CMS Calorimetry in the Very Forward Direction

1
CMS Calorimetry in the Very Forward Direction

• E. Norbeck, P. Debbins, and Y. Onel
• University of Iowa

For the 23rd Winter Workshop on Nuclear
Dynamics Big Sky Montana 11-18 February 2007
2
Outline
New thoughts about magnetic monopoles(The huge
magnetic field of CMS would make a monopole
appear at a very forward angle with a large
energy. I now claim they cant be produced.)
Detector in TAS to extend calorimeter coverage
to ? 7.7
3
Magnetic Monopoles (Dirac)
Pole strength for (Coulombs law) en/2a 68.5
en ninteger (1) Make N-S pair at point where
wave functions overlap Separation about one Bohr
radius Assume the pair is made in a 1S H-atom
type state ESep/mc2 (a/2)2 1.33 x 10-5 e4
for unit charge (positronium) For magnetic atom
(polium?) ESep/mc2 (1/2a)4 (a/2)2 (1/8a)2
293 NS NS NS
Make NS pair from vacuum using up kinetic energy
4
Will never see a single pole! Bound (NS) would
annihilate, but into what? Photons like ee-? A
jet if produced in a central Pb-Pb collision?
Photon jet? Hadron jet? Perhaps common in RHIC
data! An excited bound (NS) could emit (NS).
5
Other types of magnetic monopoles have been
proposed. These considerations have been only for
one (the most popular) type.
6
Detector in TAS Why need ? coverage to 7.7? Much
valuable p-p physics from diffractive
processes Single diffractionone proton scatters,
the other makes reaction products Rapidity
gapsangular regions with no reaction
products Different diffractive processes have
rapidity gaps in different places Requires
largest possible rapidity coverage
7
(No Transcript)
8
TAS
IP
IP5
20 cm x 20 cm slot (through the TAS)
Iron Nose
9
TAS 5.0 lt ? lt 7.7 HF 3.0 lt ? lt
5.2 CASTOR 5.2 lt ? lt 6.3 Net TAS 6.3 lt ? lt 7.7
10
For detectors in slot at shower maximum in TAS

• Generate Cerenkov light in quartz fibers
• Run fibers to back of TAS along 18 x 46 mm
  instrument slot on side of TAS
• Place PMTs behind TAS
• Use same electronics as in HF
• Instrument only uninstalled TAS

11
(No Transcript)
12
(No Transcript)
13
(No Transcript)
14
(No Transcript)
15
(No Transcript)
16
(No Transcript)
17
Quartz Fibers

• Fibers fanned out in slot to 20 cm vertical width
  of slot
• In slot fibers will be 45º to beam to maximize
  light.
• Four fiber bundles, upper and lower halves on
  both sides
• Fibers will be quartz-quartz with a polyimide
  buffer to be able to withstand 250 ºC 24 hr
  bakeout. Can stand up to 1 Grad (measured last
  summer by Iowa group). (Bake out may anneal out
  radiation damage)
• Ample room in 18 x 46 mm slot on side of TAS for
  the fibers

18
Photomultiplier tubes

• Use same PMTs as HF
• Or for fast timing use new Hamamatsu fast tubes
  with only 250 ps transit-time spread
• PMTs will be perpendicular to beam line at back
  end of TAS. Distance from TAS to allow 90º bend
  of fibers and provide thermal isolation
• PMTs will be kept cool (even during bakeout) and
  free of helium with a stream of air (or N2)
• Will fringing field from magnet affect PMTs?

19
To see rapidity gaps there must be no more than
one collision per beam crossing. Only early p-p
running will have so little beam.Will ramp up to
20 collisions per beam crossing. Will a detector
with ? out to 7.7 be useful for heavy
ions? (extremely small x- values 10-7)
Welcome any suggestions. This detector could
have a long lifetime, but how useful will it be
after initial p-p runs?