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


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 ….


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


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


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


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


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+!


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


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


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

+


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 + +


The --(1861)


width is below detector resolution

fixed target experiment at CERN - spectrometer 158 GeV/c proton beam

NA49 5(1860)


HERA-B

Null Results 5(1860)


CDFFOCUS

ALEPH and ZEUS also null result

Null Result 5(1860)


The 0c(3100)


at HERAH1


CDF

FOCUS

ZEUSNull Results


The +(1540)


Bubble Chamber No signals in the Dalitz Plots

(Taken from the PDG, 2004)


Scattering Data

K+n P-wave Phase Shifts

1MeV wide resonance at 1540


BELLE

HyperCP

Negative Results +(1540)

CDF1520) K*(892)

+?

ALEPH BaBare+e-! (p K0)X

HERA-BpC! pK0

SX

1520)

pKS

SPHINX


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


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.


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.


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


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


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)


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


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!


Use Dzierba Background

Generate 40 random spectra

3 are Fake1 is CLAS

Games


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


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


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)


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


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?


PDG 2004


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.

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