Difference between revisions of "Jan 31, 2024, Meeting with Alexander Fix (Tomsk Polytechnic University Laboratory)"

From GlueXWiki
Jump to: navigation, search
(→‎Minutes)
(→‎Minutes)
Line 12: Line 12:
  
 
Alexander went through his slides and explained the three background channels he considered: nuclear coherent, nuclear incoherent, and the excited states of the nucleus. For all three channels, his calculation starts by determining the elementary single-nucleon amplitudes ie for the proton and neutron cases. For the proton case, there are two processes at play: vector meson exchange (VME) and Primakoff. For the VME, he is using the rho and omega Regge trajectories. For the Primakoff process, there are two propagators considered but one can be neglected at t -> 0. The elementary single-proton amplitudes model can be compared to data up to 6 GeV and does a good job. Alexander pointed out that for the neutron case, the model can not be compared to data as there is no data. Igal corrected that the neutron differential cross-section was measured up to 3 GeV but below 3 GeV the nucleon resonances dominate not the Regge trajectories. All this points out that the isoscalar amplitude is the largest source of uncertainty in the calculation of the Coherent and Incoherent cross-section. For Igal, it means we have to measure photoproduction of eta off deuteron. Slide 6 is added to show the difference between proton and neutron according to Alexander's model. For the \eta the shape looks fairly similar and the ratio is 1/4 between neutron and proton while for pi0 the shapes are slightly different and the ratio is close to 1. Then Alexander went through the Initial State Interaction (ISI) and Final State Interaction (FSI) considered. Liping & Ashot asked why the ISI is not considered. [But in fact, the Impulse Approximation or the Fermi motion of the nucleon inside the nucleus is by definition an ISI and is possibly the dominant ISI contribution.] Alexander did not consider more complicate ISI has he did not know how to do it in his approach particularly the Glauber theory that Sergey included in his calculation as pointed out by Liping/Ashot/Ilya. For the FSI, a simple approach is used:  
 
Alexander went through his slides and explained the three background channels he considered: nuclear coherent, nuclear incoherent, and the excited states of the nucleus. For all three channels, his calculation starts by determining the elementary single-nucleon amplitudes ie for the proton and neutron cases. For the proton case, there are two processes at play: vector meson exchange (VME) and Primakoff. For the VME, he is using the rho and omega Regge trajectories. For the Primakoff process, there are two propagators considered but one can be neglected at t -> 0. The elementary single-proton amplitudes model can be compared to data up to 6 GeV and does a good job. Alexander pointed out that for the neutron case, the model can not be compared to data as there is no data. Igal corrected that the neutron differential cross-section was measured up to 3 GeV but below 3 GeV the nucleon resonances dominate not the Regge trajectories. All this points out that the isoscalar amplitude is the largest source of uncertainty in the calculation of the Coherent and Incoherent cross-section. For Igal, it means we have to measure photoproduction of eta off deuteron. Slide 6 is added to show the difference between proton and neutron according to Alexander's model. For the \eta the shape looks fairly similar and the ratio is 1/4 between neutron and proton while for pi0 the shapes are slightly different and the ratio is close to 1. Then Alexander went through the Initial State Interaction (ISI) and Final State Interaction (FSI) considered. Liping & Ashot asked why the ISI is not considered. [But in fact, the Impulse Approximation or the Fermi motion of the nucleon inside the nucleus is by definition an ISI and is possibly the dominant ISI contribution.] Alexander did not consider more complicate ISI has he did not know how to do it in his approach particularly the Glauber theory that Sergey included in his calculation as pointed out by Liping/Ashot/Ilya. For the FSI, a simple approach is used:  
−
Square well and Eikonal wave function. Then Alexander how he did include the nucleus excited states contribution and in particular the Giant Dipole Resonance (GDR) which is non-negligible for C. Ashot asked why it is not considered for the Helium case. Then Alexander went through his results for different nuclei (deuteron, helium, and carbon) and mesons (pi^0, /eta, and /eta'). For \eta, the quasi-free Primakoff is non-negligible for all three nuclei and is considered is enhancing the main Primakoff peak by 13%. And this contribution is increasing with the meson mass and vis-versa for lighter meson mass. The contribution is so large that Alexander has some doubts on his calculation and mentioned that independent cross-checked is warranted. Liping does believe that the quasi-free Primakoff should be beneath the main Primakoff but might produce another peak at larger angle. The FSI is both changing the shape of the Primakoff and Nuclear Coherent shapes. Then Liping pointed out that his model for pi^0 should be compared to the existing PrimEx pi0 measurement. Ashot pointed out that to do so Alexander must apply cut or more precisely as Ilya put it energy loss which is the energy transfer to the nucleon. Igal objected to this approach as this part must determined by simulation, particularly for \eta channel and the GlueX set where we can not avoid throwing nucleon and using the BCAL veto to remove the hadronic background which is mainly composed according to Ilya of omega and rho^0 decaying into a soft photon and eta.
+
Square well and Eikonal wave function. Then Alexander showed how he did include the nucleus excited states contribution and in particular the Giant Dipole Resonance (GDR) which is non-negligible for C. Ashot asked why it is not considered for the Helium case. Then Alexander went through his results for different nuclei (deuteron, helium, and carbon) and mesons (pi^0, /eta, and /eta'). For \eta, the quasi-free Primakoff is non-negligible for all three nuclei and is considered and is enhancing for the He nucleus the main Primakoff peak by 13%. And this contribution is increasing with the meson mass and vis-versa for lighter meson mass. The contribution is so large that Alexander has some doubts about his calculation and mentioned that independent cross-checked is warranted. Liping does believe that the quasi-free Primakoff should be beneath the main Primakoff but might produce another peak at larger angle. The FSI is both changing the shape of the Primakoff and Nuclear Coherent shapes. Then Liping pointed out that his model for pi^0 should be compared to the existing PrimEx pi0 measurement. Ashot pointed out that to do so Alexander must apply cut or more precisely as Ilya put it energy loss which is the energy transfer to the nucleon. Igal objected to this approach as this part must determined by simulation, particularly for \eta channel and the GlueX set where we can not avoid throwing nucleon and using the BCAL veto to remove the hadronic background which is mainly composed according to Ilya of omega and rho^0 decaying into a soft photon and eta.
  
 
To conclude, Ashot reminds us the first pi^0 Primakoff measurement was done at Tomsk.
 
To conclude, Ashot reminds us the first pi^0 Primakoff measurement was done at Tomsk.

Revision as of 11:52, 1 February 2024

Persons present

Alexander Fix, Liping Gan, Ashot Gasparian, Sasha Somov, Ilya Larin, Eugene Chudakov, Simon Taylor, Andrew Smith, Igal Jaegle

Slides

Talk of Alexander at slide 6, Alexander added the neutron differential cross-section

Minutes

Alexander went through his slides and explained the three background channels he considered: nuclear coherent, nuclear incoherent, and the excited states of the nucleus. For all three channels, his calculation starts by determining the elementary single-nucleon amplitudes ie for the proton and neutron cases. For the proton case, there are two processes at play: vector meson exchange (VME) and Primakoff. For the VME, he is using the rho and omega Regge trajectories. For the Primakoff process, there are two propagators considered but one can be neglected at t -> 0. The elementary single-proton amplitudes model can be compared to data up to 6 GeV and does a good job. Alexander pointed out that for the neutron case, the model can not be compared to data as there is no data. Igal corrected that the neutron differential cross-section was measured up to 3 GeV but below 3 GeV the nucleon resonances dominate not the Regge trajectories. All this points out that the isoscalar amplitude is the largest source of uncertainty in the calculation of the Coherent and Incoherent cross-section. For Igal, it means we have to measure photoproduction of eta off deuteron. Slide 6 is added to show the difference between proton and neutron according to Alexander's model. For the \eta the shape looks fairly similar and the ratio is 1/4 between neutron and proton while for pi0 the shapes are slightly different and the ratio is close to 1. Then Alexander went through the Initial State Interaction (ISI) and Final State Interaction (FSI) considered. Liping & Ashot asked why the ISI is not considered. [But in fact, the Impulse Approximation or the Fermi motion of the nucleon inside the nucleus is by definition an ISI and is possibly the dominant ISI contribution.] Alexander did not consider more complicate ISI has he did not know how to do it in his approach particularly the Glauber theory that Sergey included in his calculation as pointed out by Liping/Ashot/Ilya. For the FSI, a simple approach is used: Square well and Eikonal wave function. Then Alexander showed how he did include the nucleus excited states contribution and in particular the Giant Dipole Resonance (GDR) which is non-negligible for C. Ashot asked why it is not considered for the Helium case. Then Alexander went through his results for different nuclei (deuteron, helium, and carbon) and mesons (pi^0, /eta, and /eta'). For \eta, the quasi-free Primakoff is non-negligible for all three nuclei and is considered and is enhancing for the He nucleus the main Primakoff peak by 13%. And this contribution is increasing with the meson mass and vis-versa for lighter meson mass. The contribution is so large that Alexander has some doubts about his calculation and mentioned that independent cross-checked is warranted. Liping does believe that the quasi-free Primakoff should be beneath the main Primakoff but might produce another peak at larger angle. The FSI is both changing the shape of the Primakoff and Nuclear Coherent shapes. Then Liping pointed out that his model for pi^0 should be compared to the existing PrimEx pi0 measurement. Ashot pointed out that to do so Alexander must apply cut or more precisely as Ilya put it energy loss which is the energy transfer to the nucleon. Igal objected to this approach as this part must determined by simulation, particularly for \eta channel and the GlueX set where we can not avoid throwing nucleon and using the BCAL veto to remove the hadronic background which is mainly composed according to Ilya of omega and rho^0 decaying into a soft photon and eta.

To conclude, Ashot reminds us the first pi^0 Primakoff measurement was done at Tomsk.

Retrieved from "https://halldweb1.jlab.org/wiki/index.php?title=Jan_31,_2024,_Meeting_with_Alexander_Fix_(Tomsk_Polytechnic_University_Laboratory)&oldid=124522"