CMS Calorimetry in the Very Forward Direction

E. Norbeck, P. Debbins, and Y. OnelUniversity of Iowa

For the 23rd Winter Workshop on Nuclear Dynamics

Big Sky Montana 11-18 February 2007

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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 can’t be produced.)

Detector in TAS to extend calorimeter coverage to η = 7.7

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Magnetic Monopoles (Dirac)

Pole strength for (Coulomb’s law) en/2α = 68.5 en n=integer (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 = (α/2)2 =1.33 x 10-5 ~e4 for unit charge (positronium)

For magnetic atom (polium?) ESep/mc2 = (1/2α)4 (α/2)2 =(1/8α)2 =293

NS

NS NS Make NS pair from vacuum using up kinetic energy

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Will never see a single pole!

Bound (NS) would annihilate, but into what?

Photons like e+e-?

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).

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Other types of magnetic monopoles have been proposed.

These considerations have been only for one (the most popular) type.

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Detector in TAS

Why need η coverage to 7.7?

Much valuable p-p physics from diffractive processes

Single diffraction—one proton scatters, the other makes reaction products

Rapidity gaps—angular regions with no reaction products

Different diffractive processes have rapidity gaps in different places

Requires largest possible rapidity coverage

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TAS

20 cm x 20 cm slot(through the TAS)

IP IP5

Iron Nose

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TAS 5.0 < η < 7.7

HF 3.0 < η < 5.2

CASTOR 5.2 < η < 6.3

Net TAS 6.3 < η < 7.7

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For detectors in slot at shower maximum in TAS:

•Generate Čerenkov 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

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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

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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?

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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 η 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?