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

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 35 93 5.6 3.6 3.1 2.4NOMAD 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

Pentaquarks 7

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 +

What does look like? (many !)

Interesting Result

fragmentation isa good source of+!

Pentaquarks 8

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 ! PX

hep-ex/0410027

(,p,)p! PX

Quark Confinement 2004

p! PX

hep-ex/0412021

pp! PX

QNP2004 -

PRD 70 (2004) 012004

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

KN! PX

hep-ep/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/0410029

pA! PX

PRL 93 (2004) 212003

pC(N)! K X

EPJ A21 (2004) 455

AuAu! PX

J.Phys.G 30 (2004) S1201

(Table by Alex Dzierba)

Pentaquarks 9

width is below detector resolution width is below detector resolution

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

NA49 5(1860)

Pentaquarks 10

HERA-BHERA-B

Null Results 5(1860)

Pentaquarks 11

CDFCDFFOCUSFOCUS

ALEPH and ZEUS also null resultALEPH and ZEUS also null result

Null Result 5(1860)

Pentaquarks 12

at HERAat HERA

H1

Pentaquarks 13

CDFCDF

FOCUSFOCUS

ZEUSZEUS

Null Results

Pentaquarks 14

HyperCPHyperCP

Negative Results

+(1540)

SPHINX

CDFCDF

1520) K*(892)

+?

ALEPHALEPH BaBarBaBare+e-! (p K0)X

HERA-BHERA-B

pC! pK0SX

BELLE1520)

pKS

Pentaquarks 15

Bubble Chamber No signals in the Dalitz Plots

(Taken from the PDG, 2004)

Pentaquarks 16

Scattering Data

K+n P-wave Phase Shifts

1MeV wide resonance at 1540

Pentaquarks 17

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) ____________________________________E690 5000ALEPH 2800CDF 3300 16000BaBar 10000000 100000HERA-B 5000 3000 50000SPHINX 5500 23700 12000HYPERCPCOMPASSBELLE 15520____________________________________ (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

Pentaquarks 18

Low Energy ExperimentsKinematic 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)

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.