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Supersymmetric lepton flavor violation at the NLC

Description: Supersymmetric theories generally have new flavor violation sources in the squark and slepton mass matrices. If significant lepton flavor violation exists, selectron and smuon should be nearly degenerate. This leads to the phenomenon of slepton oscillations, which is analogous to neutrino oscillations, if sleptons are produced at the Next Linear Collider. The direct slepton production at the Next Linear Collider provides a much more powerful probe of lepton flavor violation than the current bounds from rare processes, such as {mu} {r_arrow} e{gamma}. 4 refs., 1 fig.
Date: April 1, 1997
Creator: Cheng, Hsin-Chia
Partner: UNT Libraries Government Documents Department

Neutrino masses and sneutrino mixing in R-parity violating supersymmetry

Description: R-parity-violating supersymmetry with a conserved baryon number $B$ provides a framework for particle physics with lepton number ($L$) violating interactions. Two important probes of the $L$-violating physics are neutrino masses and sneutrino-antisneutrino mass-splittings. We evaluate these quantities in the context of the most general CP-conserving, R-parity-violating $B$-conserving extension of the minimal supersymmetric standard model. In generic three-generation models, three sneutrino-antisneutrino mass splittings are generated at tree-level. In contrast, only one neutrino mass is generated at tree-level; the other two neutrinos acquire masses at one-loop. In many models, the dominant contribution to the radiative neutrino masses is induced by the non-zero sneutrino-antisneutrino mass splitting.
Date: June 7, 1999
Creator: Grossman, yuval
Partner: UNT Libraries Government Documents Department

Search for rare charm meson decays at FNAL E791

Description: We report the results of a blind search for flavor-changing neutral current (FCNC), lepton-flavor violating, and lepton-number violating decays of D{sup +}, D{sub s}{sup +}, and D{sup 0} mesons (and their antiparticles) into 2-, 3-, and 4-body states including a lepton pair. Such decays may involve Flavor-Changing Neutral Currents, Leptoquarks, Horizontal Gauge Bosons, or Majorana Neutrinos. No evidence for any of these decays is found. Therefore, we present 90% confidence level branching-fraction upper limits, typically at the 10{sup -4} level. A total of 51 decay channels have been examined; 26 have not been previously reported and 18 are significant improvements over previous results.
Date: August 14, 2003
Creator: Summers, D. J.
Partner: UNT Libraries Government Documents Department

Search for Lepton-Number Violating Processes in B+ to h- l+ l+ Decays

Description: We have searched for the lepton-number violating processes B{sup +} {yields} h{sup -}{ell}{sup +}{ell}{sup +} with h{sup -} = K{sup -}/{pi}{sup -} and {ell}{sup +} = e{sup +}/{mu}{sup +}, using a sample of 471 {+-} 3 million B{bar B} events collected with the BABAR detector at the PEP-II e{sup +}e{sup -} collider at the SLAC National Accelerator Laboratory. We find no evidence for these decays and place 90% confidence level upper limits on their branching fractions B (B{sup +} {yields} {pi}{sup -}e{sup +}e{sup +}) < 2.3 x 10{sup -8}, {Beta}(B{sup +} {yields} K{sup -}e{sup +}e{sup +}) < 3.0 x 10{sup -8}, {Beta}(B{sup +} {yields} {pi}{sup -}{mu}{sup +}{mu}{sup +}) < 10.7 x 10{sup -8}, and {Beta}(B{sup +} {yields} K{sup -}{mu}{sup +}{mu}{sup +}) < 6.7 x 10{sup -8}.
Date: May 17, 2012
Creator: Lees, J.P.
Partner: UNT Libraries Government Documents Department

Lepton Flavour Violation And Baryon Number Non-Conservation in tau to Lambda + h

Description: We have searched for the violation of baryon number B and lepton number L in the (B - L)-conserving modes {tau}{sup -} {yields} {bar {Lambda}}{pi}{sup -} and {tau}{sup -} {yields} {bar {Lambda}}K{sup -} as well as the (B - L)-violating modes {tau}{sup -} {yields} {Lambda}{pi}{sup -} and {tau}{sup -} {yields} {Lambda}K{sup -} using 237 fb{sup -1} of data collected with the BaBar detector at the PEP-II asymmetric-energy e{sup +}e{sup -} storage rings. We do not observe any signal and we determine preliminary upper limits on the branching fractions {Beta}({tau}{sup -} {yields} {bar {Lambda}}{pi}{sup -}) < 5.9 x 10{sup -8}, {Beta}({tau}{sup -}{yields} {Lambda}{pi}{sup -}) < 5.8 x 10{sup -6}, {Beta}({tau}{sup -} {yields} {bar {Lambda}}K{sup -}) < 7.2 x 10{sup -8}, and {Beta}({tau}{sup -} {yields} {Lambda}K{sup -}) < 15 x 10{sup -8} at 90% confidence level.
Date: November 16, 2007
Creator: Lafferty, G.D. & U., /Manchester
Partner: UNT Libraries Government Documents Department

A search for third generation scalar leptoquarks

Description: Leptoquarks (LQ) are particles with both color and lepton number predicted in some gauge theories and composite models. Current theory suggests that leptoquarks would come in three different generations. We report on a search for charge 1/3 third generation leptoquarks produced in p{bar p} collisions at {radical}s = 1.96 TeV using data collected by the D0 detector at Fermilab. Such leptoquarks would decay into a tau-neutrino plus a b-quark with branching fraction B. We present preliminary results on an analysis where both leptoquarks decay into neutrinos giving a final state with missing energy and two b-jets. Using 425(recorded) pb{sup -1} of data, we place limits on {sigma}(p{bar p} {yields} LQ{ovr LQ})B{sup 2} as a function of the leptoquark mass. Assuming B = 1, we excluded at the 95% confidence level scalar third generation leptoquarks with M{sub LQ} < 219 GeV.
Date: August 1, 2006
Creator: Zatserklyaniy, Andriy & U., /Northern Illinois
Partner: UNT Libraries Government Documents Department

Multi-Component Dark Matter

Description: We explore multi-component dark matter models where the dark sector consists of multiple stable states with different mass scales, and dark forces coupling these states further enrich the dynamics. The multi-component nature of the dark matter naturally arises in supersymmetric models, where both R parity and an additional symmetry, such as a Z{sub 2}, is preserved. We focus on a particular model where the heavier component of dark matter carries lepton number and annihilates mostly to leptons. The heavier component, which is essentially a sterile neutrino, naturally explains the PAMELA, ATIC and synchrotron signals, without an excess in antiprotons which typically mars other models of weak scale dark matter. The lighter component, which may have a mass from a GeV to a TeV, may explain the DAMA signal, and may be visible in low threshold runs of CDMS and XENON, which search for light dark matter.
Date: November 1, 2008
Creator: Zurek, Kathryn M.
Partner: UNT Libraries Government Documents Department

Search for the Baryon and Lepton Number Violating Decays tau to Lambda h

Description: The authors have searched for the violation of baryon number B and lepton number L in the (B-L)-conserving modes {tau}{sup -} {yields} {bar {Lambda}}{sup 0}{pi}{sup -} and {tau}{sup -} {yields} {bar {Lambda}}{sup 0}K{sup -} as well as the (B-L)-violating modes {tau}{sup -} {yields} {Lambda}{sup 0}{pi}{sup -} and {tau}{sup -} {yields} {Lambda}{sup 0}K{sup -} using 237 fb{sup -1} of data collected with the BABAR detector at the PEP-II asymmetric-energy e{sup +}e{sup -} storage ring. They do not observe any signal and determine preliminary upper limits on the branching fractions {Beta}({tau}{sup -} {yields} {bar {Lambda}}{sup 0}{pi}{sup -}) < 5.9 x 10{sup -8}, {Beta}({tau}{sup -} {yields} {Lambda}{sup 0}{pi}{sup -}) < 5.8 x 10{sup -8}, {Beta}({tau}{sup -} {yields} {bar {Lambda}}{sup 0}K{sup -}) < 7.2 x 10{sup -8}, and {Beta}({tau}{sup -} {yields} {Lambda}{sup 0}K{sup -}) < 15 x 10{sup -8} at 90% confidence level.
Date: November 28, 2006
Creator: Aubert, B.
Partner: UNT Libraries Government Documents Department

Search for Lepton-Flavor and Lepton-Number Violation in the Decay tau to lhh'

Description: A search for lepton-flavor and lepton-number violation in the decay of the tau lepton into one charged lepton and two charged hadrons is performed using 221.4 fb{sup -1} of data collected at an e{sup +}e{sup -} center-of-mass energy of 10.58 GeV with the BABAR detector at the PEP-II storage ring. In all 14 decay modes considered, the observed data are compatible with background expectations, and upper limits are set in the range {Beta}({tau} {yields} {ell}hh') < (0.7-4.8) x 10{sup -7} at 90% confidence level.
Date: June 29, 2005
Creator: Aubert, B.; Barate, R.; Boutigny, D.; Couderc, F.; Karyotakis, Y.; Lees, J. P. et al.
Partner: UNT Libraries Government Documents Department

Constraints on the relic neutrino abundance and implications for cosmological neutrino mass limits

Description: The authors examine a mechanism which can lead to flavor transformation of neutrino-antineutrino asymmetries in the early universe, a process which is unavoidable when the neutrino mixing angles are large. This sets the best limit on the lepton number of the universe, and hence on the relic neutrino abundance. They also consider the consequences for the relic neutrino abundance if extra neutrino interactions are allowed, e.g., the coupling of the neutrinos to a light (compared to m{sub {nu}}) boson. For a wide range of couplings not excluded by other considerations, the relic neutrinos would annihilate to bosons at late times, and thus make a negligible contribution to the matter density today. This mechanism evades the neutrino mass limits arising from large scale structure.
Date: January 1, 2004
Creator: Bell, Nicole F.
Partner: UNT Libraries Government Documents Department

Lepton family number violation

Description: At present there is evidence from neutrino oscillation searches that the neutrinos are in fact massive particles and that they mix. If confirmed, this would imply that the conservation of LFN is not exact. Lepton family number violation (LFNV) has been searched for with impressive sensitivities in many processes involving charged leptons. The present experimental limits on some of them (those which the author shall consider here) are shown in Table 1. These stringent limits are not inconsistent with the neutrino oscillation results since, given the experimental bounds on the masses of the known neutrinos and the neutrino mass squared differences required by the oscillation results, the effects of LFNV from neutrino mixing would be too small to be seen elsewhere (see Section 2). The purpose of experiments searching for LFNV involving the charged leptons is to probe the existence of other sources of LFNV. Such sources are present in many extensions of the SM. In this lecture the author shall discuss some of the possibilities, focusing on processes that require muon beams. Other LFNV processes, such as the decays of the kaons and of the {tau}, provide complementary information. In the next Section he shall consider some sources of LFNV that do not require an extension of the gauge group of the SM (the added leptons or Higgs bosons may of course originate from models with extended gauge groups). In Section 3 he discusses LFNV in left-right symmetric models. In Section 4 he considers LFNV in supersymmetric models, first in R-parity conserving supersymmetric grand unified models, and then in the minimal supersymmetric standard model with R-parity violation. The last section is a brief summary of the author`s conclusions.
Date: March 1, 1999
Creator: Herczeg, P.
Partner: UNT Libraries Government Documents Department

Neutrino Factory: Physics and R&D Status

Description: In recent years exciting experimental discoveries have shown that neutrino flavors oscillate, and hence that neutrinos have nonzero masses and mixings. The Standard Model needs to be modified to accommodate neutrino mass terms, which require either the existence of right-handed neutrinos to create Dirac mass terms, and/or a violation of lepton number conservation to create Majorana mass terms. The observation that neutrino masses and mass-splittings are tiny compared to the masses of any of the other fundamental fermions suggests radically new physics, which perhaps originates at the GUT or Planck Scale, or perhaps indicates the existence of new spatial dimensions. Whatever the origin of the observed neutrino masses and mixings is, it will certainly require a profound extension to our picture of the physical world. The first step towards understanding this new physics is to pin down the measurable parameters, and address the first round of basic questions: (1) Are there only three neutrino flavors, or do light sterile neutrinos exist? Are there any other deviations to three-flavor mixing? (2) There is one angle {theta}{sub 13} in the mixing matrix which is unmeasured. Is it non-zero? (3) We don't know the mass-ordering of the neutrino mass eigenstates. There are two possibilities, the so-called ''normal'' or ''inverted'' hierarchies. Which is right? (4) There is one complex phase {delta} in the mixing matrix which is accessible to neutrino oscillation measurements. If both {theta}{sub 13} and sin {delta} are non-zero there will be CP Violation in the lepton sector. Is sin {delta} non-zero? (5) What precisely is the value of the lightest neutrino mass and are neutrino masses generated by Majorana mass terms, Dirac mass terms, or both? All of these questions, with the exception of the last one, can in principle be addressed by accelerator-based neutrino oscillation experiments. However, getting all of ...
Date: August 3, 2004
Creator: Geer, Steve
Partner: UNT Libraries Government Documents Department

Leptogenesis from split fermions

Description: We present a new type of leptogenesis mechanism based on a two-scalar split-fermions framework. At high temperatures the bulk scalar vacuum expectation values (VEVs) vanish and lepton number is strongly violated. Below some temperature, T{sub c}, the scalars develop extra dimension dependent VEVs. This transition is assumed to proceed via a first order phase transition. In the broken phase the fermions are localized and lepton number violation is negligible. The lepton-bulk scalar Yukawa couplings contain sizable CP phases which induce lepton production near the interface between the two phases. We provide a qualitative estimation of the resultant baryon asymmetry which agrees with current observation. The neutrino flavor parameters are accounted for by the above model with an additional approximate U(1) symmetry.
Date: January 11, 2004
Creator: Nagatani, Yukinori & Perez, Gilad
Partner: UNT Libraries Government Documents Department

Conceptual design of the Mu2e production solenoid cold mass

Description: The Muon-to-Electron conversion experiment (Mu2e), under development at Fermilab, seeks to detect direct muon to electron conversion to provide evidence for a process violating muon and electron lepton number conservation that cannot be explained by the Standard Model of particle physics. The required magnetic field is produced by a series of superconducting solenoids of various apertures and lengths. This paper describes the conceptual design of the 5 T, 4 m long solenoid cold mass with 1.67 m bore with the emphasis on the magnetic, radiation and thermal analyses.
Date: June 1, 2011
Creator: Kashikhin, V.V.; Ambrosio, G.; Andreev, N.; Lamm, M.; Mokhov, N.V.; Nicol, T.H. et al.
Partner: UNT Libraries Government Documents Department

A search for charge 1/3 third generation leptoquarks in muon channels

Description: Leptoquarks are exotic particles that have color, electric charge, and lepton number and appear in extended gauge theories and composite models. Current theory suggests that leptoquarks would come in three different generations corresponding to the three quark and lepton generations. We are searching for charge 1/3 third generation leptoquarks produced in p{bar p} collisions at {radical}s = 1.96 TeV using data collected by the D0 detector. Such leptoquarks would decay into either a tau-neutrino plus a b-quark or, if heavy enough, to a tau-lepton plus a t-quark. We present preliminary results on an analysis where both leptoquarks decay into neutrinos giving a final state with missing energy and two b-quarks using 367 pb{sup -1} of Run II D0 data taken between August 2002 and September 2004. We place upper limits on {sigma}(p{bar p} {yields} LQ{ovr LQ})B{sup 2} as a function of the leptoquark mass M{sub LQ}. Assuming B = 1, we exclude at the 95% confidence level third generation leptoquarks with M{sub LQ} < 197 GeV/c{sup 2}.
Date: August 1, 2006
Creator: Uzunyan, Sergey A. & U., /Northern Illinois
Partner: UNT Libraries Government Documents Department

Searches for the baryon- and lepton-number violating decays $B^0\rightarrow\Lambda_c^ \ell^-$, $B^-\rightarrow\Lambda\ell^-$, and $B^-\rightarrow\bar{\Lambda}\ell^-$

Description: Searches for B mesons decaying to final states containing a baryon and a lepton are performed, where the baryon is either {Lambda}{sub c} or {Lambda} and the lepton is a muon or an electron. These decays violate both baryon and lepton number and would be a signature of physics beyond the standard model. No significant signal is observed in any of the decay modes, and upper limits in the range (3.2 - 520) x 10{sup -8} are set on the branching fractions at the 90% confidence level.
Date: June 22, 2011
Creator: del Amo Sanchez, P.; Lees, J.P.; Poireau, V.; Prencipe, E.; Tisserand, V.; /Annecy, LAPP et al.
Partner: UNT Libraries Government Documents Department

Gedanken Worlds without Higgs: QCD-Induced Electroweak Symmetry Breaking

Description: To illuminate how electroweak symmetry breaking shapes the physical world, we investigate toy models in which no Higgs fields or other constructs are introduced to induce spontaneous symmetry breaking. Two models incorporate the standard SU(3){sub c} {circle_times} SU(2){sub L} {circle_times} U(1){sub Y} gauge symmetry and fermion content similar to that of the standard model. The first class--like the standard electroweak theory--contains no bare mass terms, so the spontaneous breaking of chiral symmetry within quantum chromodynamics is the only source of electroweak symmetry breaking. The second class adds bare fermion masses sufficiently small that QCD remains the dominant source of electroweak symmetry breaking and the model can serve as a well-behaved low-energy effective field theory to energies somewhat above the hadronic scale. A third class of models is based on the left-right-symmetric SU(3){sub c} {circle_times} SU(2){sub L} {circle_times} SU(2){sub R} {circle_times} U(1)B?L gauge group. In a fourth class of models, built on SU(4){sub PS} {circle_times} SU(2){sub L} {circle_times} SU(2){sub R} gauge symmetry, lepton number is treated as a fourth color. Many interesting characteristics of the models stem from the fact that the effective strength of the weak interactions is much closer to that of the residual strong interactions than in the real world. The Higgs-free models not only provide informative contrasts to the real world, but also lead us to consider intriguing issues in the application of field theory to the real world.
Date: January 1, 2009
Creator: Quigg, Chris & Shrock, Robert
Partner: UNT Libraries Government Documents Department

Search for r-parity violating supersymmetry in the multilepton final state

Description: This thesis presents a search for physics beyond the standard model of elementary particles in events containing three or more charged leptons in the final state. The search is based on an R-parity violating supersymmetric model that assumes supersymmetric particles are pair produced at hadron colliders and the R-parity violating coupling is small enough so that these particles ''cascade'' decay into the lightest supersymmetric particle. The lightest supersymmetric particle may only decay into two charged leptons (electrons or muons) plus a neutrino through a lepton number violating interaction. Proton-antiproton collision events produced with {radical} s= 1.96 TeV are collected between March 2002 and August 2004 with an integrated luminosity of 346 pb{sup -1}. R-parity violating supersymmetry is sought for in two data samples, one with exactly three leptons and one with four or more leptons. The trilepton sample has a modest background primarily from Drell-Yan events where an additional lepton is a result of photon conversions or jet misidentification while the four or more lepton sample has an extremely low background. In the three lepton samples 6 events are observed while in the four or more lepton sample zero events are observed. These results are consistent with the standard model expectation and are interpreted as mass limits on the lightest neutralino and lightest chargino particles. The neutralino mass is constrained to be heavier than 97.7 to 110.4 GeV/c{sup 2}, while the chargino mass is constrained to be heavier than 185.3 to 202.7 GeV/c{sup 2}, depending on the supersymmetry scenario.
Date: November 1, 2006
Creator: Attal, Alon J.
Partner: UNT Libraries Government Documents Department

Particle physics: CP violation in hyperon decays

Description: The primary research activities under this grant were in E871 (HyperCP) at Fermilab, a search for CP violation in hyperon decays which completed data taking in January, 2000. HyperCP is an experiment designed to perform a sensitive search for direct CP violation in the decays of cascade ({Xi}) and {Lambda} hyperons by looking for an asymmetry between particle and antiparticle decay parameters. The experiment is expected to achieve a sensitivity {approx}10{sup -4} in the decay parameters. Standard model predictions for this CP-violating asymmetry range from 0.3 to 5 x 10{sup -4}. A difference between the decay parameters for particle and antiparticle is direct evidence that CP symmetry is violated. A non-zero asymmetry would be the first evidence for CP violation outside of the K{sup o} system. Recent results from KTeV indicate a direct CP violation in K{sup o} decays, which suggests that CP violation will appear in other decays. In addition, we will look at a number of rare hyperon decays involving muons. These probe important new physics topics such as Majorana neutrinos and lepton number violating processes. The latter are of great current interest because new evidence for neutrino oscillations indicate lepton flavor violation does occur. Our data will lead to an improvement in the limits on branching ratios for these processes typically by three to four orders-of-magnitude. The muon detector construction and data resulting from it have been the responsibility of the Michigan group. We are now leading the analysis of the rare muon-related decay modes, and were responsible for the muon system and beam monitor upgrades for the 1999 run.
Date: October 31, 2000
Creator: Longo, Michael J.
Partner: UNT Libraries Government Documents Department

A search for flavor changing neutral currents and lepton family number violation in neutral two-body charm decays

Description: This work presents a search for three rare/forbidden neutral charm decays, D{sup 0} {yields} {mu}e, D{sup 0} {yields} {mu}{mu}, and D{sup 0} {yields} ee. This study was based on data collected in Experiment E789 at the Fermi National Accelerator Laboratory using 800 GeV/c proton-gold interactions. Two statistical analyses are presented, one with background subtraction and the other without background subtraction. No evidence is found for any of the decays and the following upper limits are presented at the 90% confidence level.
Date: June 1, 1997
Creator: Pripstein, D.A.
Partner: UNT Libraries Government Documents Department

Experimental studies of rare K{sup +} decays

Description: Experiment E865 at the BNL AGS is a search for the lepton number violating decay K{sup +} {r_arrow} {pi}{sup +}{mu}{sup +}e{sup {minus}} with an expected sensitivity of 3 {times} 10{sup {minus}12}. The experimental apparatus involves a magnetic spectrometer with two Cerenkov counters, a calorimeter and a muon detector for particle identification. In addition, other rare K{sup +} decays are studied. The experiment has been collecting data since 1995, and preliminary results are presented.
Date: December 31, 1996
Creator: Appel, R.; Atoyan, G.S. & Bassalleck, B.
Partner: UNT Libraries Government Documents Department

Leptoquark searches at the Tevatron

Description: The authors report on searches for leptoquarks using approximately 100 pb {sup -1} of data collected by CDF and DO during Run I at the Tevatron. They also present searches for resonantly-produced leptoquarks that arise in technicolor models. Prospects for future leptoquark searches using Run II data are also discussed.
Date: June 23, 2000
Creator: Acosta, Darin E.
Partner: UNT Libraries Government Documents Department

Search for rare and forbidden charm meson decays at Fermilab E791

Description: The authors report the results of a blind search for flavor-changing neutral current, lepton-flavor violating, and lepton-number violating decays of D{sup +}, D{sub s}{sup +}, and D{sup 0} mesons (and their antiparticles) into modes containing muons and electrons. Using data from Fermilab charm hadroproduction experiment E791, they examine the {pi}{ell}{ell} and K{ell}{ell} decay modes of D{sup +} and D{sub s}{sup +} and the {ell}{sup +}{ell}{sup {minus}} decay modes of D{sup 0}. No evidence for any of these decays is found. Therefore, they present branching-fraction upper limits at 90% confidence level for the 24 decay modes examined. Eight of these modes have no previously reported limits, and fourteen are reported with significant improvements over previously published results.
Date: September 29, 2000
Creator: al., Donald J. Summers et
Partner: UNT Libraries Government Documents Department

Search for (B-L) Nonconservation in Neutron-Antineutron Transitions

Description: Proton decay into (B - L) conserving modes with rates predicted by the original SU(5) grand unification scheme was not experimentally observed. An alternative possibility for baryon instability corresponding to the nonconservation of (B - L) and evolving at the intermediate energy scale needs to be explored in new experiments. One of the most spectacular manifestations of the physics of such an energy scale would be the observation of neutron antineutron transitions. Future prospects and discovery potentials of an n{yields}{anti n} search are discussed here.
Date: December 31, 1997
Creator: Kamyshkov, Yuri A.
Partner: UNT Libraries Government Documents Department