“Introduction to LKr L1”

Gianluca Lamanna9.2.2011

“Online trigger” meeting

The LKr is a “singular” system in the NA62 TDAQ:The continuous digitization @40 MHz produces ~7 Tb/s → only 4x4 cells trigger sums (supercells) are sent to the LKr Trigger systemThe ~432 CREAMs aren’t read at L0: @1 MHz the bandwidth would be 1.7 Tb/s (~4 Gb/s/CREAM) (without zero suppr.) → no contribution to L1 trigger decision using dataThe LKr is read at L1: @100 kHz the bandwidth will be ~200 Gb/s (~0.5 Gb/s/CREAM) (without zero suppr.) → one link per board

LKr readout: reminder

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Lkr Trigger LKr L1 PC

Circular buffer (up to 10 ms)

Linear buffer (up to 15 s)

Trigger sums (16 cells)

L0 L1

To L1TP

To L0TP

CREAM

To L2

Contribution at L1

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The LKr L1 PC receives the “reduced” primitives (based on 4x4 cells):

Clusters multiplicity, distances, energy, projections and momenta are computed directly on the LKr L0 trigger systemDifficult to image further calculations on 4x4 cells granularity in the L1 LKr PC (everything is done before, in the FPGAs)

Service functions:Propagate L0 Trigger System information to L1TP (i.e. LKr Energy to build ETOT with MUV1-2,…)Consistency check on L0 trigger primitives → no consistency check on LKr data at L1

ROI readout:The LKr L0 Trigger system (concentrator board) asks to specific CREAM modules to send data to the LKr L1 PCThe ROI request is sent with a fixed delay (>1ms) after the corresponding L0 primitive The LKr L0 trigger system is in charge to send the destination address to the selected CREAMS

Regions of Interest (ROI)

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Lkr Trigger LKr L1 PC

Circular buffer (up to 10 ms)

Linear buffer (up to 15 s)

Trigger sums (16 cells)

L0 L1

To L1TPTo L0TP

CREAM

To L2

SWI TCH

ROI request

ROI data: to LKr L1 PC

ROI data

L0

One link only

The LKr L0 trigger system will ask ROI readout for particular events:

The request is based only on LKr information: single cluster with “strange” shape, too close double clusters…

For each ROI request 4/5 CREAMS will be read

Simulation to understand the increasing in readout rate

Assuming max 250 Mb/s (1/2 of the free bandwidth if the L1 is 100 kHz) dedicated to ROI r/o and flat gamma distribution → max 0.5 MHz of ROI requests

Regions of Interest (ROI)

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Pion and gamma cluster at d=17 cm in 4x4 cells and in full readout

~½ of pp0 with “signal” in LAVs→ ~102 kHz remains~90% of pp0 (after LAV) with “signal” in the SAV→ ~7 kHz remains

Effectiveness of ROI

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INITIALRATES (kHz)

CHOD_HIT_0 *MUV_ACC_CRACK*

LKR_4x4_3 (kHz)

pp0 1859 222

mn 5719 42

ppp 503 100

pp0p0 158 2

p0en 456 48

p0mn 301 2

TOT 8998 416

pnn efficiency in % 75.1

pnn (P,Z cuts) eff. % 82.0

[Spasimir October TDAQ WG]

CATEGORIES (1125 kHz in CHOD acceptance)

% kHz !LAV & !2LKR

!LKR_30cm

2 g in LKr 46% 517 ---

1 g in LKr, 1 g in SAV 15% 169 169 57

1 g in LKr, 1 g in LAV

28% 56 ---

2 g in LAV 5% 315 ---

1 g in LAV, 1 g in SAV 1% 11 ---

2 g in SAV 4% 45 45 45

The inefficiency of the 30 cm LKr cut gives 57 kHz (rejectable with !SAV)A part of the 57 kHz could be rejected using ROI, if we want to avoid to use SAV or we can’t use STRAWS If we use STRAWS (or SAV) the ROI is useless! (at least for the main trigger)

The contribution of the LKr at L1 will be relatively small

The LKR L0 trigger system will reject most of the pp0 in the LKr acceptance at L0

The LKr L1 PC is useful to transmit the primitives produced from the L0 trigger system to the L1TPThe ROI readout is easy to be implemented in the present readout scheme, but the utility depends on the way to threat at L1 the events with gammas with small angle (my favorite way is with STRAWS)

Conclusions

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