Transcript Slides - Indico

Reference Timing for FP420
z2
z1
t1
z0
t1  t0 
t0
c
c
; t 2  t0 
| z1 |  z0
| z 2 |  z0
(| zi | are distances but z0 is signed)
Stating the obvious, but
1 
c  1
z0     


 2   t1  t0 t2  t0 
if z1  z2
The reference time, given by a local (to FP420) “clock” must
(a) have no differential jitter (at few ps level) between L and R stations
(b) be calibrate-able
 dz0 
fix z0  0 and 

 d  TDC 
Mike Albrow
Picosecond Timing Workshop
UTA (April 2006)
t2
A possible scheme:
E
p
QUARTIC/
GASTOF
W
CMS
or
ATLAS
p
LHC-RF (400 MHz)
 sharp regular pulse
STOP
STOP
“TDC”
Optical fiber or Laser?
“TDC”
START
Optical Fiber
Optical Fiber
START
Comparator
(control)
 z  75.5 mm
(250 ps)
May not be necessary, but can test
for L-R propagation time
differential changes
BPM
(optimized for timing)
 z  75.5 mm
BPM
(optimized for timing)
Tell where p is w.r.t. bunch centroid. (few mm/70mm)
Fine correction on p_incident. Compare with sum time from
Mike Albrow
QUARTIC/
GASTOF
Picosecond Timing Workshop
UTA (April 2006)
t E +t W
Learn from space physics?
Mike Albrow
Picosecond Timing Workshop
UTA (April 2006)
Assuming jitter problem solved,
Calibrate with real DPE events.
Want low-ish Lum, enough single interactions L ~ 5 1032 cm2 s 1
(maybe want a special low-L bunch crossing later)
Trigger on two forward rap gaps - needs better coverage 6.5  |  |  9.5
plus central state (could be dijets, or just  ET )
z0 (timing)
“Know” central vertex and z0
z0
Ambiguities give much background
if do not select single interactions.
Could require (e.g.):
 M JJ2 
12  

s


Mike Albrow
Picosecond Timing Workshop
UTA (April 2006)
(vertex)
 We must have a good reference signal free of jitter between
E and W stations. This is as important as the detectors themselves.
Temperature control? Return path control?
To use 220m stations together with 420m, these need timing too.
 Position of interaction in bunch: tight (?) correlation with position
in time of p wrt bunch center at 420,
because no RF cavities intervene.
 Need to discuss with LHC RF/clock experts.
Mike Albrow
Picosecond Timing Workshop
UTA (April 2006)