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CMS Zero Degree Calorimeters. Laura Stiles University of Kansas 23 August 2008. Experiment Introduction CMS Experiment at the LHC. The Compact Muon Solenoid (CMS) Experiment is one of the 4 large experiments of the Large Hadron Collider (LHC) at CERN. Experiment Introduction CMS Coverage.

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Cms zero degree calorimeters l.jpg

CMS Zero Degree Calorimeters

Laura Stiles

University of Kansas

23 August 2008

Experiment introduction cms experiment at the lhc l.jpg
Experiment IntroductionCMS Experiment at the LHC

The Compact Muon Solenoid (CMS) Experiment is one of the 4 large experiments of the Large Hadron Collider (LHC) at CERN

Experiment introduction cms coverage l.jpg
Experiment IntroductionCMS Coverage

  • Nearly complete angular coverage allows study of wide range of forward physics

  • TOTEM will measure total cross section + multiplicity detectors in front of ZDC

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Experiment IntroductionCMS Zero Degree Calorimeter (ZDC)

  • Measure neutrons and photons in Pb-Pb and p-p collisions

  • Identical ZDCs at +/- 140m of the collision point

140 m

Each ZDC located in TAN absorber

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ZDC Design

Tungsten to stop beam:

Kinetic energy of N,  produces a shower of charged particles which make Čerenkovlight in fibers


EM has 5 horizontal towers

HAD section has 4 longitudinal towers

Physics zdc physics goals l.jpg
PhysicsZDC Physics Goals

Measuring Reaction Centrality

  • ZDC measures spectator neutrons of

    Heavy Ions

Heavy Ion Data from RHIC

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PhysicsZDC Physics Goals

Triggering on Ultra-peripheral Collisions (UPC)

  • UPCs are electromagnetic collisions of the heavy-ions when passing ~20 fm away from each other

When V = ~C , flux lines collapse traverse to motion

  • Interesting photon-nucleus and photon-photon studies accessible

At 90o field is 2750 times stronger

(two Pb ions passing at 20 fm → 2 x 10^20 gauss)

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PhysicsZDC Physics Goals

Diffractive Physics

  • Quasi-elastic (aka "diffractive") collisions characterized by:

    • (i) forward (leading) proton (surviving the interaction),

    • (ii) large rapidity gaps, void of hadronic production.

  • TOTEM Roman-Pots can be used to tag forward protons from diffractive interactions

  • ZDC can tag or veto (neutral) hadronic activity beyond ~8.1 → very valuable to extend rapidity-gap coverage in CMS

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TestingZDC Beam Tests

  • No injection at LHC → no data except 2006 and 2007 beam tests

Hadronic Section

EM Section

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Response to Positrons

Resolution agrees with simulation. A.S.Ayan et al., CMS IN2006/28

EM right

EM left

50 GeV

Number of Events

~12 %



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Response to Hadrons


Hadronic Signal

300 GeV

EM Signal


(The energy resolution was obtained by Landau fit)

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Current StatusZDC Installation and Testing

  • Right and Left ZDC installed in TAN

  • Laser injection system used to debug electronics chain

  • Currently, we are working on integrating the ZDC into the CMS system

  • Injection of CCW beam September 10th

    • ZDC should see photons from beam gas collision

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Current StatusZDC Beam Tuning

  • Luminosity Monitoring

    • Van der Meer Scans to obtain relative luminosity measurements

    • ZDC information will be used with other LHC detectors

This was used at RHIC to get measurement to 5%. CMS will use the forward calorimeter, ZDC and other detectors to make a 2% measurement.

Summary l.jpg

  • ZDCs help meet very important CMS goals:

    • Luminosity (p-p, Pb-Pb),

    • Heavy-ions physics (centrality, triggering: UPC, ...),

    • Diffractive/forward physics (extended rapidity-gap, ...)

  • Beam tests showed acceptable performance

  • ZDCs are installed, debugged and being integrated to CMS

  • Next step will be LHC beam tuning with aid from ZDC

  • One proton beam will be circulating September 10th

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ZDC Acceptance

  • CMS ZDCs are located 10x further from interaction point than RHIC ZDCs, but beam is 30x more energetic at LHC

  • CMS ZDC has 9x greater acceptance (3x in Px and 3x in Py)

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Acceptance for spectator neutrons

Beam crossing angle shifts Px acceptance away from zero

• neutron

• proton






CMS 5.3TeV

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Current StatusZDC Beam Tuning

EM section is sensitive to p-p bremsstrahlung with Ephoton>20GeV


Luminosity is proportional to rate of coincidence

Crossing angle tan()=(Xleft -Xright)/240m

Average X = Xleft +Xright

Z of interaction = c* (Tleft -Tright)

For pHe √S = 100GeV so ZDCs should see something