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# ATLAS dataset nomenclature

Reference: [ATL-COM-GEN-2007-003](https://cds.cern.ch/record/1070318) "ATLAS
Dataset Nomenclature" (2024 edition).

## Logical Dataset Names (LDNs)

AMI identifies all datasets via **Logical Dataset Names (LDNs)**. For centrally
produced ATLAS data the project field doubles as the Rucio scope (e.g.
`mc20_13TeV`, `data18_13TeV`).

**Data hierarchy:**

```
events ∈ files ∈ datasets ∈ dataset containers ∈ campaigns
```

## Scopes and AMI catalogs

| Scope pattern                     | AMI catalog           | Description                     |
| --------------------------------- | --------------------- | ------------------------------- |
| `mc16_13TeV`                      | `mc15_001:production` | Run-2 MC, 13 TeV (original)     |
| `mc20_13TeV`                      | `mc15_001:production` | Run-2 MC, 13 TeV (reprocessing) |
| `mc21_13p6TeV`                    | `mc21_001:production` | Run-3 MC pilot, 13.6 TeV        |
| `mc23_13p6TeV`                    | `mc23_001:production` | Run-3 MC, 13.6 TeV              |
| `data15_13TeV` – `data24_13p6TeV` | —                     | Real collision data by year     |
| `user.<cern_username>`            | —                     | Personal user datasets          |
| `group.<atlas_group>`             | —                     | Group-owned datasets            |

!!! note

    mc16 and mc20 evgen datasets live in the `mc15_001:production` AMI catalog
    because they were generated with mc15-era job options.

## Monte Carlo format

```
project.datasetNumber.physicsShort.prodStep.dataType.AMITags
```

**Example:**

```
mc20_13TeV.700320.Sh_2211_Zee_maxHTpTV2_BFilter.deriv.DAOD_PHYS.e8351_s3681_r13144_r13146_p5855
```

| Field           | Value                             | Meaning                              |
| --------------- | --------------------------------- | ------------------------------------ |
| `project`       | `mc20_13TeV`                      | MC campaign, Run-2, 13 TeV           |
| `datasetNumber` | `700320`                          | DSID — identifies the physics sample |
| `physicsShort`  | `Sh_2211_Zee_maxHTpTV2_BFilter`   | Generator, tune, process             |
| `prodStep`      | `deriv`                           | Production step                      |
| `dataType`      | `DAOD_PHYS`                       | Output format                        |
| `AMITags`       | `e8351_s3681_r13144_r13146_p5855` | Processing history chain             |

## Real data formats

**Primary datasets** (individual runs):

```
project.runNumber.streamName.prodStep.dataType.AMITags
```

```
data18_13TeV.00348885.physics_Main.deriv.DAOD_PHYS.r13286_p4910_p5855
```

**Physics containers** (preferred for analysis — groups all runs in a period):

```
project.periodName.streamName.PhysCont.dataType.contVersion
```

```
data15_13TeV.periodAllYear.physics_Main.PhysCont.DAOD_PHYSLITE.grp15_v01_p5631
```

Use `periodAllYear` to get the full dataset for a given year, or specific period
letters (`periodA`, `periodB`, …) for subsets.

## AMI tags

AMI tags record the processing history of a dataset as a chain of single-letter
codes followed by a version number:

**Tier-0 (online/express processing):**

| Letter | Step                           |
| ------ | ------------------------------ |
| `f`    | Reconstruction (bulk)          |
| `c`    | Reconstruction (commissioning) |
| `x`    | Reconstruction (express)       |
| `m`    | Merging                        |

**ProdSys (offline processing):**

| Letter | Step                          |
| ------ | ----------------------------- |
| `e`    | Event generation (evgen)      |
| `s`    | Detector simulation (simul)   |
| `d`    | Digitisation                  |
| `r`    | Reconstruction                |
| `p`    | Group production / derivation |
| `t`    | Merging                       |
| `n`    | Event picking                 |

## Common data types

| Type            | Description                                      |
| --------------- | ------------------------------------------------ |
| `DAOD_PHYS`     | Full derivation — most complete, largest         |
| `DAOD_PHYSLITE` | Lightweight derivation — preferred for analysis  |
| `DAOD_EXOT*`    | Exotic physics group derivations                 |
| `DAOD_SUSY*`    | SUSY group derivations                           |
| `AOD`           | Analysis Object Data — pre-derivation            |
| `ESD`           | Event Summary Data — large, rarely used directly |
| `EVNT`          | Generator-level events                           |
| `HITS`          | Simulated detector hits                          |
| `RDO`           | Raw detector output                              |

## Other dataset types

Beyond MC and collision data, you may encounter:

| Type           | Format                                                            |
| -------------- | ----------------------------------------------------------------- |
| Calibration    | `dataNNN_calib.xxxxxxxx.calibration_<Det>-<info>.daq.RAW`         |
| User datasets  | `user.<cern_username>.<project>.<fields>.<dataType>.<versionTag>` |
| Group datasets | `group.<atlas_group>.<project>.<fields>.<dataType>.<versionTag>`  |
| Conditions     | `project.internalCondNumber.datasetUsage.COND`                    |

## Field length limits

| Field              | Limit       |
| ------------------ | ----------- |
| `scope`            | ≤ 25 chars  |
| `name` (dataset)   | ≤ 255 chars |
| `name` (container) | ≤ 150 chars |
| `project`          | ≤ 15 chars  |
| `datasetNumber`    | 6–8 digits  |
| `physicsShort`     | ≤ 50 chars  |
| `dataType`         | ≤ 15 chars  |
| AMITag (one tag)   | ≤ 32 chars  |

## Finding MC job options

MC samples are defined by their DSID. Job options live in:

```
https://gitlab.cern.ch/atlas-physics/pmg/mcjoboptions/-/tree/master/<DSIDxxx>/<DSID>
```

where `<DSIDxxx>` is the first three digits of the DSID followed by `xxx` (e.g.
DSID 700320 → `700xxx/700320`).
