void alpha_vs_pt(TString pre ="", TString particle = ""){

	//***** Read input file *****
	TFile * inFile = new TFile(pre, "READ");


	//***** Get Data from file *****
	if (particle=="lambda"){
		
		TTree * lambda = (TTree*) inFile->Get("ntpLambda0");
		
		TString pt = "VtxFit_pt";
		TString pz = "VtxFit_pz";
		TString pzPion = "VtxFit_d0pz";
		TString pzProton = "VtxFit_d1pz";
	}
	//if else (particle=="antilambda"){
		
		//TTree * pion = (TTree*) inFile->Get("ntpPiPlus");
		//TTree * proton = (TTree*) inFile->Get("ntpAntiProton");
		//TTree * lambda = (TTree*) inFile->Get("ntpAntiLambda0");	
		
		//TString pt = "antiLambda0_pt";
		//TString pzPion = "piplus_pz";
		//TString pzProton = "antiProton_pz";
	//} 
	else{
		cout << "Use this script like alpha_vs_pt('prefix', 'particle')" << endl;
		cout << "Please chose a particle: lambda or antilambda)" << endl;
	}
	

	//***** Create Histograms and Canvas
	TCanvas *c = new TCanvas("c", "c", 0,0, 1000,600);
		
	TString alpha =TString::Format("(%s-%s)/ %s", pzProton.Data(), pzPion.Data(), pz.Data());
	TString expr = TString::Format("%s:%s", pt.Data(), alpha.Data());
	TString cut	= "McTruthMatch & VtxFit_HowGood==1 & MassFit_prob>0.01";

	TH2D * h = new TH2D("h", "alpha vs p_{t}; alpha; p_{t}", 200, 0,1,200, 0, 1.5);
	lambda->Project("h",expr,cut);
	
	h->Draw("COLZ");

}