Added input ROOT file and simple code

README.md

@@ -5,9 +5,9 @@ git clone https://eicweb.phy.anl.gov/jihee.kim/study.git
 cd study
 ```
 
-Input Root Files
-----------------
- - from lAger event generator
+Input File
+----------
+ - from `lAger` event generator
 
 Scripts
 -------

sample/read_and_print.py

+#############################
+# Read ROOT File
+# Loop over event by event
+# Print interested variables
+#############################
+import ROOT
+
+# ROOT file that you read
+fname = "input.root"
+
+# Open file and get TTree
+f = ROOT.TFile.Open(fname)
+tree = f.Get("lAger")
+print("=======")
+print("Read in ROOT file: {}".format(fname))
+
+# Total number of events in TTree
+nevt = tree.GetEntries()
+print ("total number of events: ",nevt)
+
+# Loop over event by event
+print("Loop over event by event")
+for ievt in range(0,nevt):
+    # Access info of an event
+    tree.GetEntry(ievt)
+
+    if ievt % 5 == 0: # Printing
+        print("Processing event number: {}".format(ievt))
+
+    W  = tree.W  # invariant mass: sqrt(center of mass energy virtual photon + target (Helium-4)) 
+    Q2 = tree.Q2 # virtual photon mass: four-momentum transfer of electron
+    t  = tree.t  # four-momentum transfer of Helium-4
+
+    # Total number of particles in an event
+    nptls = tree.particles.GetEntries()
+    print (nptls)
+
+    ip = 0 # index of particles
+    # Loop over particles
+    for ptl in range(0,nptls):
+        # TODO: Access leaf and Save as in array
+        # infomration needed
+        # each particles have below info
+        # particles.fPdgCode / particles.fStatusCode / particles.fE / particles.fPx / particles.fPy / particles.fPz
+
+        # Not Working...
+        #PID = tree.particles[ptl].fPdgCode
+        #PID[ip] = tree.GetLeaf("particles.fPdgCode").GetValue(ptl)
+        ip += 1
+    #print (PID)
+
+    # Just checking the first 10 events
+    if ievt > 9:
+        break
+    pass
+print("=======")