MasterClass 2013

MasterClass 2013

Introduction

Here people in charge to mentor the students of the MasterClass 2013 can find the links and fast instructions to be able to analyze the CMS event display and to add the information from each event analyzed into a common spreadsheet.

CMS Event Display

The main page of the MasterClass 2013 is in this link.

Here you can find the documentation and exercises.

Click here to access the CMS event display. To display an event, click in the first icon (yellow folder) to open a window where you can choose one of the "masteclass_XX.ig" options in the left column. In the right column will appear a list of events. Choose one of this events and click in "Load". Note that the event displayed has a correspondent number in the top of the screen (like Event_XXXXXXXXX).

You will need to adjust the event settings turning on/off the options in the left column of the display to be able to see which particles were produced in the collision. In those events, you can:

find either 2 electrons or 2 muons, which means that they come from a "Z" candidate;
find either an electron and missing energy, or a muon and missing energy, which means that they come from "W" candidate;
find either 4 electrons, or 4 muons, or 2 electrons and 2 muons, which means that they come from a "ZZ" candidate;
feel difficult to find which particles are displayed, will consider as a "Zoo" candidate.

More instructions on how to indentify the particles are here

. As soon as you realize which particles and W / Z / ZZ / Zoo appear in an event, a spreadsheet has to be fill out accordingly (instructions bellow).

Working Groups

The mentors were divided in 6 groups of 2 members. Each group will take a list of events (masteclass_XX.ig) to train and get enough expertise to help students during the MasterClass 2013.

Patríca and Juliana: masteclass_1.ig
Carlos and Eduardo: masteclass_2.ig
Cesar and Angelo: masteclass_3.ig
José and John: masteclass_4.ig
David and Sunil: masteclass_5.ig
Pedro: masteclass_6.ig

Each list has 100 events. Mentors should try to analyze all of them.

Filling Out the Spreadsheet

Download the spreadsheet from here. The third column shows the event numbers (XXXXXXXXX) with respect to the lists "masteclass_XX.ig".

In summary, after having opened the CMS event display and found which particles have been produced:

go to the spreadsheet and find the row of the event number correspondent to the analyzed event;
if that event has 2 electrons, for example, write "1" in the correspondent cell of the "electron" column and "1" in the "Z cand" column;
for this example, an invariant mass will appear in the "Mass" column, then write the round mass value in the "Mass->odd" column;
then go the "Massplot" tab and write "1" in the cell whose horizontal axis (Invariant Mass) has the same value of the "Mass->odd" column.

Here

are more instructions on how to fill out the spreadsheet.

As soon as you finalize the analysis of all events from your list, please send your speadsheet to angelo.santos@cern.ch.

Questions

How to differentiate between W+ and W-?

In this training, we consider two possibilities for the W decay:

W → μν or
W → eν (where ν ≡ neutrino).

Then a W will be positive or negative depending on the charge of the electron(e)/muon(μ).

How to verify if a electron/muon is positively or negatively charged?

Only charged particles bend in the presence of a magnectic field (B). In the CMS detector, B has the same orientation as the "z" axis. Setting the event display in such a way that the x-y plane is the plane of the screem and the "z" axis points to you, you will know that particles bending clockwise will have positive charge, while those ones bending anti-clockwise will have negative charge. (Try to verify it by yourself using the left-hand rule relating velocity, magnectic field and magnectic force.)

Thus, for example, an event where appears a muon going clockwise and also a neutrino, we probably have a W+ candidate.

How to know that an event has a neutrino?

After opening an event in the display, goes to the options in left bar. Turning the last option (Missing Et) on may pop up a yellow vector correspondent to the energy probably related to the presence of neutrinos in that event. Clicking on the arrow beside "Missing Et" will open a window showing that energy.