Double Regge Exchange Meeting

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Location

Jefferson Lab

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

Information

Google Group

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

June 21 2021

  • Experimental Update
  • Theory Update

Minutes: Colin gave a nice update on the etapi-Delta++ channel PWA. Looked at the 0.1 to 0.3 t bin with the "nominal/standard" partial wave set and with the TMD suggestions. D-waves are pretty consistent between the two wave sets but the D2 seems to go away with the TMD suggestions. This was for the eta->2g. Colin also looked at eta->3pi and there is good agreement with the 2g channel. The TMD suggestions were made for the positive reflectivity waves only (I think); Colins results in the positive reflectivity waves does show a strong D2 wave compared to the intensity of the other D waves.

GJ frame vs Helicity frame. GJ frame can be seen as in the rest frame of the exchange. In Colin's case we expect and see pion exchange to dominate at low t. If it is a real pion exchange with spin 0 then in the GJ frame only the D1 wave should populate. GJ and Helicity frame are rotations of one another and would shuffle the M projections so if we fit in the helicity frame and there was a real pion exchange then different M projections might populate the partial waves. Lawrence showed some previous fits to generated MC and does indeed see a shuffling of the different M projections when fitting in the GJ frame while simulating in the Helicity frame.

June 7 2021

  • Experimental Update
  • Theory Update

Minutes:

Lawrence showed some preliminary results on the t-dependence of the partial waves in the etapi0 channel. 0.1 - 0.3 looks similar to what was presented before at the APS meeting / collaboration meeting. 0.3-0.6 shows a shift from the D2 wave to the D1 wave. There is also some strong peak structure in the S-wave here, lower than the a0(1450) but other experiments also have seen something shifted lower. 0.6-1.0 t bin shows a bit of a mixture of D waves but D1 was the strongest still.

Zach presented a bggen study. Here he applys various cuts one after another and checks the final event topologies that are left over. Even though the relative yields of the bggen sample are not the same as it is in data it is still promising to see how the feed-through from other final states are reduced. Again, Zach and Curtis are looking into this Delta Radial cut as an alternative to a pi0pi0 cut (https://halldweb.jlab.org/DocDB/0051/005125/003/ToyMonteCarlo.pdf).

May 10 2021

  • Experimental Update
  • Theory Update

Minutes:

Zach and Rupesh showed updates on eta' pi0. Zach looked at mass differences in order to understand the enhancement he sees at threshold. He sees that he can place cuts on the mass difference of the eta and pi0 to enhance his eta' signal without cutting any true eta' events. These cuts need to be optimized and will be studied more. He also sees leakage from the 2pi0 and eta pi0 channels into this threshold region. He will study what cuts he can place on these distributions in an attempt to clean up his distributions. Rupesh recently switched to using eta' pi0 trees with the eta and pi0 masses constrained. He presented his updated plots. Adam has spent some time recently connecting the Double Regge and resonance regions. He has some small details to work out in the calculation but believes the formalism is there. Vincent will work on generating theory curves for the eta pi0 and eta pi- beam asymmetries for different exchanges.

Apr 26 2021

  • Experimental Update
  • Theory Update

Minutes:
JPAC analysis of the double Regge region in COMPASS pwa results
Adam suggested it would be helpful to have the t2 dependence, the t at bottom vertex, when doing the analysis of the double Regge region in COMPASS data. There was something about the s12 variable and the higher COMPASS energies that makes things difficult also. GlueX energies should help alleviate this problem. Looking at the phi_GJ is also helpful.

Some discussion about baryon resonances. Malte is making a mock model of the etapi0 data and will look into including baryon resonances. Lukasz has a model of baryon resonances which can be made into a generator but I am not sure how would one integrate that into the GlueX software. Would deinitely be helpful to look at though since we know there are baryon production events that remain but just not sure how it populates various distributions.


Apr 12 2021

  • Experimental Update
  • Theory Update

Minutes: Lots of random discussions. Lawrence showed preliminary pwa fits to show for APS. a2 produced dominantly in M=2 which is also preferred by models to the tensor mesons as seen in the CLAS data. Non-resonant production should also be in the positive reflectivity since it has the same quantum numbers as the a0 (need to verfiy this). Baryon production, of say the Delta+, might be evenly split between positive and negative reflectivity, probably should not have a bias towards one reflectivity. The reflectivity of a double regge exchange should depend on the naturality of the bottom exchange where the top exchange + pion + eta is lumped into one system.

The current path for double Regge model: Develop the model at high mass where we can see the effects better. Determine some observables to look at. Calculate those observables at high mass and into the resonance region and impose some continuity which we can then restrict/constrain the waveset at lower masses. Maybe comparing the integrated intensity of the waves at low mass to high mass. Rebecca is working on pushing the fits onto a GPU for faster computation. These double regge fits take awhile.

Some discussion about ambiguities and leakages which there is no prescription for to handle just yet. Here are a few things that are important: {combinatorics, resolution, acceptance}. Using the generated data removes all these effects but we can break them in turn to study leakage/ambiguities. Malte is working on generating a more realistic model of the data which we can then break. Mariana has seen a problem with the acceptance correction where S-waves can leak in where there was no generated S-wave. Getting an understanding of the magnitude of these effects are probably the next big hurdle to overcome.


March 29 2021

  • Experimental Update
    • Zach -
      • gave an update on the strong dip around the b1 mass in his M(etapi) distribution. It was mainly caused by his omega selection which was from the the other pi0 in his reaction. Will look into how to better select away these omegas
  • Theory Update

Minutes:

There was a long discussion about PWA results for the a2, tensor, production. Experimentally we are seeing M=2 projection with positive reflectivity for the neutral case whereas in the charged channel we are seeing dominance of M=1 in the negative reflectivity. It is suggested that this is due to pion exchange causing a favoring of the negative reflectivity in the charged case. Reflectivity=naturality in this case. Also for a real pion exchange, not the reggeized version, the spin is 0 so the helicity of the photon must be passed directly to the resonance. This results in M=1 projection dominating for the charged channel. Pion exchange not possible in neutral case.

As for the different M projections we can look in table 1 of Vincent's paper of the 3 models. The Tensor Meson Dominance model (which was the better fit to f2 data from CLAS, I think) suggests a stronger M=2 coupling for the tensor. TMD also suggests negative M projections are zero as well as the Minimal model. We might also be able to safely fix all the phases of the projections of a given wave to be the same. These two constraints can help lower fit complexity a bit.

The models also suggest some structure in the transfer momentum, t. Figure 2 of the paper shows a dip in the differential cross section of the a2. This dip is caused by omega exchange. omega exchange, I think, is not possible in the charged case (https://halldweb.jlab.org/DocDB/0047/004788/012/exotic.pdf) so we do not expect a dip in this channel but it is possible in the neutral case.

(Vincent's paper) https://journals.aps.org/prd/pdf/10.1103/PhysRevD.102.014003


March 15 2021

  • Experimental Update
  • Theory Update

Minutes: Verbal updates from Zach and Rebecca. Zach is trying to understand his acceptance by tracking where particles end up in the detector. Rebecca is working with the fits. Fits seems to take a long time to run so there is a need to cache the results, Rebecca is working on getting that to happen. There was a discussion about fitting the moments directly and using some relations defined in Vincent's paper to restrict some of the amplitudes. In particular, the negative M projections might not be important if a given relation between moments is satisfied.

Sean mentioned that there is a spreadsheet that we can enter the observed yields in different channels by different analyzers. From here we can make some estimates to relate the expected yields of the channels and to understand where we might be losing some events. https://docs.google.com/spreadsheets/d/1LiiByy4JIxySZIbT32Fbn9nC_xZsvh5F7omKbP8NuRg/edit#gid=0

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 - [12]
  • 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 - [13]
  • Zach

June 29

  • Theory Update
  • Rebecca - [14]

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 - [15]
  • 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