P. Bambade, LAL/Orsay TESLA collaboration meeting APDG session 22/1/2004 1 Crossing-angle-or-not physics implications report from 19-01-04 phone-meeting

P. Bambade, LAL/Orsay

TESLA collaboration meeting APDG session 22/1/2004

1

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

cold crossing-angle head-on

warm crossing-angle -

physics issues

evaluated

more IP tuning optics design constraints crab-cavity req. beam(strahlung) extraction SC mini-quad. electrostatic separators backgrounds collimation get worse at 1 TeV

technicalissues

hermetic veto post-IP diagnostics

transverse boost for energy and B and P not polarisation

no killer arguments either way - quantify physics impact consensually



2

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/DESY

Tentative 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/DESY

Tentative 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/SLAC

Tentative conclusion & further work concerning requirements on the background and very forward region

meeting agenda of the physics evaluationhttp://www-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

M. Battaglia et al. hep-ph/0306219

co-annihilationexample with g-2 constraint

J. Ellis et al. hep-ph/0310356

Acceptable solutions in mSUGRA:



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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 )



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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

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

rout=2.1cminstead ofrout=1.2cm

in-comingbeam hole

from Z. Zhang



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Preliminary result benchmark point D’ with m- = 12 GeV

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 ?

After requiring N=2 Normalized for L=500fb-1

from Z. Zhang

cuts valid for both head-on and crossing-angle collisions



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Preliminary resultbenchmark point D’ with m- = 5 GeV

Thrust axis angle in 3-dim

PT sum wrt thrust axisin the transverse plane

Azimuthal dependance in the transverse momentum

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 (R&D?) to avoid pile-upCaveat 2 : some physics backgrounds still need to be fully included in the analysis

from Z. Zhang

degradation visible but not huge



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Preliminary slepton study by H.U. Martyn



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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

0.01*ECMS transverse boost in a 20 mrad crossing-angle are corrected perfectly• radiation > 1% use calorimetric information• radiation < 1% use approximate correction( : “very good for symmetrical radiation”)

simulation exercise started to check magnitude of potential biasDesired precision ~ few 10-4 - 5 10-5 for top & W masses

(10-5 - 10-6 to improve MZ measurement)

* *'Reconstructed cot cot

2 2

s

s

S. BoogartD. Miller

T. Barklow



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Steering and depolarisation from thesolenoid with a 10 mrad crossing-angle• 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 %

K. Mönig(+ M. Woods)

Physics requirementnew physics searches SM tests @ HE SM tests @ GigaZ P ~ 0.5 % P ~ 0.2 - 0.1 % P < 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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1. Physics channels (Bhabhas, radiative Z returns, WW, We) give the relevant luminosity-weighted information but need statistics

2. pre-IP calibration needed to monitor incoming changes in E and P3. 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

Energy and polarisation calibration strategies

Head-on collisions post-IP diagnostics quasi-impossible

how essential are they ?

P. SchülerE. Torrence

Beam-beam depolarisation1. spin precession in the magnetic field2. 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 othersBoth 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



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1

2

3

45

6

X (cm)

Y (

cm)

100

80

60

40

20

0

Det

ectio

n E

ffici

ency

(%)

25020015010050

Energy (GeV)

1 2 3 4 5 6

40

30

20

10

0

Fa

ke R

ate

(%

)

7654321

No. of Bunches

2.0 - 2.5 cm 2.5 - 3.0 3.5 - 4.0 4.0 - 4.5 4.5 - 5.0

BG

SiLayers

Dep

osit

ed E

nerg

y (a

rb. U

nits

)

250 GeV e-

K. BüsserE. KousnetzovaT. Maruyama

K. MönigA. Stahl

Pair deposition and electron ID in the BeamCAL/LumCAL

Large fake-rate if more than 3 bunch crossings pile-up



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Ecm (GeV)

( )b

2.1 0.370{1 0.01[ln( )] 1.96 }s s

Assume constant for 0.3 1.5s GeV

T. Barklow

hadrons background calculation



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Tracker Occupancy = (# hits / train) / # channels

T. Barklow

Documents

P. Bambade, LAL/Orsay TESLA collaboration meeting APDG session 22/1/2004 1 Crossing-angle-or-not physics implications report from 19-01-04 phone-meeting