168 research outputs found
Фон у мерењу луминозности и развој методе за идентификацију b-кварка у експериментима ILC (International Linear Collider) и H1
No full textThe International linear collider (ILC) is a proposed electron-positron collider
operating at the centre-of-mass energy of 500 GeV, and a peak luminosity of 2.10^34
cm^-2 s^-1. Such a machine, colliding a point like particles, with well defined initial state
and low background environment, would be an ideal complement to the Large Hadron
Collider (LHC) which is operational since 2009. This machine would allow precision
measurement of the new physics phenomena that are likely to be discovered at TeV
energy scale.
In order to perform rich physics program of physics beyond the Standard
Model, the ILC detector is faced with unprecedented challenge for the most of the
subsystems. One of the most important aspects that should be considered is
measurement of the integral luminosity because its uncertainty affects many precision
measurements, and limits some of them as the additional component of a systematic
error. Precision of luminosity measurement is driven by physics requirements for the
cross-section measurements (i.e. the total hadronic cross-section at Z° resonance, 2-
fermion production at high energy) and precision EW measurements (EWSB -
anomalous gauge boson couplings). ILC physics program sets the minimal precision
of the luminosity measurement to be of order of 10-3. This may be accomplished by
construction of fine granulated electromagnetic calorimeter, which will measure the
rate of Bhabha scattering process at small angles at one hand and by the experimental
control of various systematic effects at the other.
The first part of this thesis is dedicated to the study of four-fermion
processes e^+ e^- →e^+ e^- f f^- , as a physics background in the luminosity measurement.
This SM process comes as one of the major systematic effects in luminosity
measurement at ILC due to the high cross-section and the fact that electron spectators
emitted at low polar angles can be misidentified as a signal. It has been demonstrated
that the event selection can be performed in a way that the overall relative systematic
uncertainty does not exceed 2.3 10^-3. Selection efficiency of the Bhabha signal is
maintained to limit the statistical uncertainty of the measurement at 1.2 10^-4. In
addition, background suppression potential is discussed for various selection setups.
Results of this thesis, as an integral part of the study of instrumentation of the
very forward region at ILC have been published by the FCAL Collaboration in 2010
JINST 5 P12002.
The second part of the thesis is dedicated to the physics of heavy quarks at the
H1 experiment at the accelerator HERA at DESY, Hamburg, Germany. The HERA
experiments H1 and ZEUS gave an important experimental insight of the proton
structure in the wide phase space of photon virtuality and Bjorken scaling variable.
By far the most important results of HERA experiments are measurements of
structure functions of proton and further extraction of parton density functions. This
knowledge is of the utmost importance for LHC colliding protons as composite
objects. Also, the precise knowledge of PDF’s of b-quark is an important input in
order to predict the rates of the Higgs production at LHC in its dominant channel. In
this thesis the b-content of the proton is measured that can be further used for F2 ^b and
the corresponding cross-section measurements. With the sample of 54.4 pb ^-1 of HERA II data the proton b-content is
measured, using the e^-p neutral current events of deep inelastic scattering in the
kinematic region of Q^2> 6 GeV^2 and the Bjorken scaling variable 0.0002 < x < 0.32.
The data was recorded in 2006 with the H1 detector, at the centre-of-mass energy of
approximately 319 GeV.
The heavy quark tagging method is based on an inclusive approach exploiting
the different lifetime signatures as well as the mass difference of the charm and
beauty flavoured hadrons compared to the light ones. Thus there are several sensitive
observables like impact parameter based significances of tracks, transverse momenta
of tracks and jets, jets masses and multiplicities, that can be used to distinguish
between events containing heavy flavours with respect to the light ones. These
observables are combined in the most optimal way using the multivariate analysis
techniques (TMVA). Output of the chosen multivariate method is further used in the
Barlow-Beeston fit to fit the data with the corresponding b, c and light-flavor Monte
Carlo samples. In this way, a proton b-content is determined in different Q^2
bins. The
measured values are found to be in agreement with the LO theory prediction. The
dominant component of the systematic error is coming from the choice of a QCD
production model of heavy quarks as well as from the choice of a fragmentation
function. Although the systematic error is somewhat larger than in the previous
measurements at H1, this method allows statistics of the sample to be better preserved
with the statistical error below one percent in all Q^2
bins.
The work related to the proton structure study presented in this thesis was
supported through the project of the German Research Foundation (DFG) No.
436SER113/1/0-1, carried out at DESY and at the Vinca Institute of Nuclear
Sciences, Belgrade, Serbia
Measurement of Higgs to WW in the all-jet final state at CEPC vs=250 GeV
No full textThe most important pillar in the physics case of future electron-positron colliders in high energy physics is the measurement of the Higgs boson, with its main goal to precisely measure its properties and to probe potential of associated new physics. All next generation electron positron facilities in high energy physics will make use of the Higgsstrahlung Higgs production channel. The physics potential of CEPC for measurement of the cross-section times branching ratio of subdominant decay H ? WW* is presented. The Higgsstrahnlung Higgs production channel is used, at the center of mass energy of 250 GeV. The fully hadronic decay, containing six soft-jets in the final state is of great importance for the detector design, jet pairing and reconstruction as showing the capability of CEPC for W/Z separation. The analysis is performed in full simulation. © Copyright owned by the author(s) under the terms of the Creative Common
Physics background in luminosity measurement at 1 TEV at ILC
No full textIn this paper we present the results of the investigation
of the influence of two-photon processes on luminosity
measurement at future linear collider ILC at center-ofmass
energy of 1 TeV. The overall choice of selection
criteria for the luminosity measurement with the
respect to leading sources of systematic error is
discussed. The potential of individual selection criteria
to suppress physics background is discussed and
comparison with the 500 GeV case is presented
Precision luminosity measurement at ILC
No full textIn these proceedings a novel approach to deal with the beam-induced effects in luminosity measurement is presented. Based on the relativistic kinematics of the collision frame of the Bhabha process, the beam-beam related uncertainties can be reduced to the permille level independently of a precision with which the beam parameters are known. Specific event selection combined with the corrective methods we introduce, leads to the systematic uncertainty from the beam-induced effects to be at a few permille level in the peak region above the 80% of the nominal centre-of-mass energies at ILC
Luminosity measurement at ILC
No full textIn this paper we describe a method of luminosity measurement at the future linear collider ILC that estimates and corrects for the impact of the dominant sources of systematic uncertainty originating from the beam-induced effects and the background from physics processes. Based on the relativistic kinematics of the collision frame of the Bhabha process, the beam-beam related uncertainty is reduced to a permille independently of the precision with which the beam parameters are known. With the specific event selection, different from the isolation cuts based on topology of the signal used at LEP, combined with the corrective methods we introduce, the overall systematic uncertainty in the peak region above 80% of the nominal center-of-mass energy meets the physics requirements to be at the few permille level at all ILC energies
Is a blockade of the lateral cutaneous nerve of the thigh an alternative to the classical femoral nerve blockade for knee joint arthroscopy?
No full textLuminosity Measurement at ILC
No full textMore than twenty institutes join the FCAL Collaboration in study of design of the very forward region of a detector for ILC and CLIC. Of particular importance is an accurate luminosity measurement to the level of 10-3, a requirement driven by the potential for precision physics at a future linear collider. In this paper, the method for luminosity measurement, requirements on luminometer and its integration in the forward region are presented. The impact of several effects contributing to the systematic uncertainty of luminosity measurement is given
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