Summer School on Particle Physics

Transcription

1 44 Summer Scool on Particle Pysics 6-7 June 0 Dawson Sally Brookaven National Laboratory USA

2 EWSB Beyond te Standard odel Trieste, 0 S. Dawson (BNL)

3 Supersymmetric odels as Alternative to Standard odel any New Particles: Spin ½ quarks spin 0 squarks Spin ½ leptons spin 0 sleptons Spin aue bosons spin ½ auinos Spin 0 is spin ½ isino Unbroken supersymmetry deenerate masses of partners SUSY must be a broken symmetry

4 Supersymmetric Teories Predict many new undiscovered particles (>9!) Very predictive models Can calculate particle masses, interactions, everytin you want in terms of a few parameters Solve naturalness problem of Standard odel Any Supersymmetric particle eventually decays to te litest supersymmetric particle (LSP) wic is stable and neutral (assumin R parity) Dark atter Candidate

5 SUSY odels Unify Couplin constants cane wit enery Assume new particles at TeV scale SUSY odel S

6 SUSY.Our favorite model Quadratic sensitivity to i scale pysics cancelled automatically if SUSY particles at TeV scale Cancellation result of supersymmetry, so appens at every order t ~ t (...) G F ( t ~ t ) Stop mass sould be TeV scale

7 Supersymmetry (SS version) Good areement wit EW measurements if SUSY masses are - TeV

8 Fermion asses In Standard odel, m u from c =i * L S Q u L c u R c 0 SUSY models don t allow c interactions Supersymmetric models always ave at least two is doublets wit opposite ypercare in order to ive mass to up and down quarks c mu u v S

9 General is Doublet odel 6 free parameters, plus a pase W and Z masses just like in Standard odel parameter: sin ) Im( cos ) Re( ) )( ( ) )( ( ) ( ) ( ) ( ) ( ), ( v v v v v v v v V i e v v 0 0 ) ( v v W cos W Z W = for any number of is doublets or sinlets

10 is Potential Restricted in SUSY odels 0*! 0 Two is doublets wit opposite ypercare Quartic couplins fixed by supersymmetry as Y=-/, as Y=+/ [ Q em =(T 3 +Y)/ ] SUSY Potential as F and D terms: V F a i a i a D T V * * * () : () : j a ij i j a ij i SU U Gaue couplins / enerators

11 SUSY Potential SU() identity: Scalar potential V is positive definite: minimum at <V>=< >=< >=0 kl ij jk il a kl a ij * * * V D * 8 V No electroweak symmetry breakin!

12 Te SS Pilosopy If m =0, potential is positive definite and no symmetry breakin ' 8.). ( c m m m V b a ab Gaue Couplins Add all soft (dimension 3 or less) terms allowed Tey don t introduce quadratic contributions Potential as 3 free parameters ( of wic is fixed by W )

13 inimize Potential inimize potential inimization conditions: * * 0 0 m m V m m V sin m m m 4 tan tan v v m m is naturally of O( Z ) Z

14 EWSB and SUSY odels Electroweak symmetry broken by vevs v 0 0 v W ets mass, W = (v +v )/ 5 Pysical is bosons, 0, 0,, A 0 free parameters, typically pick A, tan =v /v Predict,, A m A tan cot W

15 Neutral is asses cos 4, A Z Z A Z A Neutral is mass matrix diaonalized wit mixin anle cos cos Z A < Z cos Teory implies lit is boson!

16 Teoretical Upper Bound on At tree level, < Z Lare corrections O(G F m t ) Predominantly from stop squark loop 4 3G ~ Fmt mt Z cos ln sin mt Stop mass sould be TeV scale for naturalness

17 Teoretical Upper Bound on Upper bound on litest neutral is boson mass wit m stop = TeV t4 enancement Loaritmic dependence on stop mass

18 is asses in SS A W Lare A : Deenerate A,, and lit

19 Find is Couplins is-fermion couplins: md L dd cos W mu uu sin W imd tan cos sin d 5dA im cot d sin cos u ua W W 5 Couplins iven in terms of, Can be very different from Standard odel No new free parameters

20 is Couplins Different from S Couplins to d, s, b enanced at lare tan for moderate A Litest Neutral is, S Couplins to u, c, t suppressed at lare tan for moderate A S Decouplin limit: For A, couplins o to S couplins

21 is Couplins in SUSY eavier Neutral is, Couplins to d, s, b enanced at lare tan Couplins to u, c, t suppressed at lare tan

22 Gaue Boson Couplins to is VV + VV = VV (S) Vector boson fusion and W production always suppressed in SS VV, smvv VV, smvv sin cos Normalized to S couplins

23 Tools Calculate S and SS is brancin ratios: DECAY ttp://people.web.psi.c/spira/decay/ Calculate SS is masses and is brancin ratios: FEYNIGGS ttp:// Bot of tese prorams are very easy to use!

24 Limits from LEP cos A Complementary processes sin

25 Limits on SUSY is from LEP Active work on evadin assumptions of tis plot! t =69.3,74.3, 79.3, 83 GeV

26 Remember is Decays in S S: is brancin rates to bb and + - turn off as rate to W + W - turns on ( > 60 GeV)

27 is Decays Caned at Lare tan SS: At lare tan, rates to bb and + - lare eavy 0 SS BRs A 0 SS BRs Rate to bb and + - almost constant in SS for, A

28 Lare tan Canes Relative Importance of Production odes A b b tan 7, bb production mode larer tan b, t tan= tan=40 A 4 4 tan c m b bb tan= tan cot b b m c m c c

29 is Production Can be Larer tan S SUSY is: tan enanced couplins to b and for,a Production wit b s dominates for lare LC eavier neutral SUSY is

30 New is Discovery Cannels in SUSY bb couplin enanced for lare tan

31 any Possibilities Beyond SUSY Add sinlet is and try to evade LEP bounds Two is doublets, but not SUSY Same spectrum as SUSY ust measure is couplins Little is odels ave extended aue sectors and new care /3 quarks Effective Laranian approac needed to study EWSB sector if no new particles found at LC

32 Possibilities at te LC We find a lit is wit S couplins and notin else ow to answer our questions? We find a lit is, but it doesn t look S like ost models (SUSY, Little is, etc) ave oter new particles We don t find a is (or any oter new particles) ow can we reconcile precision measurements? Tis is te ardest case

33 Te fun is just beinnin appy is untin!