diff --git a/data/selections.py b/data/selections.py
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index 0000000..42cb414
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+++ b/data/selections.py
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+"""
+Global selection definitions for RDataLoader.
+
+Each selection is a callable: (ak.Array) -> np.ndarray[bool]
+"""
+import numpy as np
+import awkward as ak
+from typing import Dict, Callable, Union
+
+from RDataLoader import SelectionFn, RDataLoader
+import data.observables as observables
+
+# Pre-defined global selections - from TOP-20-006
+# Based on v2.2+ CMGRDF ntuple names
+SELECTIONS: Dict[str, SelectionFn] = {
+    "nL2": lambda ar: ar["nLepton_good"] == 2,  # type:ignore
+    "nJ2p": lambda ar: ar["nSelJet"] >= 2,  # type:ignore
+    "nB2p": lambda ar: ar["nBJet"] >= 2,  # type:ignore
+    "goodTop": lambda ar: ar["tr_isvalid"] == 1,  # type:ignore
+    "minMll": lambda ar: ar["dilep_mass"] > 20,  # type:ignore
+    "SameFlavorMET": lambda ar: (ak.abs(ar["lep0_pdgId"]) != ak.abs(ar["lep1_pdgId"])) | (ar["MET_pt"] > 40),  # type:ignore
+    "SameFlavorMll": lambda ar: (ak.abs(ar["lep0_pdgId"]) != ak.abs(ar["lep1_pdgId"])) | (ar["dilep_mass"] < 76) | (ar["dilep_mass"] > 106)  # type:ignore
+}
+
+# Reconstruction-level variables used for event selection that are not input features
+SELECTION_OBSERVERS = ["nLepton_good", "tr_isvalid", "lep0_pdgId", "lep1_pdgId", "MET_pt"]
+
+# testing with a single file
+if __name__ == "__main__":
+
+    # full loader
+    tt2l = RDataLoader(
+        input_paths=["/groups/hephy/cms/robert.schoefbeck/CMGRDF_ntuples/v2-2_nJ2p_nB2p_trvalid/2016/TTLep_pow_nominal.root"],
+        tree_name="Events",
+        branches=SELECTION_OBSERVERS + observables.ALL_FEATURES,
+        # selection=[SELECTIONS["minMll"], SELECTIONS["goodTop"]],
+        n_split=1,
+        splitting_strategy="events",
+        strict_branches=False,
+        weight_branches=[
+            "weight",
+        ],
+        feature_names=observables.ALL_FEATURES,
+        observer_names=SELECTION_OBSERVERS,
+    )
+
+    # loader with selection
+    tt2l_sel = RDataLoader(
+        input_paths=["/groups/hephy/cms/robert.schoefbeck/CMGRDF_ntuples/v2-2_nJ2p_nB2p_trvalid/2016/TTLep_pow_nominal.root"],
+        tree_name="Events",
+        branches=SELECTION_OBSERVERS + observables.ALL_FEATURES,
+        selection=[SELECTIONS["minMll"]],
+        n_split=1,
+        splitting_strategy="events",
+        strict_branches=False,
+        weight_branches=[
+            "weight",
+        ],
+        feature_names=observables.ALL_FEATURES,  # includes dilep_mass
+        observer_names=SELECTION_OBSERVERS,
+    )
+
+    dilep_mass = tt2l.features(feature_names=["dilep_mass"])
+    dilep_mass_with_selection = tt2l_sel.features(feature_names=["dilep_mass"])
+    print(f"minimum dilepton mass: without cut: {ak.min(dilep_mass)}; with cut: {ak.min(dilep_mass_with_selection)}")
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