Find asymmetry from cryo oven with alpha detectors. 
            a: list of alpha detector histograms (each helicity)  
            b: list of beta  detector histograms (each helicity)  1+ 1- 2+ 2-

def _get_asym_alpha_tag(self,a,b):
        """
            Find asymmetry from cryo oven with alpha detectors. 
            a: list of alpha detector histograms (each helicity)  
            b: list of beta  detector histograms (each helicity)  1+ 1- 2+ 2-
        """

        # beta in coincidence with alpha
        coin = a[:4]
        
        # beta coincidence with no alpha
        no_coin = a[4:8]

        # get split helicity asym from 
        hel_coin =      self._get_asym_hel(coin)
        hel_no_coin =   self._get_asym_hel(no_coin)
        hel_reg =       self._get_asym_hel(b)
        
        # get combined helicities
        com_coin =      self._get_asym_comb(coin)
        com_no_coin =   self._get_asym_comb(no_coin)
        com_reg =       self._get_asym_comb(b)

        # make output
        return (hel_coin,hel_no_coin,hel_reg,com_coin,com_no_coin,com_reg)