1. Discrimination of new physics models with ILC
arXiv: , Submitted to PRD
Taikan Suehara (ICEPP, The Univ. of Tokyo),
M. Asano(Tokyo), T. Saito(Tohoku), K. Fujii(KEK), R.S. Hundi(IACS), H. Itoh(Tokyo), S. Matsumoto(Tokyo), N. Okada(Alabama), Y. Takubo(KEK), H.Yamamoto(Tohoku)

2. Introduction ‘New physics with a WIMP’ is a charming scenario
Dark matter
Hierarchy problem
If LHC finds a hint of that, the characteristics must be investigated in detail -> ILC!
‘Spin of new particle’ is a first discriminator of the new physics models -> We investigate it in ILC.

3. Three models Inert Higgs SUSY Littlest Higgs with T-parity
WIMP: hI (scalar)
Visible: h± (scalar)
SUSY
WIMP: c0 (fermion)
Visible: c± (fermion)
Littlest Higgs with T-parity
WIMP: AH (vector)
Visible: WH± (vector)
All give 2W + 2WIMP fs.

4. Sample points/tools 2 points (the same for 3 models)
Point I: m(c+) = 232 GeV, m(c0) = 44.0 GeV √s = 500 GeV, 500 fb-1, full simulation
Point II: m(c+) = 368 GeV, m(c0) = 81.9 GeV √s = 1 TeV, 500 fb-1, fast simulation
Cross section is normalized (200fb & 40fb).
NO Initial polarization
Use W hadronic decay (cut leptonic events)

5. Basic strategies Selection by cuts Mass determination
Individual optimization for Point I/II studies
Mass determination
Fit to identify edges of W energy spectrum
Separate three models by spin
Production angle of c+- pair
Threshold scan
3 point scan with 50 fb-1 each

6. ILD detector & framework
Event generation (signal, SM background)
Stdhep event files
Full-MC simulation (GEANT4)
Hit, MC info(LCIO file)
Tracking
Particle Flow
Flavor tagging etc.
Event reconstruction
ILD detector (ILD00)
Vertex: Si pixel (3x2 layers)
Silicon Tracker: 4 layers
TPC(main tracker)
ECAL (0.5x0.5 cm tile, Si/W)
HCAL (3x3 cm tile, Sci/Fe)
Solenoid (3.5Tesla)
Muon detector
Particle information (ROOT tree)
Analysis
Event weighting
Separation cuts
Analysis (mass, angle…)

7. Selection cuts (Point I)
BG suppression cuts
“qqqq (non-b) + missing”
　4-jet clustering (Durham)
　# Track >= 20
　160 < Evis < 400 GeV
　each Ejet > 5GeV
　|cosq|jet < 0.99
　unlike 3jet (yth,3 > 0.001)
　each jet has >= 2tracks
　no > 25 GeV leptons
　 |cosq|miss < 0.9
　sum |cosq| < 2.6
　sum b-quark prob. < 1
　kinematic fit converged
　65 < mW < 95 GeV

8. Selection efficiency (Point I)
IH eff: 59.8%, pur (200 fb): 78.6%, pur (40 fb): 42.3%
SUSY eff: 58.3%, pur (200 fb): 77.7%, pur (40 fb): 41.0%
LHT eff: 58.9%, pur (200 fb): 78.2%, pur (40 fb): 41.8%
Acceptable selection performance

9. Mass determination PII PI 200 fb (w/bg) 40 fb (bg sub- tracted)
Empirical function with edges

10. Mass resolution Point I (MC: 231.6/44.0) Point II (MC: 368/81.9)
Visible
(200 fb)
WIMP
(40 fb)
IH-like
232.9 ± 0.1
44.2 ± 0.6
231.8 ± 0.4
46.2 ± 1.9
SUSY-like
232.7 ± 0.1
43.6 ± 0.7
232.2 ± 0.5
45.8 ± 2.3
LHT-like
232.1 ± 0.1
43.8 ± 0.5
231.5 ± 0.5
45.9 ± 1.8
Visible
(200 fb)
WIMP
(40 fb)
IH-like
367.4 ± 0.9
81.2 ± 1.1
366.5 ± 3.4
80.5 ± 4.7
SUSY-like
368.5 ± 0.8
81.6 ± 1.1
370.7 ± 2.8
82.5 ± 4.5
LHT-like
367.5 ± 0.6
82.1 ± 0.8
367.2 ± 2.0
84.0 ± 2.7

11. Production angle
Production angle of the visible new particle can be calculated from W directions with masses of new particles and back-to-back assumption.
The angle has spin info. but two-fold ambiguity (solution of 2nd equation) exists.
~30 % of the events are cut out because of negative discriminant.

12. Reco. (2 solutions added)
1D distribution PI
PII
MC truth
Reco. (2 solutions added)

13. 2D distribution
PII PI
Similar distributions between SUSY – LHT in Point I
Other pairs seem to be distinguishable
Obtain c2 of toy-MC data (with Poisson fluctuation) to each template

14. Chi-square distributionsPI
PII

15. Separation power results
Separation power is defined as (reduced c2 – 1) divided by width of (data = template) distribution PI
PII
200 fb
IH-like tmpl.
SUSY-like tmpl.
LHT-like tmpl.
IH-like - 63 43
SUSY-like 53
4.9
LHT-like 35
200 fb
IH-like tmpl.
SUSY-like tmpl.
LHT-like tmpl.
IH-like -
109
82.5
SUSY-like
216
75.0
LHT-like
156
46.0
40 fb
IH-like tmpl.
SUSY-like tmpl.
LHT-like tmpl.
IH-like -
8.9
6.0
SUSY-like
7.5
0.7
LHT-like
4.9
0.8
40 fb
IH-like tmpl.
SUSY-like tmpl.
LHT-like tmpl.
IH-like -
29.1
23.9
SUSY-like
46.8
21.6
LHT-like
30.9
9.4

16. Threshold scan PI
PII
s ~ (s-s0)0.5 (SUSY), (s-s0)1.5 (IH/LHT) near threshold
Cross section vals at 3 CMS points are fitted by two functions,
Obtain chi2 to each func. with 50 fb-1 luminosity (x3 pts)
Background, cut eff. is assumed to be same as the previous analysis
a, s0 : free params

17. Threshold scan, chi2 PI
PII
Power of 0.5
Power of 1.5

18. Summary We studied model separation using spin
Inert Higgs (scaler), SUSY (fermion) and LHT (vector)
Separation possible in both point I & II with 40 fb, 500 fb-1 statistics
For Point I, separation can be completed with combination of production angle (IH-like & others) and threshold scan (SUSY-like & others)
For Point II, production angle is enough
Future works
Mass dependence
t-channel contribution

19. Thank you for listening.