11 February 2008 Compass Trigger Meeting I. Uman

Important reaction channels and the trigger concepts of former experiments

Proposed Reactions @ 190 GeV/c with COMPASS: central Production:

diffractive Scattering: what can we learn from WA102?

and E852?

ηηX Xp,πpπ

ππX Xp,πpπ 22

ππX Xp,pπ 2ηπX Xp,pπ

sf Xpppp

Xppπ

11 February 2008 Compass Trigger Meeting I. Uman

E852 Detector

11 February 2008 Compass Trigger Meeting I. Uman

E852 Detector

Max Beam of 2x106 99%

Target Cylindrical (TCYL)Prop. Wire Chambers (TPX)

CPVA,CPVB,CPVC,EV, BV

Downs. Endcup Array (DEA)

(LGD)}

TDX4

11 February 2008 Compass Trigger Meeting I. Uman

E852 Trigger

nπηpπ 0

• Pretrigger on

BV and EV

• Level 1 trigger on

DEA CPVB CPVC TCYL PWC

• Level 2 fast trigger processor total energy and effective

mass of the LGD photon system,

‘able to handle up to 104 events/s’ at 10% dead time’:

- (#TCYL tracks)-(#TPX1 hits)-(#TPX2 hits)-Level 2 trigger:

example: @18GeV/c:

0-0-0-TriggerProcessorenergy –TriggerProcessoreta

example: @18GeV/c: 0-2-2-TriggerProcessorenergy -TriggerProcessoreta

nππηpπ

11 February 2008 Compass Trigger Meeting I. Uman

E852 Trigger

from NIM A 387 (1997) 377:

11 February 2008 Compass Trigger Meeting I. Uman

WA102 Detector

(Omega + GAMS)

11 February 2008 Compass Trigger Meeting I. Uman

WA102 Detector description

• “telescope” of ten microstrip detectors to measure beam direction

• 60 cm hydrogen target + box counter (TB)

• fifteen 2mm pitch (A and B) MWPC + one 1mm pitch MWPC + two drift chambers (DC) to measure medium momentum charged tracks

• sixteen (eight left+eight right) 2 mm pitch (C) MWPC to measure slow proton

• system of microstrip detector placed at 5 m and at 10 m downstream to measure the outgoing fast track (350-450 GeV/c)

• two Čerenkov detectors Č1 and Č2(not in 2006) + three scintillator hodoscopes HY1(not in 2006), HY2, HY3(not in 2006) for charged particle identification

• GAMS-4000 electromagnetic calorimeter for photons

11 February 2008 Compass Trigger Meeting I. Uman

WA102 Trigger

• fast particle crossing the microstrip telescope

• coincidence between two scintillator counters (A1+A2) placed close to the microstrip detectors at 5 m and 10 m (A2 split in two vertical direction A2L and A2R in order to determine the y-direction)

• slow particle left [right] defined by one hit on any of the fourteen slabs of the slow proton counter left (SPCL) [SPCR] + a hit in the left [right] element of the target box counter + >one hit in each of the two planes of the C MWPC on the left [right] side of the target

• zero hit in the other three sides of the TB to reduce backward diffraction or excitations events

11 February 2008 Compass Trigger Meeting I. Uman

WA102 Trigger

ππXXpppp sf ,

• slow left proton and a hit in A2(L) (LL trigger) or slow right right proton in A2(R) (RR trigger) exclude elastic scattering

• elastic scattering were reduced in the LR and RL case by requiring one hit in the in the downstream hodoscope HY1

example: @450 GeV/c:

LR

• observation of higher and f2(1270) in the LL or RR case which cannot be due to the trigger or acceptance (Phys. Lett. B 388(1996) 853)

• enhancement of glueball candidates at high pT

LL LL

11 February 2008 Compass Trigger Meeting I. Uman

Conclusion

• Care has to be taken to choose of a correct trigger logic which does not bias physics in central production

(maximize azimuthal acceptance)

• A choice of a common trigger which includes CP and diffractive scattering would reduce the beam time request