Der Silizium Recoil Detektor für HERMES Ingrid-Maria Gregor

Transcription

1 Der Silizium Recoil Detektor für HERMES Introduction HERMES at DESY Hamburg What do we want to measure? Recoil Detector Overview Silicon Recoil Detector Principle First measurements Zeuthen activities Summary and Outlook Technisches Seminar DESY Zeuthen 8. April 2003 HERA at DESY Hamburg 1

2 HERA with polarised beam spin of electrons are all parallel to one axis HERMES is target experiment, but beam is not stopped in its region The HERMES Spectrometer HERA Measurement of Spin yellow: : gas target red: : tracking detectors green: particle identification blue: calorimeter 4 2

3 The Polarised Internal Gas Target years longitudinal polarised since 2002 transversal polarised But what do we do there? NUCLEON nucleons consist of quarks and gluons spin of the nucleon: known to be 1/2 how contribute the different constituents to the spin? from quark parton model: quarks should carry largest part (0.6) EMC 1988: quark contribution only

4 And how do we measure? deep inelastic scattering (DIS) polarised electron interacts only with quark of oposit spin by switching the polarisation asymmetries can be measured Inclusive... semi-inclusive inclusive... exclusive inclusive semi-inclusive exclusive want to take a closer look here recoiling proton low momentum 4

5 Generalised Parton Distributions exclusive reactions,e.g. ep epγ sdfrlskdfjlskdfslkdfjslkdfjsf are becoming a promising and powerful experimental tool to investigate the spin structure of the nucleon a unified theoretical framework describing inclusive and exclusive reactions at the same time has been obtained Generalised Parton Distributions The Recoil Detector problem: with the acceptance of HERMES we can not measure the recoiling proton Position of Recoil Detector 5

6 3D Model of the Recoil Detector The Recoil Proton Spectrum proton momentum MC simulations kinematic distribution: recoil proton momentum versus polar angle silicon detects low momentum recoil protons SciFi is more suited for higher momentum protons 50<p<1400 MeV/c 0.1<θ< rad polar angle 6

7 Silicon Detector to detect protons from DVCS and to reject events with intermediate Δ resonance uses energy deposition to determine momentum 2 layers of silicon 16 double sided Si sensors (TIGRE) 300 μm m thickness 758 μm m strip pitch p min 135 MeV/c θ acceptance: rad Principle of Silicon Detectors fully depleted pn junction for particle detection signal size is depending on particle energy Δt~10ns 7

8 Bethe Bloch (1) energy deposition can be parametrised with Bethe- Bloch formalism for low momentum: de/dx falls like 1/β 2 minimum = minimal ionising particle = MIP rises very slowly for larger momenta Punch Through Points dependence of ΔE 1 on ΔE 2 which is characteristic for each particle type => PID low initial energy: particle stopped in first layer punch-through point 1: gets stuck in layer 2 punch-through 2:both layers are passed -> > total energy deposition decreases 8

9 Bethe Bloch (2) 1/β 2 region huge dynamic range to be detected up to about 100MeV : proton stuck in Si >130 MeV: Si passes both layers to get energy information: analog readout chip Helix μm m CMOS process 10 MHz sampling frequency 128 input channels Analog pipeline 141 cells deep Preamp-Shaper good noise char. Radiation tolerant 220 krad. Dynamic range +/- 40 fc or +/- 10 MIP required: +/- 280fC 9

10 Memory Pipeline channel number cell (128+trailer) read Readout Conceptual Design analogue frontend readout chip with large dynamic range necessary HELIX dynamic range is only 10 MIP charge division by capacitive coupling readout poor man s solution -> > much better than new design tested with charge directly injected into one minimal ionising particle (MIP) creates electron/hole pairs in 300 μm m silicon 10

11 Charge Injection Q in = 1 V C in in Readout Conceptual Design 10 pf dynamic range of low gain Helix: ~10MIP of high gain Helix: ~40MIP (10 pf) ~70MIP (5 pf) 22 11

12 First Prototype sensor: TIGRE, 99 x 99 mm 2, double sided 300 μm m silicon thickness strip pitch: 758 μm readout pitch: 758 μm readout: HELIX chips, 0.8 μm m CMOS 128 channels ZEUS hybrid sensor 23 Testbeam at DESYII to check if charge sharing results in reasonable values when tested under realistic conditions to scale previous charge injection studies to real MiPs carbon fibre generates Bremsstrahlungs beam metal plate --> > converts into electron/positron beam dipol magnet spreads beam out magnet used to select energy (1-6GeV) 12

13 Reference Telescope Zeus testbeam was used system with three different reference detectors device under test (DUT) movable in all three directions scintillators for trigger data is stored as digitalised ADC counts Reference Telescope sensor: 32 x 32 mm 2, single sided, p-side p strips 300 μm m silicon thickness strip pitch: 25 μm readout pitch: 50 μm readout: VA2 chips, 1.2 μm m CMOS 128 channels 13

14 Testbeam Picture Energy Loss Distribution S/N:6.5 energy loss distribution for 1GeV electrons in 300 um silicon (one strip, 10pF coupling, n-side) n Gaussian distributed noise is cut (threshold = 3 x noise) Landau fit --> > signal size = most probable peak signal to noise ratio S/N = 6.5 high gain channel: no Gaussian noise, Landau fit 14

15 Comparison p-side p and n-siden both sides were tested with 1 GeV electrons same channels were addressed signals size of both sides are within +/- 5% p-side ~100ADC counts, S/N = 7.8 (1MIP) n-side ~ 80ADC counts, S/N = 6.5 (1MIP) small S/N -> due to large capacitance of strips 20% difference -> due to large difference in total capacitance of strips Difference p-side p and n-siden can be explained by the difference in the strip capacitance p-side n-side strip capacitance C STR 34 pf 54 pf interstrip capacitance C int 9 pf 7 pf C virt : total capacitance of readout (high gain Helix, low gain Helix, fanout) calculating this network, a difference of 17% in the signal size is expected 15

16 Present Status of Mechanical Design SciFi Connector Holding Structure Target Cell Scattering Chamber Cooling Collimator Hybrid TIGRE Sensors HERA Beamline Summary Si-Detector HELIX 3.0 chosen for readout. First prototypes have been constructed and tested in test beam. Readout using charge division has been shown to work. 50% charge collection due to large sensor capacitance. S/N for 1 MIP is (n-side) With a 5 pf coupling capacitor, particles depositing 140 times the energy of a 1 MIP particle can be measured! first real hybrid is in production test stand in Zeuthen for laser tests and electrical tests 16

17 Zeuthen Activities coordination of project testbeam laser tests chip acceptance test parameter tuning hybrid testing ACC... Wolf-Dieter Nowak James Stewart Wolfgang Lange Arne Vandenbroucke Mikhail Kopytin Ivana Hristova me with lots of help from the technical staff!!! THANK YOU!! 17