* Astronomy

Members Login
Post Info
TOPIC: Neutrinos


L

Posts: 131433
Date:
Sterile neutrino
Permalink  
 


Title: On the Sterile neutrino explanation of LSND and MiniBooNE anomalies
Authors: Claudio Dib, Juan Carlos Helo, Sergey Kovalenko, Ivan Schmidt

We examine the compatibility between existing experimental data and a recently proposed explanation of the LSND and MiniBooNE anomalies, given in terms of a sterile neutrino N whose decay is dominated by a radiative mode. We find that current experimental data on \tau
ightarrow \mu\nu\nu\gamma decays are in agreement with the required sterile neutrino parameters for the explanation of the anomalies, but K
ightarrow \mu\nu\gamma shows a marginal tension with those parameters. We also propose experimental cuts on radiative K decays that could test the sterile neutrino hypothesis better. Finally, we study the consistency of the rather large value for the neutrino magnetic moment, required for the anomaly explanation, with experimental data on K\to\mu\nu e e, and find that the proposed magnetic moment is too large to fit the data and, therefore, is excluded experimentally.

Read more  (76kb, PDF)



__________________


L

Posts: 131433
Date:
sterile antineutrinos
Permalink  
 


The Amazing Disappearing Neutrino

Neutrinos have long perplexed physicists with their uncanny ability to evade detection, with as many as two-thirds of the ghostly particles apparently going missing en route from the Sun to Earth. Now a refined version of an old calculation is causing a stir by suggesting that researchers have also systematically underestimated the number of the particles' antimatter partners--antineutrinos--produced by nuclear reactor experiments.
The deficit could be caused by the antineutrinos turning into so-called 'sterile antineutrinos', which can't be directly detected, and which would be clear evidence for effects beyond the standard model of particle physics.

Read more 



__________________


L

Posts: 131433
Date:
RE: Neutrinos
Permalink  
 


A revised calculation suggests that around 3% of particles have gone missing from nuclear reactor experiments.

Neutrinos have long perplexed physicists with their uncanny ability to evade detection, with as many as two-thirds of the ghostly particles apparently going missing en route from the Sun to Earth. Now a refined version of an old calculation is causing a stir by suggesting that researchers have also systematically underestimated the number of the particles' antimatter partners - antineutrinos - produced by nuclear reactor experiments.
The deficit could be caused by the antineutrinos turning into so-called 'sterile antineutrinos', which can't be directly detected, and which would be clear evidence for effects beyond the standard model of particle physics.

Read more 



__________________


L

Posts: 131433
Date:
Permalink  
 

Title: The Reactor Antineutrino Anomaly
Authors: G. Mention, M. Fechner, Th. Lasserre, Th. A. Mueller, D. Lhuillier, M. Cribier, A. Letourneau
(Version v4)

Recently new reactor antineutrino spectra have been provided for 235U, 239Pu, 241Pu and 238U, increasing the mean flux by about 3 percent. To good approximation, this reevaluation applies to all reactor neutrino experiments. The synthesis of published experiments at reactor-detector distances <100 m leads to a ratio of observed event rate to predicted rate of 0.976(0.024). With our new flux evaluation, this ratio shifts to 0.943(0.023), leading to a deviation from unity at 98.6% C.L. which we call the reactor antineutrino anomaly. The compatibility of our results with the existence of a fourth non-standard neutrino state driving neutrino oscillations at short distances is discussed. The combined analysis of reactor data, gallium solar neutrino calibration experiments, and MiniBooNE-neutrino data disfavours the no-oscillation hypothesis at 99.8% C.L. The oscillation parameters are such that |Delta m_{new}^2|>1.5 eV^2 (95%) and sin^2(2\theta_{new})=0.14(0.08) (95%). Constraints on the theta13 neutrino mixing angle are revised.

Read more  (350kb, PDF)



__________________


L

Posts: 131433
Date:
Permalink  
 

Title: Time Reversal in Neutrino Oscillations
Authors: Ernest M. Henley, Mikkel B. Johnson, Leonard S. Kisslinger

We examine the present status of time reversal experiments in neutrino oscillations, propose experiments, and discuss the future.

Read more (65kb, PDF)

__________________


L

Posts: 131433
Date:
Sterile neutrinos
Permalink  
 


A flurry of evidence reveals that "sterile neutrinos" are not only real but common, and could be the stuff of dark matter

Neutrinos are the most famously shy of particles, zipping through just about everything - your body, Earth, detectors specifically designed to catch them - with nary a peep. But compared with their heretofore hypothetical cousin the sterile neutrino, ordinary neutrinos are veritable firecrackers. Sterile neutrinos don't even interact with ordinary matter via the weak force, the ephemeral hook that connects neutrinos to the everyday world. Recently, however, new experiments have revealed tantalising evidence that sterile neutrinos are not only real but common. Some of them could even be the stuff of the mysterious dark matter astronomers have puzzled over for decades.
Read more

__________________


L

Posts: 131433
Date:
Scalar Neutrinos
Permalink  
 


Title: Scalar Neutrinos at the LHC
Authors: Durmu A. Demir (IZTECH), Mariana Frank (Concordia U.), Levent Selbuz (IZTECH and Ankara U.), Ismail Turan (Carleton U)

We study a softly-broken supersymmetric model whose gauge symmetry is that of the standard model (SM) gauge group times an extra Abelian symmetry U(1)'. We call this gauge-extended model U(1)' model, and we study a U(1)' model with a secluded sector such that neutrinos acquire Dirac masses via higher-dimensional terms allowed by the U(1)' invariance. In this model the mu term of the minimal supersymmetric model (MSSM) is dynamically induced by the vacuum expectation value of a singlet scalar. In addition, the model contains exotic particles necessary for anomaly cancellation, and extra singlet bosons for achieving correct Z'/Z mass hierarchy. The neutrinos are charged under U(1)', and thus, their production and decay channels differ from those in the MSSM in strength and topology. We implement the model into standard packages and perform a detailed analysis of sneutrino production and decay at the Large Hadron Collider, for various mass scenarios, concentrating on three types of signals: (1) 0lep+ MET,(2) 2lep+MET, and (3) 4lep + MET. We compare the results with those of the MSSM whenever possible, and analyze the SM background for each signal. The sneutrino production and decays provide clear signatures enabling distinction of the U(1)' model from the MSSM at the LHC.

Read more (1010kb, PDF)

__________________


L

Posts: 131433
Date:
RE: Neutrinos
Permalink  
 


New limit on neutrino mass from cosmology, not particle physics

Physicists at University College London have found a new upper limit on the mass of a neutrino - one of the tightest constraints yet from either particle physics or cosmology.
Neutrinos are elementary particles that travel close to the speed of light, but are very difficult to detect because they are not electrically charged. In fact, in the time it takes you to read this sentence, thousands of billions of neutrinos will have passed through your body - and you won't have felt a thing.
According to the Standard Model of particle physics, neutrinos should be massless - just like the photons that make up light - but in reality they do have a very small mass. What the Standard Model failed to take into account is the fact that neutrinos undergo something known as oscillations, or mixing.

Read more

__________________


L

Posts: 131433
Date:
Permalink  
 

Title: Neutrino Mass Sum-rules in Flavor Symmetry Models
Authors: James Barry, Werner Rodejohann

Four different neutrino mass sum-rules have been analysed: these frequently arise in flavour symmetry models based on the groups A_4, S_4 or T', which are often constructed to generate tri-bimaximal mixing. In general, neutrino mass can be probed in three different ways, using beta decay, neutrino-less double beta decay and cosmology. The general relations between the corresponding three neutrino mass observables are well-known. The sum-rules lead to relations between the observables that are different from the general case and therefore only certain regions in parameter space are allowed. Plots of the neutrino mass observables are given for the sum-rules, and analytical expressions for the observables are provided. The case of deviations from the exact sum-rules is also discussed, which can introduce new features. The sum-rules could be used to distinguish some of the many models in the literature, which all lead to the same neutrino oscillation results.

Read more (619kb, PDF)

__________________


L

Posts: 131433
Date:
Permalink  
 

IU scientists in two collaborations see evidence that rules of particle physics may need a rewrite

Two separate collaborations involving Indiana University scientists have reported new results suggesting unexpected differences between neutrinos and their antiparticle brethren. These results could set the stage for what one IU physicist calls a "radical modification of our understanding of particle physics."
The two experiments -- MINOS and MiniBooNE -- in their own unique ways search for a phenomenon where one type, or flavour, of neutrino (there are three: electron, muon and tau) changes into another flavour while travelling through space. Previous experiments, including MINOS, have reported evidence for such transitions, the existence of which indirectly prove that the ghostly neutrinos have non-zero, albeit tiny, masses.

Read more

__________________
«First  <  1 2 3 4 5 6  >  Last»  | Page of 6  sorted by
Quick Reply

Please log in to post quick replies.



Create your own FREE Forum
Report Abuse
Powered by ActiveBoard