HGCAL BEAM TEST Detailed Report/User GUIDE
PROJECT GUIDE: DAVID BARNEY NAME: DEEPAK KUMAR CHOUBEY, AAYUSH ANAND Acknowledgement
This internship opportunity we had with HGCAL group at CERN was a great chance for learning and professional development. It is our first intern. we feel lucky to work with such highly experienced people in the world’s largest Nuclear Research Centre. Special thanks to P. Behera, D. Barney to put us here. we would also like to grab this opportunity to thank Andre David for continuously guiding us throughout this internship. We gained a lot of theoretical and practical aspect of knowledge with a motivation to use it further for ourself and the betterment of our professional career.
Deepak, Aayush
IIT Madras [email protected] [email protected]
Table of Contents
1.Introduction………………………………………………………………………………………………………………………………………….4 #. CERN
#. CMS
#. HGCAL
2.Beam Test …………………..……………………………………………………………………………………………………………………….7 #. Overview
#. Data Taking
#. Data Analysis
3.Feedback/ Experience………….…………………………………………………………………………………………………………….18
4.References and contact details…………………………………………………………………………………………………………..19
1.INTRODUCTION #.CERN
It is the world’s largest and most sophisticated Nuclear Research center, located at the border of Switzerland and France. Its provisional body was founded on 1952. It uses very large and complex instruments to study about fundamental particles. Here, particles are made to collide at a very large speed. This gives their physicists to study about the particle interactions and behavior after the collisions. European organization for nuclear research became renown after their famous discovery of Higgs boson. It has many experiments going on simultaneously at different locations in CERN. Its major experiments are *CMS (compact muon solenoid) *ATLAS ( a toroid LHC apparatus) *ALICE ( a large ion collider experiment) *LHC (large hadron collider)
• and other experiments are ASACUSA, ATRAP, AWAKE, BASE, CAST, CLOUD, COMPASS, LHCf, MOEDAL, NA61/SHINE, NA62 etc. There are many further sub-divisions in each of the experiments. Accelerating particles, colliding them, using e- beams, muon beams, knowing what happens after the collision is the major curiosity of physicists here. It is spreading like fire throughout the world. Its has collaboration in almost every continent. •
• • It was founded by 12 member states and currently has 22 member states. It involves almost 600 institutes and employs over 2500 people.
#.CMS The compact muon solenoid (CMS) is a general-purpose detector at the large hadron collider (LHC). It has a broad physics programme ranging from studying the Standard Model (including Higgs Boson) to search for extra dimensions and particles that could make up the dark matter.
The CMS detector is build around a huge solenoid magnet. This takes the form of a cylindrical coil of superconducting cable that generates a field of 4 Tesla.
An unusual feature of the CMS detector is that instead of being built in situ like the other giant detectors of the LHC experiments, it was constructed in 15 sections at ground level before being lowered into an underground cavern.
The CMS experiment is one of the largest international scientific collaborations in history, involving 4300 particle physicists, engineers, technicians, students and support staff from 182 institutes in 42 countries.
The expected High Luminosity LHC upgrade will increase the number of interactions. An upgrade is planned to increase the performance of CMS detector. Some examples for the upgrades are CO2 cooling system.
About CMS detectors:
The CMS detectors comprises of several sub-detectors to detect different kind of particles. CMS detectors are divided into various layers. *Interaction point This is the point in the centre of the detector at which proton-proton collisions occur between the two counter-rotating beams of the LHC. At each end of the detector magnets focus the beams into the interaction point. At collision each beam has a radius of 17 and the crossing angle between the beams is 285 .
휇푚 휇푟푎푑 *Tracker Momentum of particles is crucial to build up a picture of events at the heart of the collision. One method to calculate the momentum of a particle is to track its path through a magnetic field; the more curved the path, the less momentum the particle had. The CMS tracker records the paths taken by charged particles by finding their positions at a number of key points. The tracker can reconstruct the paths of high- energy muons, electrons and hadrons (particles made up of quarks). The tracker needs to record particle paths accurately yet be lightweight so as to disturb the particle as little as possible. It does this by taking position measurements so accurate that tracks can be reliably reconstructed using just a few measurement points. The CMS tracker is made entirely of silicon: the pixels, at the very core of the detector and dealing with the highest intensity of particles, and the silicon micro strip detectors that surround it. As particles travel through the tracker the pixels and micro strips produce tiny electric signals that are amplified and detected. *Electromagnetic Calorimeter The Electromagnetic Calorimeter (ECAL) is designed to measure with high accuracy the energies of electrons and photons. The ECAL is constructed from crystals of lead tungstate, PbWO4. This is an extremely dense but optically clear material, ideal for stopping high energy particles. Lead tungstate crystal is made primarily of metal and is heavier than stainless steel, but with a touch of oxygen in this crystalline form it is highly transparent and scintillates when electrons and photons pass through it. This means it produces light in proportion to the particle’s energy *Hadronic Calorimeter The Hadron Calorimeter (HCAL) measures the energy of hadrons, particles made of quarks and gluons (for example: protons, neutrons, pions and kaons). Additionally, it provides indirect measurement of the presence of non-interacting, uncharged particles such as neutrinos. The HCAL consists of layers of dense material (brass or steel) interleaved with tiles of plastic scintillators. This combination was determined to allow the maximum amount of absorbing material inside of the magnet coil. *Muon detector Because muons can penetrate several metres of iron without interacting, unlike most particles they are not stopped by any of CMS's calorimeters. Therefore, chambers to detect muons are placed at the very edge of the experiment where they are the only particles likely to register a signal.
#.HGCAL Calorimetry at the High Luminosity LHC faces two enormous challenges, particularly in the forward direction:- *Radiation challenges *Unprecedented in-time event pileup. To meet these challenges, the CMS has decided to construct a High Granularity Calorimeter (HGCAL), featuring a previously unrealized transverse and longitudinal segmentation, for both electromagnetic and hadronic compartments. This will facilitate particle-flow-type calorimetry, where the line structure of showers can be measured and used to enhance particle identification, energy resolution and pileup rejection. The majority of the HGCAL will be based on robust and cost effective hexagonal silicon sensors with ~1 or 0.5 cm^2 hexagonal cell size, with the final five interaction lengths of the hadronic compartment being based on highly segmented plastic scintillator with on- scintillator SiPM readout. I present an overview of the HGCAL project, including the motivation, engineering design, readout/trigger concept and simulated performance. HGCAL is now in R&D phase. Much progress has been done since the release of the Technical Proposal. First prototypes are being tested with electron and proton beams. A Technical Design Report is foreseen in late 2017. It will include key technical choices and improved design. The construction should start in 2020 in order to be ready for an installation during LS3.
2. BEAM TEST #.OVERVIEW
CASSETTES: The alternate absorber layer is formed by two 2.1 mm thick lead planes clad with 0.3 mm stainless steel (SS) sheets that are placed on either side of the module- cooling plate sandwich. Each plane of this structure is subdivided into 60 ◦ units called cassettes. And 14 such cassettes provide the full 28 sampling layers. These are the major detector sub-assembly of the HGCAL, which are subsequently assembled into full disks or inserted b/w absorber layer to form full disks of the detectors in the CE-H.
Each plates are prepared with well precision and after attaching many of its sub-parts. One of its major problem of getting heated was eliminated by cooling system. The assembly of the cassettes takes place in a clean room. The sequence of assembly steps is fundamentally the same for all cassette varieties, but not all steps are required for all cassettes. The assembly steps are the following: 1. A kit of components is prepared, specific for the cassette to be assembled. Each component is inspected, the documentation that is provided for it is verified, and component identifiers entered into the production database. 2. The cooling plate is placed on the assembly table. 3. Silicon modules are attached to the cooling plate. 4. Silicon module motherboards are mounted to the silicon modules. 5. Scintillator tile modules are mounted (CE-H mixed cassettes). 6. The scintillator/SiPM motherboard is mounted at the cassette edge (CE-H mixed cassettes).
7. Silicon motherboard extensions are mounted on top of the scintillator tile modules (CE-H mixed cassettes). 8. HV cables and optical fibres are routed from the silicon modules and motherboards to the cassette edge. 9. The cassette interface is mounted and connections made between it and the ends of the silicon motherboards, the HV cables and the optical fibres. 10. The cassette cover (CE-H cassettes) or lead - stainless steel absorber cover (CE-E cassettes) is mounted. 11. The cassettes is turned over and the relevant steps repeated for the second side (CE- E cassettes). 12. A complete electrical test of the finished cassette is performed.
SILICON MODULES The baseplate has precise reference holes for precision assembly and placement onto the cassettes. For the CE-E the baseplate material is a sintered CuW metal matrix composite. The copper provides excellent thermal conductivity (TC), the tungsten reduces the coefficient of thermal expansion (CTE) to align it more closely with that of the silicon, and together they form a short radiation-length material that is a significant component of the CE-E absorber. For the CE-H modules, the baseplate material is high- TC carbon fiber. It serves similar purposes except that it does not contribute significantly to the CE-E absorber material.
We have been using 6” modules (i.e. modules produced using sensors manufactured on 6” wafers) for prototyping and for measurements in test beams. Figure below shows a completed 6” module.
Six-inch module on carrier plate prior to wire bonding and encapsulation. The electronics packages seen on the PCB are four SKIROC2-CMS front end readout chips, used for the beam test, and an FPGA.
Each hexaboards are hexagonal with small cutouts at each corners. The silicon sensors and the hexaboard are hexagonal with small cutouts at each of the six corners.
The cutouts provide access to the positioning and mounting holes in the baseplate. They also provide access to a portion of the Kapton-Au layer for wire bond connections to the hexaboard, for the biasing of the sensor back-plane.
The hexaboard will contain the HGCROC front-end readout ASICs (Section 3.1.2). The signals from the sensor pads are routed to the HGCROC for on-board signal digitization. Holes in the hexaboard expose the region around the intersections of groups of up to four pads.
The layout of the module hexaboard for a 432 channel sensor, and a zoomed view of the wire bond holes.
SCINTILLATORS Scintillators can also be used in particle detectors, new energy resource exploration, X- ray security, nuclear cameras, computed tomography and gas exploration. Other applications of scintillators include CT scanners and gamma cameras in medical diagnostics, and screens in older style CRT computer monitors and television sets. The use of a scintillator in conjunction with a photomultiplier tube finds wide use in hand-held survey meters used for detecting and measuring radiation contamination and monitoring nuclear material. Scintillators generate light in fluorescent tubes, to convert the ultra-violet of the discharge into visible light. Scintillation detectors are also used in the petroleum industry as detectors for Gamma Ray logs. Scintillation detectors are generally assumed to be linear. This assumption is based on two requirements: (1) that the light output of the scintillator is proportional to the energy of the incident radiation; (2) that the electrical pulse produced by the photomultiplier tube is proportional to the emitted scintillation light.
The linearity assumption is usually a good rough approximation, although deviations can occur (especially pronounced for particles heavier than the proton at low energies).
So, here we used this in our beam test for the signal generation. Electron beam enters to the scintillators and produces the signal which gets amplified and is received. Generally, they are covered completely to avoid loss of signal produced.
COOLING SYSTEMS Cassettes were heated up because of the generated heat in the readout board and the electronics. To tackle this problem, an efficient cooling system were needed which can maintain the working temperature of the silicon modules mounted on the cassettes.
So, above while colored connecting tubes were attached to the copper wires which were looping back from the sandwiched cu plates of the cassettes. These pipes were having a continuous flow system of water at our desirable temperature from the cooling machine to the cassettes. The set pressure was 1 atmosphere. The leakage at the valves were cured by increasing the no of Teflon turns at the screws. DATA TAKING: After installations and calibrations was done we started the data taking as soon as we received the beam from H2 line. For each run we included following: - *Run no. *No. of events for that particular run. *Start time and stop time. *Pedestal/Beam. *Type of particle (electron or muon). *Energy of the beam (in GeV). Although the beam was available from 0 to 150 GeV, we choose the following (100, 80, 50, 120, 30, 10 and 150) energy for the beam to proceed. *No. of events per spill. *DQM observation. *Bias current for every channel (0, 1, 3 and 4). *Relative humidity (RH DP 4). *Temperature of cassette 7. *Humidity and temperature of air. *We also taken care of the position of the table. While taking data DAQ crashes many of the times but was better from the last beam test. Every people on the shifts observed many things which they properly wrote on the Elog. So, for every details of the data taking we can always refer to the elog of HGCAL group.
DATA ANALYSIS: My part of data analysis included plotting of the histograms for all time samples and SCA values. For all combination of Timsamp and SCA which makes it (13*13 = 169) plots. Furthermore, plotted 2-D graph with mean and RMS as their input values. After going through each of 169 plots we can see that histogram has noise for 11th and 12th time sample values for each SCA. Below is the code for getting all histograms including 2-d graph which will be automatically saved in a root file mentioned in the code. CODE:
#include
tree->SetMakeClass(1); tree->SetBranchAddress("hg", &hg, &b_hg); tree->SetBranchAddress("event", &event, &b_event); tree->SetBranchAddress("chip", &chip, &b_chip); tree->SetBranchAddress("timesamp", ×amp, &b_timesamp);//making class and detting addresses
cout<<(tree->GetEntriesFast())< for( unsigned entry = 0; entry < (tree->GetEntriesFast()); entry++){ tree->GetEntry(entry); if(chip!=0) continue; for(sca=0;sca<13;sca++){ ts=timesamp[sca]; h[sca][ts]->Fill(hg[sca][3]); } } TFile* out= new TFile("allplots.root","RECREATE"); TCanvas* c = new TCanvas("c", "c",600,500); for(sca=0; sca<13; sca++){ for(ts=0; ts<13; ts++){ h[sca][ts]->Write(); h[sca][ts]->Draw(); h[sca][ts]->Fit("gaus"); mu[i] = h[sca][ts]->GetFunction("gaus")->GetParameter(1); sigma[i] = h[sca][ts]->GetFunction("gaus")->GetParameter(2); i++; c->Print(".pdf"); } } TCanvas* c2= new TCanvas("H-2D","finalplot",0,0,700,600); float x,y,z; TGraph2D *dk=new TGraph2D(); TRandom *r= new TRandom(); for(sca=0; sca<13; sca++){ for(ts=0; ts<13; ts++){ x=sca; y=ts; z=mu[counter];// write sigma[counter] for plotting RMS values dk->SetPoint(counter,x,y,z); counter++; } gStyle->SetPalette(1); dk->SetTitle(“Mean values;sca;timesample”);//change mean torms while //plotting RMS value graph. dk->Draw("surf1"); out->Close(); } The results of the code as follows: The below 3d views explains the variation of Mean and RMS values as a function of sca and timesample values. Mean is almost flat with shallow crest shows that having a constant pedestal values works in the region for x=(0,11) and y=(0,11). So, as we can see most of the rms values are flatter which is good for us because we don’t want much noise and high amplitude noise. Here the timesamp and sca near 11 and 12 is unwanted for us as it involves too much noise. And for instance some of the following histograms are as follows: This histogram has timesample value greater than 11 are bit weird. We can see that its mean is 213.6 which is higher than the rest and most of its triggers are post 210 unlike other histograms. *The width (or range) of each of the histograms are directly proportional to noise per chip and channel. So, we can get idea of noise by directly looking at the RMS values of each of the histograms. *If the signal goes below the x-axis then it becomes difficult for the electronics to handle those. That’s why we introduce pedestal values which decreases the reference frame and the curve we get is completely above x-axis. Depending upon the signal each of the histogram has different signal and hence requires different pedestal values. So, here the mean value is flashing towards pedestal values. This histogram is for a particular value of SCA and for all timesamp less than 11 (all excluding noisy one). Here we are getting a perfect Gaussian distribution with values spreaded almost normally around its mean. The above histogram is for h_0_0. (first sca and timesamp respectively). 3.Feedback/Experience Stay of 2 months at CERN was indeed a special and interest urging experience for us towards research. Working with people from across the globe made our experience more diverse and exhaustive. Being in a work culture where sharp brains from different regions always introduces an innovative way of looking at the problems was the best part of our internship. We really gained some valuable insights about research ethics which will be helpful for our professional career. 4.References https://twiki.cern.ch/twiki/pub/CMS/EC-TDR/TDR-17-007-paper-v1.pdf https://drive.google.com/file/d/0BwWUqRCpCdiIeHQxN3ZrZk1xNXlhRmU1aG5RWXlyT0t2eFlF/view?usp =sharing https://indico.cern.ch/event/718124/ https://indico.cern.ch/event/526766/ https://cernbox.cern.ch/index.php/s/csHU32gszheluUu https://home.cern/about http://iopscience.iop.org/article/10.1088/1748-0221/12/01/C01042/meta https://cds.cern.ch/record/2272172?ln=en