O2-6235 - change pt range and bug fix

kMaxInvPt to 2 (pt>0.5)
make the inv_pt independent of the pt scale

Author: miranov25

MC/config/common/external/generator/performanceGenerator.C

@@ -208,7 +208,7 @@ namespace o2
             };
 
             // pT bounds: Max pT ~5 TeV (ALICE Pb-Pb energy)
-            const float kMaxInvPt = 1.0f;      // Min pT = 1 GeV
+            const float kMaxInvPt = 2.f;      // Min pT = 0.5 GeV
             const float kBaseMinInvPt = 2e-4f; // Max pT = 5000 GeV (unscaled)
 
             // Check if particle is a parton (quark/gluon, status=11)
@@ -262,7 +262,8 @@ namespace o2
                 int status = isParton(pdgCode) ? 11 : 1;
                 // 4. Kinematics (flat 1/pT, max ~5000 GeV / pTScale)
                 float min_inv_pt = kBaseMinInvPt / pTScale; // E.g., max pT=40,000 GeV for b quarks
-                float inv_pt = (gRandom->Rndm() / pTScale) * (kMaxInvPt - min_inv_pt) + min_inv_pt;
+                float max_inv_pt = kBaseMaxInvPt / pTScale; // E.g., max pT=40,000 GeV for b quarks
+                float inv_pt = (gRandom->Rndm() / pTScale) * (max_inv_pt - min_inv_pt) + min_inv_pt;
                 float pt = 1.0f / inv_pt;
                 float phi = gRandom->Rndm() * 2.0f * TMath::Pi();
                 float eta = gRandom->Rndm() * 3.0f - 1.5f; // ALICE TPC: -1.5 to 1.5