From 571cf72a2b4f953fa27138b72aaf2995ac74d55a Mon Sep 17 00:00:00 2001
From: Sandro Wenzel <sandro.wenzel@cern.ch>
Date: Tue, 20 Oct 2026 15:32:04 +0200
Subject: [PATCH] Add an example for UPC events in hadronic Pb-Pb pile-up

This commit provides an example script that embeds STARlight UPC events into hadronic Pb-Pb pile-up, anchored to a real run.

- Every N-th collision (default 10) is a UPC event in its own bunch crossing; the others are Angantyr Pb-Pb collisions.
- The interaction rate and the timeframe length come from the anchor run.
- The number of background events is set so that none repeats within a timeframe.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
---
 MC/run/examples/UPC/upc_in_hadronic_pileup.sh | 80 +++++++++++++++++++
 1 file changed, 80 insertions(+)
 create mode 100755 MC/run/examples/UPC/upc_in_hadronic_pileup.sh

diff --git a/MC/run/examples/UPC/upc_in_hadronic_pileup.sh b/MC/run/examples/UPC/upc_in_hadronic_pileup.sh
new file mode 100755
index 000000000..83f1c38b6
--- /dev/null
+++ b/MC/run/examples/UPC/upc_in_hadronic_pileup.sh
@@ -0,0 +1,80 @@
+#!/usr/bin/env bash
+#JDL_PACKAGE=VO_ALICE@O2PDPSuite::MC-prod-2026-v11-1
+#JDL_OUTPUT=AO2D.root@disk=2,debug_log_archive.tgz@disk=2
+#JDL_ERROROUTPUT=debug_log_archive.tgz@disk=2
+
+# Anchored Pb-Pb MC: STARlight UPC events embedded in hadronic (Pythia8 Angantyr) pile-up
+# at the interaction rate of the anchor run.
+#
+# Every UPC_EVERY_N-th collision of the anchor run's collision sequence is replaced by a
+# UPC event in its own bunch crossing; all other collisions are hadronic Pb-Pb collisions.
+# The interaction-rate dependence is obtained by choosing anchor runs at different rates.
+# In the AOD, the UPC collisions have generator ID 51 (mcCollision.getGeneratorId()).
+#
+# Knobs:
+#   UPC_PROCESS    STARlight process (as in makeStarlightConfig.py)
+#   UPC_EVERY_N    every N-th collision is a UPC event;
+#                  the hadronic pile-up density is (N-1)/N of the real one
+#   NBKG           distinct Angantyr events per job; should exceed the number of
+#                  hadronic collisions in one timeframe, so that none repeats within it
+#   ANCHOR_RUN     anchor run; the interaction rate is taken from its CTP scalers
+#   NTIMEFRAMES    timeframes per job; the background is simulated once per job,
+#                  so more timeframes per job is cheaper than many short jobs
+#
+# The timeframe length is taken from the anchor run (32 orbits for 2023 Pb-Pb).
+# Do not force longer timeframes with ALIEN_JDL_MC_ORBITS_PER_TF: with realistic
+# hadronic pile-up, TPC digitisation then exceeds the memory of a GRID slot.
+#
+# Submit to the GRID with
+#   ${O2DPG_ROOT}/GRID/utils/grid_submit.sh --script upc_in_hadronic_pileup.sh --jobname upc --cores 8 --ttl 43200
+
+UPC_PROCESS=${UPC_PROCESS:-kCohJpsiToMu}
+UPC_EVERY_N=${UPC_EVERY_N:-10}
+NBKG=${NBKG:-150}
+ANCHOR_RUN=${ANCHOR_RUN:-544868}
+
+export O2DPG_MC_CONFIG_ROOT=${O2DPG_MC_CONFIG_ROOT:-${O2DPG_ROOT}}
+
+# anchoring: Pb-Pb 2023, apass5
+export ALIEN_JDL_LPMANCHORPASSNAME=apass5
+export ALIEN_JDL_MCANCHOR=apass5
+export ALIEN_JDL_LPMANCHORYEAR=2023
+export ALIEN_JDL_LPMINTERACTIONTYPE=PbPb
+export ALIEN_JDL_LPMPRODUCTIONTYPE=MC
+export ALIEN_JDL_LPMPRODUCTIONTAG=${ALIEN_JDL_LPMPRODUCTIONTAG:-UPCPileupExample}
+export ALIEN_JDL_LPMRUNNUMBER=${ANCHOR_RUN}
+export ALIEN_JDL_LPMANCHORRUN=${ANCHOR_RUN}
+export ALIEN_JDL_LPMANCHORPRODUCTION=LHC23zzh
+# reconstruction with the software of the data pass (2-tag setup)
+export ALIEN_JDL_O2DPG_ASYNC_RECO_TAG=VO_ALICE@O2PDPSuite::async-async-2023-PbPb-apass5-v8-slc9-alidist-async-2023-PbPb-apass5-v8-1
+export ALIEN_JDL_TPCDEDXCLMASK=7
+export ALIEN_JDL_TPCCLUSTERFILTER=2
+export ALIEN_JDL_TPCCHICUTOPT=0
+export ALIEN_JDL_TPCCLUSEDGEREDEF=0.5
+
+export NTIMEFRAMES=${NTIMEFRAMES:-2}
+export NSIGEVENTS=10000          # no cap: the timeframe is filled by the interaction rate
+export SPLITID=${ALIEN_O2DPG_GRIDSUBMIT_SUBJOBID:-1}
+export PRODSPLIT=${ALIEN_O2DPG_GRIDSUBMIT_PRODSPLIT:-1}
+export CYCLE=0
+export DISABLE_QC=1
+export PUBLISH_MCPRODINFO=0     # example: do not publish to CCDB
+
+cat > simconfig.json <<'EOF'
+{
+  "ConfigParams": {
+    "TPCEleParam": {
+      "doSaturationTail" : "1"
+    }
+  }
+}
+EOF
+
+${O2DPG_MC_CONFIG_ROOT}/MC/config/PWGUD/ini/makeStarlightConfig.py --process ${UPC_PROCESS} --collType PbPb --eCM 5360 --rapidity cent_rap
+
+export ALIEN_JDL_ANCHOR_SIM_OPTIONS="-gen external -trigger external -ini ../GenStarlight.ini \
+ -confKey 'PrimaryGenerator.id=51;SimCutParams.stepTrackRefHook=true' \
+ --embedding -genBkg pythia8 -procBkg heavy_ion -nb ${NBKG} --embeddPattern r0:e${UPC_EVERY_N} \
+ --overwrite-config simconfig.json --no-tpc-digitchunking --tpc-distortion-type 2 --tpc-corrmap-lumi-mode 2"
+
+${O2DPG_ROOT}/MC/run/ANCHOR/anchorMC.sh