Future exotic physics at ZEUS and HERA

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1 Future exotic physics at ZEUS and HERA Matthew Wing (UCL) Introduction Inclusive measurements of deep inelastic scattering Deviations from the Standard Model and search for substructure Search for leptoquarks High p T lepton events from ZEUS Summary and prospects DESY seminar HH/Berlin, 4/5 January 006

2 Introduction Considering exotic, beyond the Standard Model searches for objects at high energy. Deviations from the Standard Model in inclusive reaction neutral and charged current deep inelastic scattering, jet production quark substructure, contact interactions right-handed charge currents leptoquarks Investigation of rare processes independent of model generic searches, e.g. high p T leptons Model dependent search for new particles leptoquarks R p -violating supersymmetry excited fermions

3 Should we look for everything? Where can increased statistics really help? Is a factor of 4 (L HERA II 4 L HERA I ) enough? Really want to discover something how useful is a new limit? already have a limit - is a discovery already ruled out? Factor of > in for e data can open up some opportunities Get a factor of from combining experiments Priorities, personpower and how it evolves

4 Inclusive cross section Measurements over 7 orders of magnitude in dσ/dq Demonstration of unification of electroweak force dσ/dq (pb/gev ) - HERA H e + p NC H e - p NC ZEUS e + p NC ZEUS e - p NC SM e + p NC (CTEQ6D) SM e - p NC (CTEQ6D) Input to fits to parton density functions Good description by the SM H e + p CC H e - p CC ZEUS e + p CC no new physics -5 ZEUS e - p CC SM e + p CC (CTEQ6D) set limits on quark radius, contact interactions, etc SM e - p CC (CTEQ6D) y < Q (GeV )

5 First (published) results from HERA II Measurements of charge and neutral current cross sections with polarised positrons H: DESY-05-49, ZEUS: with R-D.H. Preliminary measurements also with electrons. σ CC (e ± p) ± P e, σ NC (e ± p) H ± 0 P eh ± P e Sensitivity to right-handed W bosons, W R. Sensitivity at end of HERA II 400 GeV. (Note Tevatron lower bound is 800 GeV)

6 CC cross sections for polarised positrons + Charged Current e p Scattering (pb) σ CC 50 e + p νx H Data SM (H PDF 000) Linear Fit 0 Q > 400 GeV y < P e H Collaboration

7 CC cross sections for polarised leptons (pb) σ CC Charged Current ep Scattering (HERA II) e + p νx 50 H (prel.) H e p νx H (prel.) H ZEUS (prel.) ZEUS SM (MRST) ZEUS (prel.) ZEUS SM (MRST) 0 Q > 400 GeV y < P e Consistency with the SM - no right-handed charge currents

8 CC/NC cross sections for polarised leptons ZEUS dσ/dq (pb/gev ) ZEUS CC 04 e + p (.3pb - ) 04 e + p (.5pb - ) 3 4 (a) Q (GeV ) dσ/dx (pb) 3 - SM (ZEUS-JETS) P e = +0.3 SM (ZEUS-JETS) P e = 0.4 (b) - - x dσ/dy (pb) (c) y SM agrees well with data - more data needed for (small) effects or deviations

9 Contact interactions I H: DESY-03-05, ZEUS: DESY-03-8 Extra dimensions N/N CTEQ5D ZEUS (a) ZEUS e + p M S = 0.79 TeV M S + = 0.78 TeV Coupling strength, Large Extra Dimensions Limits η G = λ M 4 S Mass scale, M S > 0.8 TeV N/N CTEQ5D (b) ZEUS e - p Q (GeV ) Quark size Large Extra Dimensions Limits Probing Q up to 40,000 GeV f(q ) = R q 6 Q N/N CTEQ5D (c) Q (GeV ) ZEUS e ± p R q = ( cm) R q = -(.06-6 cm) Quark Radius Limits Quark radius, R q < 8 m 3 4 Q (GeV )

10 Contact interactions II General contact interactions Four-fermion interaction: L = q i,j=l,r η eq ij (ē i γ µ ) e i ) ( qj γ µ q j dσ/dq / dσ SM /dq 3 e p NC data Λ = 3.8 TeV Λ + = 3.3 TeV combined limits: Λ = 5.5 TeV Λ + = 5.3 TeV Compositeness: VV s=39 GeV e + p NC data Λ = 5.3 TeV Λ + = 4.8 TeV combined limits: Λ = 5.5 TeV Λ + = 5.3 TeV s=39 GeV η eq ij = ɛ ab(g/λ q ab ) Describe effects of leptoquarks, heavy weak bosons, electron or quark compositeness. dσ/dq / dσ SM /dq 0 3 H 3 4 Q (GeV ) H Leptoquark: S L, V L 3 4 Q (GeV ) e p NC data s=39 GeV e + p NC data s=39 GeV S L M/λ=5 GeV V L M/λ=50 GeV combined limits: S L M/λ=490 GeV V L M/λ=360 GeV S L M/λ=4 GeV V L M/λ=960 GeV combined limits: S L M/λ=490 GeV V L M/λ=360 GeV Sometimes higher sensitivity for e p than e + p data. 0 H 3 4 Q (GeV ) H 3 4 Q (GeV )

11 Contact interactions III Lower limits Λ.5 6 TeV Comparable to other experiments: Tevatron, LEP HERA sets some new limits Lower limits M LQ /λ LQ TeV H Λ (TeV) Λ + (TeV) LL.6.8 LR RL RR..8 VV AA 4..5 VA LL+RR RL+LR ελ (TeV)

12 Contact interactions - future ZEUS 3% at Q 00 GeV and % at Q 000 GeV HERA stat I HERA I measurement of NC cross section: L 0 pb. ) (pb/gev dσ/dq ZEUS NC (prel.) e p (8.4pb SM (ZEUS-S) P=+9.% ) 4 (a) Q (GeV ) Most precise HERA II measurement of NC cross section: L 50 pb. HERA II data on tape: L 00 pb. HERA II data to come: L > 300 pb. Analysis (by-product) of final high-q cross sections, and combining results. ) (pb/gev dσ/dq (P=-5.9%) (P=+9.%) / dσ/dq dσ/dq ZEUS NC (prel.) 05 e p (45.pb SM (ZEUS-S) P=-5.9% 3 - ZEUS NC (prel.) e p SM (ZEUS-S) P=+9.% / P=-5.9% ) 4 4 (b) Q (GeV ) (c) Q (GeV )

13 Leptoquarks - introduction Connecting lepton and quark sectors e ± l Objects have lepton and baryon numbers and fractional electric charge. Via s channel production and u channel exchange Search for resonant state, M lj q i e ± λ eqi LQ λlqj λ eqi l q j Dedicated search within Buchmüller, Rückl and Wyler (BRW) models Background DIS has similar topology although different lepton scattering angle q j λ lqj q i

14 Leptoquarks - base plots Events Events Events Data SM H e + p NC s ep 300 GeV H e p s ep 30 GeV H e + p s ep 30 GeV M (GeV) CC H e + p s ep 300 GeV H e p s ep 30 GeV H e + p s ep 30 GeV M (GeV) No narrow resonance seen (by either collaboration)

15 Leptoquarks - generic Both collaborations set strong limits Extend considerably beyond D0 limit β e VECTOR LQ e + d LQ e + d,ν u H λ=0.03 H λ= Further improvements from Tevatron at high β H λ= Different colliders will continue to complement each other Different beam charge: e p e + p and Coupling by changing polarisation Cleaner background in νj channel β e SCALAR LQ e u LQ e u,νd H NC only H CC only D0 limit M (GeV) β β

16 Leptoquarks - BRW model λ λ - - SCALAR LEPTOQUARKS WITH F=0 EXCLUDED ~ S /, L H CI H single prod. OPAL indir. limit D0 pair prod M (GeV) SCALAR LEPTOQUARKS WITH F= EXCLUDED S 0, L H CI H single prod. L3 indir. limit D0 pair prod M (GeV) λ λ ZEUS F=0 vector LQ V L 0 (e + d) ZEUS e ± p EXCLUDED F= scalar LQ S L 0 (e - u) ZEUS e ± p DO/ EXCLUDED OPAL (a) NC only CC only NC+CC M LQ (GeV) L3 NC only CC only NC+CC (b) M LQ (GeV)

17 Leptoquarks prospects Already have bounds on their production rate (0 pb ). What can be done with HERA II data? Have seen that HERA II inclusive NC DIS is well described by SM, but only fraction of potential data. E.g. for F = 0 LQ, manifesting itself as a resonance below 80 GeV: Luminosity σ = limit σ = 0.5*limit 350 pb 4σ.5σ 700 pb > 5σ 3.5σ Rough estimates. However, rate cannot be far away from our limits if we want to discover something. High luminosity comes from combining experiments. Might be essential. Larger discovery potential for F = (e p data). Thanks to E. Perez

18 Isolated leptons - history H: DESY-0-4, DESY-03-3 ZEUS: DESY-03-0, DESY-03-8, DESY HERA I P X T H electron muon tau obs./exp. obs./exp. obs./exp. > 5 GeV 5/.8 6/.7 0/0.5 P X T ZEUS electron muon tau obs./exp. obs./exp. obs./exp. > 5 GeV /.9 5/.75 /0.0 Note, H analysis is a W -like analysis and ZEUS single top H observes excess over the SM, ZEUS is consistent

19 Extraction of single top limits HERA e e γ q (u,c) κ γ top u,c e top top κ γ γ κ γ γ e u,c TeVatron LEP Strong limits from HERA experiments

20 W production from ZEUS H continues to see excess of such anomalous events in HERA II data. W production main source of isolated leptons with missing p T Small, but measurable cross section, pb Background mainly from poorly reconstructed NC/CC events and di-leptons Reanalysing data for W cross-section measurement Extending isolated lepton search to HERA II data θ e < 90, p e T > GeV Isolation, D track > 0.5 p miss T > GeV, φ acop > 7 Comparison with H results

21 Isolated electrons from ZEUS < PT X < 5 GeV P T X > 5 GeV obs./exp. obs./exp. ZEUS (prel.) e + p /.0 (57%) /0.9 (79%) ZEUS (prel.) e + p 0/0.5 (64%) 0/0.6 (76%) Purity and expectations for ZEUS similar to H analysis /.5 events at PT X > 5 GeV (6 pb ) - good agreement with SM ZEUS is consistent with the SM independent of final state lepton independent of initial state lepton independent of selection strategy

22 Future isolated leptons from ZEUS and HERA observed SM σ L (pb ) H e + p HERA e + p HERA e p HERA all Taking all data together, no substantial difference between data and SM. If new physics produced at the combined rate, will be difficult to observe. However, will continue this search area in the hope of finding something.

23 Summary and prospects Results at HERA are (so far) consistent with the Standard Model Lots of physics can be done with inclusive cross sections Analysis of HERA I data is generally finished H see an excess of events with isolated high-p T leptons - ZEUS does not. Analysis of HERA II data started. What shall we look for?

24 Summary and prospects Will measure high-q NC cross sections - any deviations will show up or we can set limits for contact interactions, etc. Will measure high-q CC cross sections and set limit on W R. Continue to analyse events with isolated high-p T leptons. Generic search (à la H) has not been done by ZEUS but could provide something new and provides useful information of semi-inclusive measurements. Channels with increased sensitivity due larger amount of e data.