# Millepede alignment of the Belle 2 sub-detectors after first collisions

## TL;DR

This paper reports on the initial alignment and calibration of the Belle II detector's sub-detectors using Millepede II after first collisions, establishing a foundation for subsequent physics data collection.

## Contribution

It demonstrates the application of Millepede II for rapid initial alignment of Belle II sub-detectors post-collision, with plans for further improvements.

## Key findings

- Successful initial alignment of the vertex detector
- Effective calibration procedures established
- Framework ready for full physics data collection

## Abstract

The Belle II detector at the SuperKEKB accelerator observed the first collisions in April this year. Until mid-summer, the first commissioning run uses a reduced version of the full vertex detector. Nevertheless, this phase is an excellent opportunity to improve and test the alignment and calibration procedures being prepared for the first physics runs starting in spring 2019. The procedure presented is based on Millepede II tool to solve the large minimization problem emerging in the track-based alignment and calibration of the pixel and strip detectors, the drift chamber or the muon system. The first alignment of the vertex detector was performed quickly after the first collisions and further improvements are expected with more data and with inclusion of other sub-detectors into the procedure. This contribution will show overview and status of the Millepede alignment and calibration procedure of the Belle 2 sub-detectors, after first collisions and the plans for full physics run.