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A possible origin of the endpoint anomaly in tritium beta-spectrum  [PDF]
J. Rizek,V. Brabec,O. Dragoun,M. Rysavy,A. Spalek
Physics , 1998,
Abstract: The influence of the residual T atoms appearing after the decay of T_2 molecule on the beta-spectrum shape is considered. Recent experiments performed in Mainz, Troitsk, and Livermore are briefly reviewed from this viewpoint. Aspects connected with the possible time dependent change of the tritium source composition are discussed.
Conversion electrons used to monitor the energy scale of electron spectrometer near tritium endpoint - a simulation study  [PDF]
M. Rysavy
Physics , 2006,
Abstract: Measurements of the endpoint region of the tritium beta-decay spectrum provides good possibility to determine neutrino mass. This, however, needs a perfect monitoring of the spectrometer energy scale. A parallel measurement of electron line of known energy - in particular the 83mKr conversion K-line - may serve well to this purpose. The 83Rb decaying to 83mKr seems to be a very suitable radioactive source due to its halflife of 86.2 day. In this work, we determine the amount of 83Rb which is necessary for a successful monitoring.
Pileup subtraction for jet shapes  [PDF]
Gregory Soyez,Gavin P. Salam,Jihun Kim,Souvik Dutta,Matteo Cacciari
Physics , 2012, DOI: 10.1103/PhysRevLett.110.162001
Abstract: Jet shapes have the potential to play a role in many LHC analyses, for example in quark-gluon discrimination or jet substructure analyses for hadronic decays of boosted heavy objects. Most shapes, however, are significantly affected by pileup. We introduce a general method to correct for pileup effects in shapes, which acts event-by-event and jet-by-jet, and accounts also for hadron masses. It involves a numerical determination, for each jet, of a given shape's susceptibility to pileup. Together with existing techniques for determining the level of pileup, this then enables an extrapolation to zero pileup. The method can be used for a wide range of jet shapes and we show its successful application in the context of quark/gluon discrimination and top-tagging.
Pileup Per Particle Identification  [PDF]
Daniele Bertolini,Philip Harris,Matthew Low,Nhan Tran
Physics , 2014, DOI: 10.1007/JHEP10(2014)059
Abstract: We propose a new method for pileup mitigation by implementing "pileup per particle identification" (PUPPI). For each particle we first define a local shape $\alpha$ which probes the collinear versus soft diffuse structure in the neighborhood of the particle. The former is indicative of particles originating from the hard scatter and the latter of particles originating from pileup interactions. The distribution of $\alpha$ for charged pileup, assumed as a proxy for all pileup, is used on an event-by-event basis to calculate a weight for each particle. The weights describe the degree to which particles are pileup-like and are used to rescale their four-momenta, superseding the need for jet-based corrections. Furthermore, the algorithm flexibly allows combination with other, possibly experimental, probabilistic information associated with particles such as vertexing and timing performance. We demonstrate the algorithm improves over existing methods by looking at jet $p_T$ and jet mass. We also find an improvement on non-jet quantities like missing transverse energy.
Tritium Decay and the Hypothesis of Tachyonic Neutrinos  [PDF]
Jacek Ciborowski,Jakub Rembielinski
Physics , 1998, DOI: 10.1007/s100529901062
Abstract: Numerous recent measurements indicate an excess of counts near the endpoint of the electron energy spectrum in tritium decay. We show that this effect is expected if the neutrino is a tachyon. Results of calculations, based on a unitary (causal) theory of tachyons, are presented. The hypothesis of tachyonic neutrinos also offers a natural explanation of the V-A structure of the weak leptonic current in neutrino interactions.
Pileup subtraction using jet areas
Cacciari, Matteo;Salam, Gavin P.
High Energy Physics - Phenomenology , 2007, DOI: 10.1016/j.physletb.2007.09.077
Abstract: One of the major challenges for the LHC will be to extract precise information from hadronic final states in the presence of the large number of additional soft pp collisions, pileup, that occur simultaneously with any hard interaction in high luminosity runs. We propose a novel technique, based on jet areas, that provides jet-by-jet corrections for pileup and underlying-event effects. It is data driven, does not depend on Monte Carlo modelling and can be used with any jet algorithm for which a jet area can be sensibly defined. We illustrate its effectiveness for some key processes and find that it can be applied also in the context of the Tevatron, low-luminosity LHC and LHC heavy-ion collisions.
A Possible Solution to the Tritium Endpoint Problem  [PDF]
G. J. Stephenson, Jr.,T. Goldman
Physics , 1998, DOI: 10.1016/S0370-2693(98)01092-2
Abstract: Scalar or right-chiral interaction currents may be expected to produce a neutrino coupled to the electron which is different from, and perhaps even orthogonal to, that coupled to the electron by the standard model weak interaction. We show that, using reasonable parameter values for such additional interactions, it is possible to generate a spectrum which, if analyzed in the manner commonly employed by experimental groups, produces a negative neutrino mass-squared.
Performance of MET reconstruction and pileup mitigation techniques in CMS  [PDF]
Saranya Ghosh,for the CMS Collaboration
Physics , 2015,
Abstract: The performance of missing transverse momentum reconstruction algorithms is presented using 8 TeV pp collision data collected with the CMS detector, corresponding to an integrated luminosity of $12.2 \pm 0.5$ $\mathrm{fb^{-1}}$. The scale and resolution of missing transverse momentum and the effects of multiple proton-proton interactions (pileup), are measured using events with an identified Z boson or isolated photon. They are in general well described by the simulation. Advanced missing transverse momentum reconstruction algorithms are also developed specifically to mitigate the effects of large numbers of pileup interactions on missing transverse momentum resolution. Using these advanced algorithms, the dependence of the missing transverse momentum resolution on pileup interactions is reduced significantly.
An explanation of the "negative neutrino mass squared" anomaly in tritium $ β$-decay based on a theory of mass  [PDF]
R. L. Ingraham,G. A. Luna-Acosta,J. M. Wilkes
Physics , 2000,
Abstract: A proposed solution of the anomalous behavior of the electron spectrum near the endpoint of tritium $\beta$-decay is offered. It is based on a new theory of mass in which mass becomes a dynamical variable, and the electron in the tritium $\beta$-decay has a narrow mass distribution. The predicted Kurie plots explain the main feature (``$m_{\nu}^2 < 0 $'') of this anomalous behavior.
Jet Cleansing: Pileup Removal at High Luminosity  [PDF]
David Krohn,Matthew Low,Matthew D. Schwartz,Lian-Tao Wang
Physics , 2013, DOI: 10.1103/PhysRevD.90.065020
Abstract: One of the greatest impediments to extracting useful information from high luminosity hadron-collider data is radiation from secondary collisions (i.e. pileup) which can overlap with that of the primary interaction. In this paper we introduce a simple jet-substructure technique termed cleansing which can consistently correct for large amounts of pileup in an observable independent way. Cleansing works at the subjet level, combining tracker and calorimeter-based data to reconstruct the pileup-free primary interaction. The technique can be used on its own, with various degrees of sophistication, or in concert with jet grooming. We apply cleansing to both kinematic and jet shape reconstruction, finding in all cases a marked improvement over previous methods both in the correlation of the cleansed data with uncontaminated results and in measures like S/rt(B). Cleansing should improve the sensitivity of new-physics searches at high luminosity and could also aid in the comparison of precision QCD calculations to collider data.
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