Karin DaumBEACH 2004, Chicago, June 29, 2004 1 Searches for Exotic Baryons at HERA Karin Daum – Wuppertal Outline: HERA & kinematics at HERA Strange Pentaquarks

Karin Daum

BEACH 2004, Chicago, June 29, 2004 1

Searches for Exotic Baryons at HERAKarin Daum – Wuppertal

Outline:

• HERA & kinematics at HERA• Strange Pentaquarks

+ (Hermes, Zeus) -- (Zeus)• Exotic Anticharmed Baryon (H1, Zeus)• Conclusions

6th International Workshop on Hyperons, Charm and Beauty HadronsChicago, June 27-July 3, 2004

on behalf of theH1, HERMES and

ZEUS collaborations

Karin Daum


Protons 920 GeV

Electrons 27.6 GeV

The Hera accelerator

DESYHamburgGermany

ep- collisions

eN-fixed target

Karin Daum


Hera kinematics in ep collisions

E = 27.6 GeVe E = 920 GeVp

√s = 300-318 GeV (energy c.m.)

W=m(p) (hadronic energy)

Q2=-q2 (photon virtuality)

2 kinematic regimes :Q 0 GeV : PhotoproductionQ > 1 GeV : Electroproduction (DIS)

D*p event in DIS

sKp

e

Karin Daum


Fixed target kinematics at Hera

²H

²H

√s = 10 GeV (energy c.m.)

W=m(p) (hadronic energy)

Q2=-q2 (photon virtuality)

E = 27.6 GeVe

2 kinematic regimes :Q 0 GeV : PhotoproductionQ > 1 GeV : Electroproduction (DIS)

Karin Daum


The search at HERMES+

Kinematic Range: 0.02 < x < 0.8 at Q2 > 1 GeV2 and W > 2 GeV

Dual radiator RICH for PID

Very good proton ID

Aerogel

104FC

Karin Daum


The search at HERMES+

Hadron identification using RICH

Suppress contamination from p

Define appropriate event topology

Unambiguous invariant mass reconstruction due to PID

O(1000) K0s

Peak at 15282.6 MeV=82 MeV; 3.7 Peak at 15272.3 MeV=9.22 MeV; 4.3

bumps

7818 events

e+ + ²H + + X K0s p + X

Karin Daum


The search in ZEUS+

DIS (Q2>1 GeV2):96-00 data 121 pb-1

Identify K0s ,

• Remove p and converted ’s

O(900,000) K0s DIS (Q2>1 GeV2):96-00

data 121 pb-1

Identify K0s

• Remove p and converted ’s

• Limited particle identification via

dE/dx

• select proton candidates

p(p)<1.5 GeV, dE/dx>1.15 mips

e + p + + X K0s p +

X

Karin Daum


The search in ZEUS+

Clear signal visible only at Q²> 20 GeV²

MC normalised to background,No -bumps included

Fit a 2nd Gaussian to accountfor some of the differences

Peak at 1521.51.5 MeV=6.11.5 MeV; 4.6

221 48 events

O(100,000) K0s

Signal seen for both

charges: K0s p = 9634 !-

Karin Daum


Is there a ++ at HERA

HERMES ZEUS

Clear Signal for (1520) pK-

No Signal for pK+ + isoscalar

Karin Daum


The search in eN collisions at HERA

+

Experiment Kinematics K0s p/ K0

s

HERMES √s, W, Q² small 7 %

ZEUS

√s, W, Q² largeSignal atHigh Q²small W

0.2 %

Effect of phase space/acceptance ?

Factor: 35 !

Karin Daum


Search for at ZEUS--

NA49

ZEUS analysis for DISsimilar to NA49

p-

0-

-- --

Λ Λ

ΞΞ- +

All charge combinations

• Clean Ξ(1530) P13

• No signal at (1860)

preliminary

Karin Daum


Evidence for anti-charmed baryon by H1

If a strange pentaquarkWhy not a charmed one also

Experimentally best suitedD* p

Theoretically not favoured

-

96-00 data 75 pb-1 DIS: Q²>1 GeV²

Good Signal/Background

3400 D*’s in DIS to start with

Golden channelD*+ D0

s (K)s

D* signal regionsubsequently used

{

Karin Daum


Particle identification

Reasonable PID via dE/dx

-all data calibrated- parameterisation accurate to 3-5%- MIP resolution 8%

Most probable dE/dx

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

Use dE/dx for background suppression

Karin Daum


Background well described by D* MC and “wrong charge D” from data

Apply mass difference technique

M(D*p)=m(K p)-m(K)+MPDG(D*)

no enhancement in D* Monte Carlo

no enhancement in wrong charge D

• equally significant signal visible in separate D*+p and D*-p

• signal visible in different data taking periods

_narrow resonance at M=3099 3(stat.) 5 (syst.) MeV

Opposite sign D*p mass distribution

Karin Daum


All events scanned:

No anomalies observede.g. split tracks, wrongreconstruction

K

-s

+-p

HERA-II

Typical D*p candidates

p

+

+D

0

D*

K -

HERA-I

s

Karin Daum


M(D*p) [GeV]

M(D

*) [

GeV

]

Look at the correlationof M(D*) vs. M(D*p)

Side band scaled to the widthof the signal window in M(D*p)

the (D*p) signal region is richer in D*

D*p signal region

(D*p) side bands

D*

win

dow

Does the resonance come from D*’s?

Karin Daum


Physics changes on-resonance ?

Look at momentum distribution ofproton candidates w/o dE/dx

No dE/dx cuts !

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

At large p(p) (>2 GeV)At large p(p) (>2 GeV)Signal more pronounced

Karin Daum


Photo-production more difficult due to large non-charm background but

independent confirmation of the signal

D*p in photo-production

• total: 4900 D* to start• D*p peak at the same mass in p• no enhancement in non-charm bg• 95 % bg due to non-charm Background well described

bywrong charge D from data

Karin Daum


Background only hypothesis: Nb=51.7±2.7

Background fluctuation probability: 4x10-8 (Poisson)=5.4 (Gauss)

5.4

Significance estimate

Karin Daum


Search for charmed PQ, c D*p, in ZEUS

D.I.S. Selection differs from H1 analysis

Karin Daum


Search for charmed PQ, c D*p, in ZEUSPhotoproduction + DIS

Karin Daum


Conclusions

Positive evidence for the production of + at HERA

No doubly charged partner + is an isoscalar large differences in the +/ K0

s yields from HERMES and ZEUS

Negative results on the search for -- by ZEUS

Evidence for a neutral anti-charmed baryon state decaying to D*p from H1

- not confirmed by ZEUS

prelim.

prelim.

Karin Daum


Backup Slides

Karin Daum


Like-sign D*p mass distribution

no significant peak in like-sign D*p

no enhancement in D* Monte Carlo

no enhancement in wrong charge D

Background well described by D* MC and “wrong charge D” from data

Karin Daum


M(D*p)=3.104 0.003 GeV

Use this regionwith L(p)>0.5

Does the resonance come from protons ?

P(p)<1.2 GeV

dE/dx >1.15

Signal is there for well identified protons

<L(p)> = 0.92

Karin Daum


Is the physics different in the signal region?

Single particle momentum spectraare steeply fallingThis feature is preserved in thecombinatorial background of invariant mass analyses

In decays particles are also emitted in the direction of flight Particles from a decay should have a harder spectrum than thecombinatorial background

Check the proton momentum !

H1

Karin Daum


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 the physics different in the signal region?

Karin Daum


D*p rest framewrong mass assignment

correct mass assignment M(D*) [GeV]

M(D*p) [GeV] M(D*p) [GeV]

M(D

*)

[GeV

]

221

2 )( PPM

)22( **22

* XDXDXD ppEEmm

2-Body Decay

independent of decay angle cos* only for correct mass assignment

2M

CPQ MC

CPQ MC

CPQ MC

Basics of kinematic tests

Karin Daum


wrong mass assignment

correct mass assignment M(D*) [GeV]

M(D*p) [GeV]M(D*p) [GeV]

M(D

*)

[GeV

]

221

2 )( PPM

)22( **22

* XDXDXD ppEEmm

2-Body Decay

Do we see a band like structurein the M(D*p)-M(D*x) plane indata? Let’s have a look

D*p rest frame

CPQ MC

CPQ MC

CPQ MC

Integrated in cos*

Basics of kinematic tests

Karin Daum


*2 DD

*1 DD

Sign for X D*p: available phase space in D*completely used

Go to the D*p signal region

Signal due to D* ? NO!

Karin Daum


Lots of further kinematic test

• Reflections from a possible signal in D*K mass distribution: ruled out

• Possible contributions from D* D with -conversion: ruled out

• Possible contributions from D /D D K: ruled out• Possible peak structures in all possible mass correlations with

all possible mass hypotheses of the particles making the D* and the D*p system to search for real or fake resonances, e.g , , , K ,, f no enhancements found

• Possible peak structures in all possible mass correlations among the proton candidate the remaining charged particles of the event with all possible mass assignments to search for real or fake peaks,no enhancements found

S1 S2

0 ++ 0S

2

0 0

0

Karin Daum


Remarks on D*p searches at LEP

D* signals for different xE

D* @ LEP are producedpredominantly by beauty

Rb 22%, Rc 17%

D* acceptance vs. xE?

Karin Daum



D* @ LEP are producedpredominantly by beauty

Rb 22%, Rc 17%

<xE>cc 0.488

Karin Daum



beauty

charm

Karin Daum


D* from D*p and direct D* at HERA

MC MC

<xE>cc 0.56

D*’s from D*p significantly softer than normal D*’s

Should also hold for LEP !

<xE>cc 0.43

Documents

Karin DaumBEACH 2004, Chicago, June 29, 2004 1 Searches for Exotic Baryons at HERA Karin Daum – Wuppertal Outline: HERA & kinematics at HERA Strange Pentaquarks