NuTeV anomaly : evidence for in-medium nucleon modification

In summary, the conversation discusses the NuTeV "anomaly," which is a discrepancy between the predicted and measured ratio of neutrinos and muons in a neutrino-target collision. The anomaly was initially thought to be evidence for physics beyond the Standard Model, but theorists have proposed a new interpretation involving the EMC Effect, which suggests that the structure of protons and neutrons is modified when they are bound in a nucleus. This modification may account for the discrepancy in the NuTeV data, providing further evidence for the EMC Effect and suggesting that the anomaly is not a sign of more exotic physics.
  • #1
humanino
2,527
8
NuTeV "anomaly" : evidence for in-medium nucleon modification

Dear HEP folks,

maybe some of you have missed it :
Isovector EMC Effect and the NuTeV Anomaly
A neutron or proton excess in nuclei leads to an isovector-vector mean field which, through its coupling to the quarks in a bound nucleon, implies a shift in the quark distributions with respect to the Bjorken scaling variable. We show that this result leads to an additional correction to the NuTeV measurement of sin2W. The sign of this correction is largely model independent and acts to reduce their result. Explicit calculation in nuclear matter within a covariant and confining Nambu–Jona-Lasinio model predicts that this vector field correction may account for a substantial fraction of the NuTeV anomaly. We are therefore led to offer a new interpretation of the NuTeV measurement, namely, that it provides further evidence for the medium modification of the bound nucleon wave function.
From http://www.jlab.org/news/releases/2009/NuTeV.html [Broken]
Experimenters at Fermilab's NuTeV (Neutrinos at the Tevatron) experiment sent a beam of neutrinos into a steel target and measured the ratio of two types of subatomic particles - neutrinos and muons - that emerged. They found that about one percent fewer neutrino-target collisions produced neutrinos than predicted by the Standard Model.

"Many people were convinced that they had discovered evidence for physics beyond the Standard Model," said Thomas.

He and his colleagues pored over the experimental information and began applying their theories for the EMC Effect to it. They found that one common assumption that was used in the analysis of the NuTeV data involved a correction for a natural imbalance in the number of protons and neutrons in the nucleus of iron, the most common element in NuTeV's steel target.

"The correction made for the extra neutrons involved a subtraction of the structure function of the extra neutrons," Cloët explained. "But according to our theoretical model of the EMC Effect, those extra neutrons generate a force that subtly changes the structure of every proton and neutron in the nucleus."

The theorists went further, combining this newly discovered effect with another correction for the difference in masses of different quarks in the protons and neutrons (charge symmetry violation). When they applied the two corrections to the NuTeV analysis, they found that the experiment showed excellent agreement with the Standard Model.

As a consequence, the NuTeV result may now be interpreted as providing crucial evidence for the idea that the structure of a proton or neutron is fundamentally modified when it is bound in a nucleus.
 
Last edited by a moderator:
Physics news on Phys.org
  • #2
If the theorists are right, the NuTeV anomaly may actually be an indication of a subtle but important effect in physics, rather than a sign of something more exotic.HEP folks
 
  • #3
This is known as in-medium nucleon modification, and it has been a topic of intense theoretical and experimental study for decades.

Dear colleagues,

I wanted to bring to your attention the recent findings from the NuTeV experiment at Fermilab. They have discovered an anomaly in their measurements that has been interpreted as evidence for in-medium nucleon modification. This means that the structure of a proton or neutron is fundamentally altered when it is bound in a nucleus, which has been a topic of study for many years.

The NuTeV experiment used a beam of neutrinos to measure the ratio of particles that emerged from a steel target. They found that there were about one percent fewer neutrino-target collisions than predicted by the Standard Model. However, further analysis by theorists has shown that this anomaly can be explained by taking into account the isovector EMC Effect and charge symmetry violation. This provides strong evidence for the idea of in-medium nucleon modification.

I believe this is an important development in our understanding of nuclear structure and the role of nucleons in it. It also highlights the importance of collaboration between experimentalists and theorists in advancing our knowledge in this field. I encourage you to read the full article and continue to follow developments in this area.


 

1. What is the NuTeV anomaly?

The NuTeV anomaly refers to a discrepancy between the predicted and measured values of certain properties of nucleons (protons and neutrons) in high-energy particle collisions. Specifically, the NuTeV experiment observed a higher ratio of neutral to charged current interactions than what was predicted by the Standard Model of particle physics.

2. What evidence supports the existence of in-medium nucleon modification?

The NuTeV anomaly is considered as evidence for in-medium nucleon modification because it cannot be explained by any known theoretical models or experimental uncertainties. Other experiments, such as the CCFR and CDHS experiments, have also observed similar discrepancies, providing further support for the idea of in-medium nucleon modification.

3. How does the NuTeV anomaly impact our understanding of particle physics?

The NuTeV anomaly challenges the current understanding of particle physics as described by the Standard Model. It suggests the possibility of new physics beyond the Standard Model that could explain the observed discrepancies. It also highlights the importance of conducting more precise and comprehensive experiments to further our knowledge of fundamental particles and their interactions.

4. What implications does the NuTeV anomaly have for nuclear and astrophysics?

The NuTeV anomaly has implications for nuclear and astrophysics because it suggests that the properties of nucleons may be different when they are inside a nucleus or in extreme environments such as neutron stars. It could also have implications for our understanding of the structure and behavior of matter in the early universe.

5. What future research is being done to further investigate the NuTeV anomaly?

Scientists are continuing to study the NuTeV anomaly through various experiments, including the MINERvA and T2K experiments, which are looking at neutrino-nucleon interactions at different energies and kinematics. There are also proposals for future experiments, such as the DUNE experiment, which will use a high-intensity neutrino beam to further study the properties of nucleons and their interactions with neutrinos.

Similar threads

  • High Energy, Nuclear, Particle Physics
2
Replies
35
Views
7K
  • High Energy, Nuclear, Particle Physics
Replies
2
Views
2K
  • High Energy, Nuclear, Particle Physics
Replies
1
Views
697
  • STEM Academic Advising
Replies
8
Views
825
  • Beyond the Standard Models
2
Replies
39
Views
4K
  • Beyond the Standard Models
Replies
7
Views
2K
  • Beyond the Standard Models
Replies
2
Views
2K
  • Beyond the Standard Models
3
Replies
74
Views
9K
  • Other Physics Topics
Replies
0
Views
682
  • Introductory Physics Homework Help
Replies
2
Views
2K
Back
Top