3,130 research outputs found
Looking for Instanton-induced Processes at HERA Using a Multivariate Technique Based on Range Searching
We present a method to discriminate instanton-induced processes from standard
DIS background based on Range Searching. This method offers fast and automatic
scanning of a large number of variables for a combination of variables giving
high signal to background ratio and the smallest theoretical and experimental
uncertainties.Comment: Talk given at ACAT2000 Conference at Fermila
Confronting QCD Instantons with HERA Data
The sensitivity of existing HERA data on the hadronic final state in
deep-inelastic scattering (DIS) to processes induced by QCD instantons is
systematically investigated. The maximally allowed fraction of such processes
in DIS is found to be on the percent level in the kinematic domain 0.0001 <
x-Bjorken < 0.01 and 5 < Q squared < 100 GeV squared. The best limits are
obtained from the multiplicity distribution.Comment: 5 pages, latex, entire paper w. tex, style and figure
A Search for Instantons at HERA
A search for QCD instanton (I) induced events in deep-inelastic scattering
(DIS) at HERA is presented in the kinematic range of low x and low Q^2. After
cutting into three characteristic variables for I-induced events yielding a
maximum suppression of standard DIS background to the 0.1% level while still
preserving 10% of the I-induced events, 549 data events are found while
363^{+22}_{-26} (CDM) and 435^{+36}_{-22} (MEPS) standard DIS events are
expected. More events than expected by the standard DIS Monte Carlo models are
found in the data. However, the systematic uncertainty between the two
different models is of the order of the expected signal, so that a discovery of
instantons can not be claimed. An outlook is given on the prospect to search
for QCD instanton events using a discriminant based on range searching in the
kinematical region Q^2\gtrsim100\GeV^2 where the I-theory makes safer
predictions and the QCD Monte Carlos are expected to better describe the
inclusive data.Comment: Invited talk given at the Ringberg Workshop on HERA Physics on June
19th, 2001 on behalf of the H1 collaboratio
Hadronic final states in deep-inelastic scattering with Sherpa
We extend the multi-purpose Monte Carlo event generator Sherpa to include processes in deeply inelastic lepton–nucleon scattering. Hadronic final states in this kinematical setting are characterised by the presence of multiple kinematical scales, which were up to now accounted for only by specific resummations in individual kinematical regions. Using an extension of the recently introduced method for merging truncated parton showers with higher-order tree-level matrix elements, it is possible to obtain predictions which are reliable in all kinematical limits. Different hadronic final states, defined by jets or individual hadrons, in deep-inelastic scattering are analysed and the corresponding results are compared to HERA data. The various sources of theoretical uncertainties of the approach are discussed and quantified. The extension to deeply inelastic processes provides the opportunity to validate the merging of matrix elements and parton showers in multi-scale kinematics inaccessible in other collider environments. It also allows to use HERA data on hadronic final states in the tuning of hadronisation models
Hadronic final states in DIS with Sherpa
We present an extension of the multi-purpose Monte-Carlo event generator
Sherpa for processes in deeply inelastic lepton-nucleon scattering. Hadronic
final states in this kinematical setting are characterised by the presence of
multiple kinematical scales, which were up to now accounted for only by
specific resummations in individual kinematical regions. An extension of a
known method for merging truncated parton showers with higher-order tree-level
matrix elements allows to obtain predictions which are reliable in all
kinematical limits.Comment: 5 pages, 3 figures; Contribution to the XVIII International Workshop
on Deep-Inelastic Scattering and Related Subjects, April 19-23, 2010,
Firenze, Ital
QCD Tests in High Energy Collisions
Recent measurements and theoretical developments on the hadronic final state in deep-inelastic scattering, pp and ee collisions are presented
The High Energy Jets Framework
High Energy Jets provides an all-order description of wide-angle QCD
emissions, resumming the leading-logarithmic contributions in the high-energy
limit. In this contribution, we briefly summarise the approach and its
implementation in a flexible Monte Carlo event generator. We discuss
comparisons between HEJ and recent LHC data and then go on to probe the
similarities and differences in the results obtained from High Energy Jets and
other theoretical frameworks in inclusive dijet and W+dijet production.Comment: 4 pages, 4 figures, Contribution to the proceedings of the DIS 2012
conference (Bonn, March 2012
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