Pentaquarks 1 Curtis A. Meyer Pentaquarks: An Experimental Overview n part, on work carried out with Alex Dzierba and Adam Szczepaniak ore 2003 …. searches for flavor exotic yons showed no evidence for such tes. ce 2003 …. Hadronic Physics has n very interesting.
Pentaquarks:. An Experimental Overview. Curtis A. Meyer. Based, in part, on work carried out with Alex Dzierba and Adam Szczepaniak. Before 2003 …. searches for flavor exotic baryons showed no evidence for such states. Since 2003 …. Hadronic Physics has been very interesting. - PowerPoint PPT Presentation
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Pentaquarks 1
Curtis A. Meyer
Pentaquarks: An Experimental Overview
Based, in part, on work carried out with Alex Dzierba and Adam Szczepaniak
Before 2003 …. searches for flavor exotic baryons showed no evidence for suchstates.
Since 2003 …. Hadronic Physics has been very interesting.
Pentaquarks 2
1997: Diakonov, Petrov and Polykov use a chiral soliton model to predict a decuplet of pentaquarkbaryons. The lightest has S=+1 and a mass of1530 MeV and expected to be narrow.Zeit. Phys. A359, 305 (1997).
Spectacular Development
2003: T. Nakano et al. n ! K+K-non a Carbon target.Phys. Rev. Lett. 91, 012002, (2003)
+! K+n
The Dam Breaks ….
Pentaquarks 3
LEPS
CLAS
SAPHIR
COSY
DIANA
JINR
SVD
ZEUS
HERMES
NA49
H1
PRL 91 (2003) 012002
C12! K-K+n
+
+
K+n
+
K+nPRL 91 (2003) 252001, PRL 92 (2004) 032001
d! K+K- npp! +K-K+n
+
K+nPhys.Lett B572 (2003) 127
p! K0SK+n
Phys.Lett.B595 (2004) 127
+
K0Sp
K0Sp
pp! +K0Sp
Positive Sightings
Phys.Atom.Nucl.66(2003)1715
hep-ex/0401024
hep-ex/0401024
BC at CERN & FNALhep-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
ExperimentReaction searched
publication
+
5
0c
ClaimDecay
(Table by Alex Dzierba)
Pentaquarks 4
4.6 4.8 5.2 7.8
4.4 6.7 ~5
~5 4.6 5.6 4.3
The DataReported Significance
5- - 5
0
0c
4.2
~5.5
5.2
Pentaquarks 5
A narrow structure whose width isless than experimental resolution
Summary of Results
+
Old data constrain <1MeV
5-- 5
0
c0
Na49: Mass: 1862 MeV Width < Resolution
H1: Mass : 3100 MeV Width ~10 MeV
Pentaquarks 6
Statistics Experiment Signal Background Significance Publ. 1 2 3
Produce a spin-2 or spin-3 resonance that decays to K+K- . Have non-uniform populations of |m|=0,1,2,…
Produces a broad enhancement near 1.5
a2(1320)
1020)
CLAS
Pentaquarks 19
Mass (K-n) Mass (K+K-) Mass (K+n)
Kinematic Reflection?
(Dzierba, et al.)
The CLAS d ! p n K+K- Data
Solid lines are predicted using K+K- resonances
Pentaquarks 20
Statistical FluctuationCLAS Published
Naïve Background
Simple Physics Background
Dzierba Background
Chance of the Background Fluctuating into the observed signal
You need to understand your background to claim a newdiscovery!
Pentaquarks 21
Use Dzierba Background
Generate 40 random spectra
3 are Fake1 is CLAS
Games
Pentaquarks 22
Severe Cutsp! +K+K-(n) missing
CLAS: Phys. Rev. Lett. 92, 032001,(2004)
Design cuts to remove diagrams (b),(c) and (d)
j t!-j < 0.28 GeV2
cos *K+ < 0.6
Mass (K+ n)
Uncut Spectrum
Mass (K+ n) Mass (K- K+ n)
After Cuts
Pentaquarks 23
j t!-j < 0.28 GeV2
and cos *K+ < 0.6
Raw
Monte Carlo Study
(Alex Dzierba)
a2 or f2 ! K+K-
j YML( cos, ) j2
p ! a2/f2
Y12
Pentaquarks 24
Ghost Tracks
(p>2GeV/c)! p-
-p+
Mass(+-)Select KS
Mass(pKS)“Create a +”It is easy to manufacture narrow peaks in the data near 1.5GeV that appear to decay to p KS .
(M. Longo QNP 2004)
Pentaquarks 25
5 Pentaquark
One low statistics report by NA49
Nine negative results.Null results in both similar and different production mechanisms.1-2 orders of magnitude more data in known resonances.
c PentaquarkOne low statistics report by H1
Five negative results.Null results in both the same and different production mechanisms.Factor of 10 to 1000 times for data in known resonances.
RIP
RIP
Pentaquarks 26
11 low-statistics reports near 1500 MeV
+ Pentaquark
Low-energy reports suffer from some combination of the following: (a) Fermi motion effects.(b) Severe cuts whose effects may not have been adequately studied.(c) Insufficiently constrained reactions.(d) Kinematic reflections.
15 new high-statistics searches in a number of reactions with excellent resolution that have come up empty.Bubble chamber data from decades ago show no evidence.KN scattering data severely limit this
The Zeus result is interesting. It suggests that fragmentation is a good way to produce the +.
Not really consistent with ALEPH, BaBar, BELLE, CDF, …What does H1 have to say on this?
Pentaquarks 27
PDG 2004
Pentaquarks 28
Conclusions
Pe
nta
qu
ark
Sto
ck
Va
lue
Jan. Jun. Dec.
2004The possible existence of pentaquarks is still very much an experimental question, and the data do not look very convincing.
If they exist, they not only haveexotic quantum numbers, butvery exotic production and decay modes.
I hope that the issue can be settled soon – but I am not buying stock.