Available on CMS information server                                          CMS NOTE 2009/???

                                                                                          September 4, 2009

CMS Level-1 Global Trigger Extra Algo inputs

Second Draft

 

H. Bergauer, M. Jeitler, A. Taurok

HEPHY, Wien, Austria

Abstract

The CMS Level-1 Global Trigger receives inputs from the Global Muon Trigger and the Global Calorimeter Trigger, which can be combined in logical expressions in so-called trigger algorithms, and “Technical Triggers”, which cannot be combined with other signals.

On top of these inputs, another 64 input lines are available for additional trigger objects, which can also be freely combined in logical expressions.

These “Extra Algo” inputs have to be delivered to the Global Trigger as LVDS signals, grouped in a total of 16 Channel Link cables equipped with RJ45 connectors. At the Global Trigger, these lines go into the Pipelined Synchronized Buffer (PSB) board in slot 15 of the Global Trigger crate. Cabling, data format, and timing are described.

 


1      Introduction

 

Trigger signals (“Extra Algos”) that have to be combined in logical expressions with other signals (i.e., with signals from the GCT, the GMT, or with each other) may be delivered to the GT as LVDS signals.

2      Extra Algo data to the Global Trigger

 

The Extra Algo data arrive through the so-called “GT calorimeter input channel #10”, which is physically represented by the Pipelined Synchronized Buffer (PSB) board in slot 15 of the Global Trigger crate. (Channels 1 through 8 go into the PSBs in slots 13 and 14. Channel 9 will not be used in the current scheme.)

The details of the bit mapping on the cables are shown on the twiki page

https://twiki.cern.ch/twiki/bin/view/CMS/L1ExtraAlgoBits

2.1   CASTOR

Description: not yet available.

2.2   BPTX

The BPTX (beam pickup) signal to the Extra Algos will in particular be used in anti­coincidence for the so-called “long-lived particle” trigger. This will allow to trigger on relatively low-energy objects (e.g., jets) during the proton gap, when no particles are received from the LHC accelerator.

In addition, BPTX also has 8 inputs in the “Technical Trigger” input board (PSB in slot 9 of the GT crate).

2.3   BSC

Description: not yet available.

2.4   ZDC

Description: not yet available.

2.5   RPC TTU

Description: not yet available.

2.6   TOTEM

Description: not yet available.

 

3      Hardware details

3.1   Cables and connectors

The LVDS data will arrive on Channel Link cables equipped with RJ45 connectors. (These are the same as Ethernet connectors. However, Ethernet cables may not be used as in them the signal lines are paired in a different way from Channel Link cables.)

 

3.2   Timing and synchronization

A signal (logic “1”) is to be electronically encoded as a negative differential LVDS signal. The signal length is expected to be 25 ns for a given bunch crossing.

 

3.3   Error detection

There will be no error detection bits. However, offline and online running of test pattern generation, transmission, and decoding will be used.

 

 

 

4      References

[1]  CMS collaboration, “The Trigger and Data Acquisition Project, Volume 1: The Level-1 Trigger”, CERN LHCC 2000-038.


Appendix: Definitions of bit assignments on cables

 

 

 

Table 1: Definition of Calorimeter and Extra Algo channels in the GT-system

Calorimeter channel

Cable Content

Connector on PSB

[present use]

Connector on PSB

[future use]

CA1

Isolated electron/photon objects

PSB_V2 slot #13 IN 6-7 used

PSB_OPT slot #13 fiber U3 (OGTI) used

CA2

Non-isolated electron/photon objects

PSB_V2 slot #13 IN 4-5 used

PSB_OPT slot #13 fiber U2 (OGTI) used

CA3

Central jet objects

PSB_V2 slot #13 IN 2-3 used

PSB_OPT slot #13 fiber U1 (OGTI) used

CA4

Forward jet objects

PSB_V2 slot #13 IN 0-1 used

PSB_OPT slot #13 fiber U0 (OGTI) used

CA5

Tau-flagged jet objects

PSB_V2 slot #14 IN 6-7 used

PSB_OPT slot #14 fiber U3 (OGTI) used

CA6

Energy summary information

(total Et, Ht and EtMiss)

PSB_V2 slot #14 IN 4-5 used

PSB_OPT slot #14 fiber U2 (OGTI) used

CA7

Ring rapidity HF/Et-sums, HtMiss

PSB_V2 slot #14 IN 2-3 used

PSB_OPT slot #14 fiber U1 (OGTI) used

CA8

TBD (free)

PSB_V2 slot #14 IN 0-1 or 16xRJ45 [63-0] free

PSB_OPT slot #14 fiber U0 (OGTI) or 8xRJ45 [31-0] free

CA9

TBD (free)

PSB_V2 slot #15 IN 2-3 free

PSB_OPT slot #15 fiber U1 (OGTI) free

CA10

EXTRA ALGOS

PSB_V2 slot #15

3xRJ45 used [12 bits, 11-0]

13xRJ45 free [52 bits, 63-12]

PSB_OPT slot #15

3xRJ45 used [12 bits, 11-0]

5xRJ45 free [20 bits, 31-12]

There is an option for CA9 and CA10 - using PSB_V2 for future use:

CA9

not useable

-

PSB_V2 in slot #15 with infiniband inputs

CA10

EXTRA ALGOS

-

PSB_V2 slot #15

3xRJ45 used [12 bits, 11-0]

13xRJ45 free [52 bits, 63-12]

TBD means “to be defined”


 

Table 2: Bit assignments on GT Calorimeter channel 10 (CA10, obj. 1 and 3)

For names and description of objects, see   https://twiki.cern.ch/twiki/bin/view/CMS/L1ExtraAlgoBits

(object 2 and 4 see next table)

Bit no.

CA1013

conn.

obj. 1

object 1

conn.

obj. 3

object 3

0

RJ45 3-0

RJ45 19-16

 

1

 

2

 

 

3

 

 

4

RJ45 7-4

 

RJ45 23-20

 

5

 

 

6

 

 

7

 

 

8

RJ45 11-8

 

RJ45 27-24

 

9

 

 

10

 

 

11

 

 

12

RJ45 15-12

 

RJ45 31-28

 

13

 

 

14

 

 

15

 

 

 

Table 3: Bit assignments on GT Calorimeter channel 10 (CA10, obj. 2 and 4)

For names and description of objects, see   https://twiki.cern.ch/twiki/bin/view/CMS/L1ExtraAlgoBits

 

Bit no.

CA1024

conn.

obj. 2

object 2

conn.

obj. 4

object 4

0

RJ45 35-32

 

RJ45 51-48

 

1

 

 

2

 

 

3

 

 

4

RJ45 39-36

 

RJ45 55-52

 

5

 

 

6

 

 

7

 

 

8

RJ45 43-40

 

RJ45 59-56

 

9

 

 

10

 

 

11

 

 

12

RJ45 47-44

 

RJ45 63-60

 

13

 

 

14

 

 

15