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Plans for first beams -- triggers from the BRM group

(BSC, BPTX)

Gábor Veresfor the BRM group

CMS Trigger Technical Coordination Meeting8 October, 2009

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• BSC and BPTX are primarily beam monitoring tools.

• Their secondary functionality is triggering.

• Triggers are implemented not to detract from the  primary functionality.

• Operation/readout is independent of the other CMS subsystems. i.e. BRM readouts are independent of CMS DAQ (stand-alone).

BSC, BPTX and triggering

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“Customers” for the BRM triggersBPTX zero bias; one or both beam bunches present

an essential trigger for CMS in general. QCD directly uses it.

BSC beam halo triggers: tracker group (tracker end-cap alignment)

BSC beam splash triggers: HF group (calibrations using one beam)

BSC minimum bias triggers: QCD group (min. bias analyses, trigger x-section monitoring)Heavy Ion group (min. bias trigger for Pb+Pb)

BSC high multiplicity trigger: QCD and HI group (clean high-multiplicity events)

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Beam halo triggers (4)

+z inner(beam 2)

-z inner(beam 1)

-z outer(beam 1)

+z outer(beam 2)

+/- z refers to the direction of the muon

Coincidence: at least 1 hit each side, in any segment, w/in 40 nstimed for muons moving with c

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Beam Halo trigger logic (NIM)

6Minimum bias triggers (5)

MB inner >=1(at least 1 hit)

MB inner >=2(at least 2 hits)

MB all >=1

MB all >=2

MB all OR“single sided”(any hit)

Coincidences timed for collisions

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Beam splash triggers (2)

+z beam gas(at least 2 hits)

–z beam gas (at least 2 hits)

Single-side coincidences

At startup, it will be usefulfor triggering on beam-gasevents occurring in the CMSvolume, before collisions occur

Not sensitive to single beam halo muons

Also sensitive to cosmic muonsand p+p collisions

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Minimum bias and beam splash trigger logic

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High Multiplicity trigger

8 hits each side

Selects events with very high multiplicityat the startup (when pileup<<1)

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BSC triggers - details• Logic based on NIM, converted to LVDS, width = 25 ns • Width of coincidences: 20+20 = 40 ns• LVDS signals connected to the general trigger • Connections to trigger boards testedStandalone monitoring:• Trigger signals connected to VME scalers • Analog signals are connected to ADC

https://twiki.cern.ch/twiki/bin/view/CMS/L1TechnicalTriggerBitshttps://twiki.cern.ch/twiki/bin/view/CMS/L1ExternalConditions

Bits 36-39: beam halo triggersBits 40-41: two minimum bias triggers based on all segments (>=1, >=2)Bits 42-43: beam splash triggers

"BSCMBI1" : BSC Min Bias Inner >=1"BSCMBI2" : BSC Min Bias Inner >=2"BSCOR" : BSC Min Bias Single Sided OR"BSCHIGHM" High Multiplicity

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BPTX triggersSensors picking up the mirror charge of the passing beams.Trigger: 3 cables (with max. 4 signals) to trigger boards:

Cable 1: BPTX +z .AND. BPTX –z ‘zero bias’(technical) BPTX +z

BPTX –zBPTX +z .OR. BPTX –z

Cable 2:(technical) BPTX +z .AND. BPTX –z ‘zero bias’

BPTX +z .AND. (.NOT. BPTX –z) ‘empty target’,BPTX –z .AND. (.NOT. BPTX +z) for beam gas studies

Cable 3:(external BPTX +z .AND. BPTX –z ‘zero bias’conditions) (We prefer the notation ‘BPTX1’ = beam direction +z to –z).

These triggers are important fortimingtrigger efficienciesdead-time measurementszero bias physics data taking Responsible: Vladimir Ryjov

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Plans for first beam

• set/adjust HV values (~ few days)• study MIP signals with first halos/splashes (~ few days)• set discriminator levels accordingly (~ 1 day)• time in all segments w.r.t. each other (~ few days)

(apply few ns cable delays if needed)• measure event-by-event jitters (~ 1 day)• test trigger signals/logic (~ few days)• rate checks and comparisons btw triggers with collisions (~ few days)

Some of the above can be done in parallelContinuous beam/collisions are preferred

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Conclusion

• BSC and BPTX trigger hardware is available and tested

• Full software implementation is needed/ongoing

• commissioning planned with the first beam

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BACKUPS

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Geometry of the BSC

Paddlesnot -symmetric8 channels/side

BSC1 annular rings: inner radius: 21 cm outer radius: 45 cm8 channels/side

At z = ± 10.91 mDistance: 73 ns·c

(also BSC2: a few smallersegments further away in z)

BC408 scintillators

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BSC rack S1F08 at point 5

NIM logic and NIM logic and VME readoutVME readout

NIM NIM LVDS LVDS converterconverter

TriggerTriggerboardsboards

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BSC trigger rates• Channel noise rates:

< 1Hz (about 0.1 Hz)

• Trigger rates without beam are very small: min. bias ‘OR’: few Hzother m.b. triggers: < 10-5 Hzbeam halo: < 10-3 Hzbeam gas: < 0.1 Hz

• Pulse height stability: good, less than 10% level

• Scalars: monitoring the rate of all channels and all triggers

Time [h]

Channel noise rateswith very low threshold [Hz]

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Timing of the BSC signals

• The analog signals from the 32 channels will be re-synchronized with the first beam (compensate few ns variations)

• Trigger signals will be timed in after that

• Approximate arrival time of the signals to the GT board after the bunch crossing (status at the moment):

Beam 1 halo (+z -going muon): 550 nsBeam 2 halo (-z -going muon): 490 nsMinimum bias: 570 nsBeam gas: 560 nsHigh multiplicity: 570 ns

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Simulation of BSC triggers

• CMSSW 2_2_9 was used

• PYTHIA 6.416 event generator was used with:- default CMS min-bias settings (D6T tune)- ATLAS tune with higher dN/d

Trigger cross sections for inelastic p+p:• double sided (>=1 hits each side): 51% (D6T tune), 56% (ATLAS tune)

•single sided OR (any hit): 84% (D6T tune), 90% (ATLAS tune)