The CMS Detector and the Token Bit Manager

by Wyatt A. Behn

Supervisor:  Dr. Andrew Ivanov

Kansas State University Physics Department , REU Program



Research Description††††††††††††††††††††††††††††††††††† Research Progress††††††††††††††††††††††††††††† Summer REU Activities


Welcome to my webpage. During my time at Kansas State University I worked in the High Energy Physics Department under the mentorship of Dr. Andrew Ivanov. My cohort, Alex Armstrong, and I worked with some of the technology to be used on the new CMS (Compact Muon Solenoid) detector at CERN on the LHC (Large Hadron

Collider). We primarily worked with an integrated circuit chip called the Token Bit Manager (TBM for short).


About Me/Preface

Before I discuss the details of my project, Iíd like to say a bit about myself. My name is Wyatt Behn and I attend the University of Nebraska at Kearney as a physics comprehensive major, a math and womenís studies minor. I am the current president of our chapter of the Society of Physics Students (SPS), and I also tutor math and physics for the university.

Below I will describe the overview of my project and some of the tasks that I have personally accomplished, as well as breakthroughs made by the research group as a whole. Before that, Iíd like to preface this project by pointing out that this research was more of a technical report than a groundbreaking new discovery. Mostly, due to the high-level demand of experience and specialization, I did not contribute directly to the construction or programming of the circuits we worked with. Rather, the undergraduatesí main focus was learning how research is conducted at CERN and the LHC itself and being able to see physics in action. This was achieved vicariously through independent study and coding practice, as well as reading code used on the TBM chips we tested. This is not to say our entire experience was theoretical. Much of our time was dedicated to testing TBM chips to insure their integrity and functionality.

Disclaimer: This program is funded by the National Science Foundation through grant number PHY-1157044.  Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

Project Overview

Coding:                    At the beginning of our research there was much to learn. First, conquering the programming language of C++ was crucial to our understanding of everything else that Alex and I were to see during the remainder of our time at KSU. For the first two weeks we created simple programs that captured the essence of the functions we needed to comprehend for later use. The reason why coding is so keystone to our research has to do with the nature of high energy and particle physics, itself. Detectors that are built to find and quantify the smallest of particles require a certain digital backbone that allows them to carry out complex processes and convey the data in a meaningful way. This is mostly achieved through computers and coding.

 What is The LHC?:          The Large Hadron Collider (LHC) is the largest supercollider in the world; itís located at CERN in Geneva Switzerland near the Alps. The LHC accelerates 2 beams of protons together into a collision point where a large detector gathers information from the resulting chaos of particle showers. The most recent discovery at CERN was the Higgs Boson particle validating the theorized Higgs Mechanism of Mass. This discovery was revolutionary for the field of high energy physics; however, one of the detectors at the LHC is due for an upgrade. The CMS detector is one of four primary detectors at the LHC and it is a vital part of accurately reconstructing the paths taken by particles in their creation and subsequent decay. Small pixel detectors form several layers of a barrel that is used to actually sense the particles as they pass through the detector. The device that controls the pixel detectors is the Token Bit Manager (TBM).

 A cross section of the CMS detector with simple examples of particle traversing it.

Photo credit: European Laboratory for Particle Physics



The TBM:                The Token Bit Manager collects signals from the pixel detectors as new particles are sensed, then TBM deems the data good or clears flawed data. We received a number of these TBM chips on silicon wafers and some individual ones as well. The chips themselves are very small (4.8 mm x 3.2 mm) and must be handled with extreme care and tested with special probing equipment. It was the groupís task to test these TBM chips to ensure they could complete their desired tasks through simulations and to find their highest operating frequencies. These new TBM chips, alongside the new and denser pixel sheets, will allow the LHC to track and reconstruct particle collisions with even higher fidelity than ever before.

The TBM chip (center) embedded on a pixel detector ship.

Photo credit: Comsol Conference


Final Presentation

Click here to download my presentation in PowerPoint and pdf formats

-> DOWNLOAD PPT†††††††††


Or download my poster here


Useful Links

These are a couple sites that will allow for a greater understanding of the physics discipline:

American Physical Society Statements on Ethics

American Institute of Physics

For more information on CERN, CMS, and the LHC, try these links!

CERN Homepage

CMS Experiment Public Page