Differential cross sections and polarization observables from K* - PowerPoint Presentation

Differential cross sections and polarization observables from K* Photoproduction and the Search for New N* States K. Hicks, Ohio Univesity CLAS Collaboration Meeting Nov. 4, 2016

OutlineIntroduction: missing N* states Reminder of the published K* data from Wei Tang’s PhD The suggestion of “missing” high-mass resonances The new results of spin-density matrix elements from Bonn Interpretation using the Bonn- Gatchina PWA Possible new high-mass N* resonances What more needs to be done to establish these N*’s

The N* Spectrum (lattice QCD) Hybrids J.J. Dudek and R.G. Edwards, PRD85 (2012) 054016

Physics of broad & overlapping resonances Δ (1232) Width: a few hundred MeV. Resonances are highly overlapped 　　 in energy except D (1232). →Complex PWA is necessary Width: ~10 keV to ~10 MeV Each resonance peak is clearly separated . N* : 1440, 1520, 1535, 1650, 1675, 1680, ... D : 1600, 1620, 1700, 1750, 1900, … From: H. Kamano , JAEA seminar

Missing Baryon States (2010) Empty/Yellow boxes are missing/uncertain baryon states.

Missing Baryon States (2012) Empty/Yellow boxes are missing/uncertain baryon states.

Evidence for new N* states and couplings State N((mass)J P PDG 2010 PDG 2012KΛKΣ Nγ N(1710)1/2 + *** (not seen in GW analysis)****** ***** N(1880)1/2+ *******N(1895)1/2-********N(1900)3/2 +** ******** ***N(1875)3/2- ******** ***N(2150)3/2 -******N(2000)5/2+*********N(2060)5/2-***** ***Bonn-Gatchina Analysis – A.V. Anisovich et al., EPJ A48, 15 (2012)(First coupled-channel analysis that includes nearly all new photoproduction data)

Do new states fit into LQCD projections? m π =396MeV N(1860)5/2 + N(1900)3/2 + N(1880)1/2 + N(2060) 5/2 - N(2120) 3/2 -N(1875)3/2-N(1895)1/2- Ignoring the mass scale, new candidate states fit with the J P values predicted from LQCD. Known states:N(1675)5/2-N(1700)3/2-N(1520) 3/2-N(1650)1/2-N(1535) 1/2-R. Edwards et al., Phys.Rev. D84 (2011) 074508 Lowest J- states ~ 300 MeV too high“Roper” state ~ 700 MeV too high Slide borrowed from V. Burkert.

Excited Baryons in the history of the Universe N* Excited baryons are at the transition between the quark-gluon liquid, described in hot QCD , and the confinement of quarks and gluons in nucleons, described in strong QCD . This period lasted ~ 10 -6 seconds. Do we understand this transition? Slide borrowed from V. Burkert .

Slide borrowed from S. Mukherjee.

Slide borrowed from S. Mukherjee.

Slide borrowed from S. Mukherjee.

Slide borrowed from S. Mukherjee.

Summary of IntroductionBoth Lattice QCD and the quark model predict more resonances than have been detected. Some of these are expected to couple strongly to two-pion decay, to be measured at E45. Theoretical tools to extract N*’s are improving PWA from both ANL-Osaka and BoGa find new N*Data from QCD freeze-out suggest more Y*’sL(1405) decays asymmetricPossible effect on n/p ratio in the early universe.

Theoretical models for the K* photoproduction 1. Isobar models: evaluate tree-level Feynman diagrams that include resonant and non-resonant exchanges of baryons and mesons. Advantage: Identify the dominant contributions to the final states Disadvantage: Too many parameters, tuning and fixing of those parameters sometimes are tricky. To describe the physics process completely, all possible Feynman diagrams that could lead to the final state are required to be taken into account in the calculation. Mandelstam variables: From: Wei Tang, Ph.D. Dissertation Defense, August , 2012

2. Regge-ized models: Rather than focus on selecting of all possible s, t and u channel reaction processes, the reggeized models emphasis the t-channel. The standard propagators in the Lagrangian are replaced by Regge propagators. Sho Ozaki, http://ific.uv.es/nucth/chirall10/talks/ozaki.pdf Originally applied to high energy hadron reactions Might not be able to produce the results in detail, but at least it can tell us about how t-channel mesons exchanges affects the reaction From: Wei Tang, Ph.D. Dissertation Defense, August , 2012

K*+L Differential Cross Sections Curves are simple fits using 4 th order Legendra polynomials.

K*+S0 Differential Cross Sections

Total Cross Sections Both data peak at about W=2.25 GeV . There are 3 well-known N*’s there: the N 7/2- (2190), N 9/2- (2250) and N 9/2+ (2250). Note: the N 9/2- is part of the L-forbidden [70,48] multiplet.

Comparison with theory Cyan: Oh and Kim Isobar Model Blue: Kim, Nam, Oh, Kim Regge Model Dotted curves include additional s-channel N* with M<2.2 GeV and L<3.Clearly, the currently available theoretical models cannot reproduce the data. This suggests that higher-mass and higher-L resonances are needed. 21

New analysis of K* L by the Bonn group Used the CLAS K* skim of g11 done by Wei Tang Measured K*+  K 0 p+  p+ p + p - final stateL identified using missing massPhase-space acceptance using fsgen with GSIM/GPPCompletely independent background subtraction3 methods: 1) sideband, 2) Q-value to extract K*, 3) two-level Q-factor All three methods give results consistent within statistical uncertaintiesAnalyzed angular distribution in the K* rest systemExtracted density matrix elements: r00, r 10, r11 using Log Likelihood methodFit using the BoGa PWA to search for new N* resonances

L and K* yield extraction

In the following plots:Solid curves: final PWA fit (including possible new N* states) Reduced c 2 : 0.84, 1.84, 0.76 for diff. x-sec, spin-density matrix, recoil pol. Blue dotted curves: PWA fit without the new high-mass N*’sNoticeable (but small) effect in the mass regions 2200-2350Reduced c 2: 1.92, 1.84, 0.61Red dashed curves: t-channel contributions onlyAt higher photon energies, we expect t-channel to dominate

PDG: listed high-mass N* states plus new N*’s Notes: 1) the photocoupling to the new N*’s (marked with *) are not known. 2) The N*(1880) and N*(1895) are very close to threshold—handled carefully.

Possible new high-mass resonances Comments: 1) masses and widths in the fits are fairly stable. 2) These N*’s have significant B.R. to the K* final state 3) Reasonable PWA fits even with any two of the three states

Caveat EmptorThe new N* states are seen only in this reaction We need other final states at higher masses to confirm It is likely that there is substantial coupling to two-pion decay We need hadronic-beam data to separate photocouplings .The spin-density matrix elements are useful to constrain PWA fitsThere is significant interference in the N* amplitudesToo much uncertainty in the PWA fits without the spin-density m.e.More polarization data would be nice This is, in fact, possible using g12 data

SummaryThis has been a fruitful collaboration between CLAS and Bonn There are other opportunities, such as Nick Compton’s K 0 L dataThe spin-density matrix elements were relatively easy to extract, but this work would not have gotten done without the Bonn groupIt is likely that the “missing” N* resonances are there, and just need to be “found”Reactions with high-mass thresholds are useful to explore high-mass N*’sA wide variety of final states can be explored by CLAS Polarization observables are helpful to constrain the PWAWe have 2-3 possible new high-mass N*’s here (need confirmation)

Backup Slides

Moorhouse Selection Rule The transition amplitudes for g p to all [70, 48] are zero. For gn , these transitions are allowed, e.g. the N 5/2- (1675). N 3/2- N 5/2- Data from N. Bianchi et al., PRC 54 (1996). N1/2+35

Lambda Selection Rule The [70, 4 8] resonances decouple from the K L and K*L channels.This assumes the spectator approximation, where the [ud] quarks are coupled to s=0 in the L . In the [70, 4 8] N*’s, the [ud ] are coupled to s=1.The selection rule applies to both p and n targets.This doesn’t apply to KS and K*S final states. A study of KL , K*L, KS and K* S final states will test this spectator (diquark) hypothesis.Reference: Q. Zhao and F.E. Close, Phys. Rev. D 74 (2006) 094014.36