Wits Facts from Wits Weekly of November 27th

Documentation for "Evidence for Higgs Boson Decays to the τ + τ − Final State with the ATLAS Detector"

ATLAS has just released the documentation for the evidence for the decay H->tautau. The documentation can be found at:

http://cds.cern.ch/record/1632191/files/ATLAS-CONF-2013-108.pdf

The Wits group, some of its members and close collaborators have been involved in this search for a number of years.

ATLAS releases results which show evidence of the Higgs boson decaying to fermions

The ATLAS experiment just released preliminary results that show evidence, with a significance of 4.1 standard deviations, that the Higgs boson decays to two taus (which are fermions).

More information on this very exciting result can be found here:

http://www.atlas.ch/news/2013/higgs-into-fermions.html

Improving Higgs plus Jets analyses through Fox-Wolfram Moments

The preprint with the title "Improving Higgs plus Jets analyses through Fox-Wolfram Moments" has appeared in the archive today. Among other things one can see a discussion on how the jet veto can be replaced by a moment pertaining to extra jet radiation.

The abstract can be found below:

"It is well known that understanding the structure of jet radiation can significantly improve Higgs analyses. Using Fox-Wolfram moments we systematically study the geometric patterns of additional jets in weak boson fusion Higgs production with a decay to photons. First, we find a significant improvement with respect to the standard analysis based on an analysis of the tagging jet correlations. In addition, we show that replacing a jet veto by a Fox-Wolfram moment analysis of the extra jet radiation almost doubles the signal-to-background ratio. Finally, we show that this improvement can also be achieved based on a modified definition of the Fox-Wolfram moments which avoids introducing a new physical scale below the factorization scale. This modification can reduce the impact of theory uncertainties on the Higgs rate and couplings measurements."

The link to the preprint is:

http://arxiv.org/abs/1311.5891

As Tilman likes to say

Aloha

Set up "Array" of two Cubieboard2's with MPI and HPL

Now that I have been able to get HPL working on the Cubieboard2 the next step would be to get it working on an array of boards. I was only able to get my hands on two boards so I am treating this as a proof of principle for later larger arrays.

If you do not have HPL set up on your board and would like a walk through please see my previous post: Installing HPL on Cubieboard2

Before we start. This is the setup I am using: Two Cubieboard2 running Ubuntu 13.10. Each board has one CPU and 2 cores with 1GB DDR3 RAM. In total we have 4 cores and 2GB RAM. I have called the boards cubiedev1 and cubiedev2 (Host names). OK lets get started.

MPI needs to be able to identify the nodes (actual machines or computers) so that it can execute the programs on each of the nodes cores. to do this we need to set up a hosts file.

Host names on Master Node

On the master node (Generally the node where you will issue the tests and store results) edit the host names file and add in the corresponding computers with their designated IP's. 

nano /etc/hosts

127.0.0.1 localhost
192.168.1.1 cubiedev1
192.168.1.2 cubiedev2

Note that you must not have the master node specified as localhost. I.E. You must not have 127.0.0.1 cubiedev1... Even if this is true for this board it will cause the other nodes to try connect to localhost when connecting to cubiedev1.

Using NFS for Ease of Testing

NFS allows you to mirror a hard drive over the network. This is extremely useful for us since to run a program such as HPL, the exact same version must be installed on all of the nodes. So instead of copying the program to all nodes we can mirror the drive and then do all our editing once and not have to worry about distributing the program around. 

To install run:

sudo apt-get install nfs-kernel-server

Now we need to share the folder we will work in... The sd card that the cubieboard has its OS on is only 8GB. I have an external HDD mounted in the directory /mnt/cub1/ if you want to mirror a folder on your sdcard its not a problem but the r/w speeds are generally not that great and you are limited by the size. So I created a directory called mpiuser on /mnt/cub1/ and I will run all my tests from this folder.

So now we have the directory /mnt/cub1/mpiuser and we must edit the folder exports and add the directory and restart the nfs service.

nano /etc/exports

/mnt/cub1/mpiuser *(rw,sync)
sudo service nfs-kernel-server restart

The folder mpiuser has now been shared but we need to mount this on the other nodes and link it to the master node. We can do this manually from the terminal each time we boot with the mount command or we can edit the fstab file so it mounts at boot.

nano /etc/fstab

cubiedev1:/mnt/cub1/mpiuser    /mnt/cub1/mpiuser    nfs

sudo mount -a
repeat on each node

Creating the user for all MPI programs

Creating one user with the same name and password on each board will allow us to easily access each node over ssh. We need to create the user and set the home directory to our shared folder mpiuser. We then also need to change the ownership of the folder to this user.

sudo adduser mpiuser --home /mnt/cub1/mpiuser  
sudo chown mpiuser /mnt/cub1/mpiuser 

Make sure that the password is the same on all boards.

Configure SSH to use keys and not passwords

Change to our new user:

su - mpiuser

Create the key using

ssh-keygen -t rsa

Use the default location as this is now a shared directory and will update to all nodes.
Now we need to add this key to the authorized keys:

cd .ssh  
cat id_rsa.pub >> authorized_keys

If you can ssh into the other nodes using their host names then you have set it up correctly. Test using:

ssh cubiedev2

MPI software

I have already installed the MPICH2 for my MPI program as I did this in the previous post mentioned before. You can use OpenMPI. It's up to you. 

We need to set up a machine file. This file will be a flag when running using the mpi command. It is a list of hosts with the specified number of nodes that you want to use. An example of the machines file that I have is:

cubiedev1:2 #The :2 represents the number of cores
cubiedev2:2

To test if this works we will use a simple test script which can be found on this blog. Save the content below to a file called mpi_hello.c

#include 
#include 

int main(int argc, char** argv) {
    int myrank, nprocs;

    MPI_Init(&argc, &argv);
    MPI_Comm_size(MPI_COMM_WORLD, &nprocs);
    MPI_Comm_rank(MPI_COMM_WORLD, &myrank);

    printf("Hello from processor %d of %d\n", myrank, nprocs);

    MPI_Finalize();
    return 0;
}

Compile it with

mpicc mpi_hello.c -o mpi_hello

Now run it with the correct number of specified processors (1 for each core)

mpirun -np 4 -f machines ./mpi_hello

The output I get is:

Hello from processor 0 of 4
Hello from processor 1 of 4
Hello from processor 2 of 4
Hello from processor 3 of 4

Cool... Now we know that all the processors are being "seen".

Set up the HPL files

Copy the HPL files that you have been using into the mpiuser directory on the shared hdd. Make sure the ower is set correctly via the chown hpl mpiuser command. If you are unsure of how to set up HPL please see Installing HPL on Cubieboard2

Set the HPL.dat file so that the product of P x Q = 4 (since we running it on both cubieboards) also make sure your problem size is large enough.

Now run HPL using:

mpirun -np 4 -f machines ./xhpl

The sROD Module for the ATLAS Tile Calorimeter Phase-II Upgrade Demonstrator

A proceedings to the International Topical Workshop on Electronics for Particle Physics has been reviewed and approved by the ATLAS collaboration.  This document is a milestone towards the design an implementation of the Upgrade Demonstrator for the ATLAS TileCal electronics. The abstract can be found below:


"TileCal is the central hadronic calorimeter of the ATLAS experiment at the Large Hadron Collider (LHC) at CERN. The main upgrade of the LHC to increase the instantaneous luminosity is scheduled for 2022. The High Luminosity LHC, also called upgrade Phase-II, will imply a complete redesign of the read-out electronics in TileCal. In the new read-out architecture, the front-end electronics aims to transmit full digitized information to the back-end system in the counting rooms. Thus, the back-end system will provide digital calibrated information with en- hanced precision and granularity to the first level trigger to improve the trigger efficiencies. The demonstrator project is envisaged to qualify this new proposed architecture. A reduced part of the detector, 1/256 of the total, will be upgraded with the new electronics during 2014 to evaluate the proposed architecture in real conditions. The upgraded Read-Out Driver (sROD) will be the core element of the back-end electronics in Phase-II The sROD module is designed on a double mid-size AMC format and will operate under an AdvancedTCA framework. The module includes two Xilinx Series 7 FPGAs for data receiving and processing, as well as the implementation of embedded systems. Related to optical connectors, the sROD uses 4 QSFPs to receive and transmit data from the front-end electronics and 1 Avago MiniPOD to send preprocessed data to the first level trigger system. An SFP module maintains the compatibility with the existing hardware. A complete description of the sROD module for the demonstrator including the main functionalities, circuit design and the control software and firmware will be presented."

Below is de PCB layout of the sROD:

More information is available at the CDS entry:

https://cds.cern.ch/record/1628753

Assembling scintillator counters for the TileCal

Today the assembly of the gap scintillators with Bicron plastics started in  building 175 today. The plastics were produced and machined by Bicron.

Below is a photo of Bicron plastics before being placed in the aluminum case:

Below is a photo of the assembly table. To the left is Charles Sandrock, head technician of the Wits School of Physics. His trip is supported by the SA-CERN consortium.

EDM Connector Altium Library

The Wandboard uses something called an EDM Connector to connect the mezzanine board to the base board. This connector is actually a standard MXM3.0 connector used by graphics cards in laptops. Some people over at http://www.edm-standard.org/ have begun work on developing a standard that uses this connector for multimedia and other general signals - which is exactly why the Wandboard implements this standard! Download the PDF from their web site and check it out!

I was unable to find any schematic libraries on the internet for this connector, including in the Altium libraries! Thus, I was forced to make one. I'm making it available for free use - but if you improve it please share your improvements with me, and others. The footprint is based off both the Foxconn and JAE datasheets which can be found at Digi-Key and Future Electronics.

Edit:
Note that the JAE connector will not work for the EDM standard as some of the E3 and E4 signals are not present, which means the ethernet will be unimplemented. The connector is mostly the same though. You can see the notch to the left of the picture above - this should not be there.

The JAE connector should work. The missing signals from the notch to the left of the connector are as follows: E1-10, E2-10, E3-1, E4-1. These are VCC and GND signals which are elsewhere on the connector. We can assume that the board connected is using a ground and power plane so this should not adversely affect operation.

Here's my link on Google Drive: MXM3.IntLib. You should be able to download it without already having Google Drive yourself. Google might try open it in Google Docs - I'm not sure why - but click on File -> Download and you will get the actual file!

Benchmarking of ARM processors with CMS software

CMS colleagues have recently reported benchmarking of ARM processors with CMS software. Interesting and promising results:

http://arxiv.org/pdf/1311.0269v1.pdf

Prototype of LED board for the front-end electronics test-bench of the ATLAS TileCal

The first certified prototype of the LED board for the front-end electronics the new test bench of the ATLAS TileCal is now available at Wits.

Expect next and final iteration next week and delivery to CERN early December.