[Common] ITS PID: set MC parametrisations and fix resolution term for Z=2 (#11050)

Co-authored-by: Francesco Mazzaschi <fmazzasc@alipap1.cern.ch>

Author: fmazzasc

Common/DataModel/PIDResponseITS.h

@@ -73,9 +73,9 @@ struct ITSResponse {
     // static constexpr float charge = static_cast<float>(o2::track::pid_constants::sCharges[id]);
     const float bg = momentum * inverseMass;
     if (id == o2::track::PID::Helium3 || id == o2::track::PID::Alpha) {
-      return mResolutionParamsZ2[0] * std::erf((bg - mResolutionParamsZ2[1]) / mResolutionParamsZ2[2]);
+      return mResolutionParamsZ2[1] > -999.0 ? mResolutionParamsZ2[0] * std::erf((bg - mResolutionParamsZ2[1]) / mResolutionParamsZ2[2]) : mResolutionParamsZ2[0];
     }
-    return mResolutionParams[0] * std::erf((bg - mResolutionParams[1]) / mResolutionParams[2]);
+    return mResolutionParams[1] > -999.0 ? mResolutionParams[0] * std::erf((bg - mResolutionParams[1]) / mResolutionParams[2]) : mResolutionParams[0];
   }
 
   template <o2::track::PID::ID id>
@@ -117,6 +117,14 @@ struct ITSResponse {
     mResolutionParamsZ2[2] = p2_res_Z2;
   }
 
+  static void setMCDefaultParameters()
+  {
+    setParameters(1.63806, 1.58847, 2.52275,
+                  2.66505, 1.48405, 6.90453,
+                  1.40487e-01, -4.31078e-01, 1.50052,
+                  0.09, -999., -999.);
+  }
+
  private:
   static std::array<float, 3> mITSRespParams;
   static std::array<float, 3> mITSRespParamsZ2;
@@ -129,7 +137,7 @@ std::array<float, 3> ITSResponse::mITSRespParams = {1.18941, 1.53792, 1.69961};
 std::array<float, 3> ITSResponse::mITSRespParamsZ2 = {2.35117, 1.80347, 5.14355};
 // relative resolution is modelled with an erf function: [0]*TMath::Erf((x-[1])/[2])
 std::array<float, 3> ITSResponse::mResolutionParams = {1.94669e-01, -2.08616e-01, 1.30753};
-std::array<float, 3> ITSResponse::mResolutionParamsZ2 = {8.74371e-02, -1.82804, 5.06449e-01};
+std::array<float, 3> ITSResponse::mResolutionParamsZ2 = {0.09, -999., -999.};
 bool ITSResponse::mIsInitialized = false;
 
 namespace pidits

Common/TableProducer/PID/pidITS.cxx

@@ -51,12 +51,12 @@ static const std::vector<std::string> parameterNames{"RespITSPar1", "RespITSPar2
                                                      "ResolutionPar1_Z2", "ResolutionPar2_Z2", "ResolutionPar3_Z2"};
 
 static constexpr float defaultParameters[nCases][nParameters] = {
-  {1.18941, 1.53792, 1.69961, 2.35117, 1.80347, 5.14355, 1.94669e-01, -2.08616e-01, 1.30753, 8.74371e-02, -1.82804, 5.06449e-01},
-  {1.18941, 1.53792, 1.69961, 2.35117, 1.80347, 5.14355, 1.94669e-01, -2.08616e-01, 1.30753, 8.74371e-02, -1.82804, 5.06449e-01}};
+  {1.18941, 1.53792, 1.69961, 2.35117, 1.80347, 5.14355, 1.94669e-01, -2.08616e-01, 1.30753, 0.09, -999., -999.},
+  {1.63806, 1.58847, 2.52275, 2.66505, 1.48405, 6.90453, 1.40487e-01, -4.31078e-01, 1.50052, 0.09, -999., -999.}};
 
 /// Task to produce the ITS PID information for each particle species
 /// The parametrization is: [p0/(bg)**p1 + p2] being bg = p/m. Different parametrizations are used for He3 and Alpha particles.
-/// The resolution depends on the bg and is modelled with an erf function: p0*TMath::Erf((bg-p1)/p2)
+/// The resolution depends on the bg and is modelled with an erf function: p0*TMath::Erf((bg-p1)/p2). If p1/p2 is -999, the resolution is set to p0.
 struct itsPid {
 
   Configurable<LabeledArray<float>> itsParams{"itsParams",