Far forward angle physics at the LHC

E. Norbeck and Y. OnelUniversity of Iowa

For the 24th Winter Workshop on Nuclear DynamicsSouth Padre Island 11-18 April 2008

24th WW April 11, 2008 Ed Norbeck U. of Iowa 2

24th WW April 11, 2008 Ed Norbeck U. of Iowa 3

I will consider here methods of detecting charged particles at such small angles that they sneak through the very forward calorimeter. This means angles less than 0.6º or η > 5.3

Extreme example

The FP420

Detectors 3 mm from the beam at a distance of 420 m from the IP

7 microradians = .0004º

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“By detecting protons that have lost less than 1.5% of their longitudinal momentum, a rich electroweak, Higgs, beyond the Standard Model and QCD program becomes accessible, with the potential to make measurements which are unique at LHC, and difficult even at a future linear collider. By tagging both outgoing protons in the process pp → p + X + p, the LHC is effectivelyturned into a glue-glue collider.”

Why would one want detectors at 420 m?

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Match the two protons to event in CMS

Measuring arrival time to 10 ps of both protons will identify the interaction point to 3 mm.

0.5º C will change the length of 420 m by 3 mm

Can use the tracker to recalibrate for slow drifts.

A 250 GeV proton would be 10 ps late.

24th WW April 11, 2008 Ed Norbeck U. of Iowa 6

Will the detectors at 420 m be useful with heavy ions?

The question is still under discussion.

Some say yes and provide specific examples.

Others say it is unnecessary because 50% of the time an ultraperipheral reaction can be tagged by a neutron in a ZDC.

A lead ion is easily broken up.

The 420 m detectors should be useful for p-Pb studies.

24th WW April 11, 2008 Ed Norbeck U. of Iowa 7

ZDC(Zero-Degree Calorimeter)

A ZDC at CMS is similar to those at RHIC

Difference is that it must be located deep inside of the TAN (which is 140 m from the IP)

24th WW April 11, 2008 Ed Norbeck U. of Iowa 8

24th WW April 11, 2008 Ed Norbeck U. of Iowa 9

24th WW April 11, 2008 Ed Norbeck U. of Iowa 10

Quartz fib

er

bundle

PMT

Quartz fiber

bundle

PMT

Beam Pipe

Magnet

Go to larger angles by looking at particles near the beam pipe at distances 50 to 100 m from IP. Will see showers from deflected beam particles hitting the beam pipe.Will also see beam-air events and beam halo.Want to distinguish incoming from outgoing particles.Δt < 12.5 ns for protons.

One idea making use of the directionality of Čerenkov radiation

24th WW April 11, 2008 Ed Norbeck U. of Iowa 11

24th WW April 11, 2008 Ed Norbeck U. of Iowa 12

• 100 GeV pions from TB04 test of HF

• While analyzing TB04 data during the summer of 2005, abnormally high energy events were seen in several pion runs.

• HF is ~10 λint thick• e-10 = 1/22026

A PMT is an excellent charged particle detector(Čerenkov light in front face)

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Use PMTs as the directional detectors.

Duct-tape PMTs to beam pipe.(Requires too many PMTs– excessive electronics)

Quartz

BlackAPDs

Frosted or coated with wavelength shifter

Latest idea

(avalanche photodiodes)(second in anticoincidence)

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TOTEM T2 CASTOR

HF

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CASTOR layout

IP

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CASTOR 3-D view

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CASTOR I is under construction

Iowa hopes to have funds by this summerfor CASTOR II

Will it be a copy of CASTOR I with better longitudinal resolution or a new design?

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The TOTEM T2 telescopeT2 is not a calorimeter—no absorbersThe detectors use the triple-GEM technology

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Structure of a triple-GEM detector(Gas Electron Multiplier)

The readout board has small pads that collect the electronsIn TOTEM T2 the pad readout is digital—one bit per padIf the pad signal is above threshold get a 1, otherwise a 0Each of the 10 layers has about 3000 pads

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.

Particles in a small digital calorimeter

8 GeV π+ event (early shower)A single muon

Can get better energy resolution by not measuring the energy!!

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Consider for CASTOR II

40 layers of tungsten with triple-GEMs with 10000 pads per layer

As a digital calorimeter the 400000 data bits should be manageable even at this late date.

Should work well with pp experiments

For PbPb the occupancy is too large, even with 10000 pads/layer.

We are open to new ideas.