Violation in Mixing

2.2 The BABAR detector. 75
Table 2-4. Trigger objects for the Level 1 trigger.
object description threshold
� Short track reaching ��À super-layer � Å�Î�
� Long track reaching ��À super-layer � Å�Î�
� High ÔØ track � Å�Î�
ŠAll-� MIP energy ��
� All-� intermediate energy � ��
� All-� high energy � ��
Table 2-5. Trigger efficiencies and rates at a luminosity of � Ñ × for selected triggers applied
to various physics samples. Symbols refer to the counts for each object in table 2-4.
Level 1 Trigger ¯ �� ¯ ¯Ù�× ¯�� Rate (Hz)
� � � £ � ��� ���� � � �
� � � £ � � � ��� ��� ��� ���� �
Å � Å £ � ���� ���� ���� �
� Š� � �� ��� ���� ���� �
� � � � Š� ���� ���� ���� �
Å £ � � � � � ��� � � ��� ���� �
� � � � � � � � ���� ��� ��� �
Combined Level 1 Triggers � ���� ���� ��� � ���� ��
are written like � Å meaning an � cluster back to back to an Å cluster, while the symbol denotes
requiring clusters and tracks in coincidence, a non-orthogonal selection criterion.
Level 3 trigger is part of the online farm and consists of a network of commercial processors: input are the
L1 trigger data and the full event data for events that passed the L1 trigger. Output to mass storage is the full
event and trigger data of events accepted by L3. L3 trigger algorithms have all event information available
and they operate by refining and improving the selection methods used by L1: better ��À tracking (vertex
resolution) and �� clustering filters allow for greater rejection of beam backgrounds and Bhabha events.
A cut on the vertex position can be made to reject events that did not originate at the interaction point. L3
trigger also includes a variety of filters to perform event classification and background reduction: the logging
decision is based on two orthogonal filters, one relying exclusively on ��À data and the other relying only
on �� data.
THE BABAR EXPERIMENT