Double Regge Exchange Meeting

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Location

Jefferson Lab

  • 10:00am: F326/327
Bluejeans: https://bluejeans.com/776007194

Google Group

gluex-jpac-double-regge-discussion@googlegroups.com

June 29

  • Theory Update
  • Rebecca - [1]
  • Lawrence - [2]
  • Zach

Minutes: Most of the discussion was centered around JPAC's double Regge model fit to the COMPASS PWA. One limitation in the fit is that the model allows for infinite partial waves but the data is truncated at L=6. A first look at fitting the partial waves is okay, but due to the reason above they are not ideal. Vincent has begun looking at modeling the double Regge process with a photon beam. The hope is we can use the beam asymmetry or other observables to tune this that can not be done by the partial waves. Him and Rebecca have been working on modeling this. Rebecca has been generating data using these amplitudes provided by Vincent. They both see a buildup of events at low eta pi masses. These are not physical events as the model is only valid at large eta pi masses. Eventually, a connection will need to be made between low and high eta pi masses.

We did not get around to updates from Lawrence and Zach due to time constraints. We will meet again Monday July 6th and continue biweekly from there.

June 8

  • Colin
  • Theory Update

We spent a lot of time discussing our ideas for publication. We are still trying to finalize what observables are useful for the JPAC model. JPAC is currently finishing double Regge things with Compass and will soon begin (this week or next) working on photoproduction. We will then have an idea of how sensitive the model is to different observables and kinematics. Adam suggested we look at ratios (or asymmetries) of fast pi to fast eta events as this is an easy prediction for the model to make. We also discussed making plots for eta' pi and further restricting the eta pi kinematics.

April 27

Colin showed results for the beam asymmetry when one uses the cos nphi moment method from Jon Z. The results agree with the nominal extraction method. Lawrence showed some background distributions and provided an update on monte carlo studies. Rebecca has coded up Vincent's amplitudes and has begun generating events. Adam mentioned that JPAC is finishing up the Compass double Regge analysis and hopes to show the results soon. Once they finish Compass, it will be easy to implement for photoproduction.

April 13

March 30

Colin presented updated beam asymmetries that corrected a sign issue. He also showed beam asymmetries in bins of recoil particles (eta Delta++ or pi- Delta++ mass). The results show the the beam asymmetry is independent of these variables. Lawrence presented beam asymmetries for uncertainties that were calculated from bootstrapping. For both analyses, we had a long discussion on why the beam asymmetry is ~0.5 and not 1. For the experimenters, we were tasked with looking at potential backgrounds and playing around with some cuts, such as the eta pi mass. The theorists were tasked with thinking about why the asymmetry was saturating at 0.5, and if there is a good physics reason behind it.

March 16

Minutes:

  • Colin showed asymmetries as a function of t_eta and t_pi-. There appears to be an issue with the sign based off the expectations. Eg t_eta is negative, but should be positive. Colin check his fit function and extraction of the asymmetry with Lawrence and they are using the same function and the phi0 offsets are nearly identical. Therefore, the extraction method does not appear to cause the sign issue. In discussion with Adam and Vincent, the sign may need to be flipped if one has a Delta++ as the recoiling particle. Adam and Vincent will look into this more offline.
  • Lawrence showed asymmetries as a function of t_eta and t_pi0. They agree with what is to be expected.
  • Vincent showed some slides going over the theory aspects of having 3 particle final states. This needs to be studied more for the kinematics where double Regge production is dominant (high eta pi masses). Hopefully this will give a reason for the sign difference between having a recoil proton and Delta++. It may be that the sign of the asymmetry depends on the product of naturality between the two exchange particles. If this is the case, then having a Delta++ at the bottom vertex would cause a sign flip. This has not been accounted for in Colin's asymmetries.

March 2020 Agenda

  • 9:30: Colin - γ p -> η π- Δ++
  • 10:00: Lawrence - γ p -> η π0 p
  • 10:30: Vincent - [3]
  • 11:00: Discussion
    • Study secondary exchange vertex. If η is on the upper vetex, look at yields as a function of s_{πp} and t_{p}. Do we see the features of Reggeon exchange at this vertex?
    • Calculate beam asymmetries as a function of low t_{π} and t_{η}. Can make some general cuts on the kinematics to reduce potential backgrounds. For example, with a fast π, we can cut to make sure the remaining particles are slow/backwards.
    • Vincent and Lukasz will provide the amplitudes for us to fit to out data. Can we extract reasonable values for α?
    • Can a prediction be made for ηπ+n? Yes, can use this channel as a check.
    • Work on setting up a bi weekly (or monthly) meeting to keep things moving forward.

December 2019 Agenda

Action Items