HERMES Status DESY PRC May 2007 J Stewart

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

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

Measuring DVCS with true exclusivity Recoil Detector Measuring DVCS with true exclusivity

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

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

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

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

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

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

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

Hadronization in Nuclei One Highlight from recent HERMES measurements

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

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

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

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

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

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

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

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

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

Transverse Polarized Data

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

Sivers moments pions and KAONS p+ > 0 p- ~ 0 K+ > 0 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

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

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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

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

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

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

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

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+ > 0 K- > 0 K+ and p+ consistent with u-quark dominance K- and p- complicated sea quark contr. May 2007 J Stewart - DESY PRC