FPS Status 2000

1
FPS Calibration
K.Hiller, DESY Zeuthen Antwerp FPS / VFPS
meeting 9/12/2005

• Optics of the beam line is well-defined HERA ?
  Monte Carlo.
• For the nominal beam the there is a unique
  relation between proton
• trajectory and momentum at IP.
• At HERA running the proton beam is not at the
  nominal position.
• For momentum reconstruction the measured proton
  tracks have
• to be shifted into the ideal beam line system
  where the optics is defined

2
Scattered Proton Trajectory
For precise measurement of the proton trajectory
a combination of 2 tracking stations is needed
? global track parameters These global track
parameters along the ring are uniquely
determined by the proton momentum and offset at
the IP
X(Z,E), X(Z,E) global track parameters X(0),
X(0) proton trajectory at IP AX, BX,
CX, DX, GX, HX optical constants
Assume X(0) 0 since under constraint ? enlarge
errors
In linear machines, containing only dipols and
quadrupoles, X and Y projections are completely
decoupled ? 2 independent energy
measurements !!!
3
Calibration of Vertical Pots
Kinematic range 0.1 lt Xpom lt 0.4

• leading proton by Reggeon/Pion exchange
• no well-defined process for calibration
• use local or global track hit pattern for
• calibration

Local Tracks
Global Tracks
4
Vertical Calibration Constants 2004
81V at 15 mm 90V at 65 mm (detector
insert too short ? poor data)
5
Calibration of Horizontal Pots
Kinematic range Xpom lt 0.05
? Diffractive ? Photoproduction
? p ? ? p ? ? ? p p p-
Assume soft, quasi-real photon , ? compensate by
larger errors !!!
6
Horizontal Calibration Constants 2004
Both detectors 20 - 5 mm to the proton orbit
7
Proton Momentum
Vertical Pots 500 lt Ep lt 600 GeV 0 lt t lt 0.3
GeV2
Horizontal Pots Ep gt 880 GeV 0.2 lt t lt 1 GeV2
8
Error Sources
1) real ? nominal vertex at IP 2) momentum
spread at IP ( emittance) 3) spatial detector
resolution 4) calibration constants 5)
optical constants (negligible !) 6) beam
corrections during the proton fill
Error propagation takes into account only 3) 4)
6) To account for remaining sources errors of
calibration constants are doubled Since the
energy is measured in X and Y projections
independently on can control the final errors.
9
Momentum Angular Errors
What Vertical Horizontal
?E / GeV 5.4 3.7
?Px / MeV 7 11
?Py / MeV 38 43
? PT2 /GeV2 0.0015 0.0020
10
Errors Main Contributions
What Vertical Horizontal
Spatial Resolution ?X ?Y 200 µm ?X ?Y 200 µm
Energy Error 1.7 GeV 2.6 GeV
Calibration ?X 650 µm ?Y 540 µm ?X 660 µm ?Y 170 µm
Energy Error 5.0 GeV 2.3 GeV
11
Errors - Consistency
What Vertical Horizontal
RMS 1.2 1.3
Sigma_1 0.4 0.9
Sigma_2 1.7 2.1
RMS errors 20 - 30 too small Sigma1/2
mixture of too small/large errors
12
Calibration Status

• 2004
• 1) Survey and geometry JRSU, JR3D all for
  2004 on NDB
• (no 2004 tunnel survey use of ad hoc
  values .)
• Pot positions JRPP all on NDB
• Optical constants JCDX/Y, JCEX/Y all on
  NDB
• Calibration constants JCBO all on NDB

• 2005 much more data
• Survey ???? helpful
• Pot positions done Spaskov
• Optical constants ongoing for 2004/5 e-p
• Calibration constants target H1 meeting

Who needs 2005 calibrated FPS data ?