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StrumiaVissaniIBDPXSec.cxx
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1 //____________________________________________________________________________
2 /*
3  Copyright (c) 2003-2024, The GENIE Collaboration
4  For the full text of the license visit http://copyright.genie-mc.org
5 
6  Corey Reed <cjreed \at nikhef.nl>
7  Nikhef
8 */
9 //____________________________________________________________________________
10 
11 #include <TMath.h>
12 
20 
21 using namespace genie;
22 using namespace genie::constants;
23 
25 
26 //____________________________________________________________________________
29  fXSecIntegrator(0)
30 {
31 
32 }
33 //____________________________________________________________________________
35  XSecAlgorithmI("genie::StrumiaVissaniIBDPXSec", config),
36  fXSecIntegrator(0)
37 {
38 
39 }
40 //____________________________________________________________________________
42 {
43 
44 }
45 //____________________________________________________________________________
47  const Interaction * interaction, KinePhaseSpace_t kps) const
48 {
49  // compute the differential cross section ds/dt
50 
51  if(! this -> ValidProcess (interaction) ) return 0.;
52  if(! this -> ValidKinematics (interaction) ) return 0.;
53 
54  const InitialState & init_state = interaction -> InitState();
55  const double Ev = init_state.ProbeE(kRfHitNucRest);
56  const Target & target = init_state.Tgt();
57  const bool isProt = target.IsProton();
58  const Kinematics & kine = interaction->Kine();
59  const double q2 = kine.q2();
60  const double mp = (isProt) ? kProtonMass : kNeutronMass;
61  const double mp2 = (isProt) ? kProtonMass2 : kNeutronMass2;
62  const double mn2 = (isProt) ? kNeutronMass2 : kProtonMass2;
63 
64  // calculate s-u and s-m_nucleon^2 in nucleon rest frame
65  // need E_e
66  const double Ee = Ev + ( (q2 - mn2 + mp2) / (2.000*mp) );
67  const double sMinusU = ((2.000*mp*(Ev+Ee)) - kElectronMass2)
68  * (isProt ? 1.000 : -1.000);
69  const double sMinusMp2 = 2.000*mp*Ev;
70 
71 #ifdef __GENIE_LOW_LEVEL_MESG_ENABLED__
72  LOG("StrumiaVissani", pDEBUG) << "*** Ev = " << Ev
73  << ", q2 = " << q2
74  << ", Ee = " << Ee
75  << ", s-u = " << sMinusU
76  << ", s-Mp2 = " << sMinusMp2;
77 #endif
78 
79  double xsec = dSigDt(sMinusU, sMinusMp2, q2);
80 #ifdef __GENIE_LOW_LEVEL_MESG_ENABLED__
81  LOG("StrumiaVissani", pDEBUG) << "*** dSdt = " << xsec;
82 #endif
83 
84  // apply correction factors
85  const double rdcf = RadiativeCorr(Ee);
86  const double fscf = (isProt) ? 1.00 : FinalStateCorr(Ee);
87  xsec *= rdcf * fscf;
88 #ifdef __GENIE_LOW_LEVEL_MESG_ENABLED__
89  LOG("StrumiaVissani", pDEBUG) << "*** rad.corr. = " << rdcf
90  << ", fin.st.cor. = " << fscf
91  << ", xsec = " << xsec;
92 #endif
93 
94  //----- The algorithm computes dxsec/dt, t=q^2
95  // Check whether variable tranformation is needed
96  if(kps!=kPSq2fE && kps!=kPSQ2fE) {
97  const double J = utils::kinematics::Jacobian(interaction,kPSq2fE,kps);
98  xsec *= J;
99 #ifdef __GENIE_LOW_LEVEL_MESG_ENABLED__
100  LOG("StrumiaVissani", pDEBUG) << "*** Jacobian = " << J;
101 #endif
102  }
103 
104 #ifdef __GENIE_LOW_LEVEL_MESG_ENABLED__
105  LOG("StrumiaVissani", pDEBUG) << "*** xsec = " << xsec;
106 #endif
107  return xsec;
108 }
109 //____________________________________________________________________________
110 double StrumiaVissaniIBDPXSec::Integral(const Interaction * interaction) const
111 {
112  // Compute the total cross section for a free nucleon target
113 
114  assert(interaction!=0);
115  if(! this -> ValidProcess (interaction) ) return 0.;
116  if(! this -> ValidKinematics (interaction) ) return 0.;
117 
118  assert(fXSecIntegrator!=0);
119  double xsec = fXSecIntegrator->Integrate(this, interaction);
120 
121  return xsec;
122 }
123 //____________________________________________________________________________
124 bool StrumiaVissaniIBDPXSec::ValidProcess(const Interaction * interaction) const
125 {
126  if(interaction->TestBit(kISkipProcessChk)) return true;
127 
128  // should be IBD and either nu_e + n or anu_e + p
129  if (interaction->ProcInfo().IsInverseBetaDecay()) {
130 
131  const InitialState & init_state = interaction -> InitState();
132  const Target & target = init_state.Tgt();
133  if ( (target.IsProton() && pdg::IsAntiNuE(init_state.ProbePdg())) || (target.IsNeutron() && pdg::IsNuE(init_state.ProbePdg()) ))
134  return true;
135  }
136  LOG("StrumiaVissani", pERROR) << "*** Should be IBD processes either nu_e + n or anu_e + p!";
137  return false;
138 }
139 //____________________________________________________________________________
141 {
142  if(interaction->TestBit(kISkipKinematicChk)) return true;
143 
144  const InitialState & init_state = interaction -> InitState();
145  const double Ev = init_state.ProbeE(kRfHitNucRest);
146  static const double Ecutoff = kNucleonMass / 2;
147  if (Ev > Ecutoff) {
148  LOG("StrumiaVissani", pERROR) << "*** Ev=" << Ev
149  << " is too large for VLE QEL!";
150  } else if (init_state.IsNuBarP() || init_state.IsNuN()) {
151  const KPhaseSpace & kps = interaction->PhaseSpace();
152  return kps.IsAboveThreshold();
153  }
154 
155  return false;
156 }
157 //____________________________________________________________________________
159 {
160  Algorithm::Configure(config);
161  this->LoadConfig();
162 }
163 //____________________________________________________________________________
165 {
166  Algorithm::Configure(config);
167  this->LoadConfig();
168 }
169 //____________________________________________________________________________
171 {
172 
173  // cabibbo angle
174  double cab ;
175  GetParam( "CabibboAngle", cab ) ;
176  const double cosCab = TMath::Cos(cab);
177  fCosCabibbo2 = cosCab*cosCab;
178 
179  // form factor params
180  GetParam( "QEL-FA0", fg1of0 ) ;
181  double ma, mv ;
182  GetParam( "QEL-Ma", ma ) ;
183  GetParam( "QEL-Mv", mv ) ;
184  fMa2 = ma*ma;
185  fMv2 = mv*mv;
186 
187  // magnetic moments
188 
189  double mup, mun ;
190  GetParam( "AnomMagnMoment-P", mup );
191  GetParam( "AnomMagnMoment-N", mun );
192  fNucleonMMDiff = (mup - 1.000) - mun; // *anamolous* mag. mom. diff.
193 
194  // numeric
195  int epmag ;
196  GetParam("EpsilonMag", epmag ) ;
197  fEpsilon = TMath::Power(10.000, -1.000 * static_cast<double>(epmag) );
198 
199  LOG("StrumiaVissani", pINFO) << "*** USING: cos2(Cabibbo)="
200  << fCosCabibbo2
201  << ", g1(0)=" << fg1of0
202  << ", Ma^2=" << fMa2
203  << ", Mv^2=" << fMv2
204  << ", xi=" << fNucleonMMDiff
205  << ", epsilon=" << fEpsilon;
206 
207  // load XSec Integrator
209  dynamic_cast<const XSecIntegratorI *> (this->SubAlg("XSec-Integrator"));
210  assert(fXSecIntegrator!=0);
211 
212 }
213 //____________________________________________________________________________
214 double StrumiaVissaniIBDPXSec::dSigDt(const double sMinusU,
215  const double sMinusMnuc,
216  const double t) const
217 {
218  // return the differential cross section dS/dt. eqn 3 from reference
219  // t = q^2
220  //
221  // for anue + p -> e+ + n , sMinusU = s - u and sMinusMnuc = s - m_p^2
222  // for nue + n -> e- + p , sMinusU = u - s and sMinusMnuc = s - m_n^2
223  // where s = (p_nu + p_p)^2 and u = (p_nu - p_n)^2
224 
225  const double numer = kGF2 * fCosCabibbo2;
226  const double denom = (2.000 * kPi) * sMinusMnuc*sMinusMnuc;
227  assert(TMath::Abs(denom) > fEpsilon); // avoid divide by zero
228 
229  return ( (numer / denom) * MtxElm(sMinusU, t) );
230 }
231 //____________________________________________________________________________
232 double StrumiaVissaniIBDPXSec::MtxElm(const double sMinusU,
233  const double t) const
234 {
235  // return the square of the matrix element. eqn 5 from the reference paper
236  // |M^2| = A(t) - (s-u)B(t) + (s-u)^2 C(t)
237  //
238  // factor 16 comes from eqn 6
239  //
240  // for anue + p -> e+ + n , sMinusU = s - u
241  // for nue + n -> e- + p , sMinusU = u - s
242  // where s = (p_nu + p_p)^2 and u = (p_nu - p_n)^2
243 
244  // store multiply used variables to reduce number of calculations
245  const double t4m = t / k4NucMass2;
246  const double t2 = t * t;
247 
248  const double fdenomB = 1.000 - (t / fMv2);
249  const double fdenom = (1.000 - t4m)*fdenomB*fdenomB;
250  const double g1denom = 1.000 - (t / fMa2);
251  const double g2denom = kPionMass2 - t;
252  assert(TMath::Abs(fdenom) > fEpsilon); // avoid divide by zero
253  assert(TMath::Abs(g1denom) > fEpsilon); // avoid divide by zero
254  assert(TMath::Abs(g2denom) > fEpsilon); // avoid divide by zero
255 
256  const double f1 = (1.000 - ( (1.000+fNucleonMMDiff) * t4m)) / fdenom;
257  const double f2 = fNucleonMMDiff / fdenom;
258  const double g1 = fg1of0 / (g1denom*g1denom);
259  const double g2 = (2.000 * kNucleonMass2 * g1) / g2denom;
260 
261  const double f12 = f1 * f1;
262  const double f124 = 4.000 * f12;
263  const double f22 = f2 * f2;
264  const double g12 = g1 * g1;
265  const double g124 = 4.000 * g12;
266  const double g22 = g2 * g2;
267  const double g224meM2 = 4.000 * g22 * kElectronMass2 / kNucleonMass2;
268 
269  const double g1cFsumR = g1 * (f1+f2);
270  const double f1cf2 = f1 * f2;
271  const double g1cg2 = g1 * g2;
272  const double f1cf2R8 = f1cf2 * 8.000;
273  const double g1cg2R16me = g1cg2 * 16.000 * kElectronMass2;
274 
275 #ifdef __GENIE_LOW_LEVEL_MESG_ENABLED__
276  LOG("StrumiaVissani", pDEBUG) << "*** t = " << t
277  << ", g2 = " << g2
278  << ", g1 = " << g1
279  << ", f1 = " << f1
280  << ", f2 = " << f2;
281 #endif
282 
283  // ok - now calculate the terms of the matrix element
284  const double mat = MAterm(t, t2, f124, f22, g124,
285  g224meM2, f1cf2R8, g1cg2R16me, g1cFsumR);
286  const double mbt = MBterm(t, f1cf2, g1cg2, g1cFsumR, f22);
287  const double mct = MCterm(t, f124, f22, g124);
288 
289  const double M2 = mat - (sMinusU * (mbt - (sMinusU * mct)));
290 #ifdef __GENIE_LOW_LEVEL_MESG_ENABLED__
291  LOG("StrumiaVissani", pDEBUG) << "*** Matrix element = " << (M2 / 16.000)
292  << " [16A=" << mat << "] [16B=" << mbt
293  << "] [16C=" << mct << "]";
294 #endif
295 
296  return ( M2 / 16.000 );
297 }
298 //____________________________________________________________________________
299 double StrumiaVissaniIBDPXSec::MAterm(const double t,
300  const double t2,
301  const double f124,
302  const double f22,
303  const double g124,
304  const double g224meM2,
305  const double f1cf2R8,
306  const double g1cg2R16me,
307  const double g1cFsumR)
308 {
309  // return A(t) in the matrix element calculation
310  // from eqn 6 (without the factor 16)
311  //
312  // for speed purposes, no check that |t|^2 = t2 is performed
313 
314  // store multiply used terms
315  const double tmme2 = t - kElectronMass2;
316  const double tpme2 = t + kElectronMass2;
317 
318  double r1 = f124 * ( k4NucMass2 + tpme2);
319  r1 += g124 * (-k4NucMass2 + tpme2);
320  r1 += f22 * ( (t2/kNucleonMass2) + 4.000*tpme2 );
321  r1 += g224meM2 * t;
322  r1 += f1cf2R8 * (2.000*t + kElectronMass2);
323  r1 += g1cg2R16me;
324  r1 *= tmme2;
325 
326  double r2 = (f124 + (t * (f22 / kNucleonMass2))) * (k4NucMass2 + tmme2);
327  r2 += g124 * (k4NucMass2 - tmme2);
328  r2 += g224meM2 * tmme2;
329  r2 += f1cf2R8 * (2.000*t - kElectronMass2);
330  r2 += g1cg2R16me;
331  r2 *= kNucMassDiff2;
332 
333  const double r3 = 32.000 * kElectronMass2 * kNucleonMass * kNucMassDiff
334  * g1cFsumR;
335 
336  return ( r1 - r2 - r3 );
337 }
338 //____________________________________________________________________________
339 double StrumiaVissaniIBDPXSec::MBterm(const double t,
340  const double f1cf2,
341  const double g1cg2,
342  const double g1cFsumR,
343  const double f22)
344 {
345  // return C(t) in the matrix element calculation
346  // from eqn 6 (without the factor 16)
347 
348  double bterm = 16.000 * t * g1cFsumR;
349  bterm += ( k4EleMass2 * kNucMassDiff
350  * (f22 + (f1cf2 + 2.000*g1cg2)) ) / kNucleonMass2;
351  return bterm;
352 }
353 //____________________________________________________________________________
354 double StrumiaVissaniIBDPXSec::MCterm(const double t,
355  const double f124,
356  const double f22,
357  const double g124)
358 {
359  // return C(t) in the matrix element calculation
360  // from eqn 6 (without the factor 16)
361 
362  return ( f124 + g124 - (t * ( f22 / kNucleonMass2 )) );
363 }
364 //____________________________________________________________________________
365 double StrumiaVissaniIBDPXSec::RadiativeCorr(const double Ee) const
366 {
367  // radiative correction to the cross section. eqn 14 from the reference
368  // only valid for Ev<<m_p!
369 
370  assert(Ee > fEpsilon); // must be non-zero and positive
371  double rc = 6.000 + (1.500 * TMath::Log(kProtonMass / (2.000*Ee)));
372  rc += 1.200 * TMath::Power((kElectronMass / Ee), 1.500);
373  rc *= kAem / kPi;
374  rc += 1.000;
375  return rc;
376 
377 }
378 //____________________________________________________________________________
379 double StrumiaVissaniIBDPXSec::FinalStateCorr(const double Ee) const
380 {
381  // Sommerfeld factor; correction for final state interactions.
382  // eqn 15 of the reference
383 
384  assert(Ee > fEpsilon); // must be non-zero and positive
385  const double eta = 2.000*kPi*kAem
386  / TMath::Sqrt(1.000 - (kElectronMass2 / (Ee*Ee)));
387  const double expn = TMath::Exp(-1.000 * eta);
388  assert(expn < 1.000);
389  return ( eta / (1.000 - expn) );
390 }
391 //____________________________________________________________________________
Cross Section Calculation Interface.
const KPhaseSpace & PhaseSpace(void) const
Definition: Interaction.h:73
double J(double q0, double q3, double Enu, double ml)
Definition: MECUtils.cxx:147
#define pERROR
Definition: Messenger.h:59
Cross Section Integrator Interface.
static const double kNucleonMass
bool IsNeutron(void) const
Definition: Target.cxx:267
static double MAterm(const double t, const double t2, const double f124, const double f22, const double g124, const double g224meM2, const double f1cf2R8, const double g1cg2R16me, const double g1cFsumR)
double RadiativeCorr(const double Ee) const
bool IsNuN(void) const
is neutrino + neutron?
static double MCterm(const double t, const double f124, const double f22, const double g124)
Generated/set kinematical variables for an event.
Definition: Kinematics.h:39
bool IsNuE(int pdgc)
Definition: PDGUtils.cxx:158
bool IsInverseBetaDecay(void) const
static double MBterm(const double t, const double f1cf2, const double g1cg2, const double g1cFsumR, const double f22)
enum genie::EKinePhaseSpace KinePhaseSpace_t
An implementation of the neutrino - (free) nucleon [inverse beta decay] cross section, valid from the threshold energy (1.806MeV) up to hundreds of MeV. Currently cut off at 1/2 nucleon mass. Based on the Strumia/Vissani paper Phys.Lett.B564:42-54,2003.
static const double kElectronMass
Summary information for an interaction.
Definition: Interaction.h:56
double q2(bool selected=false) const
Definition: Kinematics.cxx:141
#define LOG(stream, priority)
A macro that returns the requested log4cpp::Category appending a string (using the FILE...
Definition: Messenger.h:96
double FinalStateCorr(const double Ee) const
static const double kElectronMass2
const Kinematics & Kine(void) const
Definition: Interaction.h:71
A Neutrino Interaction Target. Is a transparent encapsulation of quite different physical systems suc...
Definition: Target.h:40
virtual void Configure(const Registry &config)
Definition: Algorithm.cxx:62
int ProbePdg(void) const
Definition: InitialState.h:64
Kinematical phase space.
Definition: KPhaseSpace.h:33
static const double kNeutronMass
double MtxElm(const double sMinusU, const double t) const
double Integral(const Interaction *i) const
bool ValidKinematics(const Interaction *i) const
Is the input kinematical point a physically allowed one?
#define pINFO
Definition: Messenger.h:62
static const double kNucleonMass2
const UInt_t kISkipKinematicChk
if set, skip kinematic validity checks
Definition: Interaction.h:48
bool ValidProcess(const Interaction *i) const
Can this cross section algorithm handle the input process?
double dSigDt(const double sMinusU, const double sMinusMnuc, const double t) const
A registry. Provides the container for algorithm configuration parameters.
Definition: Registry.h:65
ClassImp(CacheBranchFx)
bool IsNuBarP(void) const
is anti-neutrino + proton?
bool IsAboveThreshold(void) const
Checks whether the interaction is above the energy threshold.
double Jacobian(const Interaction *const i, KinePhaseSpace_t f, KinePhaseSpace_t t)
Definition: KineUtils.cxx:130
double XSec(const Interaction *i, KinePhaseSpace_t k) const
Compute the cross section for the input interaction.
const ProcessInfo & ProcInfo(void) const
Definition: Interaction.h:70
void Configure(const Registry &config)
bool GetParam(const RgKey &name, T &p, bool is_top_call=true) const
const Target & Tgt(void) const
Definition: InitialState.h:66
static const double kProtonMass2
virtual double Integrate(const XSecAlgorithmI *model, const Interaction *interaction) const =0
static const double kNeutronMass2
bool IsProton(void) const
Definition: Target.cxx:262
double ProbeE(RefFrame_t rf) const
bool IsAntiNuE(int pdgc)
Definition: PDGUtils.cxx:173
const XSecIntegratorI * fXSecIntegrator
const UInt_t kISkipProcessChk
if set, skip process validity checks
Definition: Interaction.h:47
Initial State information.
Definition: InitialState.h:48
#define pDEBUG
Definition: Messenger.h:63
const Algorithm * SubAlg(const RgKey &registry_key) const
Definition: Algorithm.cxx:345