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Fermilab. Accelerator Physics Center. Muon Collider Detector Backgrounds. Nikolai Mokhov. Muon Collider Physics & Detectors Workshop Fermilab March 5, 2008. OUTLINE. Introduction and a Little History Three Background Sources Detector Performance and Tolerable Limits IP Backgrounds

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Muon collider detector backgrounds

Fermilab

Accelerator Physics Center

Muon Collider Detector Backgrounds

Nikolai Mokhov

Muon Collider Physics & Detectors Workshop

Fermilab

March 5, 2008


Outline
OUTLINE

  • Introduction and a Little History

  • Three Background Sources

  • Detector Performance and Tolerable Limits

  • IP Backgrounds

  • Muon Beam Decay Backgrounds

  • Muon Beam Halo

  • Summary

Muon Collider Backgrounds - N. Mokhov


Introduction
INTRODUCTION

  • The high physics potential of a Muon Collider (MC) is reached only if a high luminosity of m+m- collisions in the TeV range is achieved (>1034 cm-2 s-1). The overall detector performance in this domain is strongly dependent on the background particle rates in various sub-detectors. The deleterious effects of the background and radiation environment produced by the beam in the ring are very important issues in the Interaction Region (IR) and detector design.

Muon Collider Backgrounds - N. Mokhov


References on muon collider backgrounds
REFERENCES ON MUON COLLIDER BACKGROUNDS

1. G.W. Foster and N.V. Mokhov, "Backgrounds and Detector Performance at 2x2 TeV mu+mu- Collider", Sausalito-94, AIP Conf. Proc. 352, pp. 178-190. Fermilab-Conf-95/037 (1995).

2. N.M. Gelfand and N.V. Mokhov, "2x2 TeV mu+mu- Collider: Lattice and Accelerator-Detector Interface Study", Proc. of PAC05. Also Fermilab-Conf-95/100 (1995).

3. N.V. Mokhov and S.I. Striganov, "Simulation of Backgrounds in Detectors and Energy Deposition in Superconducting Magnets at mu+mu- Colliders", Proc. of 9th ICFA Workshop, Montauk, NY, October 15-20, 1995. Also Fermilab-Conf-96/011 (1996).

4. N.V. Mokhov, "Comparison of Backgrounds in Detectors for LHC, NLC and mu+mu- Colliders", Nucl. Phys. B, 51A (1996) pp. 210-218.

5. C.J. Johnstone and N.V. Mokhov, “Optimization of a Muon Collider Interaction Region with Respect to Detector Backgrounds and the Heat Load to the Cryogenic Systems”, Fermilab-Conf-96-366 (1996).

6. C. Ankenbrandt et al., “Status of Muon Collider Research and Development and Future Plans”, Phys. Rev. ST-AB, vol. 2, 081001 (1999) pp. 1-73.

7. Snowmass 1996 Feasibility Study.

8. Muon Collider workshops, 1995-1997 (B. Foster, C. Johnstone, N. Mokhov, I. Stumer)

Muon Collider Backgrounds - N. Mokhov


Backgrounds
BACKGROUNDS

  • Three sources at Muon Collider

  • IP backgrounds: Particles originated at interaction point (IP) from m+m- collisions as well as incoherent pairs.

  • Muon beam decay backgrounds: Unavoidable bilateral detector irradiation by particle fluxes from the beamline components and accelerator tunnel – major source at MC.

  • Beam halo: Beam loss at limiting apertures; unavoidable, but is taken care with an appropriate collimation system far upstream of IP.

Muon Collider Backgrounds - N. Mokhov


Detector performance
DETECTOR PERFORMANCE

  • Backgrounds affect collider detector performance

  • in three major ways:

  • Detector component radiation aging and damage.

  • Reconstruction of background objects (e.g., tracks) not related to products of m+m- collisions.

  • Deterioration of detector resolution (e.g., jets energy resolution due to extra energy from background hits).

Muon Collider Backgrounds - N. Mokhov


Strawman mc detector concept 1
Strawman MC Detector Concept (1)

Muon Collider Backgrounds - N. Mokhov


Strawman mc detector concept 2
Strawman MC Detector Concept (2)

Muon Collider Backgrounds - N. Mokhov


Background tolerable limits
BACKGROUND TOLERABLE LIMITS

Calorimeter, tracker and vertex detectors: in smallest element, occupancy ≤ 1%.

To avoid pattern recognition problem in tracker, hit density from charged particles should be ≤ 0.2 hit/cm2/bunch.

Muon system: the RPCs (sensitive media) need 1 ms to re-charge a 1 cm2 area around the avalanche, therefore, the hit rate in excess of 100 Hz/cm2 would result in an unmanageable dead time. With 80 sensitive layers in a Muon Endcap, it corresponds to a muon flux at its entrance of about 1 m/cm2/s.

Muon Collider Backgrounds - N. Mokhov


Temporal aspects
TEMPORAL ASPECTS

  • Temporal considerations in the IP and machine background analysis are of a primary importance. Integrated levels determine radiation damage, aging and radio-activation of detector components as well as the radiation environment in the experimental hall, accelerator tunnel and their surroundings. High instantaneous particle fluxes complicate track reconstruction, cause increased trigger rates and affect detector occupancy.

  • One can define the instantaneous or effective luminosity - which determines the detector performance – for the amount of radiation in the detector active element over the drifting/integration time ∆td (“sensitivity window”) or the bunch train length, whichever is smaller. For detector elements most susceptible to occupancy problem ∆td is 40 - 300 ns.

Muon Collider Backgrounds - N. Mokhov


Ip backgrounds at mc vs lhc and ilc
IP Backgrounds at MC vs LHC and ILC

MC produces 3e-7 of LHC’s background hadrons from IP annually,

while instantaneous background rate is 0.025% of the LHC one.

Incoherent pair production might be a concern!

Muon Collider Backgrounds - N. Mokhov


Muon beam decays major source of backgrounds
Muon Beam Decays: Major Source of Backgrounds

Contrary to LHC, almost 100% of background and radiation problems at MC arise in the lattice. Muon decays is the major source. For example, the decay length for 2-TeV muons is lD ~107 m. With 2e12 muons in a bunch one has 2e5 decays per meter of the lattice in a single pass, 2e8 decays per meter per store, and 6e9 decays per meter per second.

Electrons from muon decay have mean energy of approximately 1/3 of that of the muons. At 2 TeV, these 700-GeV electrons, generated at the 6e9 m-1 s-1 rate, travel to the inside of the ring magnets, and radiate a lot of energetic synchrotron photons towards the outside of the ring.

Electromagnetic showers induced by these electrons and photons in the collider components generate intense fluxes of muons, hadrons and daughter electrons and photons, which create high background and radiation levels both in a detector and in the storage ring.

The primary concern is muon decays in the inner triplet and near IP.

Muon Collider Backgrounds - N. Mokhov


Collimating nozzles at ip
Collimating Nozzles at IP

Due to the very high energy of electrons and photons in the large aperture, the whole triplet is a source of backgrounds in the detector. As calculated, electron and photon fluxes and energy deposition density in detector components are well beyond current technological capabilities if one applies no measures to bring these levels down.

As was found, the most effective collimation includes a limiting aperture about one meter from the IP, with an interior conical surface which opens outward as it approaches the IP. These collimators have the aspect of two nozzles spraying electromagnetic fire at each other, with the charged component of the showers being confined radially by the solenoidal magnetic field and the photons from one nozzle being trapped (to whatever degree possible) by the conical opening in the opposing nozzle.

Muon Collider Backgrounds - N. Mokhov


Ip region
IP Region

Muon Collider Backgrounds - N. Mokhov


Nozzle concepts
Nozzle Concepts

R=4cm

Background reduction 30 to 500 times

Detector is not connected by a straight line with

any surface hit by decay electrons in forward

or backward directions

4m

Muon Collider Backgrounds - N. Mokhov


Spreading decay electrons along final focus
Spreading Decay Electrons Along Final Focus

SC sweep dipoles with tungsten collimators between elements implemented into inner triplet: another factor of seven background reduction

Even with all of the above, muons are orders of magnitude above the limit

Muon Collider Backgrounds - N. Mokhov


Muon collider ir
Muon Collider IR

Muon Collider Backgrounds - N. Mokhov


Occupancy for 0 3 x 0 3 mm si pads
Occupancy for 0.3 x 0.3 mm Si-pads

Muon Collider Backgrounds - N. Mokhov


Radiation damage to si
Radiation Damage to Si

Muon Collider Backgrounds - N. Mokhov


Incoherent pairs nozzles solenoid field
Incoherent Pairs: Nozzles & Solenoid Field

Muon Collider Backgrounds - N. Mokhov


Bethe heitler muons
Bethe-Heitler Muons

2x2 TeV

R=4m

L=130m

from IP

Muon Collider Backgrounds - N. Mokhov


Bethe heitler muons1
Bethe-Heitler Muons

Significant fluctuations in transverse energy and missing transverse

energy due to energy spikes in deep inelastic interactions of BH muons

BH muon and accompanying particle fluxes substantially exceed tolerable

limits, in particular in muon system: ILC-type magnetic shielding walls

upstream of IR are needed !!!

Muon Collider Backgrounds - N. Mokhov


Muon beam halo
MUON BEAM HALO

We have shown that detector backgrounds originating from beam halo can exceed those from decays in the vicinity of IP. Only with a dedicated beam cleaning system far enough from IP can one mitigate this problem.

Tracker

Muons injected with large momentum errors or betatron oscillations will be lost within the first few turns. After that, with active scraping, the beam halo generated through beam-gas scattering, resonances and beam-beam interactions at the IP reaches equilibrium and beam losses remain constant throughout the rest of the cycle.

Endcap Calor.

Particle fluxes in detector for 2-TeV beam

beam halo loss (1% per store) at 200m from IP

Without scraping: orders of magnitude above the limit

Muon Collider Backgrounds - N. Mokhov


Scraping muon beam halo
SCRAPING MUON BEAM HALO

  • We have designed two beam scraping systems to (completely) suppress beam halo contribution to detector backgrounds:

  • For TeV domain, extraction of beam halo with electrostatic deflectorreduces loss rate in IR by three orders of magnitude; efficiency of an absorber-based system is much-much lower.

  • For 50-GeV muon beam, a five meter long steel absorber does an excellent job, eliminating halo-induced backgrounds in detectors.

Muon Collider Backgrounds - N. Mokhov


Summary 1
SUMMARY (1)

  • Backgrounds originated at IP are negligible compared to other sources: hadrons from m+m- collisions; incoherent pairs are captured by nozzles in the solenoid field.

  • Backgrounds induced by beam halo losses exceed the limits by orders of magnitude, but can be suppressed with an appropriate collimation system.

  • Muon beam decays are the major source of backgrounds in the MC detectors. They can drastically be reduced by sophisticated collimating nozzles at IP, and sweep dipoles and collimators in a 100-m region upstream IP.

Muon Collider Backgrounds - N. Mokhov


Summary 2
SUMMARY (2)

Still work to do:

  • With current design, total occupancy is OK for 0.5-TeV MC, 2-3 times above the limit for 4-TeV MC, and up to 10 times above the limit at r < 15 cm for 0.1-TeV MC.

  • Bethe-Heitler muons in calorimeter and forward muon system are a few orders of magnitude above the limit; ILC-type magnetic shielding walls upstream IR needed.

Muon Collider Backgrounds - N. Mokhov


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