# Presentation: 882423

## The Rise and Fall of the Pentaquarks in Experiments 

- Reinhard Schumacher
- Carnegie Mellon University

- PANIC, Santa Fe, October 28, 2005

**Notes:**
Title

## Overview

- Pentaquarks: brief history...  predictions...
- Experimental evidence (since PANIC Oct.’02)
- The +  at LEPS, ITEP, CLAS, SAPHIR, ZEUS, HERMES...
- The  at NA49/CERN
- The 0c  at H1/HERA
- The ++  at STAR/RHIC
- Compare “+” and “–” evidence by reaction channel
- Theme: Bandwagon effect led to overly-optimistic assessments of data by many groups

- R. A. Schumacher, Carnegie Mellon University, PANIC'05

- 10/28/2005

## What are Pentaquarks?	

- Objects with 4 quarks and 1 anti-quark
- “Exotics” contain an anti-quark different in flavor than the 4 quarks **→** the anti-quark can’t annihilate! The quantum numbers are *impossible* with just 3 quarks.
- Example: uudds  (exotic);   The “+”
- Baryon number = 1/3 + 1/3 + 1/3 + 1/3 - 1/3 = 1
-     Strangeness =  0 + 0 +  0 + 0  + 1 = +1
- Early history:
- Bag models: R.L.Jaffe (76), deSwart(80)
- Soliton models: Diakonov, Petrov (84); Chemtob(85); Praszalowicz(87), Walliser(92)
- PDG’04: +  ***
- M = 1539.2 ± 1.6 MeV
- =       0.9 ± 0.3 MeV
- +→ K+ n,  K0 p

- _

- _

- R. A. Schumacher, Carnegie Mellon University, PANIC'05

- 10/28/2005

## Anti-Decuplet in a Chiral-Soliton Model

- PREDICTION
- D. Diakonov , V. Petrov, M. Polyakov,    Z. Phys. **A359**, 305 (1997).

- ~15 MeV:
- very narrow!

- R. A. Schumacher, Carnegie Mellon University, PANIC'05

- 10/28/2005

## Pentaquarks – Three Model Descriptions

- Chiral soliton model:
- (Diakonov, Petrov, Polyakov)

- Quark description:
- (Jaffe, Wilczek)

- Pentaquarks in such models emerge as  rotational excitations of the soliton  [rigid core (q3) surrounded
- by meson fields (qq)]; JP= 1⁄2 +

- Two bosonic di-quarks (ud), plus s;  fermionic state demands L=1, giving JP= 1⁄2 +
- Lattice QCD →existence and JP predictions are inconclusive.

- L=1

- (ud)

- (ud)

- s

- R. A. Schumacher, Carnegie Mellon University, PANIC'05

- 10/28/2005

## Positive Evidence (most of it...)

***SPring8***

***SAPHIR***

***JLab-p***

***HERMES***

***ITEP***

- pp → ++.

***COSY-TOF***

***DIANA***

***SVD/IHEP***

***JLab-d***

***ZEUS***

***CERN/NA49***

***H1***

- Positive Evidence (most of it...)

******5****- -****  ********5****0**

******0****c**

- R. A. Schumacher, Carnegie Mellon University, PANIC'05

- 10/28/2005

## The Data Without “Fits”

- 4.8

- 5.2

- 7.8

- 4.4

- 6.7

- ~5

- 4.6

- 5.6

******5****- -****  ********5****0**

******0****c**

- 4.2

- ~5.5

***SPring8***

***HERMES***

***DIANA***

***JLab-p***

***JLab-d***

***COSY-TOF***

***SVD/IHEP***

*CERN/NA49*

***SAPHIR***

***ITEP***

***ZEUS***

*H1*

- R. A. Schumacher, Carnegie Mellon University, PANIC'05

- 10/28/2005

## Skeptic’s Comments

-  Most of the positive evidence for pentaquark states is statistically very weak, despite claims of over 4 significance.
-  Without “guides for the eye”, many experimental spectra have low signal-to-noise, and large _poorly-known_ backgrounds.  No clean background-free peaks have been reported.
- There seems to have been a “bandwagon effect” in place from the start: frantic attempt to get on board the list of positive sightings.

- R. A. Schumacher, Carnegie Mellon University, PANIC'05

- 10/28/2005

## Anti-evidence for Pentaquarks

- BABAR

- BES

- R. A. Schumacher, Carnegie Mellon University, PANIC'05

- 10/28/2005

## Pentaquark Exp’ts Timeline

| Photoproduction on Deuteron   |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
| Photoproduction on Proton   pKs0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
| Photoproduction on Proton  nK+K-+ |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
| Exclusive K + (N) → pKs0  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
| Inclusive lepton + D, A → p Ks0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
| p + A →  pKs0 + X |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
| p + p →  pKs0 + + |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
| Other + Upper Limits |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
|  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
|  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
|  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
| p + p (or A) → - - + X |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
| Inclusive  + + → p K+ |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
| Inclusive c → D(*)  p |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
|  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
|  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
|  | 9
10 | 11 12 | 1  2 | 3 4 | 5 6 | 7 8 | 9 10 | 11 12 | 1 2 | 3 4 | 5 6 | 7 8 | 9 10  | 11 12 | 1 2 | 3 4 | 5 6 | 7 8 | 9 10 | 11 12  |

-                  2002            2003                 2004                    2005

- LEPS-C

- R. A. Schumacher, Carnegie Mellon University, PANIC'05

- 10/28/2005

## Impact on particle physics:

- Since October 2002:
-   50 + experimental papers, both pro and con
- 550 + theory papers

- R. A. Schumacher, Carnegie Mellon University, PANIC'05

- 10/28/2005

## C → K K+ X

- Inclusive measurement on Carbon target
- Detect only the two K’s
- Apply Fermi motion correction to MM (****K-)

- C → K K+ X

- T. Nakano, PRL91, 012002, (2003)

- R. A. Schumacher, Carnegie Mellon University, PANIC'05

- 10/28/2005

## First Reported Observation of + at LEPS/SPring-8

**background**

- Solid: signal sample
- Dashed: background from protons in upstream H2 target, normalized to signal above 1590 MeV
- Significance: 4.6****
- Mass 1540 ± 10 MeV
- Width < 25 MeV

- T. Nakano, PRL _91_, 012002 (2003)

- C → K K+ X

- 

- R. A. Schumacher, Carnegie Mellon University, PANIC'05

- 10/28/2005

## LEPS/SPring-8  (n)K+K-n

** ****MM******** ****(GeV)**

** ****MM******** ****(GeV)**

- Deuteron target; the proton is a spectator (undetected).
-  Fermi motion is corrected to get the missing mass spectra.
- Tight  exclusion cut is essential.
- Background is estimated by mixed events.

********

- 2004

- R. A. Schumacher, Carnegie Mellon University, PANIC'05

- 10/28/2005

## Photoproduction at CLAS/JLab

- D →  p KK(n) exclusive channel
- No Fermi motion correction needed
- FSI puts K at larger lab angles: better CLAS acceptance
- FSI not rare: in ~50% of (1520) events both nucleons detected with p>0.2 GeV/c
- CLAS Collaboration (S. Stepanyan, K. Hicks, *et al**.*), hep-ex/0307018, PRL _91_ 252001 (2003).

- d

- R. A. Schumacher, Carnegie Mellon University, PANIC'05

- 10/28/2005

## CLAS/JLab +: Exclusive Process  I

- MM(K-p)  (GeV/c2)

- Events/10 MeV

- CLAS/JLab ****+: Exclusive Process  I

********

- R. A. Schumacher, Carnegie Mellon University, PANIC'05

- 10/28/2005

## 2004: CLAS High-Stat’s Data

- p → p  

** ****CLAS g11**
**   ****preliminary**
** ****SAPHIR**

- p → K+ 

**E************GeV)**

******(********b)**

** ****CLAS g11**
**   ****preliminary**
** ****SAPHIR**

- g10 preliminary (3375A)
- World data

****** ****n ******** p ******** ****-**
- 1.05 < E < 1.15 GeV

- cosCM(-)

- d/dCM (b/sr)

-  p
- x10

-  D
- x6

- R. A. Schumacher, Carnegie Mellon University, PANIC'05

- 10/28/2005

## An Upper Limit on + Production with CLAS.

-  In previous result, the background is underestimated. New estimate of
- the original data gives a significance of ~3, possibly due to fluctuations.

**no********signal**

- An Upper Limit on + Production with CLAS.

- Published result with
- background
- from new result

- (July 2005, Lepton-Photon Conf.)

- R. A. Schumacher, Carnegie Mellon University, PANIC'05

- 10/28/2005

## Newest LEPS/SPring-8 Claim

- T. Nakano, Presented at International Conference on QCD and Hadronic Physics, Beijing, June 20, 2005.

- Select  on (1520)--> K- p
- Very forward c.m. acceptance
- Strangeness of “+” is tagged

********

- (Pentaquark 2005, Oct. 21, CLAS g10 data don’t confirm this.      (T. Mibe et al.), but for larger (1520) c.m. angles)

- R. A. Schumacher, Carnegie Mellon University, PANIC'05

- 10/28/2005

## Exclusive Reaction on the Proton

- p  + K0
-                 Ks0 +-
-                 +  nK+

- SAPHIR/ELSA  at Bonn
- M = 1540 ± 4 MeV
- width < 25 MeV
- Published:  300nb cross section. Later statement: signal smaller than shown, cross section of 50 nb.
- N(+)/N(*) ~ 10%

- J. Barth, et al., Phys Lett _B572_, 127 (2004); hep-ex/0307083.

- R. A. Schumacher, Carnegie Mellon University, PANIC'05

- 10/28/2005

## New Upper Limit on the + Cross Section

- Fit with a sum of smooth function and a Gaussian with fixed width and centroid.

- CLAS: p → K0K+n
- (APS Tampa, 5-05, hep-ex/0510061)

- p K0 < 0.8 nb @ 1.54 GeV/c2
- N(+)/N(*) < 0.2%    (95%CL)

- R. A. Schumacher, Carnegie Mellon University, PANIC'05

- 10/28/2005

## p →  KK(n)

- M(nK+)

**7.8******

********

- p →  KK(n)
- CLAS: V. Kubarovsky *et al. *
-      PRL _92_ 032001 (2004)
- Combined analysis of all CLAS data on protons for Eg <5.2 GeV
- Cuts: forward +, backward K+
- indications of production from heavy N*(2420)

- Higher statistics run planned
- for 2006.

- Exclusive Reaction on the Proton* II*

- R. A. Schumacher, Carnegie Mellon University, PANIC'05

- 10/28/2005

## Semi-Exclusive K+ (N) → pKs0

- Semi-Exclusive K+ (N) → pKs0

- 850 MeV/c  K+ beam

- K+ Xe → (**+**)**  **X → K0s p  X;

- 

- V.V. Barmin et al., Yad. Fiz. _66_ 1763 (2003); hep-ex/304040

- Cuts applied to avoid hadron re- interaction in Xe

- M=1539±2 MeV
-  < 9 MeV

- DIANA/ITEP Bubble Chamber Experiment

- Note: No strangeness “tag”
- for the K0s p final state

- R. A. Schumacher, Carnegie Mellon University, PANIC'05

- 10/28/2005

## Belle/KEKB – Low energy K+N

- momentum, GeV/c

- 1 / 50MeV

- momentum spectra
- of K+ and K-

- Momentum range possibly contributing to + formation.

- Belle/KEKB – Low energy K+N

**e****+****e****-**** ****→**** K****+/-**** X,   K****+/-****A ****→** ** pK****0****, pK****-**

-  Determine resonance width

- R. A. Schumacher, Carnegie Mellon University, PANIC'05

- 10/28/2005

## Belle – Limits on + Width 

- Belle – Limits on** ********+**** **Width** **

- 397 fb-1

- K+A **→** pK0s

- Belle limit 90%CL

-  MeV (90% CL)  @ M = 1.525–1.545 GeV

**  **

- Does not confirm previous DIANA signal.

-   from K+A **→** pK0sX &
- K+D **→** inclusive analysis

- no signal

- Belle: < 0.64 MeV (90% CL) @ M = 1.539 GeV

- Cahn,Trilling,PRD _69_,11501 (2004).

- DIANA

- R. A. Schumacher, Carnegie Mellon University, PANIC'05

- 10/28/2005

## Low Q2 , Quasi-real Photons

- v D →   K0 p X   → p X

- HERMES/HERA: Inclusive on Deuterium
- Lepton scattering: 27 GeV positron beam
- M = 1526 ± 2 ± 2 MeV
-  = 7.5 ± 2.4 MeV
- A. Airapetian et al.
-     Phys. Lett. B _585_, 213 (2004).

- Additional  required

- Airapetian et al., Int’l Workshop on DIS, Madison, 2005.

********

- R. A. Schumacher, Carnegie Mellon University, PANIC'05

- 10/28/2005

## Scattering at High Q2 , e±p → e(K0sp)X

- Signal seen at medium Q2 and
- forward rapidity in both pKs and pKs

- Scattering at High Q2 , e±p → e(K0sp)X

- * ~ 5% (independent of Q2)

**Fragmentation, Q****2****>20GeV****2**

- ZEUS/HERA

- 

- 

- R. A. Schumacher, Carnegie Mellon University, PANIC'05

- 10/28/2005

## Tomography with pKs0 Vertices

- SVT

- Beampipe

- SVT support tube

- DCH inner wall

- e–

- e+

- Vetobeamspot R  2 cm

- Y [cm]

- X [cm]

- Tomography with pKs0 Vertices

- Y [cm]

- X [cm]

-  Quasi-real photoproduction scattering on nuclei (e on BeO)

- z profile

- R. A. Schumacher, Carnegie Mellon University, PANIC'05

## eBe Electroproduction

- HERMES (e+dKS0p + X)

- HERMES: acceptance loss in low mass region?
- (PID requires p(p) >4.1 GeV/c; p(KS0)>3 GeV/c)

- Preliminary233 fb–1 e+e– data

- HERMES

- HERMES/BaBar comparison is valid.
- ZEUS : High Q2, no signal seen for Q2<1
- BaBar: Quasi-real photons Q2~0.

- R. A. Schumacher, Carnegie Mellon University, PANIC'05

## All of the World’s Neutrino Scattering Data 

-  A → (K0 p) X
-           →(p) X
- Data mining: sum of 5 bubble-chamber experiments from CERN and Fermilab
- M(+)=1.533±.005 GeV
-  < 30 MeV
- A.E.Asratyan *et al. **(ITEP), * Yad. Fiz. _67_, 704 (2004) hep-ex/0309042

**( ********)**

- +

- R. A. Schumacher, Carnegie Mellon University, PANIC'05

- 10/28/2005

## SVD-2 – New Analysis

-  New analysis improves + signal
-     by factor 8. Total significance ~8

- M       = 1522 MeV
- =    12  MeV
- Nevnt =  205

- Two independent data set:
- KS decays inside or outside
-  the Vertex Detector

- Ep = 70 GeV

- hep-ex/0509033

- R. A. Schumacher, Carnegie Mellon University, PANIC'05

- 10/28/2005

## Cascade Pentaquarks Another Exotic Member of the Anti-Decuplet ? 

********

- R. Jaffe, F. Wilczek hep-ph/0307341

**JM hep-ph/0308286**

**SZ hep-ph/0310270**

- Two bosonic di-quarks (ud), plus s;  fermionic state symmetry demands L=1, giving JP= 1⁄2 +

- Mass Prediction for ******− −**** **was 1.75 instead of 2.07 GeV

- D.P.P.,  Z. Phys. _A359_, 305(1997).

- R. A. Schumacher, Carnegie Mellon University, PANIC'05

- 10/28/2005

## Cascade Pentaquarks - -(1862)

- (1530)

- −−

- 0

- NA49/CERN
- p+p →  X  at 17 GeV c.m. energy
- Signal for Exotic       S = -2, Q=-2
- Signal for *Non*-exotic S=-2, Q=0
-  M=1.862± 0.002 GeV
- C. Alt *et al* .  PRL _92_ 042003 (2004); hep-ex/0310014.

- Cascade Pentaquarks** **********- -(1862)

- R. A. Schumacher, Carnegie Mellon University, PANIC'05

- 10/28/2005

## Cascade Pentaquarks  - - (1862)

- CDF

- HERA-B  (p A)

** ****State not produced in quark **
**fragmentation or is severely suppressed.**

- FOCUS

- A

- R. A. Schumacher, Carnegie Mellon University, PANIC'05

- 10/28/2005

**Notes:**
Returning to the other pentaquark candidates, a lot of new evidence has come out against the exotic – and its 5-quark partners claimed by CERN experiment NA49. There is overwhelming evidence against the signal which the HERA-B group claims to be incompatible with their results. The HERA-B data are shown in the left graph with no signal visible in the channels.. Another example is CDF that also see no signal while in both cases the 1530) is clearly visible, allowing to extract upper limits for the ratio.   

## Charmed Pentaquark 0c(3100)  

- Charmed Pentaquark 0c(3100)

-  ep collisions at HERA
- Possible production
-    mechanism – photon-gluon
-    fusion: (*)g → cc**  **

** ****FOCUS experiment also claims **
**   ****incompatibility with H1.**

- uuddc

- hep-ex/0403017

- R. A. Schumacher, Carnegie Mellon University, PANIC'05

- 10/28/2005

## ++ Evidence: is it Isovector?

- ++ Evidence: is it Isovector?

- STAR Preliminary

- STAR/RHIC, Huang et al.
- 		APS Tampa, April 2005; nucl-ex/0509037
- d-Au collisions, pK+ and pK- at 200 GeV/A
- ...but hardly at all in Au-Au (!?)
- K+ coalescence?

- R. A. Schumacher, Carnegie Mellon University, PANIC'05

- 10/28/2005

## Present Pentaquark Candidates

-  Best “Survivors” (pre-2005)
- CLAS p → +K-+
- COSY-TOF p-p → ++
- ZEUS e p,  Q2>20 GeV2
- Newcomers (2005)
- STAR/RHIC d-Au →Kso p
- LEPS D → +(1520)
- SVD-2 p-A →Kso p X
- refuted by WA89

- R. A. Schumacher, Carnegie Mellon University, PANIC'05

- 10/28/2005

## Outlook – future experiments

- Spring-8/LEPS   D
- COSY-2             p p
- JLab/CLAS        D
- JLab/Hall A       D
- KEK or JPARC   K p
- HERA/ZEUS     e p

- R. A. Schumacher, Carnegie Mellon University, PANIC'05

- 10/28/2005

## Summary

- After 3 years of intense activity, pentaquarks have come and (nearly) gone...
- Most positive sightings have been contradicted or placed in doubt by better measurements
- Remaining candidates have no common phenomenological connection.
- No single truly convincing measurement has appeared
- Recent new candidates suffer (again) from low statistics and poorly-understood backgrounds
- Bandwagon effect in 2003/4 led to numerous over-optimistic positive results to be claimed.

- R. A. Schumacher, Carnegie Mellon University, PANIC'05

- 10/28/2005

## Backup slides

- R. A. Schumacher, Carnegie Mellon University, PANIC'05

- 10/28/2005

## Positive Sightings

|  |  |  |  |
| --- | --- | --- | --- |
|  |  |  |  |
|  |  |  |  |
|  |  |  |  |
|  |  |  |  |
|  |  |  |  |

- LEPS

- CLAS

- SAPHIR

- COSY

- DIANA

- JINR

- SVD

- 

- ZEUS

- HERMES

- NA49

- H1

**PRL 91 (2003) 012002**

- C12! K-K+n

- +

- +

- K+n

- +

- K+n

**PRL 91 (2003) 252001, PRL 92 (2004) 032001**

- d! K+K- np
- p! +K-K+n

- +

- K+n

**Phys.Lett B572 (2003) 127**

- p! K0SK+n

**Phys.Lett.B595 (2004) 127**

- +

- K0Sp

- K0Sp

- pp! +K0Sp

**Phys.Atom.Nucl.66(2003)1715**

**hep-ex/0401024**

**hep-ex/0401024**

**BC at CERN & FNAL**
**hep-ex/0309042**

**Phys.Lett.B585(2004) 213**

**Phys.Lett.B592(2004)7**

**PRL 92(2004)042003**

**Phys.Lett.B588(2004)17**

- +

- +

- +

- +

- +

- 5

- 0c

- K0Sp

- K0Sp

- K0Sp

- K0Sp

- K0Sp

- K+Xe! K0SX’

- p+C3H8! K0SpX

- pA! pK0SX

- A! K0SpX

- ep! e’pK0SX

- (quasi-real photoproduction)

- ep! e’pK0SX

- pp!  X

- ep! e’pD*-X

- Experiment

- Reaction searched

**publication**

- +

- 5

- 0c

- Claim
- Decay

- (Table by Alex Dzierba)

- 

- D*-p

- R. A. Schumacher, Carnegie Mellon University, PANIC'05

- 10/28/2005

## Negative Reports

| CDF |  | ALEPH |  |
| --- | --- | --- | --- |
| HyperCP |  | DELPHI |  |
| SELEX |  | L3 |  |
| FOCUS |  | WA89 |  |
| E690 |  | ZEUS |  |
| BES |  | HERA-B |  |
| BELLE |  | SPHINX |  |
| BaBar |  | PHENIX |  |
| COMPASS |  |  |  |

******+**

******+**

******+**

******+**

******+**

******+**

******+**

******+**

******+**

******+**

******+**

******+**

******+**

******+**

******+**

******5**

******5**

******5**

******5**

******5**

******5**

******5**

******5**

******5**

******c****0**

******c****0**

******c****0**

******c****0**

******c****0**

**hep-ex/0408025,0410024**

**(********+****,K****+****,p)Cu ****!**** PX**

**hep-ex/0410027**

**(********,p,********)p****!**** PX**

- Quark Confinement 2004

******p****!**** PX**

- DPF 2004

**pp****!**** PX**

- QNP2004 -

**PRD 70 (2004) 012004**

**e****+****e****-****!**** J/******** (********(2S)**

**KN****!**** PX**

**hep-ex/0411005**

**e****+****e****-****!**** ******** (4S)**

**hep-ex/0408064**

**Hadronic Z decays**

- Submitted to **Phys. Lett. B**

**Hadronic Z decays**

**hep-ex/0410080**

**hep-ex/0410080**

**hep-ex/0410029**

******-****N****!**** PX**

**ep****!**** PX**

**hep-ex/0407026**

**pA****!**** PX**

**Accepted in PRL**

**pC(N)****!**** ******** K X**

**hep-ex/0407026**

**AuAu****!**** PX**

**nuc-ex/0404001**

- (Table by Alex Dzierba)

**LASS**

- hep-ex/0412031

**K****+****p****!**** K****+ ****n ********+**

- +

- R. A. Schumacher, Carnegie Mellon University, PANIC'05

- 10/28/2005

## Summary of LQCD 

| Group | Method of analysis/criterion | Conclusion |
| --- | --- | --- |
| Alexandrou  and Tsapalis | Correlation matrix, Scaling of weights | Can not exclude  a resonance state. Mass difference seen in positive channel of right order but mass too large |
| Chiu et al. | Correlation matrix | Evidence for resonance in the positive parity channel |
| Csikor et al. | Correlation matrix, scaling of energies | First paper supported a pentaquark , second paper with different interpolating fields produces a negative result |
| Holland and Juge | Correlation matrix | Negative result |
| Ishii et al.
 | Hybrid boundary conditions | Negative result in the negative parity channel |
| Lasscosk et al. | Binding energy | Negative result |
| Mathur et al. | Scaling of weights | Negative result |
| Sasaki | Double plateau | Evidence for a resonance state in the negative parity channel. |
| Takahashi et al. | Correlation matrix, scaling of weights | Evidence for a resonance state in the negative parity channel. |
| J. Negele, Lattice 2005 | Correlation matrix, scaling of weights | Maybe evidence for a resonance state? |

- C. Alexandrou