| | Summer Students 2012
Table of contents: |
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- Higgs WW, ZZ, gammagamma
- upgrade/ high pileup related
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< | Javier |
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> | Javier Duarte |
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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. |
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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. |
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< | Emanuele |
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> | Emanuele Di Marco |
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- 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". |
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- 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. |
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< | Adi |
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> | Adi Bornheim |
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- 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. |
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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. |
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< | Alex |
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> | Alex Mott |
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| | 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. |
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> | Artur Apresyan
Many searches for new physics involve signatures of missing transverse energy (MET), which signify presence of weakly interacting particles, such as neutrinos or dark matter candidates. To reliably establish presence of new signal, full control of the MET reconstruction is necessary, free of instrumental noise mimicking the genuine MET. It has been observed in CMS data that sometimes calorimeters record anomalous signals that correspond to particles hitting the transducers which appear as large energy deposits. Such events can then appear as signatures of new physics. The project will study in detail the origins of this noise in HCAL forward detector, by studying MC simulation of such noise hits, and optimizing the identification algorithms based in simulation. As a final stage, the algorithms will be tested in real data, and will be included in default CMS reconstruction to battle the increased rate of HCAL noise in 2012 high luminosity running.
Many searches for new physics involve signatures of missing transverse energy (MET), which signify presence of weakly interacting particles, such as neutrinos or dark matter candidates. To reliably establish presence of new signal, excellent resolution of MET reconstruction is crucial, to separate signals of new physics from known processes, and to measure the parameters of decays of such particles. In 2012 the LHC will attempt to collect as much data as possible by raising number of simultaneous collisions in each bunch crossing, expected average number of collisions being around 30 per crossing. This increased interaction rate will provide more chances to create rare particles. The large occupancy of events will however have a detrimental effect on MET reconstruction, reducing the sensitivity of searches of new physics, since MET resolution will be significantly reduced. The project will work to improving the MET reconstruction performance in CMS, by optimizing the reconstruction parameters used in CMS, and fine-tuning the thresholds of objects used in the MET calculation. The effect will be first studied in high occupancy events using MC and deducing the correlation with generator level quantities, and the results will be compared to CMS data. The improvements in the MET reconstruction will then be tested in the context of searches of new physics in events involving MET, such as SUSY searches. |
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General Information |
