Madevent is a package derived from MadGraph (which is quite stable and has been around for a long time). It produces events according to SM and BSM processes at the parton level, but also interfaces with Pythia. This isn't new. What is unique is that this can all be originated from a web interface.

The web page is: http://madgraph.hep.uiuc.edu/

Detailed instructions from Reinhard, May 24, 2007:

To get started, you should get registered on the registration web page. That will generate a username-password for you which you need to produce any processes.

Then go to the "Generate Process" page and start playing around with it. You can look at the example processes that it provides for you, for

example uu~>dd~ as the input process. You can look at many other example processes as well, for example an electroweak one: ud~>e+ve. To generate something Tevatron or LHC related, you would use pp as the input particles, for example pp>e+ve. Once you enter this you'll see that there are more Feynman diagrams that can produce this process. (Note that as far as madgraph is concerned, p and p contain the same partons.)

After you click "Generate Process", the program will take a little while and then direct you to a page for this process. If you click on the "Process Information" link you get to see all of the relevant processes and links to all of the Feynman diagrams.

Play with these a little bit, and enter different processes that you can think of to get an idea. Examples that I can think of are pp>tt~ or including decays: pp>tt~>bb~w+w-.

Two processes you should look at are the two single top ones: pb>tj, which is t-channel single top quark production, and pp>tb~, which is s-channel single top quark production.

For these last two, you should not only look at the Feynman diagrams but also produce events. Here's how to do that: The button "Code Download" allows you to download a .tar.gz file that does some event generation. Download it. Untar it and follow the instructions in the README file to run it. You should edit the Cards/run_card.dat file and adjust the following parameters:

---

#*********************************************************************
# Collider type and energy                                           *
#*********************************************************************
        1     = lpp1  ! beam 1 type (0=NO PDF)
       -1     = lpp2  ! beam 2 type (0=NO PDF)
      980     = ebeam1  ! beam 1 energy in GeV
      980     = ebeam2  ! beam 2 energy in GeV 

If you are on one of the Fermilab machines, then you will need to do a "setup D0RunII" in order to get the compiler set up before you generate events. If you are anywhere else in the world, the compiler should already be set up properly. Run the ./bin/generate_events script. You should run serial and give a reasonable name, and then you just wait for events to be generated.

Then when you have an output file, you can use the web interface again to produce a root file and decay the top quark. Go to the "Tools" -> "Decay Interface" page. Browse to the Events/*_unweighted_events.lhe.gz file and load it. Select that you do want root output. Since your two single top files have a top quark in them, select the decay t > b ve e+. Then click on "Upload & Decay". After a while you'll get a page with links, one of which is the root file. Download the root file.

Download the ExRootAnalysis package from the "Downloads" tab. Follow the instructions to produce the library and then run the simple macro given in the Readme file at http://madgraph.hep.uiuc.edu/Downloads/ExRootAnalysis/README in order to produce your first histograms.

Once you have a histogram of jetPT and Mass as in the example macro we should talk again.

These instructions are quite long and it is likely that I missed something somewhere. There are also many steps involving topics you probably aren't familiar yet, and this is supposed to be a learning experience. Let me know if you get stuck or if you have any questions.

Emily Johnson has done a study of single top with CDF-style cuts.

-- ChipBrock - 24 May 2007 -- ReinhardSchwienhorst - 10 Sep 2007

Instructions for New Users of MadEvent by Andrew Chegwidden and Jacob Parsons, 11 July 2011:

We've created these instructions as a starting point for any student using MadEvent. The scope of these instructions is limited to generating a ROOT file from MadEvent, performing cuts, and creating histograms from code.

They are meant as a starting point from which one can develop a more in-depth analysis of SM and BSM processes at the parton level.

The first step in the process is signing up for an account at http://madgraph.hep.uiuc.edu/. Once your account is established you can begin to generate your processes. You have a choice of what model you want MadEvent to follow as well as the process you wish to study. There is a decent list of examples and formats in a link next to the input field. Our initial study focused on the production of the W Boson together with the top quark (p p > w- t). Once you've input your desired process you'll need to select your desired p and j definitions. Our study required p to stand for all possible quarks (the last line of the drop down menu).

Clicking submit will send you to a page where you can download the output code. You will get the appropriate Feynman diagram if it worked properly. On this page you can download the the output code as a "tar" file which you can use the command line "tar -xzf" to unpack it.

Once the files are unpacked you have the ability to change certain attribtues before you generate events. In our analysis we changed the beam energies in the ~/Cards/run_card.dat file (lines 38 and 39) to better represent what's coming out of the LHC.

Once you've made your changes you can generate events from the command line by "./bin/generate_events". We ran a serial run because the calculations were so short. In some instances the ~Cards/param_card.dat file may need to be edited. If this is the case you can utilize MadEvent's calculators under the Tools heading. One should use this tool as opposed to doing the editing by hand.

Once the events have been generated a locally produced output "LHE" file will be created. If a decay is requested this LHE file can be uploaded to the MadEvent site under Tools-->Decay Interface. You'll need to upload the locally produced LHE file and request a SM model decay. If you only want to look at one decay and would like a ROOT output then just click Upload & Decay. If, however, you would like to further decay the events then you will need to perform multiple decays on sucessive LHE files.

Once you've finished running the decay process you can download the final ROOT file which you can analyze and use to generate various histograms.

Specific histograms can be created by utilizing c++ code to create macros. This is most easily done by utilizing the ROOT command line to open up the ROOT file. Once open, use the .ls command to view the list of trees within the ROOT file. Usually there are only 1 or 2 trees within the file. Use the MakeClass command on the tree you want to work on (for example, one of the trees we found using .ls was called "LHEF", so we entered "LHEF->MakeClass("myMacro")" where "myMacro" is the name you choose to give the .h/.C files outputted by the process. In this example the files myMacro.h and myMacro.C will be created automatically). The .h file's purpose is to associate the raw data of the root file with variables the user can work with, the .C file is used to loop through each event containing these variables. After spending some time figuring out the internal structure of these files, the user can edit them to create histograms specific to desired particles/properties/cuts/etc.

An additional file (with extension .C) must be created from scratch. In this file, an object of the class defined in the .h/.C files must be created and the Loop function defined in the original .C file must be applied to the object. Make sure that all four files (the original root file, the auto-generated .h/.C files, and the final .C file) are in the same directory and then execute the final .C file as a macro in ROOT. The attached files take the input root file and generates a histogram of electron transverse momentum. The attached files have specific comments embedded in the code:

• input.root: Input ROOT file from MadEvent

• myMacro.C: Loop through each event

• myMacro.h: Associate raw data with defined variables

• myMacroEx.C: Executable to be run in ROOT

Any number of histograms can be generated using this code as a format. Additionally, users can make cuts and loop over all events.

One such historgram which the user may be interested in creating is the MET (missing transverse energy). Neutrinos pass right through a real detector leaving missing energy. This missing energy can be calculated. MadEvent, which is an ideal detector simulator, tracks these neutrinos. The user could utilize 4-vectors to determine the transverse energy of these neutrinos within MadEvent which would be missing within a real detector.

Once you become familiar with utilizing the computational advantages of MadEvent and developing ROOT macros you can begin to filter out any background which may obsure the specific process you wish to study.

In MadEvent the user asks the program to create events involving only one process with subsequent decays into a final state. Our initial study concentrated on the production of a W Boson together with a top quark (W- t) with a final state consisting of two leptons (electron and positron), two electron neutrinos, and one jet. Other processes may leave very similar final states. Consider the production of a top quark along with a top anti-quark (ttbar). If both W Bosons (W+ from top quark decay and W- from top anti-quark decay) decay into leptons and neutrinos (dileptonic channel) then the final state is exactly the same as the W- t process except for the presence of another jet (the hadronization of the bbar which came from the tbar decay). Producing the same histograms for the ttbar process would allow the user to look for possible differences between the two processes and may allow the user to subtract out the background (the ttbar process). All of this is transparent within MadEvent but not a physical detector. Herein lies MadEvent's usefulness.

-- AndrewChegwidden - 19 July 2011 -- JakeParsons - 11 July 2011

Histograms and Source Code by Andrew Chegwidden and Jacob Parsons, 1 Aug 2011:

Below we present our source code for our initial anaylsis of single top production in the W-t channel. While the W-t process has numerous backgrounds associated with it, we chose to only focus on the ttbar background. We have chosen not to include our histograms in this TWiki because it is much easier to upload changes in code than it is to upload all new histograms. If the user wishes to view the historgrams he/she must download the "Pre.root" file as well as copy and past the code into an editor. It is important to note that the file names should not be changed. Once all files are saved in a common directory the user should use the following terminal commands:

bash-3.2$ cd foldername
bash-3.2$ root WTEx.C
root [0] .q
bash-3.2$ root WTOutput.root
bash-3.2$ TBrowser tb

This will open up the TBrowser where the user can view, manipulate, and save any histogram

***Insert Code Here****

-- AndrewChegwidden - 1 Aug 2011 -- JakeParsons - 1 Aug 2011