Double Regge Exchange Meeting

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Location

Jefferson Lab

  • 10:30am: F326/327
Bluejeans: https://bluejeans.com/776007194

Google Group

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


March 1 2021

  • Experimental Update
  • Theory Update

Minutes: A review is happening late march where there will be some discussion of the EtaPi systems. Malte will organize some slides and some plots that should be presented. There is some discussion of constraining the waveset (reflectivity and m-projections) since even for the D-wave there will be 5 m-projections and 2 reflectivites, lots of degrees of freedom. In the EtaPi0 system seems like m=2 is dominant projection in the D-wave, might be expected comparing with previous results from (Belle?). m=1 wave is dominant in EtaPi- probably due to pion exchange. Had a small discussion about ambiguities we are seeing (Malte/Lawrence) given a specific waveset. Malte looked at phases and Lawrence looked at the wave intensities. Lawrence also talked about using the b1 photoproduction cross section to determine an expected yield to gain some insight into what physical processes might leak into the data.

February 15 2021

  • Experimental Update
  • Theory Update

Meeting canceled due to time conflicts

February 1 2021

  • Experimental Update
  • Theory Update

Minutes: Lawrence talked about multiphoton backgrounds that can leak into etapi final state. b1(1232) is probably pretty important and also potentially pi0pi0. Next steps are to use photoproduction cross sections to actually obtain an estimate.

Zach showed some comparison plots between the etapi0 where eta->3pi and eta->2g. M(pi0p) and M(etapi) looks very similar. Zach did a more in depth study of the distributions of the baryon resonances by selecting a forward going eta (with GJ cut) within the delta region.

January 18 2021

  • Experimental Update
  • Theory Update

Minutes: Zach had an update on the asymmetries (fixed the negative asymmetries he was seeing before) for the charged decay of the eta. Things look relatively consistent between his asymmetries and Lawrence's (neutral decay of the eta). The asymmetry vs teta distributions starts of small and saturates around 0.6 whereas in Lawrence's case it is closer to 0.4. Binning in u3 (t proton) the asymmetries increase in both cases. The Mpi0eta distibution looks similar and overlaying the two channels can give a hint at the separation between the a0 and a2 where a b1 bkg can live in the neutral eta decay channel.

Interesting that Zach's acceptance is higher in the forward whereas in the neutral case the opposite is true.

December 7 2020

  • Experimental Update
  • Theory Update

Minutes: Zach still seeing a negative beam asymmetry (will talk with Lawrence+Colin). Colin showed some acceptance/mass plots with an updated gen_amp generator. The generator now considers Delta++ as the recoiling particle instead of a resonance at the bottom vertex (proton+pi0). The t-slope is now calculated with respect to the Delta++ instead of the recoiling proton of the breit-wigner shaped resonance. One year worth of meetings are done!


November 23

  • Experimental Update
  • Theory Update

Minutes:

Zach gave an update of the beam asymmetries in the eta(')pi channels for just the 2017 data. Looking to include GlueX phase 1 soon. Saw mostly negative asymmetries.

Vincent gave a nice presentation on the COMPASS double Regge study they have been working on. They generated pseudodata according to the published COMPASS amplitudes+errors which extend up to M(etapi)=3 GeV (consistency checks were performed but would be interesting to hear how they generated the pseudodata). At high energies in this channel natural parity exchange is dominating. 6 double Regge diagrams can contribute (a2/P, a2/f2, f2/P, P/f2, P/P, f2/f2}. COMPASS did their analysis with L<=6 and with this number of waves the fits did not reconstruct the sharp peaks at forward/backward directions - needed more waves (~10). a2 at the top vertex would produce a peak in the forward direction whereas f2/P would produce a peak in the backward direction. The regge trajectories for a2/f2 are the same whereas the pomeron has a flatter slope + larger intercept. By looking at the relative contributions to each of these diagrams extracted from fits to the psuedodata it appears that pomeron exchange is more prevalent in eta'pi channel than it is in the etapi channel. This is sort of expected since eta'pi should have more gluonic content in the wavefunction.

Seems like it would be interesting to look at the cross sections as a function of t which is split into the forward and backward directions. From the slope of the cross section we might be able to determine which diagrams might contribute more in the channels we are looking at in GlueX

November 9

  • Experimental Update
  • Theory Update

Minutes: Rebecca working on fits. Vincent talked about their progress with the COMPASS Deck analysis and is close to finalizing their results, maybe a week or so to do the bootstrapping for the etaprime channel. In the coming weeks they will give a talk about the physics/interpretations. Vincent has also been working on the theory with a photon beam - spin structure. Takes a little more work to get beam asymmetry predictions since they need normalizations. Zach gave an update on the eta(')pi -> 4gamma pi+ pi reactions. Measured some asymmetries, saw a weird effect in the 2018 data where the yields were ~doubled. Colin was thinking about how baryon decays might change the acceptance but it might be a small order effect anyways.

October 26

No meeting, collaboration meeting and DNP preparations

October 12

  • Experimental Update
  • Theory Update

Minutes: Lawrence, Mariana, Rebecca, and Zach gave updates on the near term goals. Lawrence's near term goals are focused on backgrounds/MC. Mariana talked about PWA and working on reviving/updating moments code. Rebecca showed a fit and a simulation using Vincent's model. Fits need more data (only 2017 right now, Lawrence is working on that). Simulation was probably not made properly since there was a Gamma function factor that was missing in the parameterization. Zach gave a first look at the etapi0 where eta->3pi channel. Some trouble with GetAsymmetry not returning an asymmetry that is centered at 0. Vincent gave an update on the model he is developing.

September 27

  • Experimental Update
  • Theory Update

Minutes: Short meeting, no updates. Fixing bugs. Classes/Teaching.

September 14

  • Experimental Update
  • Theory Update
    • Vincent - Discussion of the model being developed

Minutes: Rebecca is currently working on updating and cross checking Vincent's models. Vincent talked about the Double Regge model he is developing. Zach is working on getting beam asymmetry measurements for that are similar to what Colin and Lawrence have shown before. The channel Zach is looking at is gamma p -> eta pi0 p -> pi+ pi- 4gamma p.

August 31

  • Experimental Update
    • Rebecca - update
  • Theory Update

Minutes: Rebecca showed some initial moment fits in the a0 and a2 regions. Vincent suggested some studies to debug the fits better. Sean pointed out that backgrounds from other processes could still exist in these regions. Rebecca is coding up the new Double Regge model from Vincent. Vincent agreed to present more model details at the next meeting.

August 17

  • Experimental Update
  • Theory Update
  • Rebecca - [7]
  • Zach - update

Minutes: Rebecca showed the results of her current fits to the 2-3 GeV region with the JPAC model. It was suggested that with a 3-parameter fit, she can try fitting the data in smaller M(pi0eta) bins. Also, it would be worth generating events only in that mass range, then trying to reconstruct them to see what the distribution looks like - the attempt to include lower masses did not work, but it might be an affect of the accept/reject method with the amplitude. Possible improvements to the model will be discussed in some detail in tomorrow's JPAC meeting. Zach showed some initial results from his etapi data. Some yield asymmetries were shown, also mass distributions showing differing contributions of various baryon excitations. Among other studies, he will try to understand why the efficiency for backward eta's is so low by using MC samples.

August 03

  • Experimental Update
  • Theory Update

July 20

  • Experimental Update
  • Theory Update

July 6

  • Theory Update
  • Lawrence - [8]
  • Zach

June 29

  • Theory Update
  • Rebecca - [9]

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 - [10]
  • 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