Bachelor-, Master- and PhD Theses

in Experimental Particle Physics

within the ATLAS SCT Group

at the Max-Planck-Institut fur Physik

[GeV]topm150 160 170 180 190 200

0.5

13

0.0± 0.0 ± 0.0

Tevatron July 2011 0.8± 0.6 ±173.2

CDF l+jets prl. (Run-II best) 1.1± 0.7 ±173.0

D0 l+jets, (Run-I best) 3.9± 3.6 ±180.1

CMS-10 prl. 2.7± 1.9 ±173.4

CMS-10 l+jets prl. 2.5 2.8 ± 2.1 ±173.1

CMS-10 di-l 4.6± 4.6 ±175.5

ATLAS-10+11 l+jets prl. 2.8± 0.9 ±175.9

ATLAS-11 l+jets prl. 2.9± 0.8 ±175.5

+jets prl.µATLAS-11 2.9± 1.0 ±176.0

ATLAS-11 e+jets prl. 3.3± 1.2 ±174.0

ATLAS-10 l+jets prl. 4.9± 4.0 ±169.3 LHC -- Top-Mass Summary -- July 2011

Top Quark Physics

Pixel Detector Development

Supervisor:

Privatdozent Dr. Richard Nisius

Richard.Nisius@mpp.mpg.de

Phone: 089-32354-474

Group web page: https://www.mpp.mpg.de/forschung/experimental/atlas/01_sct/

September, 2015

Figure 1: The ATLAS Experiment.

1 Introduction

Since many years the Max-Planck-Institut fur Physik (MPP) [?] is a member of the ATLAS collab-oration. At the MPP, the SCT Group has made important contributions to many aspects of theexperiment including design, construction, commissioning, calibration and operation of the Semi-Conductor Tracker (SCT), hence the name of our group. In 2009 we changed our focus to the PixelDetector. Since then we are contributing to the operation of the Pixel Detector. In the first longshutdown of the LHC, we participated in the construction, quality assurance and commissioningof the additional innermost layer of the Pixel Detector, called the Insertable B-Layer (IBL). Inaddition, we designed and produced parts of the novel CO2 cooling system of the IBL. Finally, wehave constantly contributed to the physics analyses programme of ATLAS proton-proton collisiondata.

The ATLAS experiment shown in Figure ??, is operated at the Large Hadron Collider (LHC)at the European research centre CERN in Geneva, Switzerland. Due to the high proton energyand the high data rate of this proton-proton collider we are exploiting a new regime of particlephysics, allowing for the discovery of new particles and precision measurements of parametersof the Standard Model (SM), the present theory of elementary particle physics. The study ofthe mechanism of electroweak symmetry breaking has already lead to the discovery of the Higgs-boson [?, ?]. The search for extensions of the SM, like the search for signatures of Supersymmetry,is ongoing. Other important topics are the determination of the SM parameters. In the context ofthese precision measurements, we perform measurements of the mass of the top quark, the heaviest

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elementary particle known to date, for details see Section ??.

To perform precision measurements, the detector components have to be very precise and re-liable. In this area, we contribute to many aspects of the Inner Detector (ID) that measures thetrajectories of charged particles. Presently, we contribute to the operation and calibration of theupgraded 4-layer Pixel Detector.

Our present main detector R&D focus is the development of new detector modules for the nextupgrade of the Pixel Detector, for details see Section ??. This upgrade is needed to operate theATLAS detector at the HL-LHC, the High Luminosity upgrade of the LHC accelerator to startoperation at around 2026.

You can contribute to our research by addressing one of the research topics of different complex-ity and time schedules in your Bachelor-, Master- or PhD Thesis. Depending on the task, differentexpertise will be gained and different skills are required.

We offer

• The possibility to gain experience in solving interesting physics questions in the field ofexperimental particle physics in an international collaboration.

• Participation in the determination of fundamental parameters of the SM.

• Analyses of huge data sets using the worldwide grid computing infrastructure.

• Expertise in modern analysis and fitting techniques.

• Hands-on experience in the commissioning, operation and calibration of a pixel detector.

• Participation in the development of new pixel detectors, including design and performanceevaluation using laboratory set-ups and test beams.

• Software development in C++ and Python.

We expect

• Highly motivated candidates that are eager to face the complex challenges of modern particlephysics experiments.

• Experimental skills and the wish to participate in our work at MPP and CERN.

I am Privatdozent at the LMU Munchen, therefore I mainly address LMU students. However,in our group I have also supervised several students writing their thesis at the TU Munchen. Ifyou are a TUM student interested in our work, please do not hesitate to contact me. We can finda solution such that you can write your TU thesis in our group.

The details of the thesis topics offered are given in the following. They are meant as examples,adaptations are always possible according to the specific interests of the student. In case of questionsrelated to a specific thesis topic, please feel free to contact me or the other persons mentioned belowby e-mail, using Firstname.Lastname@mpp.mpg.de.

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Einfuhrung LHC ATLAS Top Quark Physik Einschub Schluss

Ein Topquark-Paarereignis

g

g

b - Jet

W

Neutrino

Lepton

b - Jet

Wq - Jet

q - Jet

t

t

tνe

e

b-Jet

tt → (b e ν) (b q q)

Jet

Jet

b-Jet

M(qq) = mW

M(bqq) = mtop

Messungen von mtop in ATLAS LMU Munchen 11. Juli 2012 Richard Nisius 11Figure 2: A candidate for a tt decay in the lepton + jets channel observed in the ATLAS experiment.

2 Top Quark Physics

The top quark (t) is the heaviest elementary particle. With a weight corresponding to approximately185 protons and a very short lifetime it is the only quark that decays before it can form boundstates such that its properties are preserved in the kinematics of the decay products. Together withthe measured mass of the W-boson, the top quark mass (mtop) can be used to verify the internalconsistency of the SM given the mass of about 125 GeV of the recently discovered Higgs-boson,and to constrain possible extensions to the SM.

Presently, the main interest of the top quark physics analysis work of our group is the in-vestigation of the tt production process and particularly the determination of mtop in the decaytt→ bb W+W−. Aiming at the best experimental precision, presently our analyses use two decaychannels of the W-boson pair. These are: the di-lepton channel, where the W-boson pair decaysinto a charged lepton and a neutrino `ν`ν with ` = e, µ, with a branching ratio of BR = 4%,and the lepton + jets channel, where the W-boson pair decays into `ν qq′ (BR = 30%), i.e. oneW-boson decays into quarks (q, q′), the other into leptons as above. A candidate event for thisdecay channel is shown in Figure ??. The all-jets channel, where both W-bosons decay into a qq′

pair (BR = 44%) has not yet been studied in our group.

Given the large data samples at the LHC, right from the beginning these measurements arelimited by the size of the systematic uncertainties that can be achieved. Consequently, in these

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channels a number of different estimators of mtop are investigated to find the best possible choice.Within ATLAS we are one of the leading institutes for the measurements of mtop in the di-leptonand lepton + jets channels. Results in the di-lepton channel, obtained within a Diploma- and anongoing PhD thesis, can be found in Refs. [?, ?]. The latest result in the lepton + jets channel, canbe found in Refs. [?, ?]. We have also worked on the combination of ATLAS and CMS measurementsof mtop performed in Ref. [?] and finally, on the combination of measurements of mtop performedat the Tevatron and the LHC documented in Ref. [?]. Given the complexity of the analyses, andthe limitation by the systematic uncertainty, a large variety of investigations has to be made tofurther improve on the precision of mtop. In this context the students will gain experience in manyaspects of the reconstruction of physics objects. Examples are: the jet energy scale calibration andb-tagging algorithms.

2.1 Bachelor Theses

- Comparison of the hadronic final state in tt signal events for different Monte Carlosimulations: Different implementations of the signal process and variations of the parametersthat control the hadronisation process result in variations of the observable distributions. Ina comparison of a number of predictions to ATLAS data the most appropriate one to properlydescribe the data distributions will be selected. In addition, in search for a better agreementwithin a given model, parameter variations will be studied.

2.2 Master Theses

- Determination of the top quark mass in the lepton + jets channel with 2015 AT-LAS data: Building upon the present analysis using the template method [?] the measure-ment of mtop with 2015 data should be performed. The 2015 data will be collected at ahigher centre-of-mass energy and thereby larger production cross-section, such that there isthe possibility to further optimise the analysis for obtaining the best compromise of statisticaland systematic precision, i.e. the most precise result.

- Determination of the top quark mass in the di-lepton channel with 2015 AT-LAS data: Similarly to above, the measurement of mtop in the di-lepton channel should beperformed on 2015 data.

- Determination of the top quark mass in the all-jets channel with 2015 ATLASdata: The measurement of mtop in the all-jets channel should be performed on 2015 data.For this channel results from ATLAS exists [?]. Within this thesis, our analyses methodsdeveloped for the lepton + jets channel should be extended to the needs of the all-jets channel.

- Investigation of the correlation of systematic uncertainties in different measure-ments of the top quark mass: In the combination of measurements of mtop the knowledgeof the correlation of each source of systematic uncertainty amongst all observables is of centralimportance for a proper evaluation of the uncertainty of the combined result. An evaluationfor the electron + jets and muon + jets samples should be performed. For each lepton species,and in a combined likelihood fit, mtop should be measured. The results should be comparedto a simple combination of the results in the individual lepton channels using the Best Linear

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Unbiased Estimate (BLUE) method [?, ?, ?].

2.3 PhD Theses

- Constraining the Jet Scale factors in the lepton + jets channel with 2015 ATLASdata The precision of the knowledge of the jet energy scale for all jets and particularly for b-quark initiated jets (b-jets), is the limiting factor in any mtop analysis if no counter measuresto mitigate their impact are taken. One possibility is the determination of global scales fromthe tt events themselves. These scales are called the jet scale factor JSF for all jets, andthe bJSF for b-jets. This is achieved by selecting additional observables that constrain oneof these scales, while being mostly insensitive to the other, see Ref. [?]. An example is thedetermination of the JSF from constraining the measured 2-jet invariant mass (within thetop quark decay) to the known W-boson mass, a method known as in-situ calibration [?].The main aim of this thesis is to improve on the top quark mass determination by developingnew observables that allow to better constrain the bJSF in a multi-dimensional fit to datafor decreasing the systematic uncertainty.

- A combined determination of the top quark mass in different decay channels with2015 ATLAS data: For any combination of measurements, the improvement in precisionwith respect to the most precise result strongly depends on the correlation of the estimators forthe various common sources of systematic uncertainty [?]. This also applies to the combinationof the top quark mass measurements obtained in different decay channels. The main aim ofthis thesis is to improve on the top quark mass determination by constructing the estimators,or the selected phase space, in such a way as to minimise their correlation.

Contact: Richard Nisius, Giorgio Cortiana.

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p-substrate

Thin read-out chip

Thin sensor/active edgen+

HV

ICV

SLID60 µ

m 7

5 µ

m–

200

µm

inactivedBR

(a) The MPP module concept. (b) The first SLID interconnected module

Figure 3: Sketch of the MPP module concept (a), and the first SLID interconnected MPP module(b).

3 Pixel Detector Development

In many aspects the LHC is performing better than expected. After ten years of operation atthe LHC with the design luminosity profile the complete Inner Detector has to be replaced dueto radiation damage, which accumulates to as much as 2 · 1015 particles/cm2. In addition, a highluminosity upgrade of the LHC accelerator, the HL-LHC, is planned to reach a ten-fold increase indata rate. Consequently, for a given radius the expected radiation dose and hit occupancy at theHL-LHC are an order of magnitude higher than what is presently observed at the LHC.

The ATLAS upgrade, mandatory for running at the HL-LHC, demands a new design for theInner Detector. A baseline design for this Inner Tracker (ITk) has been made. While the geometricallayout of the baseline ITk detector is made, the detector concepts for use at various radii are stillunder study. For the innermost layers of the new Pixel Detector (NewPix), our group is developing aconcept for new pixel detector modules. The main ingredients to this concept are: 1) the use of thinn-in-p sensors to increase the radiation tolerance, to operate at comparably low power consumption,and reduce the multiple scattering, 2) the implementation of an active edge technology to enlargethe active area of the sensors, 3) the use of a novel interconnection technology named Solid LiquidInterDiffusion (SLID) for attaching the readout electronics to the pixel sensors to reduce the costand increase the interconnection density, and 4) Inter Chip Via (ICV) to avoid the presently usedwire bonding area on the front side of the electronics. This R&D is conducted in close collaborationwith industrial partners, CiS [?], HLL [?] and Advacam [?] for the production of silicon sensors,and Advacam, CEA-LETI [?] and two Fraunhofer institutes for the interconnection of sensors andread out chips. Here we work with Advacam and the IZM [?] for conventional bump-bonding, andwith the EMFT [?] for the novel SLID interconnection. A sketch of the proposed pixel module isshown in Figure ??(a) and a photo of the first SLID interconnected module (still without ICV) isshown in Figure ??(b). Finally, an overview of the results of our research within the last years canbe found in Refs. [?, ?, ?, ?].

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3.1 Bachelor Theses

- Characterisation of n-in-p pixel modules for the upgrades of the ATLAS exper-iment: Within our R&D, several productions of n-in-p sensors by different vendors areperformed. The sensors are then interconnected to the read-out electronics. For each sensorproduction, the electrical performance of the modules has to be investigated, before and alsoafter irradiating the modules with protons and/or neutrons. The data are taken in the MPPlaboratory using a 90Sr β-source and 241Am and 109Cd γ-sources, and also with particle beamsat CERN.

Presently, the first batch of n-in-p pixel sensors on six inch wafers from CiS is available. Thesewill be interconnected both with bump-bonding and with SLID. A second production of pixelsensors with active edges interconnected with bump-bonding is under way at Advacam. Wehave already interconnected the first prototypes of so called Quad modules, i.e. 2x2 matricesof pixel sensors. These Quad modules are candidate modules for the outer radii layers of theNewPix detector. Future productions will follow. The characterisation of each production isa topic for a separate Bachelor thesis.

3.2 Master Thesis

- Comparative studies of the radiation hardness of different pixel technologies forthe upgrade of the ATLAS experiment: We work with a number of pixel sensor pro-ducers. Also for the interconnection two options, bump-bonding and SLID interconnectionare available. In this thesis the performance of the pixel modules of various types should beevaluated and compared.

3.3 PhD Thesis

- Design and development of radiation hard pixel modules interconnected withvertical integration technologies for the ATLAS experiment: Our R&D on radiationhard pixel detectors is a long term project that has been strongly driven by the work containedin two finished PhD theses [?, ?]. Two additional PhD thesis are presently performed withinour group, one of which will be finished soon. The newly advertised PhD thesis will beconcerned with sensor design and simulation, characterisation of various module types withradioactive sources, laser set-ups and particle beam data. The PhD student is expected tomake original contributions to future developments of our R&D program in close collaborationwith our industrial partners.

Contact: Richard Nisius, Anna Macchiolo.

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References

[1] Max-Planck-Institut fur Physik, Fohringer Ring 6, 80805 Munchen, http://www.mpp.mpg.de.

[2] ATLAS Collaboration, Observation of a new particle in the search for the Standard ModelHiggs boson with the ATLAS detector at the LHC, Phys. Lett. B716 (2012) 1,http://dx.doi.org/10.1016/j.physletb.2012.08.020.

[3] CMS Collaboration, Observation of a new boson at a mass of 125 GeV with the CMS experi-ment at the LHC, Phys. Lett. B716 (2012) 30,http://dx.doi.org/10.1016/j.physletb.2012.08.021.

[4] A.A. Maier, Investigations towards a Measurement of the Top-Quark Mass in dileptonic De-cay Channels of Top-Antitop Quark Pairs at ATLAS, Diploma thesis, Technische UniversitatMunchen, MPP-2012-160, October 2012,https://publications.mppmu.mpg.de/2014/MPP-2012-160/FullText.pdf.

[5] ATLAS Collaboration, Measurement of the Top Quark Mass in Dileptonic Top Quark PairDecays with

√s = 7 TeV ATLAS Data, ATLAS-CONF-2013-077,

http://cds.cern.ch/record/1562935.

[6] ATLAS Collaboration, Measurement of the Top Quark Mass with the Template Method inthe tt→ lepton + jets Channel using ATLAS Data, Eur. Phys. J. C72 (2012) 2046,http://dx.doi.org/10.1140/epjc/s10052-012-2046-6.

[7] ATLAS Collaboration, Measurement of the Top Quark Mass from√s = 7 TeV ATLAS Data

using a 3-dimensional Template Fit, ATLAS-CONF-2013-046,https://cds.cern.ch/record/1547327.

[8] ATLAS and CMS Collaborations, Combination of ATLAS and CMS results on the mass ofthe top quark using up to 4.9 fb−1 of data, ATLAS-CONF-2012-095,https://cds.cern.ch/record/1460441.

[9] ATLAS Collaboration, Measurement of the top-quark mass in the fully hadronic decay channelfrom ATLAS data a

√s = 7 TeV, CERN-PH-EP-2014-208, Submitted to Eur. Phys. J. C,

http://arxiv.org/abs/1409.0832.

[10] The ATLAS, CMS, CDF and D0 Collaborations, First combination of Tevatron and LHCmeasurements of the top-quark mass, http://arxiv.org/abs/1403.4427.

[11] L. Lyons, D. Gibaut and P. Clifford, How to combine correlated estimates of a single physicalquantity, Nucl. Instr. and Meth A270 (1988) 110.

[12] R. Nisius, On the combination of correlated estimates of a physics observable,Eur. Phys. J. C74 (2014) 3004, http://dx.doi.org/10.1140/epjc/s10052-014-3004-2.

[13] R. Nisius, BLUE: a software package to combine correlated estimates of physics observableswithin ROOT using the Best Linear Unbiased Estimate method - Program manual,http://blue.hepforge.org.

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[14] The ATLAS Collaboration, ATLAS Insertable B-Layer Technical Design Report, ATLAS-TDR-19, https://cds.cern.ch/record/1291633.

[15] The ATLAS Collaboration, ATLAS Pixel IBL: Stave Quality Assurance, ATL-INDET-PUB-2014-006, http://cds.cern.ch/record/1754509.

[16] CiS, Institut fur Mikrosensorik und Photovoltaik GmbH, Konrad-Zuse-Straße 14, 99099 Erfurt,Germany, http://www.cismst.org/.

[17] Max-Planck-Institut Halbleiterlabor, Otto-Hahn-Ring 6 81739 Munchen, Germany,http://www.hll.mpg.de.

[18] Advacam Ltd, Tietotie 3, FI-02150 Espoo, Finland, http://www.advacam.com/.

[19] IZM, Fraunhofer Institut fur Zuverlassigkeit und Mikrointegration, Gustav-Meyer-Allee 25,13355 Berlin, Germany, http://www.izm.fraunhofer.de/.

[20] EMFT, Fraunhofer-Einrichtung fur Modulare Festkorper-Technologien, Hansastraße 27d,80686 Munchen, Germany, http://www.emft.fraunhofer.de/.

[21] L. Andricek, M. Beimforde, A. Macchiolo, H-G. Moser, R. Nisius, R.H. Richter, S. Terzo,P. Weigell, Production and Characterisation of SLID Interconnected n-in-p Pixel Moduleswith 75 Micrometer Thin Silicon Sensors , Nucl. Instr. and Meth A758 (2014) 30,http://dx.doi.org/10.1016/j.nima.2014.05.046.

[22] M. Beimforde, Development of thin sensors and a novel interconnection technology for theupgrade of the ATLAS pixel system, Ph.D. thesis, Technische Universitat Munchen, MPP-2010-115, July 2010,https://publications.mppmu.mpg.de/2014/MPP-2010-115/FullText.pdf.

[23] P. Weigell, Investigation of Properties of Novel Silicon Pixel Assemblies Employing Thin n-in-p Sensors and 3D-Integration, Ph.D. thesis, Technische Universitat Munchen, MPP-2013-5,January 2013,https://publications.mppmu.mpg.de/2014/MPP-2013-5/FullText.pdf.

[24] B. Paschen, Investigation of the Performance of Pixel Modules from thin Silicon Sensors withactive Edges, Master thesis, Ludwig-Maximilians-Universitat Munchen, MPP-2014-557, De-cember 2014, https://publications.mppmu.mpg.de/2014/MPP-2014-557/FullText.pdf

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