Hadron Trigger

Overview

The task of the 2008 hadron triggers is to select potentially good diffractive and centrally produced events. As both production processes has a recoil proton from the LH2 target in common, the minimum selection criteria is to have:

• a beam particle -> Beam Trigger (BT)
• a recoil proton -> Recoil Proton Detector (RPD)
• an interaction in the target -> Veto systems

The Beam Trigger was first planned to be a coincidence of the OR of the six FI01X dynode signals with the OR of the six FI01Y dynode signals. This Trigger is known to be the BT. To respect the round shape of the target cell and to better match the geometrical properties, it was decided to provide a new alternative Beamtrigger, known a the aBT. It is a concidence of the OR of the six FI01X dynode signals with the Beamcounter (BC), which is a scintillating disc inside an air-lightguide system with a diameter of 32mm and a thickness of 3mm (placed at Z=-670cm during Primakoff 2009 data taking). The readout is done via a 2" PMT (EMI 9813KB) and a special designed active base with a high rate capability.

For details concerning the triggering on recoil protons please cf. the Proton Trigger page and the RPD Detector Wiki page.

The task of the Veto system is to veto on secondary particles coming from hadronic interaction in the beamline, Halo particles, non-interacting particles and interactions going outside the angular acceptance of the COMPASS spectrometer to guarantee exclusivity. The Veto system therefore is divided in three subsystems:

• Hodoscope Vetos
• Sandwich Veto
• Beamkiller

The hodoscope veto system in the known muon veto system, consisting of Veto_Inner1, Veto_Inner2 and Veto_Outer. For 2008 it was decided not to use the Veto_veryOuter as there are 2m thick concrete walls in front of it shielding all the possible hadronic particles. The Beamkiller system is a coincidence of both Beamkiller1 and Beamkiller2, the first one placed ca. 70cm downstream of the PGEM03 having the same design as the Beamcounter, but with a 35mm diameter scintillating disc. The second one is placed in front of the ECAL2 beam hole, using a 35mm x 5mm scintillating discs and a passive base. The Sandwich Veto is a 1.8m x 1.8m large sandwich calorimeter downstream of the RPD with a nearly round hole respecting the angular acceptance of the COMPASS spectrometer.

In 2009 data was taken with the same diffractive trigger as in 2008, while in late 2009 some new triggers for special data taking for all t ranges were introduced. The momentum tranfer t between the target and the recoil particle is an important observable to judge on the nature of the formation process of a resonance. As the RPD introduced an acceptance cut on the lower t region (< 0.07 GeV^2/c^2), active elements in the forward direction were used to trigger on multiplicities of outgoing charged tracks from the target instead of a direct observation of the recoiling particle. The Mainz Counter fits the hole of the Sandwich Veto and has a 32mm hole in the central part. It consists of 12 independent segments, which detect charged particles. In the inner hole of the Mainz Counter the Munich Counter is situated which closes the left over acceptance in the very forward direction. As this counter sees also the full beam, a threshold corresponding to 2.5 MIPS (465mV) was set.

Trigger definitions

The components are defined:

• MzC = Mainz Counter (12x segmented 3mm thick hodoscope downstream of the target matching the angular acceptance of the first spectrometer)
• MuC = Munich Counter (3mm thick 32mm diameter scintillator disc with double air lightguide + PMT read out)
• FH = Forward Hodoscope (12x segmented 10mm thick hodoscope upstream of ECAL2 matching the Monte-Carlo predicted region of the fast hadron occupancies from central prod. events)
• BK = BK1 && BK2
• Veto = Veto_hodo || Veto_Sandwich || BK

Diffractive 2008

The h- triggers for the year 2008 are mapped on the prescaler module as following:

Bit	Name	Definition
01	DT0	aBT && RPD && !(Veto)
02	DT1	DT0 && (MzC or HCAL2)
03	KaonT	aBT && CEDAR1* && CEDAR2* && !(Veto)
04	CT1	DT0 && FH
05	NIT	aBT && BK
06	VI	Veto_Inner1 && Veto_Inner2
07	Halo	Veto_Outer && HOuter4
08	BT	Beamtrigger
09	aBT	altern. Beamtrigger
10	RPD	Proton Trigger
11	accT	accepted synchronous triggers
12	random	Noise generator

h+ triggers:

Bit	Name	Definition
01	DT0	aBT && RPD && !(Veto)
02	DT1	DT0 && (MC or HCAL2)
03	CTP	CT1 && (CEDAR1* or CEDAR2*)
04	CT1	DT0 && FH
05	NIT	aBT && BK
06	VI	Veto_Inner1 && Veto_Inner2
07	Halo	Veto_Outer && HOuter4
08	BT	Beamtrigger
09	aBT	altern. Beamtrigger
10	RPD	Proton Trigger
11	accT	accepted synchronous triggers
12	random	Noise generator

* CEDAR1 and 2 set on Kaons, signal is a majority of 6 from 8 PMTs. For h+ running since 2008-09-25 CEDARs are set on protons.

NOTE: From 2008-10-02 we switched back to h- beam and therefore the CEDARs are back on kaons.

Diffractive 2009

The h- triggers for the so called 2009 low-t-campaign were set up as follows:

Bit	Name	Definition
01	DT0	aBT && RPD && !(Veto)
02	LOWT2	aBT && !(Veto) (minimum bias)
03	LOWT3	aBT && MuC (2.5MIPS threshold = 465mV) && !(Veto)
04	LOWT1	aBT && MzC (low threshold 50mV) && !(Veto)
05	NIT	aBT && BK
06	VI	Veto_Inner1 && Veto_Inner2
07	Halo	Veto_Outer && HOuter4
08	BT	Beamtrigger
09	aBT	altern. Beamtrigger
10	RPD	Proton Trigger
11	Laser	ECAL1 Laser Trigger
12	TRand	True Random Trigger

Primakoff 2009

Bit	Name	Definition
01	DT0	aBT && RPD && !(Veto)
02	LOWT2	aBT && !(Veto) (minimum bias)
03	LOWT3	aBT && MuC (2.5MIPS threshold = 465mV) && !(Veto)
04	LOWT1	aBT && MzC (low threshold 50mV) && !(Veto)
05	Laser	On-spill ECAL1 Laser Trigger
06	VI	Veto_Inner1 && Veto_Inner2
07	Halo	Veto_Outer && HOuter4
08	BT	Beamtrigger
09	aBT	altern. Beamtrigger
10	Prim1	ECAL2(thr.0) && LOWT2
11	Prim2	ECAL2(thr.1) && LOWT2
12	TRand	True Random Trigger

ECAL2(thr.0) = 40 GeV

ECAL2(thr.1) = 60 GeV

During 2009 hadron beam, Prim1 was pre-scaled by factor 2, whereas for muon beam, Prim1 was not pre-scaled.

Primakoff 2012

Bit	Name	Definition
01	DT0	aBT && !(Veto) && RPD
02	Prim1	aBT && ![Veto_hodo || Veto_Sandwich] && ECAL2center(thr.0)
03	Prim2	aBT && ![Veto_hodo || Veto_Sandwich] && ECAL2cluster
04	Prim3	aBT && ![Veto_hodo || Veto_Sandwich] && ECAL2center(thr.1)
05	minBias	aBT && !(Veto)
06	VI	Veto_Inner1 && Veto_Inner2
07	Halo	Veto_Outer && HOuter4
08	BT	Beam trigger
09	aBT	altern. Beam trigger
10	KT	aBT && !(Veto) && [CEDAR1(>6) || CEDAR2(>6)]
11	TRand	True Random Trigger
12	NRand	Noise Random Trigger

ECAL2(thr.0) = 60 GeV ECAL2(thr.1) = 20 GeV; Prim3 pre-scaled by factor 20 For more details on the digital ECAL2 triggers see here.

NOTES:

• Bit 01 was changed from DT0 to low-t trigger = aBT && !(Veto) && MultCounter on 2012-07-30 17:26; see comment 43674
• Bit 11 was changed to a multiplexed random trigger using a second pre-scaler module from 2012-07-06 22:36 on; see comment 42951
• Pre-scale factor of Bit 10 (KT) was set to 1 from run 102791 on; see comment 42513
• Bit 12 changed to DT0 from run 105492 on; see comment 44625

TBNames of trigger elements (2008/09)

• Forward Hodoscope - HF04*
• Mainz Counter - HM01*
• Beam Counter - HBC01*
• Sandwich - SW01*
• RPD - RP01*

The other trigger elements are put on the so-called "misc channels TDC" - HMSC1. Channel numbers:

• 0 Beam Killer 1
• 2 OR of Forward Hodoscope channels
• 3 Central Production Trigger 1 = DT0 && Forward Hodoscope
• 4 OR of Sandwich Veto channels
• 6 Beam Killer 2
• 8 Diffractive Trigger 1 = DT0 && (Mainz Counter || HCAL2)
• 12 Mainz Counter
• 14 CEDAR kaon = (CEDAR1 || CEDAR 2)
• 16 Diffractive Trigger 0 = aBT && RPD && !(Veto_hodo || Sandwich || BK)
• 18 alternative Beam Trigger = (Beamcounter && FI01X_dynodes)
• 20 Kaon minimum bias Trigger = (CEDAR1 || CEDAR 2) && aBT && !(BK)
• 22 no interaction ("Yann") Trigger = (aBT && BK)
• 27 BK = (Beamkiller 1 && Beamkiller 2)
• 31 Recoil Proton Detector

How to use the Trigger Mask

You may find information at TriggerMask.

Positions of the Trigger elements