Low-x Wshop, 18.9.04, Prague Jan Hladký, Exotic Anti-Charm Baryon State 1 Evidence for a Narrow Exotic Anti-Charmed Baryon State *) Jan Hladký, Institute

Low-x Wshop, 18.9.04, Prague

Jan Hladký, Exotic Anti-Charm Baryon State

1

Evidence for a Narrow Exotic Anti-Charmed

Baryon State *)

Jan Hladký, Institute of Physics AS ČR Prague,

H1 Collaboration

*) published in Phys. Lett. B588 (2004) 17-28



2

~ Introduction

~ D* and D*p

analysis

~ Conclusions

Outlook:



3

Motivation:

Pentaquark problem

HERA is also charm factoryH1 detector has Si vertex detectorsD* golden channelCharm baryons searches



4

Pentaquarks proposals

Gell-Mann 1964

Several model concepts

Lot of experiments - several successfull ?



5

Pentaquarks from meson and baryon multiplets

3 3 3 10 8 8 1

8 8 27 1 00 8 8 11

3 3 8 1 Baryons qqq from SU(3)f

Baryons built from meson-baryon, or qqqqq

Mesons qq from SU(3)f

Quantum numbers of the states cannot be described by only 3 quark states, minimal configuration is 5 quarks !!!For all the rest it is enough 3 quark

- - + - +

+ + + 0

- + - +

p K Θ K K n

pp Σ Θ Σ K p

n K Θ K K n

Diakonov et al. Z.Phys. A359, 305 (1997)

+

−−

C H A R G E

-2

-1

0

1 ST

RA

NG

EN

ES

S S-2

-10

+1



6

e p

Liquid Ar Calorimeter “Spaghetti” Calorimeter

Central Jet Chambers

Drift chambers, acceptance: 15O < θ < 165O charge and timing information B = 1.15 T → measure transverse momentum of charged particles

Tracking , Particle ID via dE/dx

H1 experiment at HERA

27.6 GeV 820, 920 GeV



7

• 1996 – 2000 Data• Lint = 75 pb-1 • 1 GeV2 < Q2 < 100 GeV2

0.05 < y < 0.7• pt (D*) > 1. 5 GeV• -1. 5< |η(D*)| < 1. • pt (K) + pt (p) > 2 GeV• Elasticity z(D*) > 0.2

D* signal regionsubsequently used

{

D* meson selection

Good Signal/Background

3400 D*’s to start with



8

Proton selection

• dE/dx calibrated for 1996-2000 data

• parameterization accurate to 3-5%

• 8% average resolution

dE/dx used for background suppression

Most probable dE/dx

Normalized likelihood based on:measured dE/dx & expectationsfor π, K, p and resolution: L(π)+L(K)+L(p) = 1

Final proton selection:( L(p)>0.1 && p(p)>2 ) .or. L(p)>0.3



9

The D*- p analysis

• Looking for a narrow state near threshold

• Expected 4-particle mass resolution about 35 MeV not favourable for a narrow state use mass difference technique: m(D*p)-m(D*)

• Cut on the normalized proton likelihood L(p) for pion suppression

• Take a D* candidate add a track consistent with a proton and opposite charge of the D* using mp for its mass

K

-s

+-p



10

Pentaquark in H1 setup

K p

e 27,6 GeV p

820/920 GeV

S



11

M(D*p) = m(Kp)-m(K)+m(D*)PDG

Significant peak inopposite sign D*p

No enhancement in D* MC (RAPGAP)

2)

2) Also no peak from CASCADE or Beauty MCBackground well described by D* MC and wrong charge D from data

No enhancement inwrong charge D

1)

1) Mass of same sign K± ± in m(D0) window

D*-p + cc in DIS for 1996 - 2000



12

Signal in both D*- p and in D*+ p M(D*p) = m(Kp)-m(K)

+m(D*)PDG

Signal of similar strength observed for both charge combinations at

compatible M (D*p)

Events1.78.25 Events6.84.23

M(D*p)=3.096 ± 0.006 GeVM(D*p)=3.102 ± 0.003 GeV



13

M(D*p) = m(Kp)-m(K)+m(D*)PDF

M(D*p) [GeV]

M(D

*) [

GeV

]

D*p signal region

{ {D*p Side bands

Normalization to the widthof the windows in M(D*p)

Signal region in D*- p richer in D*-



14

M(D*p) = m(Kp)-m(K)+m(D*)PDF

Use this regionwith L(p)>0.5

920= .)( pL

Is the D*-p signal due to protons?

M(D*p)=3.104 ± 0.003 GeV



15

Fit slope with exp {-p(p)}

The momentum spectrum of the particlesin the signal region is harder than in the M(D*p) side bands

Signal region=1.270.09

D*side band=1.860.13

D*p side bands=1.740.06

M(D*p) [GeV]

M(D

*) [

GeV

]Is physics different in signal region?



16

Lot of different tests

have been made…

…signal is not affected !!!



17

Significance estimation

Significance estimate based on the background only hypothesis Nb= 51.72.7 Use of different background functions as well as the background model from data and MC Significance determined in a binning free methodBackground fluctuation probability 4 x 10-8 (Poisson) 5.4 σ (Gauss) Change in likelihood of fits: 6.2 σ

NS + Nb = 95 D*p candidates(within 2

Nb = 45.02.8 frombackground + signal

hypothesis (fit)

5.4



18

CONCLUSIONS * H1 has observed a narrow resonance in both D*- p and D*+ p

M(D*p) = 3099 3 (stat.) 5 (syst.) MeV ,Gaussian width = 12 3(stat.) MeV.

* Significance is 5.4 sigma. * Background fluctuation probability is smaller than 410-8. * The signal is also observed in an independent photoproduction sample. * It is interpreted as an anti-charmed baryon decaying into D*p and its charge conjugate. * The minimal quark content is uudd . It is a candidate for a charmed pentaquark state. * Up to now is not confirmed by other experiments.

c



19

HAVE A GOOD TIME

IN THE GOLDEN CITY

PRAGUE !OF



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• H1 has observed a narrow resonance in both D*- p and D*+ p withM(D*p) = 30993 (stat.) 5 (syst.) MeV

= 12 3(stat.) MeV• The background fluctuation probability is smaller than 410-8.• The signal is also observed in an independent photoproduction

sample• The signal region is richer in D* mesons and show a harder

momentum spectrum of the proton candidates• No simple explanation for this resonance could be found.

It is interpreted as an anti-charmed baryon decaying to D* p and its charge conjugate.

• Its quantum numbers are C= -1 and B=1. The minimal quark content is uuddc, It is a candidate for a charmed pentaquark state.

CONCLUSIONS

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Low-x Wshop, 18.9.04, Prague Jan Hladký, Exotic Anti-Charm Baryon State 1 Evidence for a Narrow Exotic Anti-Charmed Baryon State *) Jan Hladký, Institute