Hermes Recoil Detector Status Ignazio Vilardi On behalf of the HERMES Collaboration DUBNA-SPIN-07 September 3 – 7, 2007 Ignazio Vilardi DUBNA SPIN 07, September 2007

Outline GPD’s and hard exclusive processes; Hermes results: Beam Spin Asymmetry (BSA) and Beam Charge Asymmetry (BCA); The Hermes Recoil Detector: Motivation and Design; Hermes Recoil Detector Status; Outlook; Ignazio Vilardi DUBNA SPIN 07, September 2007

The Hunt for Lq Study of hard exclusive processes leads to a new class of PDF’s Generalized Parton Distributions a theoretical framework that provides the most complete description of the nucleon possible access to Lq Ji’s sum rule exclusive: all reactions are reconstructed missing energy (DE) and missing Mass (Mx) = 0 from incl.-DIS: HERMES ~0.3 A. Airapetian et al, Phys. Rev. D 75 (2007) 012007 Ignazio Vilardi DUBNA SPIN 07, September 2007

GPD’s Introduction AUT,sp+ AUT,sr,F,w AC,ALU, AUT, AUL What do GPD’s characterize? unpolarized polarized conserve nucleon helicity flip nucleon helicity not accessible in DIS DVCS pseudo-scalar mesons vector mesons Observables: AUT,sp+ AUT,sr,F,w AC,ALU, AUT, AUL Data from HERMES on tape Ignazio Vilardi DUBNA SPIN 07, September 2007

Deep Virtual Compton Scattering HERMES kinematics: BH c.s. >> DVCS c.s. two experimentally indistinguishable processes: DVCS Bethe-Heitler isolate BH-DVCS interference term non-zero azimuthal asymmetries beam helicity asymmetry: HERA (polarised electrons and positrons) only place in the world so far to measure the complete Compton amplitude beam charge asymmetry: Ignazio Vilardi DUBNA SPIN 07, September 2007

DVCS event selection at HERMES Exactly 1 DIS lepton in the spectrometer and 1 photon in the calorimeter; Recoiling proton undetected  Exclusive reactions via the missing mass technique  ; exclusive region: Overall background contribution  15% in exclusive region Ignazio Vilardi DUBNA SPIN 07, September 2007

A factor of 9 more data on tape!! Beam Spin Asymmetry (BSA) A. Airapetian et al., Phys. Rev. Lett. 87 (2001) 182001 Expected sin dependence in exclusive region  Im H sin amplitudes small and positive above exclusive region A factor of 9 more data on tape!! Ignazio Vilardi DUBNA SPIN 07, September 2007

Expected cos() dependence  Re H Beam Charge Asymmetry (BCA) A. Airapetian et al., Phys. Rev. D75 (2007) 11103 Symmetrizised BCA in exclusive bin   ||  Cancel sin dependence Solid curve – 4 Parameter fit P1 + P2 cos + P3 cos2 + P4 cos3 cos - amplitudes zero for higher missing masses Expected cos() dependence  Re H A factor of 9 more data on tape!! Ignazio Vilardi DUBNA SPIN 07, September 2007

The end of polarized targets at HERMES Improve Exclusivity Selection Detect recoiling proton modify target region Detector to measure recoiling proton Ignazio Vilardi DUBNA SPIN 07, September 2007

3D Model of the Recoil Detector 1T Magnet not shown Scintillating Fibers Tracker (SFT) 10 cm BEAM Photon Detector (PD) Silicon Strip Detector (SSD) Ignazio Vilardi DUBNA SPIN 07, September 2007

Performance of the Recoil Detector detection of the recoiling proton p: 135 -1200 MeV/c; 76% f acceptance (because of layout of SSD); p/p PID via dE/dx; MONTECARLO Ignazio Vilardi DUBNA SPIN 07, September 2007

Benefits of the Recoil Detector background suppression semi-incl. DIS: 5% -> <<1% associated BH: 11% -> ~1% Ignazio Vilardi DUBNA SPIN 07, September 2007

Target cell inside beam pipe Thickness = 75 m and length = 150 mm Ignazio Vilardi DUBNA SPIN 07, September 2007

Silicon Detector: protons < 0.5 GeV/c 16 double sided Silicon sensors, size 99 x 99 mm2, 300 µm thickness; 128 strips per sensor side, 8192 read out channels in total, 758 µm strip pitch; High and Low Gain read out;  strip orientation for space point reconst.; p-measurements from dE/dx 135 - 500 MeV/c; PID /p from dE/dx for p < 250 MeV/c; 76% azimuthal acceptance (); Ignazio Vilardi DUBNA SPIN 07, September 2007

SFT Detector: protons > 0.3 GeV/c 2 barrels with each parallel and stereo layer (10°) for space point reconstruction and tracking; 4992 fibers (1 mm diameter) in total; p - measurements 300-1200 MeV/c; PID /p from dE/dx for p < 700 MeV/c; 100% azimuthal acceptance; Ignazio Vilardi DUBNA SPIN 07, September 2007

Photon Detector:  from + (+p0p) 3 layers of scintillators after tungsten converter: the first parallel and the last 2 stereo (± 45°); 60 strips in the parallel one and 44 in the other ones; Detects photons from intermediate  resonance (+  p0  p  ); Reconstructs 0 if both  are detected; Contributes to PID /p (together with SFT) for p > 600 MeV/c; can provide cosmic trigger; Ignazio Vilardi DUBNA SPIN 07, September 2007

Magnet: Møller e- suppression and track bending Provides a 1T solenoid longitudinal superconducting magnetic field for tracking. For this reason the homogeneity of the field has to be better than 20% in either direction; Removes Møller (and Bhabha) electrons by letting them spiral forward and in this way protects the silicon detector from background; Ignazio Vilardi DUBNA SPIN 07, September 2007

Data Taking and general performance Data taking started in February 06 with electron beam Fiber tracker fully operational 2.5 Mio. DIS from hydrogen target; 0.5 Mio. DIS from deuterium target; Switch to positron beam in July 06 Fiber tracker and Photon detector fully operational; Finished commissioning of Silicon Detector in September 06; 28 Mio. DIS events from hydrogen target; 7 Mio. DIS events from deuterium target; Recoil Detector ran stable for 10 months Ignazio Vilardi DUBNA SPIN 07, September 2007

DATA First Recoil Detector Results (SSD) Signal from the Silicon detector divided by a coupling capacitor (10 pF) into HG and LG readout channels: its ratio OK; Correlation between inner and outer Silicon modules OK (different disposition of Silicon strips); <SRIM> Protons 106 MeV/c stopped in 2nd layer 135 MeV/c Energy deposition in inner Silicon module vs. outer Silicon module OK; DATA 500 MeV/c Deuterium target OK; Ignazio Vilardi DUBNA SPIN 07, September 2007

Momentum reconstruction with Recoil D. Low momentum protons (stopped in outer Silicon)  Sum of energy deposits; Higher momentum protons  dE/dx (Bethe-Block formula); High momentum particles  Bending in magnetic field; Ignazio Vilardi DUBNA SPIN 07, September 2007

Internal Alignment (magnet-off data) 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; Ignazio Vilardi DUBNA SPIN 07, September 2007

Residuals for the SFT from cosmic data Parallel top  = 0.28mm SFT Parallel Bottom  = 0.31mm 1mm fibers Ignazio Vilardi DUBNA SPIN 07, September 2007

Residuals for SSD (magnet-off data) inner  = 0.26strip SI outer  = 0.28strip Ignazio Vilardi DUBNA SPIN 07, September 2007

Tracking SFT DATA SI 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 ghost tracks; Ignazio Vilardi DUBNA SPIN 07, September 2007

e-p elastic scattering Clear correlation can be observed; First recoil-spectrometer correlation Z correlation e-p elastic scattering Selection of single recoil tracks by making cuts on the momentum of the lepton detected by the forward spectrometer. Clear correlation can be observed;  correlation  correlation Ignazio Vilardi DUBNA SPIN 07, September 2007

Demonstration of recoil principle Mx < 1.7 Gev The Detector works!!! p - + Use Recoil Detector to remove background!!! Ignazio Vilardi DUBNA SPIN 07, September 2007

Outlook ... see you next year with physics results from Analysis with Recoil Detector; Conventional analysis (without Recoil Detector); Once background contribution is measured: refine analysis of pre-recoil DVCS data; DVCS Beam Charge Asymmetry (BCA) challenging as only Fiber Tracker operational during e- running DVCS Beam Spin Asymmetry (BSA) Hard exclusive meson production (, 0, 0) ... see you next year with physics results from HERMES with Recoil Detector Ignazio Vilardi DUBNA SPIN 07, September 2007

Ignazio Vilardi DUBNA SPIN 07, September 2007

HERA: e+/e- (27.6 GeV) - proton (920 GeV) collider HERMES @ HERA HERA @ DESY HERA: e+/e- (27.6 GeV) - proton (920 GeV) collider Ignazio Vilardi DUBNA SPIN 07, September 2007

HERMES: DIS e+/- (27.6 GeV) on p Internal Gas Target: He , H , D , H unpol: H2,D2,He,N2,Ne,Kr,Xe Particle ID: EM-Calorimeter: energy measurement for leptons and g Preshower, TRD, a1997: Cherenkov, 1998a: RICH + Muon-ID Momentum: measured by deflection of particle in magnetic field Particle trajectories: measured by hits in tracking chambers Ignazio Vilardi DUBNA SPIN 07, September 2007

The spin structure of the nucleon Gluons are important !! Sea quarks Dqs DG Don’t forget the orbital angular Momentum!! Naïve parton model BUT 1989 EMC measured S = 0.120 0.094 0.138 ± Spin Puzzle Quark orb. ang. mom. Gluon orb. ang. mom. Proton spin Gluon spin Quark spin Ignazio Vilardi DUBNA SPIN 07, September 2007

BCA – Comparison to Model calculations M. Vanderhaegen et al., Phys. Rev. D 60 (1999) K. Goeke et al., Prog. Part. Nucl. Phys. 47 (2001) P1 = - 0.011 ± 0.019 P2 = 0.060 ± 0.027 P3 = 0.016 ± 0.026 P4 = 0.034 ± 0.027 Large contribution from associated production in last t-bin (not included in models) GPD’s Model (only protons) Regge-inspired with D-term disfavored Ignazio Vilardi DUBNA SPIN 07, September 2007