1. HERMES Status
DESY PRC
May 2007
J Stewart

2. Outline Status of running HERMES Recoil Detector Update
Two recent Physics Highlights
Understanding Hadronization
Hadron Attenuation
pt-broadening
Transverse polarized target results
May 2007
J Stewart - DESY PRC

3. Running 7.4M DIS e- 2006 20M DIS e+ 2006 13M e+ 2007
maybe 20M in July
47M DIS for the unpol. Run
1M DIS ~24pb-1
~ 1 fb-1 proposed for our recoil detector running.
Not e+ e- balanced due to the initial startup problems.
10 M DIS on deuterium in addition.
May 2007
J Stewart - DESY PRC

4. Measuring DVCS with true exclusivity
Recoil Detector
Measuring DVCS with true exclusivity

5. Recoil Detector Overview
1 Tesla Superconducting Solenoid
Photon Detector
3 layers of Tungsten/Scintillator
PID for higher momentum
detects Δ+pp0
Scintillating Fiber Detector
2 Barrels
2 Parallel- and 2 Stereo-Layers in each barrel
10° Stereo Angle
Momentum reconstruction & PID
Silicon Detector
16 double-sides sensors
10×10 cm2 active area each
2 layers
Inside HERA vacuum
momentum reconstruction & PID
HERA BEAM
Target Cell
May 2007
J Stewart - DESY PRC

6. HERMES Recoil Detector timeline
From 1996 through 2005 HERMES ran with the polarized H/D target.
November 2005 the ABS was removed.
In January 2006 the recoil detector was installed.
February started data taking.
Scintillating fiber detector worked immediately.
Silicon detector had serious beam induced noise.
Target and silicon damaged in May 2006.
Modified target installed July with repaired SI.
Timing problem with Photon detector also fixed in July.
Full detector operations since September 2006.
Timing on silicon final.
May 2007
J Stewart - DESY PRC

7. First experience with the Recoil Silicon Detector
Pedestal Stability
~1-2 channel shift expected caused by HERA.
Observed typically 4.
Surprise! 0.5% of the strips couple much stronger to the beam.
Pedestal correction due to beam current now implemented.
Fine tuning still necessary.
High-Low gain ratio OK.
Energy Calibration
Offline calibration seems not valid.
Use “punch-though” point as absolute gain.
Use MIP particle for a strip by strip relative calibration.
Crosstalk/clustering still under study
<SRIM>
Protons
DATA!
1MIP
Constant gain for all Strips assumed
Noise = 1-2 ch.
Single strip.
All pedestal measurements for 1.5 months!
Pedestals measured and zero subtraction recomputed here.
May 2007
J Stewart - DESY PRC

8. Recoil Detector Alignment
Six parameters (three translations and three rotations) which are common for all tracks are fitted
Each track is fitted with a straight line taking into account alignment parameters at current iteration
After iterative procedure converges it is repeated with new initial values of alignment parameters to be sure that alignment procedure does not depend on initial approach
Residuals and dependence of residuals on coordinates used as a tool to check alignment procedure
May 2007
J Stewart - DESY PRC

9. Residuals for the SFT from cosmic data
Parallel
top
=0.28mm
SFT
Parallel
Bottom
=0.31mm
1mm fibers
May 2007
J Stewart - DESY PRC

10. Residuals for SSD (magnet-off data)
May 2007
J Stewart - DESY PRC

11. Tracking Data Full tracking is in production including alignment.
Efficiency of the tracking algorithm studied on MC and found to be 98.4 %.
Starting to study the efficiencies residuals and ghost tracks.
May 2007
J Stewart - DESY PRC

12. Hadronization in Nuclei
One Highlight from recent HERMES measurements

13. Hadronization Goals for understanding the hadronization process:
Space-time evolution of the hadron formation process.
Parton energy-loss mechanisms in nuclei.
Help understand ion-ion collisions.
Excellent momentum match to RHIC FS hadrons.
SIDIS with nuclear targets offers an excellent opportunity to study hadronization.
HERMES kinematics and spectrometer is an excellent experiment for these studies.
May 2007
J Stewart - DESY PRC

14. Why Semi-Inclusive-DIS?
DIS is clean.
No initial state interactions as in P-P or ion-ion.
The kinematics is known for DIS from the scattered lepton.
Need PID to know what hadron was formed.
 and z in the Lund model define the formation time/formation length
Lf ~1-10 fm for HERMES kinematics
May 2007
J Stewart - DESY PRC

15. Nucleus as a laboratory
In e+-e- collisions only the initial and final states are known.
Want to study the intermediate evolution.
Use the nuclear medium to influence the hadronization process.
Perturb the system and measure the influence.
The struck parton and the produced hadron are affected differently by the nuclear medium.
Quark energy loss by gluon radiation.
The hadron nucleon cross sections are well know.
Interactions in the medium shift the kinematics.
Vary the size of the nucleus (DXe) and look at how the hadron yield changes. Radius 1-5 fm.
Use D as lightest isoscalar target.
May 2007
J Stewart - DESY PRC

16. Data collected with End-of-Fill running
Hydrogen
Neon
Target
1999 (pb-1)
2000
(pb-1)
2004
2005
Sum
(pb1) D
32.3
119.7
35.7
61.7
249.4
4He
27.9 Ne
84.2 Kr
26.1
29.5
21.1
76.7 Xe
21.2
21.4
42.6
World best data
set on semi-inclusive
DIS from nuclei!!!
Identified hadrons: +, -, 0, K+, K-, p, pbar
May 2007
J Stewart - DESY PRC

17. Multiplicity ratio: Attenuation
Experimental access to the hadronization process through the measured multiplicity ratio:
May 2007
J Stewart - DESY PRC 17

18. from HERMES 1D Binning Positive Hadrons Negative Hadrons
Strong dependence on A.
increased partonic or hadronic effects.
R increases as  increases.
More likely that hadron formed outside nucleus (Lorentz boost).
Decrease with larger z values.
High z implies short formation time due to quark energy loss.
R is similar for + - 0.
K+ K- similar trends.
p pbar different.
Production mechanisms for p and pbar differ
Final statistics allows 2D binning.
Important for tuning available models.
Data now Final!
Sub Nucl Phys B.
May 2007
J Stewart - DESY PRC

19. 2D-analysis n –ranges and pt2 –ranges also explored
Final statistics makes 2D binning possible.
Combine all pion statistics.
z-ranges
Positive n slope for all z –bins
Slight slope changes
Disentangle kinematic dependences.
Mesons shifted to higher pt2 in heavy nuclei.
Little “broadening” of pt2 for highest z-range.
n –ranges and pt2 –ranges also explored
May 2007
J Stewart - DESY PRC

20. Latest Results: pt-broadening in nuclei
First direct measurement of pt-broadening in lepto-production.
Linear increase with A1/3.
around 0.25 GeV2 large effect.
May 2007
J Stewart - DESY PRC

21. pt-broadening Decreases with increasing z.
As z 1 tp must go to zero.
Hadron has all  so can not have interacted.
Q2 and  dependencies also available.
All show a clear A-dependence.
Great theory interest (B. Kopeliovich, X.-N. Wang).
May 2007
J Stewart - DESY PRC

22. Transverse Polarized Data

23. Azimuthal angles and asymmetries
angle of hadron relative to final quark spin (Collins)
(Collins)
angle of hadron relative to initial quark spin (Sivers)
(Sivers)
chiral-even naïve T-odd DF
related to parton orbital momentum
violates naïve universality of PDF
peculiarity of f^1T
different sign of f^1T in DY
related to parton orbital momentum
May 2007
J Stewart - DESY PRC

24. Sivers moments pions and KAONS
p+ > p- ~ 0
K+ > K- ~ 0
non-zero orbital angular
momentum in p-wave fct.
Lq !
… and Sivers K+» p+ ! |p+>=u d … |K+>=u s
L large for anti-quarks ?
May 2007
J Stewart - DESY PRC

25. Summary The experiment is running well.
Good progress is being made on understanding the recoil detector.
Data from our nuclear targets will be invaluable for understanding hadronization.
First results with our final data set with the transverse polarized target are available.
May 2007
J Stewart - DESY PRC

26. backup

27. Alignment Status
SFT alignment information from the DESY22 alignment run is included and checked on cosmic data
SSD sensors are aligned individually relative to the SFT using magnet-off data
PD alignment is done relative to the SFT with magnet-off data
Next step is Recoil-Hermes alignment using e-p elastic
May 2007
J Stewart - DESY PRC

28. 2D-analysis n –ranges Final statistics makes 2D binning possible.
Combine all pion statistics.
z-ranges
Positive n slope for all z -bins
No broadening of pt2 for highest z-range.
n –ranges
Q2 and pt2 dependences are similar for different values of n
Different slopes of the z-dependence in different n-bins.
First part of the z–dependence at high n might reflect partonic mechanism; drop at higher z in the lowest n-bin due to hadron absorption.
pt2 –ranges
Larger R at higher pt2 and..
.. smooth n-dependence (red points)
- related to the pt2 broadening which is correlated with n
Broadening gone at high z –parton can’t lose energy at z->1 (Kopeliovich)
May 2007
J Stewart - DESY PRC

29. pt-broadening . Called pt-broadening.
Measure of the production time p.
Nucl. Phys. A740,211
For t> p. no broadening occurs.
Inelastic scattering suppressed (fast hadrons)
elastic very small
 mean free path > 20 fm
“Pre-Hadron”
Color neutral
Same quantum Nr as final hadron.
Wavefunction diff.
Smaller size.
May 2007
J Stewart - DESY PRC

30. The 3rd Twist-2 structure function
unpolarised quarks
and nucleons
q(x): spin averaged
vector charge
well known
longitudinally polarized
quarks and nucleons
Dq(x): helicity difference
 axial charge
known
transversely polarized
quarks and nucleons
dq(x): helicity flip
 tensor charge
measuring!
May 2007
J Stewart - DESY PRC

31. Peculiarities of transversity
relativistic nature of quark:
in absence of relativistic effects h1(x)=g1(x)
Q2 –evolution: unlike for g1p(x),
the gluon doesn’t mix with quark in h1p(x)
(no gluon analog for spin-½ nucleon)
sensitive to the valence quark polarisation
q and q have opposite sign. _
tensor charge: first moment of h1
(large from lattice QCD)
chiral odd FF
CHIRAL ODD NOT ALLOWED IN E.M. INTERACTIONS
transversely polarized
quarks and nucleons
dq(x): helicity flip
 tensor charge
measuring !
double helicity flip
single helicity flip
May 2007
J Stewart - DESY PRC

32. Collins moments Collins moment: p+ > 0 p- < 0
p- unexpected large
role of unfavoured FF
Hfav = - Hunfav
first data for Collins-FF
available from Belle
extraction of h1 from
Hermes asymmetries
K+ > K- > 0
K+ and p+ consistent with
u-quark dominance
K- and p-
complicated sea quark contr.
May 2007
J Stewart - DESY PRC