Gobinda  Majumder

Professor  (H)

Experimental  High  Energy  Physics
Tata  Institute  of  Fundamental  Research (TIFR)
Mumbai  400 005

As a graduate student I have joined TIFR in Aug 1992 . Though my thesis topic was
"Search for supersymmetric particle in $e^+e^-$ collisions at LEP", I have not done much
on that.  My other contributions were R&D for CMS calorimeter,

All these studies along with many other subgroups were used to design and build the CMS Electromagnetic (EM) Calorimeter, which is one of the main subdetectors were used for the discovery of the Higgs boson.
4. Cosmic test setup for CMS outer hadron calorimeter (HO)

In March 1998, I went to Syracuse University for my post doctoral work.  Some
of my contributions were,
1.  Analysis of RICH test beam data
2.  Coding of RICH material in the CLEO3 Geant simulation, event display of RICH
3.  Alignment of RICH in the CLEO3 detector using Bhabha event, The CLEO RICH Detector
4.  Simulation study for the optimised BTeV EM calorimeter
5.  Study of physics potential for the BTeV detector, Workshop on B-physics at the Tevatron
6.  CLEO data analysis: $f_{D_S}$ from $D_S^{*+}$ events (incomplete document)

Have returned back to TIFR as a Fellow (D) on 1st December 2000.

Since last 15 years I am/have been working (or tried to work) in the four following experiments,

BELLE

CMS

ILC detector and

INO ICAL

Till 2005-6, I was mainly concentrated on the detector calibration and physics analysis with the BELLE detector.

My BELLE notes  are

502 Energy resolution of photons around 400 MeV from $D^{*0} -> D^0 + \gamma$
508  neutrino reconstruction for exclusive semileptonic B decays
515  Improvement of Klong angular resolution and $B \rightarrow J/\psi K_L$ event selection
576  Energy resolution of photon with D* events
618  Effect of pre showering & shower leakage in ECL
620  Observations of $B -> D^{*-} 5\pi}$ and $B^+ -> D^{*-} \pi^+ \pi^+ \pi^+ \pi^-$
641  Uncertainty of track finding efficiency with embedded tracks
670  Proton identification efficiency and fake rate
702  Observation of $B^- \to D^0\,D^-$, $B^- \to D^0\,D^{*-}$ and $B^0 \to D^+\,D^-$
718  Linearity test of ECL detector with Radiative Mupair Event
781  Observation of near-threshold enhancement in the D0\bar{D0}pi0 invariant mass in B -> D0\bar{D0}pi0 K

I was also involved with fabrication, testing and calibration of  CMS outer hadron calorimeter(HO) at TIFR. In 2006, I have switched my analysis effort from Belle to CMS and in the same time started developing  INO simulation and reconstruction software, and insignificanly contributed towards the R&D on ILC detector. Since the starting of INO traing school in 2008, I am training those students and since last few years, I am spending a substantial amount of my time for the INO detector development.

I have started developing software code in CMSSW framework to monitor and calibrate HO along with the participation of test beam data analysis as well as cosmic muon data collected by the CMS detector. Eventually, developed an algorithm for HO calibration with muon event in pp collision data. Some documents are available as  Software code1,  code2,  validation,  twiki,  CMS internal note1,  note2,  note3,  note4,  note5. In the year 2011, I have coordinated the HO task force , which has shown the usefulness of HO in Jet/MET measurement and developed algorithms to incorporate HO in CMS physics analysis. I was a co-coordinator the prompt feedback group of HCAL system to identify unknown/unforeseen problems in HCAL system and to find solutions to these problems and then now demoted to the co-ordinator of HCAL Data analysis Group.

In analysis front, I have stated with the  Onium procution at LHC, but later on move to Electroweak and QCD physics at LHC. In EW, I am involved with the measurement of W +/W - charge asymmetry to identify the best set of Parton Distribution Function (PDF) for LHC as well as tune it at unexplored (x,Q2) range. My main efforts are distributed to choose the best selection criteria by minimising error on asymmetry measurement,   decay-in-flight/punch/sail-though background,   Charge misidentification from data,  pdf uncertainty, muon trigger efficiency/MET calculation in data . In QCD, I am looking for  event shape variables , where initially, I was mainly concentrating only on tracker information. But, the using different type of Jets, I have calculated events shape variables and  have compared different MC models with data. I am pursuing these studies since 2010 data and continuing with 13 TeV data to make a precise measurement of the strong coupling constant, &alphas at TeV scale.

Some of my other major contrinutions in the CMS experiment to indentify, provide necessary software tools and data analysis are on the following topics:

1.  Muon charge misidentification (misId) : Remove the common bias/misunderstanding in HEP community is that, using $Z\to \mu^+\mu^-$ sample, one can calculate the chargemisId of muon.
2.  MET smearing in W-asymmetry analysis : Use of double ratio of isolated and anti-isolated leptonic signal in data and MC to model MET distribution of QCD sample.
3.  Modulation of MET-$\phi$ ($\phi_{MET}$ : Identification of major sources of this modulation in hadron collider.
4.  Jet trigger efficiency in data : Derived new technique (which is not new, commonly used for leptonic events) to calculate unbiased calculation, that also has smaller error in the estimated efficiency (larger statistical power).
5.  Madgraph sample : Tune of its paramter for different HT bins, which is not necessarily shows a stability in cross-section.
6.  New technique to identify the bias in the corection of Jet Energy Scale (JES).
7.  Tools for HB monitor : Isolated muon can be used to monitor the stability of gain in HBHE towers also.
8. HO in the CMSSW PF algorithm and upgraded software : With the help of Patrick Janot and Saranya, have developed CMSSW software code to include HO in the CMS Particle Flow algorithm. This same concept is ported in the reconstruction of upgraded CMS HCAL detector geometry, where HBHE system will be readout in 4-5 depths.

High Energy physics laboratories/experiments related to my research activities

L3          Experiment in the  LEP machine, my first experience with HEP experiment as a Ph.D. student

CMS     One of the experiment at the World's largest hadron collider,  LHC

CERN    The World's largest particle physics laboratory

CLEO    One of the pioneer of B-physics experiment at  Cornel University

BTeV    A proposed detector for B-physics in the  Tevatron ring of  Fermilab (not granted)

BELLE   Dedicated B-physics experiment at   KEK

INO   India-based Neutrino Observatory at Pattipuram, Tamilnadu