After Discovery: Exploring Higgs Properties. S. Dawson BNL Jan 11, 2012

Transcription

1 After Discovery: Exploring Higgs Properties S. Dawson BN Jan 11, 01 1

2 Suppose we find a Higgs-like Object? H (GeV) H (GeV) What comes next?

3 Our Prejudices say the Higgs is ight asses inferred from precision measurements and Higgs searches* asses inferred from precision measurements W (GeV) S Predictions Higgs boson wants to be light t (GeV) * Post-ICHEP 011 3

4 From Gfitter (011) Higgs imits If you don t include direct search limits for Higgs, 95% C upper bound: H < 169 GeV If you include EP, Tevatron, HC limits, 95% C upper bound: H < 143 GeV Test of consistency of Standard odel Not hard to fit bounds with new physics *Post-ICHEP011 4

5 inimal Higgs theory is predictive Higgs couples to fermion mass argest coupling is to heaviest fermion m v ffh Top-Higgs coupling plays special role? No Higgs coupling to neutrinos Higgs couples to gauge boson masses g f W W W Only free parameter is Higgs mass m H v f f f R g Z cos W f Z R f Z H H... 5

6 Very Precise Predictions Precise predictions from HC Higgs cross section working group argest production channel, gg H, can have contributions from unknown new physics in loop HC Higgs Xsections: arxiv:

7 Where do uncertainties come from? Unknown higher order terms (TH) Scale dependence (TH) PDFs/ s (TH + EXP) Other parameters: m b,. (TH+EXP) Effects of cuts (TH + EXP) Do cuts script the result? BS effects (TH) This is the biggest unknown ij f x 1) f j ( x ) ij sˆ, k, n, cuts... i( 7

8 Do Theory Errors atter? Useful to have limits for individual channels H (GeV) 8

9 Higgs Searches What do they mean? Do the limits tell us anything about physics at the TeV scale? We measure the event rate in each channel: B ( pp H X ) ( pp H ) BR( H X ) imits tell us that if H >135 GeV (pp H) < S (pp H) or BR(H X) < BR(H X) S 9

10 10 easure couplings to fermions & gauge bosons easure spin/parity easure self interactions ake sure there s only one Higgs-like particle 3 ) ( ) ( m m H bb H b 0 PC J H v H v H V H H H Is it the Higgs?

11 Standard odel Higgs Gluon fusion rate is extremely sensitive to BS physics argest contribution is top loop b-loop contributes ~-5% Predictions at NNO, NNN all assume S 11

12 Explore BS Contributions to gg H any possibilities: Supersymmetry (squarks in loop) Color octets New operators present in strongly interacting theory New fermions How far can Higgs production get from the S prediction? See talks by Rattazzi, Wulzer, Santiago, Harlander 1

13 Effective Theory anguage for gg H eff NO(pb) g 16 s 1 3 F log gg H, s=7 TeV H v NO H (GeV) H G A G A, True when only source of mass is EWSB and t >> H Effective theory accurate except near tt threshold eff verified at NNO in S: See Harlander talk 13

14 Example: Heavy Fermions If fermion gets mass from Spontaneous Symmetry Breaking, then m Q ~ v If mass from Yukawa couplings, nm =y nm v Generalize low energy theorem: eff F H A A, G s 1 v log( F ) G F log( v) Use ow Energy Theorem for BS models and test gg H rate Falkowski, arxiv: ; ow and Vichi, arxiv: ; ow, Rattazzi, and Vichi, arxiv:

15 15 Chiral Fermions Suppose there are chiral fermions contributing to gg H Fermions might be too heavy to observe directly Simplest example is 4 th generation Restricted by precision measurements R R R R E N E N D U D U,,,, ln ln D U E N E N D U W W Y Y S s T Adjust masses Kribs, Plehn, Spannowsky,Tait, arxiv:

16 S 4 th Generation Allows Heavy Higgs S 4 th generation almost gone H =600 GeV gg H enhanced by ~9 in 4G model H decay suppressed in 4G model H (GeV) Rate known at NNO: Anastasiou, Buehler, Furlan, Herzog, azopoulos, arxiv: ; Anastasiou, Boughezal, Furlan, arxiv: EW corrections to decay: Denner et al, arxiv:

17 UED odels Universal extra dimension models have new chiral fermions odels have heavy copies of top quark, T n T n doesn t get all of its mass from EWSB Higgs couplings to T n ~ ( t /v)( t / Tn ) T Tn ~1/R S 17

18 Higgs Production can t get too far from S Allowed couplings restricted by STU gg H, s=14 TeV Tn =500,700,1000, 150,1500 GeV / H (GeV) odels with new chiral fermions tend to have enhanced gluon fusion rate Petriello,

19 ittle Higgs odels ittle Higgs like models Higgs is Goldstone Boson of broken global symmetry Top quark has a weak singlet partner which mixes with top Higgs production can be significantly suppressed (gg H)/S Note decoupling for large f f/f min [ow & Vichi] f min is minimum scale allowed by precision EW ( GeV) 19

20 Top Seesaw, ittle Higgs. These are all just special cases of models with with weak singlet vector like charge /3 quark, U, which mixes with S-like third generation q ~(u,d ), u R, d R Generic mass matrix ~ ~ aq Hu bq HU cu u du U hc d is Dirac mass, typically >> other parameters Physical top is mixture of (u, U) t T R c s R s c u U R R SD, Furlan, in preparation 0

21 1 Interesting Effects Assume d >> a,b,c T ~ d s ~ vb/ T Constraints from S/T/U Higgs production from gluon fusion: 5 log 18 1 log 16 t T T W W c t T T t c m s b N S m m b N T Decoupling for large T (General property of vector like fermions) 1 T t S gg m b Same scaling observed in composite Higgs models

22 imits from STU Global Scan Can t go too far from the S (the moral of this story) T H =10 GeV T (GeV) s(max) aximum mixing allowed by STU scan T (GeV) For heavy Higgs: Bai, Fan, Hewett, arxiv:

23 NNO with Vector Fermions Compute gg H for arbitrary fermions and Yukawa couplings: IHIXS Only a few diagrams which mix mass scales gg H, s=7 TeV H =10 GeV, T = 1TeV Rate suppressed from S (pb) ow energy theorems very accurate b IHIXS: Furlan, arxiv: ; Anastasiou, Buehler, Herzog, azopoulos, arxiv:

24 Framing the Question Experiments limit B/ (B) S How low do we need to go? New physics limited by direct search and by STU Direct channels (VBF, VH, tth) critical because they are not sensitive to BS loops at leading order 4

25 easuring Higgs Couplings S coupling measurements with 30 fb -1 at 14 TeV gh 10-30% measurements for H =10 GeV H (GeV) Parameterize couplings in terms of deviation from S g H ~g S (1+) Coupling measurements: Rauch, arxiv: ; afaye, Plehn, Rauch, Zerwas, arxiv:

26 Direct easurements Crucial VH, VBF, tth measure couplings directly WH known at NNO, tth & VBF at NO Reliable theory predictions VH can give Hbb coupling, tth gives Htt coupling odern studies rely on high p T region Now have distributions at NO Theory uncertainties larger at tails of distributions Direct processes implemented in POWHEG, mc@no (see Frixione talk) Time to rethink tth! Higgs XSection Working Group YR 6

27 Can we reconstruct the Higgs potential? H 3 4 V H 3vH 4 H 4 S : 3 4 v H Fundamental test of model! 7

28 Double Higgs Production from Gluons Sensitive to heavy fermions (top quark) Contribution is dominantly triangle Destructive interference g H g H ~ t ~ t 3 S: loops are mostly top, but sensitive to BS physics 8

29 Small rate for HH production (pb) For H =160 GeV, 10 events in all channels with 3 fb -1 H (GeV) HH Production can be enhanced in models with new physics 9

30 Small sensitivity to HHH coupling Can we do better? pp H H W + W - W + W - leptons + 4 jets 3 For lighter Higgs try HH bb H (GeV) [Baur, Plehn, Rainwater 00] 30

31 easuring Higgs Self-Couplings Need this to nail down EWSB mechanism Small rates for gg HH Very (!) hard at HC 150 < H < 00 GeV, HC (300 fb -1 ) can exclude no self coupling C.. (14 TeV) H < 140 GeV, need 6000 fb -1 to measure -.66 < HHH <.8 Physics driver for next generation machine [Baur, Plehn, Rainwater] 31

32 Single Higgs vs Double Higgs Production New physics can affect single and double Higgs production differently Heavy fermions which get mass from entirely from EWSB contribute to effective operator (low energy theorems): O s HH s H H C GG log CG G 8 v 4 v v New physics can induce operator: O 1 s HH s H H C 1GG C1G G 4 v 4 v v 3

33 New Physics changes -Higgs Production Easily get enhancements of 10-0 in -Higgs total rate Distributions very different with BS physics (gg HH)(pb/50 GeV) S HH (GeV) S-like fermion: c 1 =0,c =4/3 BS physics large in tails of distributions Effective theory: Pierce, Thaler, Wang, arxiv: Color Octets: Dobrescu, Kribs, artin, arxiv:

34 Higgs Spin If we see H Higgs can t be spin 1 Correlations in decay angles of H ZZ l + l - l + l - can determine Higgs spin (if there are enough events) ultivariate analysis, 10 fb -1 gives 3 significance for H =00 GeV Number of events H ZZ 4l, H =150 GeV 100 fb -1 at s=14 TeV How to get to lower H? BR(H ZZ) falls rapidly with decreasing H H (GeV) iller et al, hep-ph/01003; ykken et al, arxiv:

35 Conclusions Once we find the Higgs boson, we re just beginning the exploration of EWSB Need to measure couplings and spin Need to check for more Higgs-like particles Higgs production is a window into BS physics Sensitive to whether fermion masses come from EWSB Sensitive to new operator structures Double Higgs production can potentially discriminate between models 35

36 Pheno 01: ay 7-9, oopfest XI, ay