4-APR-06 CMS SLHC Perugia - Baden 1 Forward Jet Triggering for an Upgraded CMS Drew Baden - University of Maryland Jeremy Mans - University of Minnesota.

4-APR-06 CMS SLHC Perugia - Baden 1

Forward Jet Triggering for an Upgraded CMS

Drew Baden - University of Maryland

Jeremy Mans - University of Minnesota

Chris Tully - Princeton University


HF Basics

• HF covers ~3<<5 located at ±11.1m from IP• Steel absorber and rad hard quartz fibers

– Cerenkov light collected via phototubes, uniform HCAL readout

• 36 and 12 = 432 towers per side– =10° and =0.166

• Each tower has long and short fibers running along z– Short (S) is in the back ~ “ETHAD”– Long (L) is front to back ~ “ETEM+HAD”

– Readout after ganging all S and all L– Makes 2x432=864 towers per side

HF


Jets in Level 1• TPGs

– HB/HE: 0.087x0.087 x0.5 x 0.35 in HF

• CMS Level 1 Jets– Calorimeter organized into “Regions”

• 4x4 TPGs per region in HB and HE, formed by RCT

• 1 TPG per region in HF, formed by HCAL HTRs and transmitted thru RCT

– Regions are sent GCT for jet finding• Jet finding via “sliding window”

• Sliding window using 3x3 regions

Calorimeter “Region” Barrel/Endcap

TPG (x) Region

HB/HE 0.087x0.087 4x4 TPGs

HF 0.5 x 0.35 1 TPG


CMS Calorimeter Segmentation

Tower # TPG ( x ) Calorimeter RCT Regions

1-4

0.087 0.087 0.87 x 0.87

1: 0.000 < < 0.348 - 0.3480.348

HB

5-8 2: 0.348 < < 0.695 - 0.3480.348

9-12 3: 0.695 < < 1.044 - 0.3480.348

13-15 4: 1.044 < < 1.392 - 0.3480.34816 HB/HE overlap

17-20 0.087 0.087 0.87 x 0.87 5: 1.392 < < 1.740 - 0.3480.348

HE

21 0.09

0.174

0.090 x 0.087

6: 1.740 < < 2.172 - 0.4320.348

HE, split into 2 equal half energies in

22 0.10 0.100 x 0.087

23 0.113 0.113 x 0.087

24 0.129 0.129 x 0.087

25 0.15

0.174

0.150 x 0.087

7: 2.172 < < 3.000 - 0.8280.348

26 0.178 0.178 x 0.087

27 0.15 0.150 x 0.087

28 0.35 0.350 x 0.087

29-31

0.167 0.174 0.348 x 0.5

8: 3.000 < < 3.500 - 0.50.348

HF

32-34 9: 3.000 < < 3.500 - 0.50.348

25-37 10: 3.000 < < 3.500 - 0.50.348

38-40 11: 3.000 < < 3.500 - 0.50.348


Min Bias

Atlas CERN/LHC 96-40

• Min bias distributions @ 1034

– <n>~20 (assumes ~80mb inelastic)– <dn±/d> ~ <dn0/d> ~ 8 @ 14TeV

– <ET> ~ few GeV (and falls exponentially)

– 20<n> x 8ch x 10dx 2GeV = 3.2 TeV/interaction (Had)

– HF...40% of CMS in coverage• 640 GeV, 72 TPGs/side, ~10 GeV/TPG (@<n>=20)

– Current TPG = 0.5 x 0.348 x

• SLHC upgrade– Increase ET/TPG from minbias scales with increase in <n>

– Clearly, the only way to keep up without ramping thresholds up is to look at TPGs on finer scale

• New Level 1 triggering will need to…– Sharpen efficiency– Move HLT-like algorithms and resolution as close to L1 as

possible


SLHC Background Reduction

• Beat down the background L1A rate– LHC Design luminosity of 1034 has large backgrounds:

– Depending on the scheme for high luminosity• <n> ~ current for 25ns SLHC, rates scale with Luminosity• for continuous beam….smaller <n> but large pileup...not sure

– 100kHz L1A rate is ingrained, will most likely hold• Size of derandomizing buffers, etc.• Bandwidth to HLT• Number of HLT processors....

• CMS Calorimeter trigger based on TPGs– In HF…

• 1 TPG = 6 towers (3 x 2)• Lack of granularity might make it useless for Level 1 jet triggers with large

number of multiple interactions without drastic threshold increases

– In HB and HE…• Jet-finding in Level 1, saturation effect due to pileup at high luminosity

• trigger (requires most energy to be in 1 region) difficultie at high pileups

• Ditto for isolated e and triggers

Condition Process Rate

1 ET>60 Jet0 10Hz

2 ET>15 Jets 0s 10Hz

1l pT>60 W l, jet l 10Hz

2l pT>15 Z l l 20Hz

ETmiss > 150 QCD jets 10Hz


SLHC Signal Enhancement

• Add functionality

– W Boson Fusion (WBF) dominant experimentally accessible rate

• Forward jets + central Higgs decay

• Tag jets are in HF+HE so HE will need to be included

– Higgs id without a tag is very hard• Gluon fusion backgrounds are too high, esp at 1035

– Current trigger at high luminosity will be difficult• Depends on scheme for increasing luminosity of

course…

C. Tully & H. Pi JetMetPRS Aug 2004

(tagged “forward” jets)


Forward Jets in Level 1

• Jeremy Mans, Chris Tully, monte carlo simulations using ORCA

• Try to optimize forward jet trigger to keep the thresholds on central objects from increasing due to pileup at high luminosity– Plot of forward jet trigger rate shows huge

effect at low ET

– Pileup effects at ~1034 will cause thresholds of ~50-60 GeV to get away from pileup dominating real jets

• Signal is reduced to almost nothing

• NB: this does not take into account central object trigger…so it’s not as bad as that but it’s still a big loss due to pileup


Jet Shape and Pileup

• Diagram for WBF has no “color string” across the detector

• QCD forward jets will be much more “active”

• This can be seen in the jet shape (2nd moment)– Energy is from pileup is

added to jet far from core

– Easier to deal with using smaller regions


Another Look at Shapes…

• Current scheme– Jet candidates using 3x3 CR sum, x=1.5 x 1.0 – Slides window by 1 CR, x=0.5 x 0.35

• New scheme– Construct jet candidates from 4x4 tower sums,

x=0.67 x 0.7– Slide window by 1 tower, x=0.17 x 0.17

• Feature bit on if number of cells needed to sum 60% of ET (n60) in 4x4 cluster < cut– Use n60 < 7 to set feature bit– Prelim studies show QCD jets are narrow & well

contained• Jets from .5 cone all have 2nd moment < 0.3 in R

• Require jet candidate threshold && feature bit = 1• Can also require perimeter “quiet” for isolation

– Not studied yet…


Hardware Design

• We propose NOT changing current HTR– 48 QIE channels input

– 6 SLB sites• Each SLB transmits 2 TPGs/link over 4 links/cable

– For HF, 1TPG = 6 QIE channels• 48/6 = 8 TPG output• HF HTRs will only populate 1 SLB site• We will have 5 free SLB sites to use

12.5ns

• Proposal: – Luminosity: dedicate 1 SLB site

– Jet trigger: dedicate 3 SLB sites• Means running L and S fibers @ 80MHz, or L+S after summing @ 40MHz

– Send data to…TBD…during CMS running parasitically…study study study


HF Forward Jet Study Elecctronics

• HF Transmitter (HFT)– 3-SLB-site mezzanine card on HTRs

– Transmits raw HF towers for clustering investigations

– Optical transmitters, 1.6Gbps 8B/10B using 12-way MTP connectors (18 per side)

– Already being laid out – expect to have something available for studies at H2 summer 06

• HF Jet Processor (HFJ)– Jeremy Mans/UMN

– Receives fiber data and processes into jets…

– New GCT Leaf/Wheel cards might be ideal for rapid development for studies

HTR HFT

SLB

HLX

RCT

Luminosity “consumers”

HFJ

2 HTRs = 4() x 12()

18 HTRs per + and – side of CMS


Rack Topology

• Chris Tully worked this out with Rohlf and Ianos Schmidt, ok’d by Wesley Smith• New “Luminosity” VME crate in the center minimizes distance from the 3 HF crates

and doesn’t break topology for Level 1– Can put any electronics developed for HF forward jet trigger studies here


R&D Program

• Scrub design so that we can piggyback on existing system and build cards that can be implemented by LHC startup– Keep entire current VME architecture, but add new capability

– Run parasitically, collect data, study, iterate

• R&D list for Trigger project– Much simulation needed to settle on algorithm approach

– HLT card:• Learn how to use new FPGA’s with embedded processing, DSP, built-in deserializers….• Continue to verify HTR to HLT @ 80MHz

– HLT to HJF transmission• Implement transmitting signals over MTP fiber ribbons @ 1.6Gbps using Rocket IO• Use crystals to drive transmitter as an alternate scheme (asynchronous fifo’s on both ends)

– HFJ• Study algorithms for clustering – lots of simulation needed here• Build new types of 9U boards or follow GCT project?

4-APR-06 CMS SLHC Perugia - Baden 1 Forward Jet Triggering for an Upgraded CMS Drew Baden - University of Maryland Jeremy Mans - University of Minnesota.

Documents

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