Download - Pentaquarks:
March 2, 20051Argonne
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 such states.
Since 2003 …. Hadronic Physics has been very interesting.
Outline Overview of the positive evidence data, statistics, specific results
Overview of the negative results The and c The +
Issues with some of the data
Summary & Conclusions
hep-ex/0412077
March 2, 20052Argonne
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 ….
March 2, 20053Argonne
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)
D*-p
March 2, 20054Argonne
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
March 2, 20055Argonne
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
Charge Exchange
March 2, 20056Argonne
Statistics Experiment Signal Background Significance Publ. 1 2 3
Spring8 19 17 4.6Spring8 56 162 4.4 3.8 2.9SPAHIR 55 56 4.8 7.3 5.2 4.3CLAS (d)** 43 54 5.2 5.9 4.4 3.5CLAS (p) 41 35 7.8 6.9 4.7 3.9DIANA && 29 44 4.4 4.4 3.4 2.7 18 9 6.7 6.0 3.5 3.0 HERMES 51 150 4.3-6.2 4.2 3.6 2.7COSY 57 95 4-6 5.9 4.7 3.7ZEUS 230 1080 4.6 7.0 6.4 4.7SVD 41 87 5.6 4.4 3.6 2.8NOMAD 33 59 4.3 4.3 3.4 2.7
NA49 38 43 4.2 5.8 4.2 3.4NA49 69 75 5.8 8.0 5.8 4.7
H1 50.6 51.7 5-6 7.0 5.0 4.1** An improved analysis shows a less significant peak!&& Shown to be charge exchange
5
c
March 2, 20057Argonne
Zeus ResultPhys. Lett. B591 (2004) 7.
(U.Karshon, Pentaquark-04)
Fragmentation, Q2>20GeV2
Observe: + mass=1.521 GeV width=6.1 MeV 230 Events on 1080 Background
No Signal for: 5 , 0c
Mass=1465Width=15368 Events
?~6000 ~200 (1520) 230 +
KS p is not manifestlyExotic. It could be a
Interesting Result
fragmentation isa good source of+!
March 2, 20058Argonne
LEPS C ! K+ K- X Assume that the reaction is n ! + K-
Calculate Missing Mass( n ! K- X )
d ! K+K-X Assume n ! +K-
Cuts to remove: ! K+K-
(1520)! p K-
d ! K+K- dMissing Mass( d, KK X) is a neutronFermi Momentum CorrectionsBackgrounds: KKN phase space (1020) ,
Highly unconstrained final statesUnknown BackgroundsMany Cuts to pull out the signal
March 2, 20059Argonne
CLASd ! K+K- p (n) miss
Independent analysis of the data: energy loss corrections from target 1C-Kinematic fit to final state
Flat confidence level Known resonances get sharper and have the right mass: (1520) (1020)
Evidence for higher mass ‘ s and either the a2(1320) or f2(1270) is sharper.
Published
Fit
NOT AN OFFICIAL CLAS RESULT
Disturbing Effect on the + !
+
Reaction is unknown
March 2, 200510Argonne
COSY
pp! ++
+! KS p KS ! +-
+! n +
2 Hits in the first hodoscope + & p4 Hits in the 2nd and 3rd planes +-+ p (2-plane hodoscopes so ambiguous)
No Particle Identification, No Momentum Measurement, No charge measurement.Pure Geometry and a zero constraint fit to the reaction
p
KS
+
March 2, 200511Argonne
Negative ReportsCDF 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
c0 c
0
c0
c0
c0
hep-ex/0408025,0410024
(+,K+,p)Cu ! PXhep-ex/0410027
(,p,)p! PXQuark Confinement 2004
p! PXDPF 2004
pp! PX
QNP2004 -
PRD 70 (2004) 012004e+e-! J/ ((2S)
KN! PXhep-ex/0411005
e+e-! (4S)hep-ex/0408064
Hadronic Z decaysSubmitted to Phys. Lett. BHadronic 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 Xhep-ex/0407026
AuAu! PXnuc-ex/0404001
(Table by Alex Dzierba)
LASShep-ex/0412031
K+p! K+ n + +
March 2, 200512Argonne
The --(1861)
March 2, 200513Argonne
width is below detector resolution
fixed target experiment at CERN - spectrometer 158 GeV/c proton beam
NA49 5(1860)
March 2, 200514Argonne
HERA-B
Null Results 5(1860)
March 2, 200515Argonne
CDFFOCUS
ALEPH and ZEUS also null result
Null Result 5(1860)
March 2, 200516Argonne
The 0c(3100)
March 2, 200517Argonne
at HERAH1
March 2, 200518Argonne
CDF
FOCUS
ZEUSNull Results
March 2, 200519Argonne
The +(1540)
March 2, 200520Argonne
Bubble Chamber No signals in the Dalitz Plots
(Taken from the PDG, 2004)
March 2, 200521Argonne
Scattering Data
K+n P-wave Phase Shifts
1MeV wide resonance at 1540
March 2, 200522Argonne
BELLE
HyperCP
Negative Results +(1540)
CDF1520) K*(892)
+?
ALEPH BaBare+e-! (p K0)X
HERA-BpC! pK0
SX
1520)
pKS
SPHINX
March 2, 200523Argonne
SPHINX 70 GeV p on Carbon Targets
The detector is sensitive to charged particles and the direction of neutrons and KL by hits in the BCAL.
p + N ! p K+ K- Np + N ! p KS KL Np + N ! p KS KS Np + N ! n K+ KS Np + N ! p KL KL Np + N ! n K+ KL N
Detect
Don’t See
1520) in p K-, n KS
~16000 (1520)
No in either p Ks or n K+
nK+
pKL pKS
Monte Carlo
March 2, 200524Argonne
Belle
1520)
pKS
e+e- with an interesting twistLook at the pKS pK- and pK+ final states whose primary Vertex is from material in the detector
16000 (1520)! K- p
Exclude: N ! (1520) K-p ! (1520) Signal comes from KN! (1520)X
pK-
No signal in KS pIt is very hard to produce the + In K+N interactions, but it falls apart into this just fine.
March 2, 200525Argonne
SELEX600Gev Beams (-,-,p,+ )
Mass (K-p)
1520)
2,800,000
Mass (KS p)
0.1% of Data
Mass (KS p)
No +
(67%,14%,18%, 1%)
Very significant charmed baryon results.
March 2, 200526Argonne
CDF
Resonance Min. Bias Jet>20GeV1520) 3276§ 327 4915§ 702K*+ 15695§ 775 35769§ 1390+ 18§ 56 -56§ 10090% CL + <89 <76
pK- + cc +KS p KS + cc
March 2, 200527Argonne
Experiment s b (1520) Spring 8 19 17 25Spring 8 56 162 180SAPHIR 55 56 530CLAS(d) 43 54 212 126CLAS(p) 41 35 DIANA 29 44 1152 19 8HERMES 51 150 850COSY 57 95ZEUS 230 1080 5700* 193SVD 35 93 260NOMAD 33 59________________________________________ s b D*________________________________________NA49 38 43 1640H1 50 52 3000________________________________________
Experiment (1520) c
____________________________________E690 5000ALEPH 2800CDF 3300 16000BaBar 10000000 100000HERA-B 5000 3000 50000SPHINX 5500 23700 12000HYPERCPCOMPASSBELLE 15520SELEX 2,800,000____________________________________ (1530) D D*
________________________________________________________
E690 15000ALEPH 3350 200 25000CDF 36000 1000 3000000 536000BaBar 258000 17000HERA-B 18000ZEUS 2600 160WA89 676000FOCUS 84000 36000
The NumbersPositive Results Some Negative Results
* Estimate from cross section
March 2, 200528Argonne
Low Energy Experiments Kinematic Reflections
+(1540)
a2(1320)! K+K-
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)/f2(1270)1020)
CLAS
Mass(+-)
f2(1270)
March 2, 200529Argonne
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
Kinematic Fit
March 2, 200530Argonne
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!
March 2, 200531Argonne
Use Dzierba Background
Generate 40 random spectra
3 are Fake1 is CLAS
Games
March 2, 200532Argonne
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
March 2, 200533Argonne
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
March 2, 200534Argonne
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)
March 2, 200535Argonne
5 PentaquarkOne 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.Possible ghost track in D* Decay
5(1860)
c(3100)
X
X
March 2, 200536Argonne
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 +. KS p is not strangeness exoticNot really consistent with ALEPH, BaBar, BELLE, CDF, …What does H1 have to say on this?
March 2, 200537Argonne
PDG 2004
March 2, 200538Argonne
Conclusions
Pen
taqu
ark
Stoc
k 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.