Surrounding the tracker, the calorimetry system measures with high accuracy the energy of electrons and photons as well as individual hadrons with 7500 channels. These systems are compact enough to fit inside a solenoid magnet capable of producing a field of nearly 4T. The outermost region of the detector is composed of muon systems designed to identify and measure muon momenta.

MET Quality Monitoring at the CMS DetectorAlfredo Gurrola, Roy Montalvo, Teruki Kamon

Physics and Astronomy Department, Texas A&M UniversityCMS Collaboration

In November 2009 the Large Hadron Collider (LHC) successfully delivered proton-proton (pp) collisions at the center-of-mass energies of 900 GeV and 2.36 TeV. The data recorded by the Compact Muon Solenoid (CMS) detector allowed us to understand the behavior of the detector and prepare for the search for dark matter in 7 TeV pp collisions which started in March 2010. The creation of dark matter in proton collisions is inferred by the measurement of the missing transverse energy (MET) in each event. This measurements, on which the Texas A&M group has been working, is very sensitive to the performance of all sub-detector systems of the CMS detector and thus is crucial to monitor the quality of the data recorded. Here we report the performance of a monitoring program that we designed and tested with 900 GeV, 2.36 TeV and 7 TeV data.

Abstract

MET Monitoring (METMon) Scheme and Results (7TeV)

Summary

.

SUSY Decay

The Large Hadron Collider

The CMS Detector

MET is the imbalance of energy in the plane transverse to the beam direction.It is calculated by summing individual energy deposits having energy En, in the polar angle θn and azimuth angle ϕn.

An example of weakly interacting particles in the standard model (SM), which are a source of missing energy in experiments, are neutrinos..

Missing Transverse Energy (MET)

MET is very sensitive to the status of the detector since it can be easily effected by various types of noises. As a part of the CMS commissioning tasks, we proposed a powerful MET monitoring (METmon) framework that we successfully tested using data at 900 GeV and 2.36 TeV collisions and now at 7 TeV collisions. Further improvements are currently underway for data taking at even higher luminosities and higher energies. We thank Shuichi Kunori (FNAL) and Mayda Velasco (Northwestern University) for their collaborative work on the development of METMon.

Event Displays

METMon Multi-Run Analysis (7TeV)

A typical noise on hadron calorimeter (HCAL), appearing in the same azimuthal location on the HCAL channels (blue).

Within minutes of collisions an express stream of data (about 10%) is ran through our monitoring code, which performs several studies on anomalous and clean events. We can then get an immediate ‘feel’ for the state of the detector during the run as well as comparing the data to Monte Carlo predictions.

The left figure is a typical plot from METMon, showing MET distributions for “clean” events and “anomalous” events.

Then, any changes in the state of the detector will be noticed immediately when plotting the rate of anomalous events vs. different runs (right). This is a key feature of MET Mon.

The world’s largest accelerator lies in a tunnel 17 miles in circumference. It uses 1323 dipole magnets and other 8000 magnets to accelerate two opposing protons beams, to energies up to 14TeV, in a circular trajectory. The LHC It is the home to 4 main detectors:

ATLAS (A Toroidal LHC AparatuS)ALICE (A Large Ion Collider Experiment CMS (Compact Muon Solenoid) LHCb (LHC-beauty)

As well as two other smaller ones: TOTEMLHCf

The CMS detector is designed to study many aspects of pp collisions at 14 TeV. Its innermost system, the tracker, consists of three layers of pixels with 66 million total, followed by ten layers of silicon strips with 9.6 million strip channels.

Missing transverse energy (MET) is one of key variables in any search for new particles that are weakly or non-interacting. Supersymmetry (SUSY) is one of leading models, predicting the lightest neutralino ( ) is a heavry weakly interacting particle and a good candidate for the dark matter. The right figure is an example illustration of squark-gluino ( ) production and their cascade decays, resulting in multi-jets final state.

qg ~/~

01~

A clean event with two jet-like clusters (i.e. it passes all cuts) though its topology suggests that is likely anomalous event.