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Derivation of a transfer function to estimate the Z(vv)+jets background from photon+jets in a search for dark matter at the ATLAS detector

Olsson, Emelie LU (2019) FYSM60 20191
Particle and nuclear physics
Department of Physics
Abstract (Swedish)
It has for long been known that dark matter must exist in our universe. Despite massive
efforts to detect dark matter, its constituents remain a mystery. One strategy to unveil
this mystery is to produce dark matter by colliding Standard Model particles. The most
common signature of dark matter production is an excess of missing transverse energy, MET. Such an event would be very rare, which is why it is important to have a precise
background estimation. One irreducible background in the search for dark matter is a Z
boson decaying to two neutrinos. In this thesis, events with a photon are used to create
a transfer function that can be used in the estimation of this background. First, events
are selected with the same... (More)
It has for long been known that dark matter must exist in our universe. Despite massive
efforts to detect dark matter, its constituents remain a mystery. One strategy to unveil
this mystery is to produce dark matter by colliding Standard Model particles. The most
common signature of dark matter production is an excess of missing transverse energy, MET. Such an event would be very rare, which is why it is important to have a precise
background estimation. One irreducible background in the search for dark matter is a Z
boson decaying to two neutrinos. In this thesis, events with a photon are used to create
a transfer function that can be used in the estimation of this background. First, events
are selected with the same characteristics as the Z(vv) background events, but with a
photon instead of the Z. The two samples are compared by adding the photon pT to
the missing energy, to replace the missing transverse energy from the Z boson decaying
to two neutrinos. The two samples show similar distributions for all studied variables.
Next, the transfer function is created, by fitting the ratio of MC samples for the two
bosons. The transfer function reflects the relation between the production cross sections
and selection differences for the Z and
and changes slightly with boson pT. It is for
the range 500-2000 GeV determined to 0.2895 e-5 * MET [GeV], with an uncertainty of 18%.
To make a Z(vv) background estimate the transfer function can be multiplied by photon +
jets data. After further validation, this transfer function will be used in the background
estimation of the Z(vv) background for the mono-Higgs(bb) ATLAS analysis, aiming to
improve its sensitivity in the full run II. (Less)
Please use this url to cite or link to this publication:
author
Olsson, Emelie LU
supervisor
organization
alternative title
Härledning av en funktion för bakgrundsuppskattningen av Z(vv)+jets från foton+jets i jakten på mörk materia vid ATLAS detektorn
course
FYSM60 20191
year
type
H2 - Master's Degree (Two Years)
subject
language
English
id
8983778
date added to LUP
2019-06-24 16:39:09
date last changed
2019-06-24 16:39:09
@misc{8983778,
  abstract     = {{It has for long been known that dark matter must exist in our universe. Despite massive
efforts to detect dark matter, its constituents remain a mystery. One strategy to unveil
this mystery is to produce dark matter by colliding Standard Model particles. The most
common signature of dark matter production is an excess of missing transverse energy, MET. Such an event would be very rare, which is why it is important to have a precise
background estimation. One irreducible background in the search for dark matter is a Z
boson decaying to two neutrinos. In this thesis, events with a photon are used to create
a transfer function that can be used in the estimation of this background. First, events
are selected with the same characteristics as the Z(vv) background events, but with a
photon instead of the Z. The two samples are compared by adding the photon pT to
the missing energy, to replace the missing transverse energy from the Z boson decaying
to two neutrinos. The two samples show similar distributions for all studied variables.
Next, the transfer function is created, by fitting the ratio of MC samples for the two
bosons. The transfer function reflects the relation between the production cross sections
and selection differences for the Z and 
 and changes slightly with boson pT. It is for
the range 500-2000 GeV determined to 0.2895 e-5 * MET [GeV], with an uncertainty of 18%.
To make a Z(vv) background estimate the transfer function can be multiplied by photon +
jets data. After further validation, this transfer function will be used in the background
estimation of the Z(vv) background for the mono-Higgs(bb) ATLAS analysis, aiming to
improve its sensitivity in the full run II.}},
  author       = {{Olsson, Emelie}},
  language     = {{eng}},
  note         = {{Student Paper}},
  title        = {{Derivation of a transfer function to estimate the Z(vv)+jets background from photon+jets in a search for dark matter at the ATLAS detector}},
  year         = {{2019}},
}