Crossing-angle-or-not physics implications report from 19-01-04 phone-meeting

1
Crossing-angle-or-not physics implicationsreport
from 19-01-04 phone-meeting
cold crossing-angle
head-on warm
crossing-angle -
more IP tuning optics design
constraints crab-cavity req.
beam(strahlung) extraction SC mini-quad.
electrostatic separators backgrounds
collimation
? get worse at 1 TeV
technical issues
physics issues evaluated
hermetic ?? veto post-IP
diagnostics transverse boost
for energy and B and P not
polarisation

no killer arguments either way - quantify
physics impact consensually
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1. Introduction, specification and context of
study, meeting goals 10
P. Bambade/LAL 2.  Smuon and stau searches with
small slepton-neutralino mass differences
Implications for dark matter interpretation in
co-annihilation scenarios 25 Z.
Zhang/LAL 3. Smuon and stau searches with small
slepton-neutralino mass differences 20
U. Martyn/DESYTentative conclusion further
work concerning impact on slepton search
capabilities 4. Crossing angle and
luminosity spectrum measurement
10 D. Miller/UCL 5.  News
from the ALPCG SLAC Workshop
20 E.
Torrence/Oregon 6. Polarisation effects of the
crossing angle
10 K. Mönig/DESY 7.
Review of arguments for upstream / downstream
polarimetry 15 G.
Mortgat-Pick/Durham





P. Schüler/DESYTentative conclusion
further work concerning impact on energy and
polarisation 8. Status of the
detector background simulations Comparison
of recent beamstrahlung pair calculations
20 K.
Büsser/DESY 9. Electron identification veto
in the LCAL / LumCAL Comparison with recent
results from Takashi Maruyama
20 K. Kousnetzova/DESY 10. Update
on gamma-gamma to hadrons calculation
20 T.
Barklow/SLACTentative conclusion further work
concerning requirements on the background  and
very forward region


meeting agenda of the physics evaluation http//ww
w-flc.desy.de/bdir/BDIRmeetings.html
Conclude by LCWS04 - strengthen international
collaboration (GLC)
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SUSY motivation for head-on mode

• Some popular dark matter SUSY explanations need
  the LSP ?0 to be quasi mass-degenerate with the
  lightest sleptons ?, ?,
• ? co-annihilation
  mechanism
• mSUGRA new dark matter constraints from WMAP
  cosmic microwave background measurements point in
  this direction
• Scenario considered also relevant more generally
  in the MSSM

Acceptable solutions in mSUGRA
M. Battaglia et al. hep-ph/0306219
co-annihilation example with g-2 constraint J.
Ellis et al. hep-ph/0310356
4
efficient / hermetic ?? veto crucial for ?
measurement
Signal
Main background ee ? ? ?0 ? ?0
ee ? (e)(e) ? ?
? 10 fb
? 104 fb
Transverse view
imperfect spectator electron veto ? R 1.2 cm
hole at 20 mrad ? 10-3 background efficiency

• Important LC channel, complementary to LHC
• Precise slepton masses ? DM ? CMB constraints
  from Planck
• ( luminosity energy strategy ) (
  LC ? cosmology )

5
Forward region geometries

• Specs for study
• l 4.1m ? veto at 3.7m
• holes 1.2cm radius
• (2.1cm likely for x-angle)

1. head-on 1 bunch 2. x-angle 1 bunch 3.
x-angle n bunches (pile-up)
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Ideal vs. realistic veto and head-on vs.
cross-angle
from Z. Zhang
in-coming beam hole
rout2.1cm instead of rout1.2cm

• Low angle veto essential to reduce
  photon-photon background
• Veto power is better in head-on collision mode

7
Preliminary ? result benchmark point
D with ?m?-? 12 GeV
from Z. Zhang
After requiring Nm2
Normalized for L500fb-1
cuts valid for both head-on and crossing-angle
collisions

• signal efficiency 80
  spectrum end-points preserved
• ? ms? and mLSP can be measured with precision for
  this benchmark point
• ? more model-independent smallest ?m s?-?
  detectable wrt to veto angle and quality ?

8
Preliminary ? result benchmark point D with
?m?-? 5 GeV
from Z. Zhang
Thrust axis angle in 3-dim
? PT sum wrt thrust axis in the transverse plane
Azimuthal dependance in the transverse momentum
degradation visible but not huge

head-on
crossing-angle
signal efficiency 11
8
S/B ratio
3.1 ? 1.3 2.4 ?
1.1 Caveat 1 TESLA ? electron veto
efficiencies with beamstrahlung pairs from
single bunch crossing warm LC
will need fast read-out (RD?) to avoid
pile-up Caveat 2 some physics backgrounds still
need to be fully included in the analysis
9
Preliminary slepton study by
H.U. Martyn
10
Effect of crossing-angle on cms energy calibration

• Acollinearity angle of Bhabha events monitor the
  luminosity-weighted centre-of-mass spectrum in
  the presence of ISR and beamstrahlung
• radiation 0 ? changes in angles from the
• 0.01ECMS transverse boost in a 20 mrad
• crossing-angle are corrected perfectly
• radiation gt 1 ? use calorimetric information
• radiation lt 1 ? use approximate correction
• ( very good for symmetrical
  radiation)
• ? simulation exercise started to check magnitude
  of potential bias
• Desired precision few 10-4 - 5 10-5 for top W
  masses
• (10-5 -
  10-6 to improve MZ measurement)

S. Boogart D. Miller
T. Barklow
11
Steering and depolarisation from the solenoid
with a 10 mrad crossing-angle
K. Mönig ( M. Woods)

• Solenoid B field not aligned to momentum ?
  deflection 0.4 mrad
• (assumes total length 8 m, B 4 T, Eb
  250 GeV)
• 100 longitudinal polarisation ? spin precession
  to IP 115 mrad
• is known and can be corrected ? ?P 1-
  cos(0.115) 0.7
• If measurement error of polarimeter ?P 0.5 ?
  additional spin misalignment 100 mrad ? ?P
  cos(0.115) cos(0.215) 1.6 !
• Must include effects from fringe fields ? ?P
  0.7

• Physics requirement
• new physics searches SM tests _at_ HE
  SM tests _at_ GigaZ
• ?P 0.5 ?P
  0.2 - 0.1 ?P lt 0.1
• extra vertical bends ( some tuning ) required
  to correct for both effects ( M. Woods et al. are
  working on this )

G. Mortgat-Pick
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Energy and polarisation calibration strategies

• Physics channels (Bhabhas, radiative Z returns,
  WW, We?) give the relevant luminosity-weighted
  information ? but need statistics
• pre-IP calibration needed to monitor incoming
  changes in E and P
• post-IP very desirable to measure beam-beam
  effects and validate
• simulated predictions and biases they
  provide important redundancy and can also be used
  in single-beam mode

Head-on collisions ? post-IP diagnostics
quasi-impossible
how essential are they ?
P. Schüler
E. Torrence
Beam-beam depolarisation 1. spin precession in
the magnetic field 2. spin-flip probability in
beamstrahlung total depolarisation 4 ? lumi
- weighted
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Bottom-line on crossing-angle-or-not physics
implications (preliminary)

• Head-on is quantifiably
• better for some topics
• while crossing-angle is
• preferable for some others
• Both are acceptable for
• physics
• With TESLA one can in principle choose one or the
  other
• ? Proposed intermediate
• solution 0.3 mrad x-angle

Comparison and optimisation of cold/warm very
forward veto capability and more comprehensive
background studies seem more important
14
Pair deposition and electron ID in the
BeamCAL/LumCAL
K. Büsser E. Kousnetzova T. Maruyama K. Mönig A.
Stahl
Large fake-rate if more than 3 bunch crossings
pile-up
15
background calculation
T. Barklow
Assume constant for
Ecm (GeV)
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Tracker Occupancy ( hits / train) / channels
T. Barklow