3,375 research outputs found
Challenges for precision measurements at the LHC
Challenges for precision measurements at the LHC are discussed and a proposal
how to move forward to overcome the LHC-specific precision brick-walls is
presented.Comment: 4 pages, Presented at the ICISE Inaugural Conference "Windows on the
Universe" - Quy Nhon, Vietnam, August 11-17, 201
Summary of the Experimental part of the XXXIVth Rencontre de Moriond
I summarise the experimental results presented during the hadronic session of
the XXXIVth Rencontre de Moriond.Comment: Moriond summary talk, Les Arcs, March 20-27, 1999, 15 page
Charge asymmetries of lepton transverse momenta in Drell-Yan processes at the LHC
Charged lepton transverse momenta in the Drell-Yan processes play an
important role at the LHC in precision measurements of the Standard Model
parameters, such as the W-boson mass and width, their charge asymmetries and
sin^2(theta_W). Therefore, their distributions should be described as accurate
as possible by the Monte Carlo event generators. In this paper we discuss the
problem of matching the hard-process kinematics of the Monte Carlo generator
WINHAC with the parton-shower kinematics of the PYTHIA 6.4 generator while
interfacing these two programs. We show that improper assignment of the quark
and antiquark effective momenta in the LO matrix element computations may
affect considerably the predicted lepton transverse momenta and even completely
reverse their charge asymmetries at the LHC. We propose two matching schemes in
which the NLO QCD distributions of the leptonic kinematical variables can be
well reproduced by the LO WINHAC generator.Comment: 18 pages, 8 figure
Drell-Yan processes with WINHAC
We present the Monte Carlo event generator WINHAC for Drell-Yan processes in
proton-proton, proton-antiproton, proton-ion and ion-ion collisions. It
features multiphoton radiation within the Yennie-Frautschi-Suura exclusive
exponentiation scheme with O(alpha) electroweak corrections for the
charged-current (W+/W-) processes and multiphoton radiation generated by PHOTOS
for neutral-current (Z+gamma) ones. For the initial-state QCD/QED parton shower
and hadronisation it is interfaced with PYTHIA. It includes several options,
e.g. for the polarized W-boson production, generation of weighted/unweighted
events, etc. WINHAC was cross-checked numerically at the per-mille level with
independent Monte Carlo programs, such as HORACE and SANC. It has been used as
a basic tool for developing and testing some new methods of precise
measurements of the Standard Model parameters at the LHC, in particular the
W-boson mass. Recently, it has been applied to simulations of double Drell-Yan
processes resulting from double-parton scattering, in order to assess their
influence on the Higgs-boson detection at the LHC in its ZZ and W+W- decay
channels.Comment: 8 pages; presented at the XXXVII International Conference of
Theoretical Physics "Matter To The Deepest", Ustron, Poland, 1-6 September
2013; to appear in Acta Physica Polonica
Luminosity measurement method for the LHC: The detector requirements studies
Absolute normalisation of the LHC measurements with a precision of O(1%) is
desirable but beyond the reach of the present LHC detectors. This series of
papers proposes and evaluates a measurement method capable to achieve such a
precision target. In our earlier paper we have selected the phase-space region
where the lepton pair production cross section in pp collisions at the LHC can
be controlled with < 1 % precision and is large enough to reach a comparable
statistical accuracy of the absolute luminosity measurement on the day-by-day
basis. In the present one the performance requirements for a dedicated
detector, indispensable to efficiently select events in the proposed
phase-space region, are discussed.Comment: 26 pages, 13 figure
Gamma Factory high-intensity muon and positron source -- exploratory studies
One of the fundamental challenges for the future leptonic colliders and
neutrino factories as well as for the high-sensitivity studies of lepton
universality is to design and construct new high-intensity sources of muons and
positrons. The next-generation sources should increase the intensity of the
presently operating ones by at least three orders of the magnitude and include
an important option of producing longitudinally polarised leptons. The main
effort to achieve this goal has been focused, so far, on the proton-beam-driven
muon sources and electron-beam-driven positron sources. In this paper, we
present exploratory studies of an alternative scheme which is based on
high-intensity megawatt-class photon beams. Such beams could be delivered in
the future by the Gamma Factory (GF) project. One of the GF multiple goals is
to increase the energy range (by more than one order of magnitude) and the
intensity (by more than six orders of magnitude) of the presently operating
photon sources. Such a leap can be achieved by extending the present
hadron-collider modus operandi of the LHC with the new GF-operation-mode,
allowing to collide atomic beams with laser pulses. The exploratory studies
presented in this paper demonstrate that more than 10 muons of both
signs and more than 10 electrons/positrons per second can be produced by
the GF source
Luminosity Measurement Method for LHC: The theoretical precision and the experimental challenges
This is the first of the series of papers which present a precision method of the day-by-day monitoring of the absolute LHC luminosity. The method is based on the measurement of the rate of coplanar lepton pairs produced in peripheral collisions of the beams' particles. In the present paper we evaluate the modeling precision of the lepton pair production processes in proton-proton collisions, optimize the measurement region to achieve better than 1% accuracy of the predicted rates, and discuss the experimental challenges to filter out the luminosity monitoring lepton pairs at LHC
Z-boson as "the standard candle" for high precision W-boson physics at LHC
In this paper we propose a strategy for measuring the inclusive W-boson
production processes at LHC. This strategy exploits simultaneously the unique
flexibility of the LHC collider in running variable beam particle species at
variable beam energies, and the configuration flexibility of the LHC detectors.
We propose their concrete settings for a precision measurement of the Standard
Model parameters. These dedicated settings optimise the use of the Z boson and
Drell-Yan pair production processes as ``the standard reference candles''. The
presented strategy allows to factorise and to directly measure those of the QCD
effects which affect differently the W and Z production processes. It reduces
to a level of 10^{-4} the impact of uncertainties in the partonic distribution
functions (PDFs) and in the transverse momentum of the quarks on the
measurement precision. Last but not the least, it reduces by a factor of 10 an
impact of systematic measurement errors, such as the energy scale and the
measurement resolution, on the W-boson production observables.Comment: 20 pages, 4 figure
The Gamma Factory path to high-luminosity LHC with isoscalar beams
There are two main ways to increase LHC luminosity without upgrading CERN injectors: (1) modification of beam-collision optics and (2) reduction of beam transverse emittance. The former is followed in the ongoing high-luminosity upgrade of the LHC (HL-LHC), while the latter, applicable only to ion beams, is described in this contribution. The reduction of the beam emittance can be achieved by employing a laser-cooling technique to bunches of partially stripped ions at the SPS flat-top energy. In the case the isoscalar calcium beams fulfilling the presentbeam-operation constrains, the transverse beam emittance can be reduced in this way by a factor of 5 during the 8 second long cooling phase. This would allow to reach the nucleon–nucleon luminosity L_NN = 4.2 x 10^34 s^(-1)cm^(-2), which is comparable to the levelled luminosity for the HL-LHC proton–proton collisions, but with reduced pile-up background. The calcium–calcium collisions have several advantages over the proton–proton collisions for the electroweak physics, such as precision measurements of the W-boson mass and sin^2_W, clean observation of the Higgs boson decay into bbar in its photoproduction channel or BSM phenomena. If this scheme is confirmed by the future Gamma Factory proof-of-principle experiment, it could be implemented at CERN with minor infrastructure investments. This contribution is based on Ref. [1
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