LHC News

1
LHC News

• End of June The LHC is expected to be cooled
  down
• End of July First particles may be injected,
  and the commissioning with beams and collisions
  will start.
• Sept/Oct First collisions at 10 TeV.

Cooldown status 13/5/08
2
Magnet tests

• Sector 4-5 Power Tests
• Several training quenches were observed above 5
  TeV equivalent currents
• Stable conditions10 TeVHopefully!
• The magnet training for full 14 TeV operation
  will then be completed over the winter shutdown
  2008 - 2009

Ramp of 138 power converters to a current
equivalent to 5.3 TeV (including all high current
magnets realistic LHC optics )
3
What are minimum bias events?

• Minimum bias are inelastic collisions of two
  protons
• Includes very rare high-pt scatters and very
  common low-pt scatters
• Minimum bias is an experimental definition
• Defined by experimental trigger and analysis
• Relation between experiment and physics is

fi are acceptances for different physics
processes determined by the trigger Trigger bias
4
Triggering Minimum bias
75ns _at_ L1031cm-2s-1 mean of interactions/crossi
ng 0.06

• Two Triggers implemented
• 1. Randomtrack trigger
• L1 Filled bunch trigger
• Bunch crossing rate 13.3MHz
• Mean no events/crossing0.06 ? 946
  emptyinteraction
• Use L2 pixel and SCT spacepoints to reject empty
  events
• Use tracks in EF to reject beam-gas

2. L1 using Minimum bias trigger scintillators
5
MBTS

• Trigger scintillation counters mounted on end of
  LAr calorimeter covering same radii as ID
• Cover 2lthlt4
• Can be used for first data BUT!
• Not rad-hard
• Uses 1/8th of tilecal readout
• ? Lifetime unknown
• At L1 S/N is modest
• Now in simulation can be tuned to measurement in
  the summer
• Can do better at L2 with precision readout

UA5
6
MBTS trigger Trigger bias
preliminary
preliminary

• MBTS_1_1 requires hits in both hemispheresThis
  should be similar to earlier NSD triggers
• MBTS_2 requires two paddles to be hit, can be
  same side
• Trigger bias efficiency of trigger for specific
  processNot trigger rates!

Will Bell
7
Inner Detector Trigger at L2
L1 random trigger
preliminary
preliminary
Use pixel and SCT spacepoints to reject empty
events EmptyInteraction 946 Still have large
beamgas contribution
Will Bell and Regina Kwee
8
Inner Detector Trigger
SCT Space Points gt 3 Pixel Space Points gt12

preliminary
? lt 2.5 pT gt 200 MeV Z0 lt 200.0 mm Track
constraint removes beamgas through vertex
constraint
Will Bell and Regina Kwee
9
Tracking in MB events
1000 events
dNch/d?

• Acceptance limited in rapidity and pt
• Rapidity coverage
• Tracking covers hlt2.5
• pT problem
• Need to extrapolate by x2
• Need to understand low pt charge track
  reconstruction

h
10
Low pT track reconstruction
M.Leyton
preliminary
preliminary
Use tracks pTgt150MeV
preliminary
Track-particle correction Acceptanceefficiencyf
ake subtraction
Technical details Release 13.0.40 low pT
tracking Now improved see later
11
Minimum bias distributions
ATLAS has the tools to trigger on and reconstruct
minimum bias events
preliminary

• Minimum bias sample
• Selected by MBTS_2
• Corrections for
• track reconstruction
• vertex reconstruction
• Multi-vertex events not looked at!

MB sample
PYTHIA
preliminary
Distributions have pTgt150MeV
6
NSD sample Corrected for trigger bias -- change
trigger bias
NSD sample
12
Particle Composition

• MB particle dominiated by low pT pions and 10
  K
• Pions
• 150MeV can traverse to edge of SCT but reduced
  efficiency due to inelastic collisions in ID
• Kaons
• Much larger inefficiencies due to increased
  inelastic collisions in ID
• Efficiencies depend on relative rates of particle
  production in MB interactions
• (Sadly CMS can do PID with analog readout)

Ian Dawson
13
Coming soon Improved low pT tracking

• Based on two-pass tracking
• Find tracks with pTgt500 MeV
• Find tracks with 100ltpTlt500MeV from remaining
  hits, widens track finding roads

Improved low pT turn-on
0.1 lt PT 0.5 (GeV)
14
Coming Soon Improved low pT tracking
0.1 lt PT 0.5 (GeV)
15
Track Reconstruction efficiencies by track
insertion
D.Clements

• Insert a track into a minimum bias event by
  overlapping an RDO-DIGI file of a single track
  event.
• Reconstruct merged event and look for inserted
  single track to determine efficiency.

Muons pTgt0.5GeV
Muons pTgt0.5GeV

• Uses InDetOverlay-00-00-02 (by Andrei Gaponenko)

16
PHOJET
PHOJET implemented in ATHENA Important for
systematic cross-checks
17
More work to be done

• Release 14
• Multi-vertex analysis
• Identification of SD, DD, ND?
• Alignment study

18
Startup Conditions

• Current expectations 2 months single beam
  running from the end of July
• Beam stability poor
• Single beam running provides
• Clean environment to study beam backgrounds
  Beam halo and beam gas
• Alignment and commissioning of endcap systems
• When to switch-on?
• Aim to trigger on beam gas and beam halo events
• Beam gas events distributed along Z following gas
  density
• Beam halo events mainly coming from upstream
  tertiary collimators (TCT)

n
19
L1 for single-beam running

• Make a trigger decision from a loose time
  coincidence between Beam Pickup (BPTX) and
• 2 or more Minimum bias trigger scintillators
  (MBTS) above threshold (MBTS overlaps EC-SCT)
• OR
• 1 or more BCM above threshold
• The HV of the TGCs will be switched on when the
  beam is stable enough.
• The TGCs may be used to trigger on beam halo by
  faking a hit in the TGC1 station.
• This is similar to the current cosmic setup in
  the barrel.

20
Track Reconstruction

• Beam halo tracks can be reconstructed by using
  cosmic style tracking code
• First go beam-halo muons in endcap SCT
• Alignment
• Rate 130Hz?

A. Salzburger