From bd7772df71ad6f4bfb61407a3eba301c39f55c9f Mon Sep 17 00:00:00 2001
From: Nicola Amapane <nicola.amapane@cern.ch>
Date: Thu, 28 May 2015 15:21:17 +0200
Subject: [PATCH] Do not apply DT vdrift correction (that accounts for field in
 phi SLs of wheels+-2 of MB1) when B=0

---
 .../DTRecHit/plugins/DTLinearDriftFromDBAlgo.cc      | 12 +++++++++++-
 .../DTRecHit/plugins/DTLinearDriftFromDBAlgo.h       |  5 +++++
 2 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/RecoLocalMuon/DTRecHit/plugins/DTLinearDriftFromDBAlgo.cc b/RecoLocalMuon/DTRecHit/plugins/DTLinearDriftFromDBAlgo.cc
index a726524e028ed..6eef48c24871b 100644
--- a/RecoLocalMuon/DTRecHit/plugins/DTLinearDriftFromDBAlgo.cc
+++ b/RecoLocalMuon/DTRecHit/plugins/DTLinearDriftFromDBAlgo.cc
@@ -17,12 +17,17 @@
 #include "CondFormats/DTObjects/interface/DTRecoUncertainties.h"
 #include "CondFormats/DataRecord/interface/DTRecoUncertaintiesRcd.h"
 #include "FWCore/MessageLogger/interface/MessageLogger.h"
+#include "MagneticField/Engine/interface/MagneticField.h"
+#include "MagneticField/Records/interface/IdealMagneticFieldRecord.h"
 
 using namespace std;
 using namespace edm;
 
 DTLinearDriftFromDBAlgo::DTLinearDriftFromDBAlgo(const ParameterSet& config) :
   DTRecHitBaseAlgo(config),
+  mTimeMap(0),
+  field(0),
+  nominalB(-1),
   minTime(config.getParameter<double>("minTime")),
   maxTime(config.getParameter<double>("maxTime")),
   doVdriftCorr(config.getParameter<bool>("doVdriftCorr")),
@@ -57,6 +62,11 @@ void DTLinearDriftFromDBAlgo::setES(const EventSetup& setup) {
   setup.get<DTMtimeRcd>().get(mTimeHandle);
   mTimeMap = &*mTimeHandle;
 
+  ESHandle<MagneticField> magfield;
+  setup.get<IdealMagneticFieldRecord>().get(magfield);
+  field = &*magfield;
+  nominalB = field->nominalValue();
+
   if (useUncertDB) {
     ESHandle<DTRecoUncertainties> uncerts;
     setup.get<DTRecoUncertaintiesRcd>().get(uncerts);
@@ -172,7 +182,7 @@ bool DTLinearDriftFromDBAlgo::compute(const DTLayer* layer,
   }
   
   //only in step 3
-  if(doVdriftCorr && step == 3){
+  if(doVdriftCorr && step == 3 && nominalB !=0){
     if (abs(wireId.wheel()) == 2 && 
 	wireId.station() == 1 &&
 	wireId.superLayer() != 2) {
diff --git a/RecoLocalMuon/DTRecHit/plugins/DTLinearDriftFromDBAlgo.h b/RecoLocalMuon/DTRecHit/plugins/DTLinearDriftFromDBAlgo.h
index 53b9d6e4bdb03..3f3c793eb7d06 100644
--- a/RecoLocalMuon/DTRecHit/plugins/DTLinearDriftFromDBAlgo.h
+++ b/RecoLocalMuon/DTRecHit/plugins/DTLinearDriftFromDBAlgo.h
@@ -13,6 +13,7 @@
 
 class DTMtime;
 class DTRecoUncertainties;
+class MagneticField;
 
 class DTLinearDriftFromDBAlgo : public DTRecHitBaseAlgo {
  public:
@@ -83,6 +84,10 @@ class DTLinearDriftFromDBAlgo : public DTRecHitBaseAlgo {
   //Map of meantimes
   const DTMtime *mTimeMap;
 
+  // MF field
+  const MagneticField* field;
+  int nominalB;
+
   // Map of hit uncertainties
   const DTRecoUncertainties *uncertMap;