Sebastián Ordoñez-Soto

Universidad Nacional de Colombia

 

Internship tutor: Patrick Robbe

Guidance: Liupan An

 

July 7th, 2023

 

Study of VELO-ECAL timing for U1b using the Hybrid-MC toolkit

Internship update-IJCLab LHCb group meeting

Outline

  • Introduction
    • LHCb VELO and ECAL
    • ECAL upgrade scenarios
    • Motivation
  • Simulation 
    • Hybrid-MC toolkit
    • Workflow
  • Results
    • Truth level
    • Full ECAL simulation
    • Reco level
  • Summary

Introduction

  • LHCb Electromagnetic CALorimeter (ECAL)
    • Designed to measure and identify electromagnetic particles, such as photons and electrons.
    • Main purposes: energy measurement, particle identification and precision timing.

 

  • LHCb VErtex LOcator (VELO)
    • Provides measurements of track coordinates close to the interaction region.
    • Main purposes: reconstruct production and decay vertices of \(b\) and \(c\) hadrons.

Introduction

  • Run 1-3
    • Shashlik cells \(4\times4\), \(6\times6\) and \(12\times12\) cm\(^{2}\) 
  • Upgrade 1b (Run 4)
    • Innermost: SPACAL W+Poly \(2\times2\) cm\(^{2}\)
    • Second inner: SPACAL Pb+Poly \(3\times3\) cm\(^{2}\)
    • Outer: Shashlik \(4\times4\), \(6\times6\) and \(12\times12\) cm\(^{2}\)
    • No longiudinal segmentation
    • Timing readout for SPACAL
  • Upgrade 2 (Run 5)
    • Innermost: SPACAL W+GAGG \(1.5\times1.5\) cm\(^{2}\)
    • Second inner and outer same as for Run 4.
    • Longitudinal segmentation 
    • Dual timing readout for all modules

Introduction

  • This project
    •  Analyze the feasibility of estimating U1b VELO timing from VELO/CALO track positions and CALO timing using the Hybrid-MC toolkit.
\boxed{t_{\text{VELO}} \approx t_{\text{CALO}} - \frac{\text{FD}}{\text{V}}}
\boxed{\text{Adding timing will be key to remove a lot of expected pile-up!}}

\(B^{0}\rightarrow K^{*0}\gamma \rightarrow (K^{\pm}\pi^{\mp})\gamma\)

Comparison of the time properties for signal and background candidates in the \(B^{0}\rightarrow K^{*0}\gamma\) decay using Upgrade II simulation.

X

CALO

Vertex

Locator

\boxed{\Delta t = t_{\text{CALO}} - t_{\text{VELO}}}

X

X

Track

\text{FD}
t_{\text{VELO}} \approx t_{\text{CALO}} - \frac{\text{FD}}{\text{V}}
\text{FD} = \vec{r}_{CALO} - \vec{r}_{VELO}
(t_{\text{CALO}},\vec{r}_{\text{CALO}})
(t_{\text{VELO}},\vec{r}_{\text{VELO}})

Simulation

  • Workflow
  1. Official LHCb MC sample is used as input
    • Gauss_kstargamma_full_*.sim
  2. Generate the flux.root file
  3. VELO reconstruction done by VELO team
    • B2Kstgamma_VELO_reco.root file
  4. Select events with \(K^{\pm}\pi^{\mp}\) from a \(B^{0}\)
    • Kpi_tree.root
  5. Keep only events with Kpi reconstructed
    • match_flux.root 

Generate flux files

Full ECAL simulation

Reconstruction

  1. Main config file
    • Global characteristics of the ECAL
  2. Module config files
    • Standard configuration files of SPACAL and Shashlik modules
  3. Map of module types and positions
  4. CAD drawing of the region(s) 

 

Output: OutTrigd_*.root

https://gitlab.cern.ch/spacal-rd/reconstruction

  1. Reads OutTrigd files and gives the final ntuple with cluster reconstructed variables.
    • Reconstructed_*.root
  2. Combine with Kpi_tree.root
    •  Reconstructed_combined_*.root

Results

  • Truth level
    • Flux files
      • It is possible to take a look at the timing of tracks which hit the ECAL from the *.sim Gauss files
p
p
\gamma
K^{\pm}
\pi^{\mp}
B^{0}
  • Velo reconstruction
    • It is possible to reconstruct the \(B^{0}\) mass spectrum
      • Only kaons and pions from a \(B^{0}\) are considered
      • As expected, the samples have high levels of background

Results

  • Full ECAL simulation output
    • Output of the jobs are OutTrigd_*.root files, which contains:
      • ID of the modules hit during the event
      • Total number of optical photons detected in the whole calorimeter.
      • Number of photons detected in the i-nth cell of the #-nth module in the given event.
    • It is possible to obtain the energy deposition from the photon yield in each module for a given configuration.

Evt: 1evt w/ nPV = 40. Sim: Run 5 config.

Results

  • Reconstruction
    • At this point we have the timing (\(t_{K\pi}\)) and position (\(r_{K\pi}\))  of the \(K\pi\) vertex, which are the origin timing and position of the photon.
      • We can calculate the flight time from the origin to the ECAL: \(t_{f}\)
      • The expected time of the photon to enter ECAL: \(t_{exp} = t_{K\pi}+t_{f}\)
    • As result of the simulation we obtain the measured time of the photon cluster: \(t_{obs}\)

Measured timing of the photon cluster (\(t_{obs}\))

Calculated entry timing of the photons (\(t_{exp}\))

Resolution  \(\text{SpaCal}\) \(t_{obs}-t_{exp}\) 

\boxed{\text{SpaCal}}
\boxed{\text{Shashlik}}

Summary

Thank you!

  • It was carried out a review of the most important aspects of the U1b and U2 LHCb calorimeters with a focus on the timing of the tracks.

 

  • There were performed full ECAL simulations using the Hybrid-MC toolkit. The VELO reconstruction and both U1b and U2 configurations were considered in this study.

 

  • Preliminary results include obtaining the entry time of the photons in the calorimeter using VELO and CALO information as well as the reconstructed time after full ECAL simulation.

 

  • Next steps:
    • Examine PV positions after full simulation and analyze how to estimate their time using only ECAL timing