Performance Study of BESIII Trigger System Z.-A. Liu, D. Zhao, D. Jin, H. Xu, S. Wei, W. Gong, K. Wang, Q. Wang, N. Berge, K. Zhu, IHEP Q. An, USTC May 25, 2010, Lisbon, RT2010

Outline  Brief hardware description  Trigger table settings and Data samples  Efficiency determination  Summary

System Block diagram of BESIII Trigger TCBA Global Trigger Logic 6.4  s TOF FEE MDC FEE EMC FEE MU FEE TOFPR MFT Mu track FastOR Track Finder Etotal Energy Hit/Seg Count Track Seg. Finder BEPCII RF TTC TC Sum L1P MHz Track Match Energy Balance Cluster Counting Fast Control FC Daughters Near DetectorsCounting Room MHz High Lights: Optical Isolation-no ground loop current

May LIU,Zhen'An, RT2010,Lisbon4 List of Trigger Conditions

May LIU,Zhen'An, RT2010,Lisbon5 List of Trigger Conditions(2)

May LIU,Zhen'An, RT2010,Lisbon6 List of Trigger Conditions(3) Not used in data taking in 2009

May LIU,Zhen'An, RT2010,Lisbon7 Trigger Table settings for the 2009 ψ′ running.  Channel 0 is designed for endcap Bhabha events  channels 1 to 5 for events with charged particles in the barrel region and  channel 11 for all-neutral events.

May LIU,Zhen'An, RT2010,Lisbon8 Trigger Table settings for the 2009 J/ψ running  Channel 0 is designed for endcap Bhabha events  channels 1 to 5 for events with charged particles in the barrel region  channel 11 for all-neutral events.  The only difference with regards to the ψ′ running is the removal of channel 3 due to high noise.

May LIU,Zhen'An, RT2010,Lisbon9 Data Samples  Trigger settings for the 2009 ψ′ trigger test running. Channel 0 is used for MDC trigger checks, channel 1 for EMC trigger checks and channel 2 for ToF trigger checks. RUN taken in May 2009  Trigger settings for the 2009 J/ψ trigger test running. Channel 0 is used for MDC and ToF trigger checks, channels 1, 2 and 3 for EMC trigger checks and the other channels served as a backup RUN , taken in July 2009

May LIU,Zhen'An, RT2010,Lisbon10 Sample Selection  a polar angle ϑ in the range | cos ϑ | < 0.97 are considered.  The barrel region is defined as | cos ϑ | < 0.8,  the endcap region as 0.83 < | cos ϑ | < 0.97  Bhabha: Two EMC showers with energy ± 10% beam energy Showers with |cos(θ)| < 0.97 (< 0.8 for barrel), shower opening angle > 166 Two good tracks with opening angle > 175 two Kalman-fitted tracks are required with their dis-tance of closest approach to the origin  < 1 cm in the radial direction and  < 5 cm along the beam direction. Use EMC triggered events (channel 1) to check MDC and ToF Use MDC/ToF triggered data (channels 2,3,4) to check EMC

May LIU,Zhen'An, RT2010,Lisbon11 Sample Selection(2)  a polar angle ϑ in the range | cos ϑ | < 0.97 are considered.  The barrel region is defined as | cos ϑ | < 0.8,  the endcap region as 0.83 < | cos ϑ | < 0.97  Charged Hadron: good tracks with a distance of closest approach to the origin of less  < 1 cm in the radial direction and  < 5 cm along the beam direction. Two or more such tracks are required to be present in the event. If there are exactly two tracks, their opening angle is required to be less than 170◦ in order to suppress Bhabha and dimuon events

May LIU,Zhen'An, RT2010,Lisbon12 Sample Selection(3)  a polar angle ϑ in the range | cos ϑ | < 0.97 are considered.  The barrel region is defined as | cos ϑ | < 0.8,  the endcap region as 0.83 < | cos ϑ | < 0.97  Dimuon Selection: two good charged tracks with opposite charges and the spacial angle between them should be larger than 3.1 rad. The definition of a good charged track is identical to the one in the Bhabha selection. In addtion we require that the momentum of each track is less than 2 GeV and the deposited energy in the EMC is less than 0.7 GeV. The total four-momentum (E, px, py, pz) is required to fall in the (3.2 4,− ,− ,− )GeV region after assuming each track is muon

May LIU,Zhen'An, RT2010,Lisbon13 Sample Selection(4)  a polar angle ϑ in the range | cos ϑ | < 0.97 are considered.  The barrel region is defined as | cos ϑ | < 0.8,  the endcap region as 0.83 < | cos ϑ | < 0.97  ψ′ −> π + π − J/ψ Selection: Four good charged tracks, two positive and two negative. The good charged tracks are defined as in the previous selections. Then we assume the softer tracks of each charge are pions and harder tracks are leptons. After that assumption we also require the recoil mass of the two pions to fall into the region (3.08, 3.12)GeV, the invariant mass of two leptons is required to be in the region (3.0, 3.2)GeV, and the total energy of the event should be in the range (3, 4)GeV

May LIU,Zhen'An, RT2010,Lisbon14 Efficiency Determination  Determination of Trigger Condition Efficiencies. N stands for the number of events, sel for events passing the physics selection, channel for events having triggered the reference channel and condition for events with the trigger condition under study active. The reference channels used for the various data samples can be found in table

May LIU,Zhen'An, RT2010,Lisbon15 Efficiency Determination  Determination of Trigger Channel Efficiencies. . N stands for the number of events, sel for events passing the physics selection, channel for events having triggered the reference channel and condition for events with the trigger condition under study active. The reference channels used for the various data samples can be found in table

May LIU,Zhen'An, RT2010,Lisbon16 Trigger condition efficiencies for ψ′ data taking  The numbers have statistical errors of the order of 0.1% in efficiency

May LIU,Zhen'An, RT2010,Lisbon17 Trigger condition efficiencies for J/ψ data taking  The numbers have statistical errors of the order of 0.1% in efficiency

May LIU,Zhen'An, RT2010,Lisbon18 Determination of EMC Threshold behavior Threshold energies and resolutions  Threshold scan. At the end of the 2009 ψ′ running, a threshold scan was performed, where the settings for both low and medium thresholds were changed from run to run.

May LIU,Zhen'An, RT2010,Lisbon19 Trigger Channel Efficiencies  Global trigger efficiencies for ψ′ running.  The statistical errors are below 0.1% in efficiency

May LIU,Zhen'An, RT2010,Lisbon20 Trigger Channel Efficiencies  Global trigger efficiencies for J/ψ running.  The statistical errors are below 0.1% in efficiency

May LIU,Zhen'An, RT2010,Lisbon21 Conclusions  BES III trigger efficiencies studied for both the 2009 ψ′and J/ψ running.  In general the efficiencies are high enough that they contribute less than 0.5% overall efficiency loss for events with and energy deposition above 1 GeV and/or at least two charged tracks in the barrel.  For events not fulfilling these criteria, some care is needed as there are inefficiencies up to 3% (for endcap dimuons), stemming from localized inefficiencies in the EMC and global inefficiencies of the ToF system.  All efficiencies quoted here are valid only for the BES III active solid angle, i.e. the very forward and backward regions as well as the cracks between the barrel and the endcaps are not included.

May LIU,Zhen'An, RT2010,Lisbon23 Backups

May LIU,Zhen'An, RT2010,Lisbon24 ψ′ ： Group Channel （ GC ）： Endcap ， charged,Barrel charged, neutral  Here gcn is the efficiency of group channel n, cn is the efficiency of channel n, ǫ n is the efficiency of condition n, P(n|m) is a conditional probability, i.e. the probability of condition n given condition m. Our readeres should notice that if the trigger conditions are not in dependent of each other, we have to consider the correlations of among them

May LIU,Zhen'An, RT2010,Lisbon25 J/ψ ： Group Channel （ GC ）： Endcap ， charged,Barrel charged, neutral  Here gcn is the efficiency of group channel n, cn is the efficiency of channel n, ǫ n is the efficiency of condition n, P(n|m) is a conditional probability, i.e. the probability of condition n given condition m. Our readeres should notice that if the trigger conditions are not in dependent of each other, we have to consider the correlations of among them