HERMES in 2002

Gerard van der Steenhoven, Dec. ‘02The origin

of proton spin

HERMES run II (2002-2006)• Transversity:

– Spin structure of thenucleon without gluons:

• Generalized Parton Distributions:– Orbital angular momentum– Parton correlations

Transverse magnetic fieldorienting the spin of thetarget protons in a directionperpendicular to the e+-beam.

• The origin of spin:

• Three leading order distributions:

momentum carried by quarks

longitudinal quark spin, lattice QCD:

transverse quark spin, lattice QCD:

½ = ½ q + G + Lq

[“Traffic Lights” – P.J. Mulders]

Spin Physics: Transversity

HERMES data taking in ‘02

Goal for March 2003: 1.3 Million DIS events

Polarization at HERA

35% e+-polarization observedH.P. Blok, P. van der Nat, B. Zihlmann

The HERMES spectrometer

e+ BEAM

Target area

~1.5m

MagnetTRD + CaloRICH

Lambda Wheels

Beam Loss Monitor

Lambda Wheels

• Physics:– spin structure– Transverse spin

• Operations:– Commissioned– Interference with

transverse field

? // us

M. van Beuzekom, V. Mexner, A.J. Reischl, J.J.M. Steijger

Shut down ’03: new capacitive couplings

Lambda Wheels results I

J.J.M. Steijger

Energy loss in ohmic () andjunction (j) side of one counter

Single Si-stripADC overflow

Energy loss in two countersof one LW silicon module

Bethe Bloch

Lambda Wheels results II

J.J.M. Steijger

Hits with Eloss > 6 MIPin LW at z = 45 cm

Broken bond

Normal HERMESdetector acceptance

Lambda Wheelsare operational!

Beam Loss Monitor

• Purpose:– Generate trigger in case

of excessive beam losses– Trigger to HERA kicker– Monitor radiation

• Custom built• Operational

since Febr ‘02

M. van Beuzekom, V. Mexner, A.J. Reischl, J.J.M. Steijger

e+

Integrated dose from BLM

M. Demey

Maximum dose HELIX > 200 krad Lambda Wheels ok

Physics Results: 4 PhD’s

• Higher twist effects in DIS on 1,2H – J. Visser

• Flavour decomposition of nucleon spin – M.C Simani

• Semi-inclusive DIS off84Kr – E. Garutti*

• Hyperon and C+ photo-

production – D. Heesbeen

*next talk: first evidence for (QCD prediction!) 2LEmatter

Higher twist effects

J. Visser No evidence for higher twist at low Q2

NMCHERMESNMCHERMES RR 22 Qhigh 22Q low22 pdpd FFFF

Gottfried Sumrule

J. Visser

Isospin asymmetryof the seais Q2-independent!

dxxdxudxFxFxS npGSR )]( )([ 3

2 31 ])([ 1

1

022

1

0

22 GeV 5at 007.0228.0 QS NMCGSR

22 GeV 2at 025.0256.0 QS HERMESGSR

|)()(| xdxu

Flavour decomposition I

• Sea quarks: unpolarized

• for strange sea? 0 )(1

0

dxxq

M.C. Simani

Flavour decomposition II

• First data on:

• Data zero• Calculations:

– Instantons (QSM):

– Gas of massless quarks:

du

M.C. Simani

|| || dudu

|| || dudu

(Goeke)

f0(980) Scalar Meson

• f0(980) structure:– – – Glue ball (comp.)

molecule KK hybrid qqqq

E. Garutti

f0(980)

• No strong A-dependence:–

• Q2 and Pt2 dep.:

unlikely very molecule KK

state?- 03 qqP

C+photoproduction I

• First observation of C

+ near threshold:

D. Heesbeen

0C

Xp* C

Charm photoproduction

10 Xp* nGluonFusioPhoton

C

C+photoproduction II

• Spin-dependent C

+ production:

• Partial C+ rec.:

D. Heesbeen

ˆ arg

Xp

*

*

beamettPGFPGF PPDaf

A

GG C

0.440.380.99 GG

14%) (BR 0 XC

Outlook • What to expect in 03+04:

– Lambda Wheel data– Transversity data

• Beyond 2004:– Recoil Detector (GPDs) – Orbital angular momentum– …. Spin physics @ STAR?

Henk Blok, Erika Garutti Michiel Demey, David HeesbeenWillem Hesselink, Louk LapikasArmen Laziev, Vanessa MexnerPaul van der Nat, Andreas ReischlChiara Simani, Jos Steijger Gerard van der Steenhoven Jan VisserGabriel Ybeles Smit Beni Zihlmann

The cast: