| Compact Muon Solenoid Experiment


Compact Muon Solenoid Experiment


School Intern Klara Meusburger and Kaspar Leuze

Klara Meusburger and Kaspar Leuze visited the QCD group as a school intern from 13. - 24. June 2022. They investigated in detail Z+jet production at the LHC and studied effects of different jet algorithms, in particular with the "winner-take-all" clustering scheme.

At the internship

Heng Yang's PhD defense 27 May 2022

Heng Yang performed an analysis of azimuthal correlations of Z+j events in the back-to-back region with CMS. Her results, both experimentally and phenomenologically are important to understand so-called factorization-breaking effect when using Transverse Momentum Dependent parton densities.

After the defense

Luis Ignacio's PhD defense 17 May 2022

Luis Ignacio performed a detailed analysis of azimuthal correlations of high pt jets with CMS. His results shed a new light on the large number of additional jets in association to a high pt jet pair in the back-to-back region.

After the defense

School Intern Amelie Henke

Amelie Henke visited the QCD group as a school intern from 28. Feb - 11. March 2022. She investigated in detail the kinematic effects in Monte Carlo simulation of Deep Inelastic Scattering with Parton Branching Transverse Momentum Dependent (TMD) parton densities. Amelie studied in very detail effects of the transverse momentum of partons inside the proton on the calculation of the structure functions

At the internship

School Intern Madleen Hammer

Madleen Hammer visited the QCD group as a school intern from 31.Jan - 11. Feb 2022. She contributed to Monte Carlo simulation of Deep Inelastic Scattering with Parton Branching Transverse Momentum Dependent (TMD) parton densities. She calculated azimuthal correlations between electron and jet and compared the results with recent measurements from H1.

At the internship

Summerstudents at CMS QCD 2021

During the DESY summerstudent program 2021, young scientists from more than 13 different countries joined together, connecting from remote, working in virtual meetings 2 times a day together, to provide the tools for future comparison of HERA measurements with moderns computer predictions, for the MC4TMD porject as well as on POWHEG with TMDs.

At the end of the program, a CookBook was produced including the most famous dishes from the countries of the summerstudents.

At the end of the summerstudent program

Icon Cook Book (25.5 MB)
Recipe Cook book CMS QCD Summerstudents 2021

Jindrich's PhD defense 3 Sept 2021

Jindrich performed the first analysis of high pt vector boson production in the fully hadronic channel, using fat jets and jet substructure to identify the vector boson in a huge cross section of jet production.

After the defense

Who we are and what we do

The DESY Schülerlabor has recorded a small video about our group, who we are and what we do, and why we find it fascinating, what we do.
You can can find a link to the Schülerlabor under


School Intern A. Wiebers

Antonia Wiebers visited the QCD group as a school intern from 5-16 Oct 2020. She contributed to Monte Carlo simulation of B-jet production at the LHC and calculated the effects of initial, final state parton showers as well as Multi-Parton Interactions (MPI).

At the end of her internship

Master thesis defense: Thomas Wening

Thomas defended his master thesis on 7 Oct 2020. He has determined the transverse momentum dependent (TMD) parton density of the photon. This is the first ever TMD density for the photon.
In his thesis he describes in detail the theoretical background and the steps needed for the calculation. He uses the Parton Branching (PB) to calculate the parton density. He shows that the collinear photon density agrees very well with the one obtained in conventional approaches.
His work lays the ground for the determination of parton densities (and TMD densities) for heavy gauge Bosons like, Z, W and Higgs.

After the defense

Guest scientists from Moscow

Artem Lipatov and Maksim Malyshev (from Moscow State University) visit the CMS QCD group for studies of LHC processes. One issue is the understanding of TMD parton distributions. They investigate associated production of heavy quarks with vector-bosons, using off-shell matrix elements and TMD parton densities.

in sunny Hamburg

Master thesis defense 7. Oct 2019: Melanie Viola Schmitz

In the master thesis with title "Drell-Yan Production with Transverse Momentum Dependent Parton Densities", Melanie developed a method to obtain TMDs from standard parton shower MC event generators and compared pythia8 and herwig6. She calculated DY production with MC@NLO and PB TMDs (which is already published as an article on arXiv and PRD). And, she used CMS open data to measure the DY pt spectrum with Run1 data.

Melanies defense brownies

PhD defense 10. Sept 2019: Daniela Dominguez Damiani

Daniela defended very successfully her thesis with title: "Cross Section measurements of t𝒕̅ pair production in the boosted regime in proton-proton collisions at √s = 13 TeV with the CMS experiment at the Large Hadron Collider".
Her thesis describes a very new and innovative measurement of top-jets in a kinematic region, which was never accessed before. The measurement can help to understand the differences in top predictions and measurements at large transverse momenta.

Daniela's defense

CMS outing August 2019

At the CMS outing, organized by active members of DESY CMS, sportive activities and BBQ brought young and older CMS members together.
The QCD team, supported by summerstudents, won a match in Volleyball

QCD team with summerstudents

Meeting with Nobel Laureates

Armando Bermudez Martinez, a member of the DESY CMS QCD group joined the Lindau meeting of Nobel laureates, and could talk to the Nobel Prize winner David Gross on QCD.

Meeting with Nobel Laureate David Gross

Visiting Scientists on Parton Branching TMDs

Several scientists cams to visit the DESY CMS group to collaborate on further development and improvement of the Parton Branching TMD concept. The Parton Branching method for a precision determination of Transverse Momentum Dependent (TMD) parton densities was developed within the DESY CMS group together with F. Hautmann (Oxford).

Fernando Guzman (InSTEC, Havana, Cuba) is visiting scientist at DESY from July - September 2019.
Francesco Hautman (CERN, Oxford University) is short term visitor at DESY.
Martin Hentschinski (Universidat de las Americas Puebla, Mexico) is "Theorist of the Month" of Terascale.
Aleksander Kusina (Instytut Fizyki Jądrowej Polskiej Akademii Nauk, Cracow) has a Polish National Agency for Academic Exchange grant from July - September 2019.
Krzysztof Kutak (Instytut Fizyki Jądrowej Polskiej Akademii Nauk, Cracow) has a DAAD fellowship from July - September 2019.
Aleksandra Lelek, Lissa Keersmaekers (University Antwerpen) are short term visiting scientists.

Cooperation agreements exist between DESY and InSTEC (Havana) and University Antwerpen, a cooperation agreement with IFJ Cracow is under preparation

Visiting Scientists on Parton Branching TMDs

PhD defense 21. June 2019: Armando Bermúdez Martínez

The PhD thesis of Armando "Measurement and phenomenology of azimuthal correlations in high transverse momentum multi-jet topologies in CMS at the center-of-mass energy of 13 TeV" describes very very new and exciting measurement of azimuthal correlations of high pt jets up to the TeV range in the back-to-back region.
This back-to-back region has never been investigated before, and fixed order calculations fail to describe this region.

PhD defense: Armando Bermúdez Martínez

PhD defense 26. April 2018: Aleksandra Lelek

The thesis of Aleksandra "Determination of TMD parton densities from HERA data and application to pp processes" describes in very detail the Parton Branching method for determination of Transverse Momentum Dependent (TMD) parton densities.
This method is very new and has many applications to LHC physics and beyond. Especially this method enables a perfect description of the Z-boson transverse momentum spectrum.

Ola's defense

PhD defense 28.March 2018: Patrick Connor

In his thesis "Precision measurement of the inclusive b jet production in proton-proton collisions with the CMS experiment at the LHC at 13 TeV", Patrick describes a first measurement of B-jet production at highest energies and at transverse momenta in the TeV range, a range which was never accessed before.
He shows that at these high transverse momenta, B-hadrons inside the jets come mainly from gluon splitting during the jet formation process.

Patricks defense

PhD defense of Juan Grados Luyando

In his thesis "Charged particle spectra in different final states at 13 TeV with the CMS Experiment", Juan describes the first measurement of charged particle production at 13 TeV, with a special investigation of diffractive like processes.

Juans defense

QCD at the extremes

The LHC has opened a new window for studies of strong interactions which today are described remarkably well in the bulk of the phase space by Quantum Chromo Dynamics (QCD). However, there are also a number of corners in the phase space which challenge our understanding of QCD and its predictions.

At the LHC, protons are collided - composite objects consisting of quarks and gluons each carrying a momentum fraction x of their mother proton. The behavior of protons in the medium-x range is well understood and has been studied extensively e.g. at HERA and the Tevatron; here, the dynamics of the partons inside the proton are well described by the DGLAP evolution equations which are also at the heart of most modern Monte Carlo (MC) generators. We work on improving the description of high energy processes by using Transverse Momentum Dependent (TMD) parton densities, which we determined with the Parton Branching method.

QCD at the Extremes is covering different areas - we first cover the area of medium x, where we believe we have the proper theory and we compare measurements with those theory predictions. The very low x region we have already investigate by a couple of the measurements. And finally, with the high luminosity and high energy reached at the LHC run II we can investigate the up to now unexplored region of very high pt and very large x.

QCD at the Extremes is far from being understood; QCD is NOT ``bread-and-butter physics’’, serving only to describe backgrounds for searches of new physics! The LHC offers the unique possibility to test QCD at the extremes and to gain new insight into very fundamental (but by no means simple) physics.

QCD at the extremes