F. Palla INFN Pisa

Status ofL1 Pixel Trigger implications on ROC

data rates

Fabrizio Palla (INFN Pisa and CERN)On behalf of the TTI group

F. Palla INFN Pisa2

Pixel Trigger framework• Two possible schemes depending on rates and latencies

(two options under considerations: 10 and 20 µs)• “Push” architecture: pixel data readout at 40 MHz and provided to the L1

trigger• “Pull” architecture: Calorimeter/Muon L0-triggers (at a latency of <6 µs?)

and/or L1-Tracks from outer tracker (at a latency of <10 µs?).

See R. Horisberger talk at DESY CMS Upgrade weekhttps://indico.cern.ch/getFile.py/access?contribId=5&resId=0&materialId=slides&confId=253700

F. Palla INFN Pisa3

Introduction• Track Trigger Integration group is currently investigating

the usage (and usefulness) of a L1-Trigger based on pixels• At the moment three use cases studied

• Primary vertex reconstruction for jets• https://indico.cern.ch/getFile.py/access?contribId=11&resId=0&materialId=slides&confId=277737

• Tau → 3 prongs reconstruction• https://indico.cern.ch/getFile.py/access?contribId=7&resId=0&materialId=slides&confId=288250

• Electrons • https://indico.cern.ch/getFile.py/access?contribId=1&sessionId=3&resId=0&materialId=slides&confId=

290480• No data rate estimates yet

• None of the above have (yet) demonstrated a compelling evidence about the necessity of a L1-pixel trigger• L1-Tracks with outer tracker have same rejections powers for similar

(or better efficiencies). • However, have smaller precision on impact parameter (secondary

vertices) or cannot reach pT<2 GeV (might result needed for isolation)

• Other use cases being investigated (b-tagging, secondary vertex tagging)

F. Palla INFN Pisa4

Jets primary vertex reconstruction

A. Rizzi, S. Donato

F. Palla INFN Pisa5

• Algorithm uses pixel cluster information only from chips in the line-of-sight of jets • Two possible use cases

1. Make clusters on chip@40 MHz and read out reduced information to keep the data rate low

2. Read full pixel information for a subset of the detector (reduction x 5-10) only for Calo-jets with some threshold as L0-trigger (and if latency allows)

• Performance depends on Jet ET. Typical reduction factors ~5 with ~90% efficiency.

• CAVEAT: does not do better than L1 Tracks~4 mm resolution (RMS)

Jets primary vertex reconstruction

Similar resolution with L1-Tracks

F. Palla INFN Pisa6

Data rate estimate

Data rate (Gbps/cm2)1 (r-phi) x1 (r-z) cm2

segmentation2 (r-phi) x1 (r-z) cm2 segmentation

LAYER 1 All clusters Only clusters with size-X=2 *

All clusters Only clusters with size-X=2 *

Read all clusters with coarse position 3 1.8 3 1.8

Read clusters grouped per cluster size 1.3 0.95 0.88 0.7

As above but only ≥ 2 clusters of the same width within a 1x1 cm2 area

0.68 0.38 0.57 0.39

Numbers will scale down depending on the L0 rate. E.g. for 500 kHz L0 ratethey will be reduced by 80, but the complication will be to add extra latency.

Data rates too large at 40 MHz: from 2.5 to 20 Gbps per chip (2.56x2.56 cm2).Rates could become affordable (a few hundred Mbps) at the expenses of a longer latency.

* At all effects a pT cut on tracks

F. Palla INFN Pisa7

Tau to 3 prongs• One “solution” using pixel-stand alone “tracking” at 40 MHz. (results presented here)

• Another one is being investigated to use L1-track seeded regions (no results yet)

M. T. Grippo, K. Androsov et al.

F. Palla INFN Pisa8

Tau to 3 prongs1. Identify triplets in a pixel chip of compatible cluster size in first two layers

(using beam spot as a third point is in effect a pT cut) 2. Look for compatible triplets in the third layer and form all track

combinations, requiring ≥2 GeV track pT.3. Estimate tau decay vertex position in both R-Z and R-Phi planes.

L1 rate 300 kHz and 75% efficiency with L1-tracksOr factor 4 reduction of L1 Calo Trigger at 40 GeV

F. Palla INFN Pisa9

Data rate

F. Palla INFN Pisa10

Electrons• Match a E/gamma cluster with pixel stand alone

tracks

To be compared with L1 track E/gamma rejection at 20 GeV ~6 with an efficiency of ~90%

C.S. Moon, A. Savoy-Navarro et al.

F. Palla INFN Pisa11

Conclusions• At the moment no clear “smoking gun” for the L1

pixel trigger• L1-Tracks Algorithms have similar (or better) performances

than those tried with the pixels• Still a large phase space of investigations with pixels

• “Pull” architecture seems more favorable in terms of data rates• Need however firm statements of what is needed from the

Physics• Imply data to be available at ~few µs latency.

• Isolation with low pT tracks (especially in taus)• Secondary vertex reconstruction/impact parameter

• B-tagging (Higgs?)• B-hadron reconstruction (low pT for B-physics?)