LHeC Steering Committee meeting, 27 Oct. 2007

1. LHeC and Physics Beyond the Standard Model Emmanuelle Perez CERN • Sensitivity to new physics in ep collisions at 1.4 TeV : • quark radius, electron-quark resonances, • eeqq contact interactions. • LHeC w.r.t. the interpretation of LHC discoveries : • are there limitations due to our limited • knowledge of high x pdfs ? • Crude studies so far, and only a few topics. 3 June 2006 LHeC Steering Committee meeting, 27 Oct. 2007

2. Beyond the Standard Model in ep collisions : introductory remarks • Since ep is not an annihilation machine, the cross-section is “small” • for (heavy) pair-produced new particles. •  Investigate single particle production instead •  The sensitivity depends, in addition to the new particle mass, on • its coupling to SM particles. •  In case of a discovery: information not only on M but also on this • coupling. • Examples : Leptoquarks, Rp-violating SUSY, excited fermions, … • HERA vs. Tevatron showed nice examples of the complementarity between • both facilities, in such model-driven BSM searches. • Once LHC has discovered “something”, additional data from ep and/or ee • may be necessary to tell what the “something” is. October 07

3. 2 < > r 2 2 f( ) 1 - Q Q = 6 Assign a finite size < r > to the EW charge distributions : d/dQ2 = SMvalue x f(Q2) DIS at highest Q2 : towards quark substructure ? Global fit of PDFs and < r > using d/dxdQ2 from LHeC simulation, 10 fb-1 per charge, Q2 up to 500000 GeV2 : < rq > < 8. 10-20 m One order of mag. better than current bounds. At LHC : quark substructure may be seen as a deviation in the dijet spectrum. Such effects could also be due to e.g. a very heavy resonance. Could we establish quark substructure with pp data only ? October 07

4. e+  (unknown) coupling l-q-LQ ’1jk Rp _ dk ( u j ) ~ ~ u Lj ( dRk*) Electron-quark resonances Apparent symmetry between the lepton & quark sectors ? Exact cancellation of QED triangular anomaly ? • “Leptoquarks” (LQs) appear in many extensions of SM • Scalar or Vector color triplet bosons • Carry both L and B, frac. em. charge difficult, large backgrounds LQ decays into (lq) or (q) : • ep : resonant peak, ang. distr. • pp : high ET lljj events Such eq resonances also predicted in Supersymmetry with “R-parity” violation: e+ and e- probe different squarks & couplings Example: resonant stop production in e+ p, resonant sbottom in e- p. October 07

5.  A.F. Zarnecki • Tevatron probes large masses for large •  (LQ  eq)independently of . • But large  (LQ  q) is difficult. em • HERA better probes LQs with small  • provided that  not too small LHC pair prod LHeC 1 TeV MLQ (GeV) “Leptoquarks” : pp versus ep  = BR( LQ  eq )  = BR (LQ  eq) • LHC vs LHeC : MLQ (GeV) LHC could discover eq resonances with a mass of up to 1.5 – 2 TeV via pair production. Quantum numbers ? Might be difficult to determine in this mode. October 07

6. + e F = -1 * e q _ F = +1 q e, _ q or q ? q e+ q or q ? e- Determination of LQ properties pp, pair production ep, resonant production • Fermion • number F=0 LQs : (e+) higher F=2 LQs : (e- ) higher (high x i.e. mostly q in initial state) _ _ • Scalar • or • Vector cos(*) distribution gives the LQ spin. qq  g  LQ LQ : angular distributions depend on the structure of g-LQ-LQ. If coupling similar to WW, vector LQs would be produced unpolarised… • Chiral • couplings Play with lepton beam polarisation. ? October 07

7. F = 2 F = 0 ep : golden machine to study LQ properties F = 0 or 2 ? Compare rates in e-p and e+p Spin ? Angular distributions Chiral couplings ? Play with polarisation of lepton beam Couples to  ? Easy to see since good S/B in j channel Classification in the table below relies on minimal assumptions. ep observables would allow to disentangle most of the possibilities (having a polarised p beam would complete the picture). October 07

8. F=0  e+ g q q e- “LQ spectroscopy” : LHeC versus single LQ production at LHC Single LQ production at LHC brings information in principle. But cross-section e.g. at 1 TeV is a factor ~ 400 lower than at LHeC. Example : Fermion Number F. Look at signal separately when resonance is formed by (e+ + jet) and (e- + jet). Sign of the asymmetry gives F, but could be statistically limited at LHC. Easier in ep ! LHeC: 10 fb-1 per charge  = 0.1 Idem for the simultaneous determination of coupling  at e-q-LQ and the quark flavor q. Asymmetry If LHC observes a LQ-like resonance, M < 1 TeV, with indications (single prod) that  not too small, LHeC would solve the possibly remaining ambiguities. LHC: 100 fb-1 MLQ (GeV) October 07

9. e e 0 ~ q q Pair production via t-channel exchange of a neutralino. • Cross-section sizeable when • M < 1 TeV i.e. if squarks are “light”, could observe selectrons up to ~ 500 GeV. • Could extend a bit over the • LHC slepton sensitivity • Possible information on • couplings by playing with • e+ / e- / L / R Beyond LQs… To be further studied :  SUSY with R-parity conservation ~  in pb, e- p  in pb, e+ p  Single production of excited fermions October 07

10.  Further models … Esp. models which predict new effects - “easy” to see in ep because of low, well-understood backgrounds - more difficult to establish in pp because of large bckgs Example from HERA experience: Anomalous top production via BSM coupling tu. Single top analysis at Tevatron is difficult (large W+jets bckgd). October 07

11. p structure & interpretation of LHC discoveries The interpretation of discoveries in AA at Alice may require direct measurements on pdfs in A – not covered here. Here, focus on ATLAS & CMS discoveries : highest masses  highest x. Constraints on d and g at high x still limited : October 07

12. _ d W ’ _ u s ’ ~ _  c Current high x uncertainties and NP processes at LHC : qq processes Example: new W ’, resonant slepton production in RpV SUSY (reach for a W’ with SM like couplings) CMS Physics TDR Vol II 40% uncertainty on part. lum. For a 6 TeV W ’.  g(W ’) ? RpV SUSY : reach would depend on the strength of the coupling ’ . With sea quarks involved, uncertainties large already well below the kinematical limit. Would make the measurement of the coupling difficult. October 07

13. Drell-Yan mass spectrum 4 TeV 8 TeV (shown uncertainties: from CTEQ 61 sets) CMS Physics TDR Vol II Example : new Z’ boson, KK gravitons in Randall-Sundrum models etc.. Signal = a mass peak. Partonic luminosities can be “normalised” to the side-bands data if enough stat. But close to the discovery limit, couplings of a Z’ boson may not be measured accurately. October 07

14. LHeC HERA  / 2  / 2 DY mass spectrum and “Contact Interactions” NP in Drell-Yan spectrum might not manifest itself as a mass peak… e.g. large extra-dimensions, interference with very heavy boson etc… Effective “contact-term” Lagrangian : d/ds = SMvalue + …  s /2 + … ( s / 2) 2 LHeC sensitivity (10 fb-1 e- & e+) : 25 – 45 TeV VV model VV model depending on the model Similar to the expected sensitivity at LHC. (GeV-2) October 07

15. eeqq Contact interactions in DY and DIS • LL model,  = 30 TeV, sign = -1 : • effect in DY can be “absorbed” in pdf unc. • In some cases, may be difficult to • determine the sign of the interference • of the new amplitude with SM. LHeC, e- p, LL • At LHeC, sign of the interference • can be determined by • looking at the asym. between • /SM in e- and e+. • Polarisation can further help • disentangle various models. October 07

16. Mc = 2 TeV Mc = 4 TeV S. Ferrag, hep-ph/0407303 High x gluon and dijets at LHC Some NP models predict deviations in dijet mass spectrum at high mass. Example : some extra-dimension models. Mjj (GeV) Mjj (GeV) Due to pdf uncertainties, sensitivity to compactification scales reduced from 6 TeV to 2 TeV in this example. [ sensitivity has to be checked taking into account jet energy scale uncert… ] October 07

17. Conclusions For “new physics” phenomena “coupling” directly electrons and quarks (e.g. leptoquarks, eeqq contact interactions) : LHeC has a sensitivity similar to that of LHC. The further study, in ep, of such phenomena would bring important insights : leptoquark quantum numbers, structure of the “eeqq” new interaction. These studies may be difficult, if possible at all, in pp. LHC sensitivity to new (directly produced) particles not much limited by our pdf knowledge. “Contact-interactions” deviations may be more demanding. However, the interpretation of discoveries at LHC may require a better knowledge of the high x pdfs : e.g. determination of the couplings of a W ’ or Z ’ if “at the edge” . October 07

18. Work ahead … (not an exhaustive list) • Determination of LQ quantum numbers at LHC : real MC analysis with realistic • simulation & backgrounds. • Contact interactions : systematic analysis of • - how pp data could discriminate between various models. • - the complementarity between pp, ep, ee (cf A. Zarnecki, Tevatron/LEP/Hera) • Assess the limitations due to our poor knowledge of high-x gluon in • searches with jets. • Further study of the LHeC potential especially in Supersymmetry. • If slepton + squark accessible at LHeC, what additional information do we • learn compared to LHC ? Need to involve people familiar with analysis in Atlas / CMS. Establish contacts on BSM at LHeC with theorists / phenomenologists. October 07

19. Backups October 07

20.   Single LQ production at LHC Single LQ production also possible at the LHC.  (pb) g LQ g LQ ep q q e- q e- pp •  ee followed by eq -> LQ not considered yet. Not expected to change much the results shown here (Tevatron). Smaller x-section than at LHeC. And large background from Z + 1 jet. 1200 GeV 200 GeV MLQ (GeV) Can be used in principle to determine the LQ properties in pp. October 07

21. ~ d d ~ d d Estimated LHC sensitivity (SUSY) ~ g Current high x uncertainties and NP processes at LHC : quark-quark processes (shown uncertainties: from CTEQ 61 sets) Example: squark production (pdf) on the relevant partonic luminosities instead of that on the  of a given BSM process. But better if couple to u quarks as well… For a process involving high x d quarks, pdf uncertainty ~ 20% at the corner of the LHC phase space. Could be ~ 50% with extended sensitivity (e.g. LHC upgrade) October 07