Summer Students 2012

Table of contents:

Proposals

Procedure

• Please go ahead and submit your proposal for CERN summer students urgently tomorrow Feb 15.
• Link for potential supervisors to submit a project proposal(s): http://hrapps.cern.ch/auth/f?p=112:1
• Login: AIS login name and password
• Once you have completed your proposal please don't forget to hit the "create" button in order to submit your proposal as otherwise it will not be registered.

1. laser calib (and possibly more ECAL related)
2. HCAL noise
3. JetMET
4. photons in pile-up
5. razor pheno (optimization of variables etc) more than one can go in here (chris look the bayesian prop by sezen also)
6. Higgs WW, ZZ, gammagamma
7. upgrade/ high pileup related

Javier

• Razor 1

In the inclusive hadronic razor analysis in CMS, searches for supersymmetry and other new physics are performed using a two-dimensional shape analysis in the razor kinematic variables, R and MR. A maximum-likelihood fit in a control region in R and MR is performed to model the Standard Model (SM) background independently in six different boxes (final state categories). One important feature of the analysis is the universal exponential scaling behavior of the SM backgrounds in the two variables, independent of type (ttbar+jets, W/Z+jets, etc.). The project is to impose this universality at the level of the ML fit by building a simultaneous maximum-likelihood fit workspace for all six boxes in RooFit (thus correlating the exponential shape parameters in all six boxes). This will promote the empirical universal scaling to a fundamental, rather than emergent, part of the razor analysis. The student will also explore how to optimize this procedure in order to use it to interpret the results of the analysis in the framework of the Constrained Minimal Supersymmetric Standard Model as well as simplified models.

• Razor 2

In the inclusive hadronic razor analysis in CMS, searches for supersymmetry and other new physics are performed using a two-dimensional shape analysis in the razor kinematic variables, R and MR. Though the analysis is successful in hadronic channels, it is not known how to modify the analysis to look for new physics involving direct electroweak production in leptonic channels . Specifically, in di-lepton channels, if the leptons emerge from separate cascade decay chains, and thus are well separated, the razor variables are a suitable choice to characterize the event. If the leptons emerge from the same cascade decay, the razor variables do not characterize the event well. One direction the student may explore is how to classify events in the two categories, and thus modify the analysis chain based on the different signatures.

with this expected value for the student:

The student will learn advanced computing methods, data regression, maximum-likelihood fitting, and modern statistical methods. The student will also learn about beyond-the-Standard-Model physics, such as supersymmetry, and the phenomenological implications of LHC results.

Emanuele

• H->ZZ: low pt electrons and look-alikes:

Recent CMS data collected at pp collisions at 7 TeV excuded, at 95% confidence level, a Standard Model Higgs boson in the mass domain 127 < mH < 600 GeV, while the direct LEP limit is mH>115 GeV. In the allowed range, CMS finds a 1.9sigma excess at mH=124 GeV. The golden mode in terms of purity and sensitivity to the Higgs mass is H -> ZZ -> 4 leptons final state. The student will work on low level quantities to raise the sensitivity for a mH<130 GeV Higgs boson, such as recostruction of low pT electrons, definition of data control samples to characterize the backgrounds, and will define the custom identification to cope with the new LHC running conditions (8 TeV with increased pileup). He will also study the applications of the full kinematics available in this channel to characterize the properties of a possible signal for a resonance in the still allowed mass range to distinguish a Standard Model Higgs boson from Higgs "look-alikes".

• H->WW: use of singularity variables and razor to enhance mass sensitivity

Recent CMS data collected at pp collisions at 7 TeV excuded, at 95% confidence level, a Standard Model Higgs boson in the mass domain 127 < mH < 600 GeV, while the direct LEP limit is mH>115 GeV. In the allowed range, CMS finds a 1.9sigma excess at mH=124 GeV. For this Higgs mass, due to the large BR and very clean final state, the most sensitive channel at CMS is H->WW->2l2nu. The problem with this decay mode is the absence of a clear mass peak due to two undetected neutrinos. The student should start from the baseline analysis, and revisit the strategy of the usage of available decay kinematics. Recent theory and phenomenological sudies propose the usage of a plethora of singularity variables to search for this mode, and in particular to separate the signal from non-resonant WW production. The student will implement this strategy, and compare the gain in sensitivity using these techniques. He will use the full CMS dataset available.

Adi

• New ECAL laser data analysis

The CMS ECAL is optimized for an excellent energy resolution for photons. This is crucial in the search for the Higgs boson decay into two photons. As the mass range in which the Higgs boson is being searched for is narrowing down, the decay mode into two photons is now the most relevant experimental signature for the Higgs search. The CMS ECAL performance depends critically on maintaining the stability of the detector response. This is ensured by a laser monitoring system which measures any instabilities in the hardware with a precision of about 0.1%. This data is used to correct the energy measurement of the ECAL. The light source for the monitoring system will be upgraded in March 2012. The goal of the project is to analyze the monitoring data using the new equipment, quantify its performance and make a comparative study based on physics data to demonstrate the expected improvements in the ECAL resolution.

• Hgg background studies

The search for the Higgs boson is one of the most important objectives of the LHC physics program. As the mass range in which the Higgs boson is being searched for is narrowing down, the decay mode into two photons is now the most relevant experimental signature for the Higgs search. The characteristics of the Higgs boson signal is that of a narrow resonance which has to be disentangled from a large, irreducible background. Optimizing the experimental sensitivity requires an excellent resolution for the photon energy measurement, a very good modeling of the detector response and a detailed understanding of the shape of the signal peak as well as the background spectrum underneath it. The goal of this project is to study various techniques to enhance the sensitivity for the Higgs search by optimizing the description of the signal and background shapes.

Alex

• Trigger

The razor analysis in CMS searches for supersymmetry in a many different channels covering a wide variety of final states and has proven extremely sensitive in 2011. The analysis uses many sophisticated techniques in order to increase the sensitivity to a new physics signal, including careful understanding of the background through maximum-likelihood fits. As with all analysis, this takes quite a bit of time and study to achieve. In 2012, we seek to maximize the likelihood of discovery by implementing a real-time version of the analysis that can look for signs of new physics emerging in the data in real time. The student will implement an analysis to be on a high priority analysis cluster located at CERN, which will be extremely important for maximizing the potential of CMS for discovering supersymmetry in 2012.

Benefits to the student: The student will learn about beyond the Standard Model physics and cutting edge analysis techniques. The student will also learn about online operations and triggering, high-performance computing techniques and event reconstruction.