Improvement of the separation between W and Z dijet mass peaks in view of Higgs boson precision measurements at CERN future FCC-ee

Stage numéro : M2-2021-AT-03
Laboratoire :Centre de Physique des Particules de Marseille Case 902
 163 avenue de Luminy - 13288 Marseille Cedex 9
Directeur :Cristinel Diaconu - -
Correspondant :William Gillard - -
Groupe d'accueil :Atlas
Chef de groupe :Marlon Barbero - -
Responsable de stage :Steve Muanza - 04 91 82 72 75 -

Thématique : Physique des particules

Despite the impressive amount of data under collection at the LHC and those anticipated at its high luminosity upgrade,

the HL-LHC [1], the design of future post-LHC colliders are currently under intense scrutiny.

Following the discovery of the Higgs boson in 2012 by the ATLAS [2] and CMS [3] experiments using data collected at the LHC Run 1

(pp collisions at √s =7-8 TeV in 2011-2012), the top priority for the next collider is an e+e collider

which will serve primarily as a Higgs boson factory.

At CPPM we started a group to contribute to the physics studies and detectors design for this future facility. In this trainingship

we intend to work on an issue of great importance for the Higgs boson physics program at the FCC-ee [4]. The FCC is a project of the

largest collider (100 km in circumference) to be possibly built at CERN and operated after the HL-LHC.

The problematic we want to tackle the so-called W-Z separation, i.e. the separation between the mass peaks constrcuted with the W

and Z hadronic decays. More precisely we propose an improvement of the current methods, based upon the kinematics of the dijets from

these vector bosons decays, by adding a new discriminating variables based upon the jet charges.

We want to address this complex problem stepwisely. This traininship will concentrate of the first step which will consist in

discriminating the two mass peaks in a fast simulation of the FCC-ee IDEA [5] detector. The further decisive step will be to refine

this study using the full Geant4 [6] simulation of IDEA within the FCCSW framework.

The student will produce Monte Carlo samples such as e+e − > W(− > lν)W(− > q′q) and e+e − > Z(− > νν)Z(− > qq)

at √s = 240 GeV. Then he/she will process these samples using the Delphes [7] fast simulation and produce ROOT [8] ntuples.

He/she will write an analysis code in C++ to implement the current kinematic separation methods in a first stage. Furthermore the

variables based on the jet charges will be added and the improvement in the discrimination will be evaluated.

If the student is successful in getting a PhD bursary, we'll propose him/her a PhD subject on the ATLAS experiment or a mixed one

mostly on ATLAS and partly on FCC-ee.

Desired skills: C++, ROOT



[1] The HL-LHC Collaboration, High-Luminosity Large Ha-dron Collider (HL-LHC), Technical Design ReportNo. CERN-2017-007-M, CERN,

Geneva, 2017, Chap. 1.

[2] Observation of a new particle in the search for the standard model Higgs boson with the ATLAS detector at the LHC, ATLAS

Collaboration, Phys. Lett. B716(2012) 1, arXiv:1207.7214 [hep-ex]

[3] Observation of a new boson at a mass of 125 GeV with the CMS experiment at the LHC, CMS Collaboration, Phys. Lett. B716(2012) 30,

arXiv:1207.7235 [hep-ex]

[4] A. Abada et al., FCC-ee: The Lepton Collider (FCC Conceptual Design Report, Vol. 2),Eur. Phys. J. Spec. Top. (2019) 228: 261 (2019)

[5] R. Aly et al. [INFN RD-FA], First test-beam results obtained with IDEA, a detector concept designed for future lepton

colliders," Nucl. Instrum. Meth. A958 (2020), 162088

[6] S. Agostinelli et al. [GEANT4], GEANT4-a simulation toolkit," Nucl. Instrum. Meth. A506 (2003), 250-303

[7] S. Ovyn, X. Rouby and V. Lemaitre, DELPHES, a framework for fast simulation of a generic collider experiment," arXiv:0903.2225


[8] R. Brun and F. Rademakers, ROOT: An object oriented data analysis framework," Nucl. Instrum. Meth. A389 (1997), 81-86