Geometrical constraints to the T 9 beam photon

Geometrical constraints to the T 9 beam photon tag Set-up Nicola Mazziotta INFN Bari mazziotta@ba. infn. it May 17, 2006 Nicola Mazziotta, May 17 2006

Photon tag set-up The center of the two SSDs upstream the magnet is assumed to be coincident with the beam axis The two SSDs downstream the magnet are assumed to be shifted with respect to the beam axis in order to provide a larger acceptance for the deflected electrons The distances between the two pairs of upstream (downstream) SSDs are set to 50 cm Nicola Mazziotta, May 17 2006 2

Displacement Vs. Photon momentum l Input pe D Deflected electron p*e(Ge. V/c)> 0. 3 B(T) l(m) Electron displacement, δ B field region Nicola Mazziotta, May 17 2006 p = pe - p*e 3

Photon momentum Vs. Angle Photon momentum resolution /p = (dp /dθ) θ/p Nicola Mazziotta, May 17 2006 4

Angular resolution • SSD resolution = Strip pitch/sqrt(12) = 228 micron/sqrt(12) – the uncertainty on the electron position depends on the SSD pitch • Beam divergence = 1 mrad – the trajectories in B field depend of the input angle • Beam momentum resolution = 2% – the deflected angle depends on the electron momentum • Multiple scattering in the SSDs – multiple scattering can cause fluctuations of the input angle of the electron in the B-field region – the multiple scattering angle decreases (increases) with the deflected electron momentum (photon momentum) Nicola Mazziotta, May 17 2006 5

Angular resolution: fast MC result (preliminary) A fast MC has been implemented that takes into account the effects discussed above Nicola Mazziotta, May 17 2006 6

Photon momentum resolution Nicola Mazziotta, May 17 2006 7

Summary • Given an angular range, several photon momenta can be observed, by properly setting the magnetic field and the input electron momentum • The photon momentum resolution depends on the input electron momentum, on the magnetic field and on the angular resolution, it worsens with decreasing photon momentum. • Bremsstrahlung production angle, that has not been taken into account, could worsen the momentum resolution • Eventual bremsstrahlung photons generated after the magnet, have not been taken into account. Nicola Mazziotta, May 17 2006 8

Bending power calibration procedure • Set beam momentum (i. e. pin=3 Ge. V/c) and B field value – Alignment run with B=0 using pions (SSDs have to be disposed along the beam axis in order to perform proper alignment) • Look for the beam optics magnets current settings that allow to obtain normal incidence on SSDs • Evaluate the relative SSD strip positions – Calibration runs with B>0 using pions with different momenta (number of runs and momentum values TBD) up to pin • Set the beam magnet currents to have normal incidence on SSDs • Study the pion deflection angle as a function of momentum • For pin=1 Ge. V/c lower beam momenta could be not available (maybe the beam momentum can be decreased up to 0. 5 Ge. V/c). Calibration data at higher momenta can be used, taking into account that angular deflection depends on B/p. Nicola Mazziotta, May 17 2006 9

Photon test beam set-up and trigger EM Cal Beam: electron/positron SSDs C 2 (3%X 0) S 2 2 SSDs (1%X 0) SV S 4 GLAST CU C 1(3%X 0) S 1 Sh (2. 5%X 0) S 3 TRIG = S 1 S 2 S 4 Sh C 1 C 2 S 3 Nicola Mazziotta, May 17 2006 10

Bari SSD modules 6 X-Y wafer module: 1 module is equipped with two MICRON SSDs 400 m thick and 228 m strip pitch, each with three TA 1 chips (384 strips) 1 module is equipped with two ST SSDs 500 m thick and 228 m strip pitch, each with three TA 1 chips (384 strips) 2+1 modules are equipped with two GLAST SSDs 400 m thick and 228 m strip pitch, each with three TA 1 chips (384 strips) 1 module is equipped with two GLAST SSDs 400 m thick and 228 m strip pitch, each with three VA 1 chips (384 strips) The two wafers are read-out in chain to have 768 strips in a single FADC channel. The items in red will be delivered to Bari later this week. Nicola Mazziotta, May 17 2006 11

Bari SSD modules 3 TA 1 IDEAS chips Nicola Mazziotta, May 17 2006 12

Bari SSD ladder box Ladder module: 1 GLAST ladder equipped with three TAI chips, and 4 GLAST wafer each equipped with 3 VA 1 chips. The wafer strips are oriented orthogonal to the ladder strips. The wafers are located on both surfaces of the box. Two wafers are read-out in chain to have 768 strips in a single FADC channel. The ladder (384 strips) is read-out in a different FADC channel. The ladder will be delivered to Bari later this week. Nicola Mazziotta, May 17 2006 13

INFN Bari plastic scintillator • 2 fingers of 1 x 6 cm 2, 1 cm thick (upstream trigger) • 1 of 10 x 10 cm 2, 1 cm thick (upstream beam monitor) • 1 of 15 x 30 cm 2, 1 cm thick (downstream trigger) • 2 of 15 x 50 cm 2, 1 cm thick (downstream VETO) • 1 of 15 x 40 cm 2, 1 cm thick with hole in the middle (halo VETO) – The scintillators are equipped with XP 2020 photomultiplier and mu-metal shielding Nicola Mazziotta, May 17 2006 14

Set up … Nicola Mazziotta, May 17 2006 15