Tdp Posted 9 years ago

PhD Motivational Letter + Research proposal

' /experiment name/ Group in task of measuring the Higgs Boson decaying into two tau leptons. After a short settling-in period I immediately started working on par with the other PhD students, taking part in the discussion and producing key results. (Even if I was the only undergraduate in the group not once I felt that my contributions were inferior to others.) The internship also contribute to growth my communication skills, with weekly presentations and discussions at group working meetings and a final presentation at a collaboration wide workshop. The importance of my work on the measurement of the efficiency corrections for the analysis has been recognized by the /experiment name/ collaboration granting me authorship of the related article, an outstanding acknowledgement for an undergraduate student. The internship at /leading research centre/ was an excellent preparation for your programme and an important milestone in my young career.
Currently I am collaborating with the the /experiment name/ group in /City/ on preliminary studies for the next B-Physics analyses.

%why /City/
One of the topic that I found most interesting in modern particle physics is the study of decays of hadrons containing heavy quarks, since they offer the most direct way to explore the physics of CP violation. During the PhD programme I would like to focus my research activity on the physics of the bottom quark with the /experiment name/ experiment. The bottom quark is of particular interest since it's the heaviest quark involved in a hadronic decay, leading to distinctive experimental signatures easy to exploit, and the /experiment name/ group in /City/ have a long legacy in producing high quality results in B-physics. I am sure that given my (strong) track record with the /experiment name/ experiment I will bring high level contributions to the field and your institution. One of the prominent result published by the /City/ group is the measure of the weak mixing phase $\phi_s$ and the decay width difference $\Delta\Gamma_s$ in the golden channel $B^0_s\rightarrow \text{J}/\Psi\,\phi(1020)$ at a centre-of-mass energy of 8 TeV. Since the value predicted by the SM for $\phi_s$ and $\Delta\Gamma_s$ are very precise, any significant deviation of the measured value from this prediction would be particularly interesting, as it would indicate a possible contribution of new, unknown particles to the loop diagrams describing $B^0_s$ mixing. The measured values were consistent with other experiments and the SM, but there is big room for improvements.

%what I wanna do
I'd like to improve the above-mentioned measure with a brand new analysis using the data collected by the /experiment name/ experiment during Run 2.
This new analysis will not only drastically improve the current result, but also it will greatly benefit /City/ University in various aspects, such as undergraduate thesis opportunities, numerous secondary scientific results, and the reinforcement of /City/ University and /experiment name/ collaboration as leading figures in modern experimental B-Physics.

I plan to improve the precision of the current measurement tackling the following key experimental aspects: higher statistics, better time resolution and a new MVA flavor tagging algorithm.

/experiment name/ is expected to collect more than six times the integrated luminosity collected in Run 1, at a higher center-of-mass energy. Taking into account that the $\text{pp}\rightarrow\text{b}\overline{\text{b}}$ production cross section has doubled with the energy increase, I estimate a reduction by a factor of $3.5$ of the statistical uncertainties, with substantial improvement on the final uncertainties. Since higher luminosity also means a higher number of pile up interactions, I plan to study and implement a new more efficient High Level Trigger in the first period of my research activity. Given my experience on high pile up analyses and HLT efficiency measurements, gained during my /*leading research centre/ internship, I am certain that I will be a key person on this matter.

The analysis is based on precise characterization of $B^0_s-\overline{B}^0_s$ system time evolution, therefore improving time resolution directly leads to improving the sensitivity of the measurement. This March the /experiment name/ pixel tracker has been replaced with an upgrade that features an additional layer of silicon pixel detector, improving spatial and time resolution by $50-60\%$. This is going to increase the sensitivity of the analysis by a factor of approximately 1.4. Since this would be one of the first B-Physics analysis that takes advantage of the new tracker, starting the analysis now would confirm the pioneering role of /City/ University inside the /experiment name/ collaboration.

The critical point of B-Physics analyses is to understand if the J$/\Psi\phi$ final state comes from a $B^0_s$ or a $\overline{B^0}_s$. This tagging process is achieved with various methods based on the unique features of b-jets. The old analysis infers the flavor of the signal $B^0_s$ identifying the semileptonic decay of the other B hadron in the event. I would like to spend most of my research activity improving the tagging algorithm, implementing multiple other tagging techniques in a multivariate (MVA) algorithm trained with cutting-edge classificators such as Deep Neural Network. Since I personally study one of these techniques in my /experiment name/ internship in 2015 I am sure that this is feasible (and that I am most suitable person for the job). Moreover I plan to further enhance the tagging efficiency implementing the new MVA Muon Identification discriminator developed for the $B^0\rightarrow \mu^+\mu^-$ search, which is about $10\%$ more efficient than currently used one. This MVA algorithm will achieve performances that largely outclass single tagging methods and I expect to increase by $50\sim 100\%$ the current tagging power, enhancing the sensitivity of the analysis by a factor of approximately 1.3. This new algorithm, and the above-mentioned new High Level Trigger, may also be used to improve other B-Physics analyses, leading to benefit to all the /experiment name/ B-Physics group, in particular the /City/ section.

All things considered, the analysis I propose will improve the precision of the $\phi_s$ and $\Delta\Gamma_s$ measurements by a factor 6 to 7, leading to the most precise single measurements to date. I plan to carry out this study in the three years of the PhD programme, broken down as follows: the first year will be mainly dedicated to the high level trigger study, the analysis framework development and the programme courses; in the second year I will focus on developing the MVA tagging algorithm; in the third year when all the Run 2 dataset will be available I will perform the $\phi_s$ and $\Delta\Gamma_s$ measurement.

The analysis is very flexible since all the tools I plan to develop are implementable in other studies. In this regard various less complex measurements that both benefit from, and contribute to improve, the main analysis are worth of consideration, such as, but not limited to, measuring the $\text{pp}\rightarrow\text{b}\overline{\text{b}}\text{b}\overline{\text{b}}$ cross section and the mixing on the recoil of $B^+ \rightarrow \Psi K^+$. These research topics would make excellent thesis and internship opportunities for undergraduate students at /City/ University, allowing them to work alongside a world-class study.

%conclusioni
Given the opportunity this study will help to further understand the physics of the CP-violation, to develop cutting-edge analysis tools, and to establish /experiment name/ as a leading experiment in the field of B-Physics. I am confident that with my academic background and competences as well as my aspirations I will match your expectations and enrich your programme.


Respectfully yours,

My name

I will owe a beer too anyone who will help me.

Thanks for your time.