Karin Daum

Hadron07, Frascati, Oct., 11th 2007 1

Baryon, Heavy Stable Particle and Strange Meson Production in ep-Collisions

Karin Daum – Wuppertal

on behalf of theH1 and ZEUS

collaborations

XII International Conference on Hadron SpectroscopyFrascati, October 8th-12th, 2007

Outline:

• HERA & kinematics at HERA• Charged particle fragmentation function• Proton & Deuteron production• Strange particle production• Bose Einstein correlations• Conclusions

Karin Daum

Hadron07, Frascati, Oct., 11th 2007 2

The HERA accelerator

DESYHamburg-Germany Protons 920 GeV

Electrons 27.6 GeV

Results based on HERA-I data (~120 pb-1)- 3 times more to come

Karin Daum

Hadron07, Frascati, Oct., 11th 2007 3

HERA kinematics

E = 27.6 GeVe E = 920 (820)GeVp

ep-Kinematics:

√s = 300-318 GeV (energy c.m.)

Q2=-q2 (photon virtuality)

x=xBJ (fraction of proton momentum carried by the struck quark)

2 kinematic regimes :Q² 0 GeV² : Photoproduction (p)Q² > 1 GeV² : Electroproduction (DIS)

Dh(xp,)FFq

Fragmentation process:

xp (fraction of quark momentum carried by the hadron)

(energy scale of the quark)

PDF

h = PDF M.E. FF

Karin Daum

Hadron07, Frascati, Oct., 11th 2007 4

Models for ep scattering

Dh(xp,)FFq

PDF

h = PDF M.E. FF

How well do we understand

particle production?

PYTHIA for pLEPTO for DIS

LO ME+

Parton showers+

String fragmentation

Hadrons

ARIADNE for DIS

Color dipol model (CDM)

+String fragmentation

Karin Daum

Hadron07, Frascati, Oct., 11th 2007 5

Charged particle fragmentation function

Dh(xp,)FFq

PDF

±

K±

pdK0

s

h = PDF M.E. FF

H1

Inclusive fragmentation function:No distinction between ±, K±, p

Restricted to 100<Q²<10000 GeV²

Suppresses HO QCD effects not present in e+e-

(e.g. boson-gluon-fusion, ISR)

Use a reference frame closest tothe situation in e+e-: (Breit-Frame)

Energy scales: ep-collisions: =Q/2 e+e--annihilation: =s/2=Ebeam

Karin Daum

Hadron07, Frascati, Oct., 11th 2007 6

Charged particle fragmentation function

(ep)=Q/2, (e+e-)=s/2

Steep fall with Q at large xp

Depletion due to gluon radiation

Steep rise with Q at small xp

Population due to gluon splitting

Overall agreement with e+e-

except at large Q + small xp

Karin Daum

Hadron07, Frascati, Oct., 11th 2007 7

Charged particle fragmentation function

(ep)=Q/2

Comparison with NLO QCD predictions based on different fragmentation functions extracted from e+e- data

Quite different QCD predictions

Strong scaling violations in data

- All calculations fail to

describe them!

Karin Daum

Hadron07, Frascati, Oct., 11th 2007 8

Charged particle fragmentation function

ZEUS prel.

HERA-I + HERA-II: 0.5 fb-1

very good agreement with H1 but 10 times more statistics

Karin Daum

Hadron07, Frascati, Oct., 11th 2007 9

Production of protons and deuterons

Dh(xp,)FFq

PDF

±

K±

pd

K0s

h = PDF M.E. FF

ZEUS DIS: Q²>1 GeV²

Coalescence Model:

Baryons uncorrelated &inv. cross section same for p and n

Relates proton to deuteron production:

Coalescence parameter B2

(defines region of nucleon overlap): - Same for deuteron & anti-deuteron? - Process dependent?

Ed d3σd Ep d3σp

σtot dpd3 σtot dpp

3 =B2( )2

Karin Daum

Hadron07, Frascati, Oct., 11th 2007 10

σinv(d) 10-3·σinv (p)

σinv(d) ≠ σinv(d)

Production of protons and deuterons

Not expected fromcoalescence model

Karin Daum

Hadron07, Frascati, Oct., 11th 2007 11

Coalescence parameter B2

Coalescence parameter B2 depends on - primary process - centre-of-mass energy (less dependent in scattering off

protons)

B2(d)=(3.32±0.34 )10-2GeV2

B2(d)=(0.89±0.14 )10-2GeV2

+1.13-1.15

+0.19-0.20

Karin Daum

Hadron07, Frascati, Oct., 11th 2007 12

Strange particle production

Dh(xp,)FFq

PDF

±

K±

pdK0

s

h = PDF M.E. FF

ZEUS

Different regimes is ep-kinematic:

1. DIS: Q²>25 GeV² 2. DIS: 5<Q²<25 GeV²

3. p: Q²≈0, 2 jets, ET > 5 GeV acts as a quasi-real target may get internal structure (resolves into partons)

Distinction of direct from resolved via observable x calculated from the two jets:

x≈1 direct x«1 resolved

jet

Due to the s-quark mass ms

fragmentation into K0s, is

suppressed w.r.t. , p

Strangeness suppression factor s

Karin Daum

Hadron07, Frascati, Oct., 11th 2007 13

Strange particle production (DIS)

ARIADNE s=0.3 (CDM) overall reasonable – but shapes not so goodARIADNE s=0.22 systematically too small (from previous result)

LEPTO s=0.3 (PS) fails

5<Q²<25 GeV² Q²>25 GeV² 5<Q²<25 GeV² Q²>25 GeV²

pT pTpTpT

Karin Daum

Hadron07, Frascati, Oct., 11th 2007 14

Strange particle production p

PYTHIA reasonable in pt and PYTHIA off in shape of x (small x)

Resolved Intact (direct)

x x

pT pT

Karin Daum

Hadron07, Frascati, Oct., 11th 2007 15

Strange baryon-to-meson ratio

Model in DIS (ARIADNE) s=0.3 quite good (10%)

Model in p (PYTHIA) off in all distributions

p

Resolved Intact (direct)

x

pT pT

pT

DIS 5<Q²<25 GeV² Q²>25 GeV²

- especially @ small x

for x=1 same baryon-to-meson ratio as in DIS and e+e-

Karin Daum

Hadron07, Frascati, Oct., 11th 2007 16

Bose-Einstein correlations for K±K±, Ks

Ks 0 0

Identical bosons prefer to be produced close in phase space

Distance in phase space characterized by: r = source size of particle emission Q12 = distance in 4-momentum space

= -(p1-p2)2

Correlation function (static Gaussian source):R(Q12) = 1 + exp(-r2Q2

12)

experimentally:

R(Q12) =

Double ratio (reduced sensitivity to models)

R(Q12) =

P(Q12)

Pref(Q12)

P(Q12)data

Pmix(Q12)data

P(Q12)MCnoBEC

Pmix(Q12)MCnoBEC

Karin Daum

Hadron07, Frascati, Oct., 11th 2007 17

Bose-Einstein correlations for K±K±, Ks

Ks 0 0

Q12 Q12

R(Q

12)

=0.37±0.07+0.09-0.08 =0.70±0.19+0.47

-0.53

r=0.57±0.09+0.15-0.08 r=0.63±0.09+0.11

-0.08

Bose-Einstein correlations clearly established for K±K± pairsMarginal for Ks Ks pairs due background from f0(980) Ks Ks

Consistent results on source radius

0 0 0 0

Karin Daum

Hadron07, Frascati, Oct., 11th 2007 18

Bose-Einstein correlations

Consistent results on r: - ep (DIS) vs. e+e-

- K±K± vs. Ks Ks

- Kaons vs. charged particles

0 0

Karin Daum

Hadron07, Frascati, Oct., 11th 2007 19

Charged particle fragmentation function in ep collisions

shows significant scaling violations agrees reasonably with e+e- annihilation data NLO QCD calculations fail to describe scaling violations

Deuteron/Anti-deuteron production invariant d(d) cross section 1/1000 of p(p) coalescence parameter B2 (nucleon overlap) not universal

Strange particle production in ep collisions reasonably described in DIS with s=0.3 (LEP tuning) model fails to describe (Λ+Λ)/K0

s in resolved p consistent (Λ+Λ)/K0

s ratios in DIS, direct p and e+e-

a single parameter s not sufficient

Bose-Einstein correlations established for K±K± and K0

s K0s in DIS

consistent source radii for all processes & boson pairs

Conclusions

Karin Daum

Hadron07, Frascati, Oct., 11th 2007 20

Production of protons and deuterons

d/p in DIS (ZEUS)same as in p (H1)

p/p 1

d/d « 1

Karin Daum

Hadron07, Frascati, Oct., 11th 2007 21

Strange-to-light meson ratio

Data prefer strangeness suppression factor 0.3 in DIS and p

Range of T consistent with values obtained in e+e-

pT

DIS p

pT

N(Ks0)

Nch

T=

Karin Daum

Hadron07, Frascati, Oct., 11th 2007 22

Possible f0(980) contribution in Ks Ks 0 0

Simultaneous fit of MC with BEC and Flatté for f0(980)