s3 * c_T3.first * c_T4.first
* (c_T3.first * c_T4.first * alpha0.second.first + s3 * c_T4.first * c_T3.second
+ s3 * c_T3.first * c_T4.second)
+ (disc
* (-9 * s2 * s3 * c_T2.first * c_T3.first * c_T4.first * c_T2.second
+ 9
* ((1 - alpha0.first * (3 + 2 * alpha0.first)) * c_T3.first * c_T4.first
* alpha0.second.first
- s2 * s3 * c_T4.first * c_T3.second
- s2 * s3 * c_T3.first * c_T4.second)
* s4
+ 8
* (c_T3.first * c_T4.first * alpha0.second.first
+ s3 * c_T4.first * c_T3.second + s3 * c_T3.first * c_T4.second)
* s1 * s5 * s6))
/ (4 * pow(3 + alpha0.first, 3) * pow(c_T3.first, 3) * pow(c_T4.first, 3)
- 9 * s2 * s3 * c_T3.first * c_T4.first * s4)))
/ (disc + 2 * s1 * s5 * s6)))
/ (2. * pow(c_T3.first, 2));
double aP_P =
(c_T4.first * sqrt(-((disc + 2 * s1 * s5 * s6) / (s2 * s6)))
* (-2 * c_T3.second - (2 * alpha0.first * c_T3.first * alpha0.second.second) / s2
+ (c_T3.first
* (4 * s3 * c_T3.first * c_T4.first
* (c_T3.first * c_T4.first * alpha0.second.second + s3 * c_T4.first * c_T3.second
+ s3 * c_T3.first * c_T4.second)
+ (disc
* (-9 * s2 * s3 * c_T2.first * c_T3.first * c_T4.first * c_T2.second
+ 9
* ((1 - alpha0.first * (3 + 2 * alpha0.first)) * c_T3.first * c_T4.first
* alpha0.second.second
- s2 * s3 * c_T4.first * c_T3.second
- s2 * s3 * c_T3.first * c_T4.second)
* s4
+ 8
* (c_T3.first * c_T4.first * alpha0.second.second
+ s3 * c_T4.first * c_T3.second + s3 * c_T3.first * c_T4.second)
* s1 * s5 * s6))
/ (4 * pow(3 + alpha0.first, 3) * pow(c_T3.first, 3) * pow(c_T4.first, 3)
- 9 * s2 * s3 * c_T3.first * c_T4.first * s4)))
/ (disc + 2 * s1 * s5 * s6)))
/ (2. * pow(c_T3.first, 2));
book(est, 2, 1, 1);
est->set(aM, make_pair(-aM_M, -aM_P));
book(est, 2, 1, 2);
est->set(aP, make_pair(-aP_M, -aP_P));
book(est, 2, 1, 3);
est->set(0.5 * (aM - aP),
make_pair(0.5 * sqrt(sqr(aM_M) + sqr(aP_P)), 0.5 * sqrt(sqr(aM_P) + sqr(aP_M))));
// now for Delta
double sDelta = (-2. * (3. + alpha0.first) * c_T3.first) / (aM * sqrt(1 - sqr(alpha0.first)));
double cDelta = (-3 * (3 + alpha0.first) * c_T2.first) / (aM * aP * sqrt(1 - sqr(alpha0.first)));
double Delta = asin(sDelta);
if (cDelta < 0.) Delta = M_PI - Delta;
double ds_P = (-9 * c_T2.first
* ((-1 + alpha0.first) * (1 + alpha0.first) * (3 + alpha0.first) * c_T3.first
* c_T4.first * c_T2.second
+ c_T2.first * c_T4.first
* (c_T3.first * (alpha0.second.first + 3 * alpha0.first * alpha0.second.first)
- (-1 + alpha0.first) * (1 + alpha0.first) * (3 + alpha0.first)
* c_T3.second)
- (-1 + alpha0.first) * (1 + alpha0.first) * (3 + alpha0.first) * c_T2.first
* c_T3.first * c_T4.second)
* disc)
/ (pow(1 - pow(alpha0.first, 2), 1.5) * pow(c_T4.first, 3)
* pow(-((disc + 2 * s1 * s5 * s6) / (s2 * s6)), 1.5) * (-9 * s2 * s4 + 4 * s1 * s5 * s6));
double ds_M = (-9 * c_T2.first
* ((-1 + alpha0.first) * (1 + alpha0.first) * (3 + alpha0.first) * c_T3.first
* c_T4.first * c_T2.second
+ c_T2.first * c_T4.first
* (c_T3.first
* (alpha0.second.second + 3 * alpha0.first * alpha0.second.second)
- (-1 + alpha0.first) * (1 + alpha0.first) * (3 + alpha0.first)
* c_T3.second)
- (-1 + alpha0.first) * (1 + alpha0.first) * (3 + alpha0.first) * c_T2.first
* c_T3.first * c_T4.second)
* disc)
/ (pow(1 - pow(alpha0.first, 2), 1.5) * pow(c_T4.first, 3)
* pow(-((disc + 2 * s1 * s5 * s6) / (s2 * s6)), 1.5) * (-9 * s2 * s4 + 4 * s1 * s5 * s6));
ds_P /= sqrt(1. - sqr(sDelta));
ds_M /= sqrt(1. - sqr(sDelta));
book(est, 3, 1, ih);
est->set(Delta / M_PI * 180., make_pair(-ds_P / M_PI * 180., -ds_M / M_PI * 180.));
}
++ih;
}
}
/// @}
/// @name Histograms
/// @{
map<string, Histo1DPtr> _h;
string _sqs = "";
/// @}
};
RIVET_DECLARE_PLUGIN(BESIII_2020_I1791570);
} ```