---
title: Run-2 Proton-Proton Collision Dataset
url: https://www.emergentmind.com/topics/run-2-proton-proton-collision-dataset
type: topic
---

# Run-2 Proton-Proton Collision Dataset

The Run-2 Proton-Proton (pp) Collision Dataset denotes the collection of proton-proton collision data acquired during Large Hadron Collider (LHC) Run 2 (2015–2018), predominantly at a center-of-mass energy $\sqrt{s} = 13$ TeV. Both the CMS and ATLAS experiments, as well as specialized systems such as the Precision Proton Spectrometer (PPS), utilized dedicated data-taking, calibration, and validation workflows to enable high-precision Standard Model measurements and searches for new physics. This dataset is characterized by its unprecedented integrated luminosity, meticulous absolute luminosity calibration, detailed quantification of systematic uncertainties, and rigorous cross-detector consistency verification [2208.08214], [2106.09609], [2107.08701].

## 1. Integrated Luminosity and Data Collection

During Run 2, the LHC provided proton beams at $E_{\rm beam} = 6.5$ TeV, resulting in $\sqrt{s} = 13$ TeV collisions. Data-taking extended from 2015 to 2018, with annual and total integrated luminosities as summarized in the following table, which aggregates values from CMS and ATLAS:

| Year   | CMS $\mathcal{L}_{\rm int}$ (fb$^{-1}$) | ATLAS $\mathcal{L}_{\rm int}$ (fb$^{-1}$) |
|--------|--------------------------|----------------------------|
| 2015   | 2.27 $\pm$ 0.04          | —                          |
| 2016   | 36.3 $\pm$ 0.44          | —                          |
| 2017   | 41.5 $\pm$ 0.96          | —                          |
| 2018   | 59.8 $\pm$ 1.50          | —                          |
| **Total** | **139.9** $\pm$ 1.8      | **139** $\pm$ 2.4            |

For ATLAS, the total good-quality integrated luminosity is $139$ fb$^{-1}$ with a systematic uncertainty of $1.7\%$ from LUCID-2 calibration. CMS quotes an overall Run 2 precision of $1-2\%$, with the total relative uncertainty at approximately $1.5\%$ [2208.08214], [2106.09609].

## 2. Absolute Luminosity Calibration

The absolute luminosity scale for pp collisions in Run 2 was established via van der Meer (VdM) beam-separation scans. During dedicated VdM fills, LHC beams were moved in steps in the transverse ($x$, $y$) directions. The observed luminometer rates $R(\Delta x,0), R(0,\Delta y)$ were fitted to double-Gaussian profiles to extract the overlap widths $\Sigma_x, \Sigma_y$. The visible cross section $\sigma_{\rm vis}$ for each luminometer was determined by
$$
\sigma_{\rm vis} = \frac{2\pi \Sigma_x \Sigma_y}{N_1 N_2 \nu_{\rm LHC} / R_0}
$$
where $N_{1,2}$ are the bunch populations (corrected for ghost and satellite charge), $\nu_{\rm LHC} = 11\,245$ Hz is the revolution frequency, and $R_0$ is the head-on rate. Instantaneous luminosity $L(t)$ in physics fills was derived as $L(t) = R(t)/\sigma_{\rm vis}$ [2208.08214], [2106.09609].

ATLAS utilized the LUCID-2 Cherenkov detector, also calibrated via VdM scans. The primary methods and performance metrics were consistent across major LHC experiments.

## 3. Systematic Uncertainty Quantification

Systematic uncertainties in the luminosity measurement are categorized as arising from VdM-scan calibration and physics-fill integration. Quantitative breakdowns for each year (for CMS) include:

- **Calibration (VdM scan):**
  - Ghost & satellite charge: $0.1\%$
  - Beam-current normalization: $0.2-0.3\%$
  - Orbit drift: $0.2\%$
  - Residual scan-to-scan differences: $0.1-0.8\%$
  - Beam–beam effects: $0.2-0.6\%$
  - Length scale calibration: $0.2-0.3\%$
  - Transverse non-factorizability: $0.5-2.0\%$

- **Integration (physics fill):**
  - Out-of-time pileup Type-1 (afterglow): $0.1-0.3\%$
  - Out-of-time pileup Type-2: $0.1-0.4\%$
  - Cross-detector stability: $0.5-0.6\%$
  - Linearity (extrapolation effects): $0.3-1.5\%$
  - CMS DAQ deadtime: $<0.1-0.5\%$

Total per-year uncertainties for CMS are $1.6\%$ (2015), $1.2\%$ (2016), $2.3\%$ (2017), and $2.5\%$ (2018). The final combined uncertainty across Run 2 is $O(1-2\%)$, which surpasses the $2-4\%$ precision achieved in previous LHC and Tevatron runs [2208.08214].

ATLAS quotes an integrated luminosity uncertainty of $1.7\%$ on the full dataset, validated by cross-checks between LUCID-2 and supplementary luminometers [2106.09609].

## 4. Data Quality, Triggering, and Pile-Up Mitigation

Run 2 data-taking imposed stringent quality requirements, including stable beams and full operational status of all detector subsystems. Events passing these criteria constitute the good-run lists (GRL). Peak instantaneous luminosities reached $2.1 \times 10^{34}\ \mathrm{cm}^{-2}\ \mathrm{s}^{-1}$ in 2018. The mean pile-up $\langle\mu\rangle$ was $33.7$, with instantaneous values up to $60$.

ATLAS employed single-lepton triggers with online $E_T$ thresholds of $24-26$ GeV (electrons) and $p_T$ thresholds of $20-26$ GeV (muons). Trigger efficiency turn-on reached plateau by $p_T \approx 28$ GeV [2106.09609]. Offline, reconstructed objects were matched to trigger objects, with jets and leptons subjected to pile-up mitigation using:

- Jet–Vertex Tagger (JVT) to associate jets with primary vertices,
- Track-based soft terms in $E_T^{\text{miss}}$ using tracks matched to the primary vertex,
- Lepton isolation and dedicated BDTs for suppression of non-prompt leptons.

Pile-up modeling in Monte Carlo overlaid inelastic pp events with minimum-bias events (Pythia 8, A3 tune, NNPDF2.3lo), and pile-up weights corrected to match the observed distribution:
$$
w_{\rm pu}(\mu) = \frac{P_{\rm data}(\mu)}{P_{\rm MC}(\mu)}
$$
[2106.09609].

## 5. Cross-Detector Linearity and Stability Validation

CMS employed a comprehensive suite of stability and linearity checks:

- **Emittance scans:** Short "mini‐VdM" scans at the start and end of physics fills probed detector response vs. beam overlap and pile-up.
- **Afterglow corrections:** Correction for out-of-time pileup in luminometers with long response tails, performed by subtracting measured rates in empty bunch crossings.
- **Time-dependent corrections:** Efficiency drifts in channels (e.g., HFET/HFOC) addressed via time-dependent correction factors from emittance-scan data.
- **Cross-detector cross-checks:** Comparison and correlation studies across luminometers (PLT, BCM1F, HF, PCC, VTX, DT, RAMSES) to ensure alignment within systematic uncertainties. Any residual non-linearity or response drift is included in the “cross-detector stability” systematic [2208.08214].

## 6. The PPS Run 2 Dataset and Proton Reconstruction

The Precision Proton Spectrometer (PPS) collected 110 fb$^{-1}$ (2016–2018), covering approximately $80\%$ of the CMS pp dataset. Alignment and optics calibration proceeded in three stages:

- **Absolute alignment:** Roman Pots (RP) inserted down to $5\sigma_{\rm beam}$ using collimator-scan techniques, achieving $10\,\mu$m precision.
- **Relative alignment:** Internal alignment within each arm attains $<20\,\mu$m precision.
- **Transfer to physics fills:** Correction of ($x$, $y$) shifts ensures matching between the alignment fill and physics data, with typical combined position uncertainties of $10–30\,\mu$m.

Optics calibration used first-order transport equations, with parameters matched to LHC optics databases and updated using minimum-bias and exclusive dilepton events:
$$
x(s) = v_x(\xi) x^* + L_x(\xi) \theta_x^* + D_x(\xi) \xi
$$
where $\xi$ is the proton fractional momentum loss. Calibration of the horizontal dispersion $D_x$ has reached precisions $\Delta D_x / D_x \lesssim 1\%$, with optical-uncertainty contributions to $\xi$ at the $10^{-3}$ level.

Proton reconstruction is performed via:

- **Single-RP method:** $\xi \approx x/D_x$, $\sigma(\xi) \approx 2–3 \times 10^{-3}$,
- **Multi-RP global fit:** using full transport matrices, achieving $\sigma(\xi) \approx 10^{-3}$ and $\sigma(t) \lesssim 0.02$ GeV$^2$, with systematic uncertainties on $\xi$ at the few $10^{-4}$ level.

Validation utilizes exclusive $\gamma\gamma \rightarrow \ell^+\ell^-$ events, where $\Delta \xi$ (proton-determined minus central detector-determined) agrees within $(1–2)\times 10^{-3}$ between data and simulation.

## 7. Significance and Impact

The Run-2 proton-proton dataset delivers an integrated luminosity ($\sim$140 fb$^{-1}$) with a relative precision of $1-2\%$, representing the most precise luminosity determination to date at bunched-beam hadron colliders [2208.08214], [2106.09609]. The resulting data underpin a broad range of Standard Model and beyond-the-Standard-Model analyses, from R-parity-violating supersymmetry searches to measurements of central exclusive production channels. The infrastructure of beam-based calibration, cross-checks among luminometers, and advanced reconstruction (e.g., PPS optics and tracking) ensures high-fidelity measurements suitable for future precision physics at the highest LHC luminosities [2107.08701].

Source: https://www.emergentmind.com/topics/run-2-proton-proton-collision-dataset