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Search for Leptoquarks and Compositeness at D0

Search for Leptoquarks and Compositeness at D0. Maxim Titov (on behalf of D0 Collaboration). University of Freiburg. European Physics Conference (EPS 2005), Lissabon, 21. 07. 2005. Tevatron & D0 Detector & Luminosity in Run II. Run II started March 2001: Higher energy (1.8 TeV -> 1.96 TeV)

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Search for Leptoquarks and Compositeness at D0

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  1. Search for Leptoquarks and Compositeness at D0 Maxim Titov (on behalf of D0 Collaboration) University of Freiburg European Physics Conference (EPS 2005), Lissabon, 21. 07. 2005

  2. Tevatron & D0 Detector & Luminosity in Run II • Run II started March 2001: • Higher energy(1.8 TeV -> 1.96 TeV) • Higher antiproton intensity • (6*6 bunches -> 36*36 bunches) Acceptance: Electrons: |h| < 3.0 Muons: |h| < 2.0 Jets: |h| < 4.2 1 fb-1 Results presented in this talk are based on integrated luminosity of 200 – 400 pb-1 More than double of this dataset is already on the tape

  3. Leptoquarks Phenomenology • Leptoquarks (LQ) predicted to exist in various SM extensions (e.g. GUT, technicolor, • SUSY with R-parity violation, composite models, superstring-inspired E6-models): • Connection of lepton and quark sector • (color-triplet field, fractional electric charge, both lepton and quark numbers); • HERA: Buchmuller–Ruckl–Wyler (BRW) Minimal LQ Model(Phys. Lett.B191(1987) 442) • (7 scalar and 7 vector leptoquarks with fermion numbers F = - (3B + L) = 0 or 2) • TEVATRON: LQ pair production does not depend on its electroweak properties  • No need to use specific model, but number of constraints on LQ are coming from: • Atomic parity violation (APV) experiments • Baryon and Lepton number conservation (to avoid rapid proton decays) • Family diagonal – LQ couples to a single leptonic and quark generation (to avoid FCNC) • Chiral coupling (to avoid deviations from universality in leptonic p decays) D0 Limits for scalar leptoquarks are only presented in this talk: Scalar leptoquarks are less model dependent & typically have lower production cross section limits could be valid for vector LQ

  4. Scalar Leptoquarks at Tevatron Scalar LQ Production (sNLO ~ 0.3 pb at MLQ ~ 200 GeV): • Scalar LQ pair production: • Quark-antiquark annihilation and gluon fusion • (qq annihilation is dominant for MLQ > 100 GeV) • Phys.Rev Lett.79(1997)341; Phys.Rev.D59,015001(1998) • The gluon-leptoquark coupling is simply • given by the strong coupling • Cross section is independent of Yukawa • leptoquark-lepton-quark coupling (lLQ): • ( lLQ contributes only ~ 1% of total cross • section in t-channel of qq annihilation) LQ Decay: LQ experimental signatures: 1st generation: 2e+2j, e+2j+MET, 2j + MET 2nd generation: 2m+2j, m+2j+MET, 2j + MET Combined D0-CDF Run I 1st generation LQ limit: MLQ1 > 242 GeV for b = 1.0 (hep-ex/9810015) b = LQ branching fraction to charged lepton and quark

  5. Pair Production of 2nd Generation Leptoquarks NEW ! ! ! Run II D0 analysis have been performed in mmqq channel (294 pb-1): Selection: 2m (ET> 15 GeV) + 2 jets (ET> 25GeV) + Z veto; Main SM backgrounds: Z/Drell Yan + jets, ttbar Only the combination with the smaller mass difference min(M1(mj)-M2(mj)) of the two LQ candidates in the event is chosen ST = ET(j1) + ET(j2) + ET(m1) + ET(m2):

  6. Pair Production of 2nd Generation Leptoquarks NEW ! ! ! Sensitivity to LQ decays is studied using a two-dimensional distribution: Scalar sum of transverse energies (ST) vs. Dimuon invariant mass Mmm All events are arranged in 4 bins  choice of binning follows the ratio of the expected signal over background (S/B) for a leptoquark mass of 240 GeV Modified frequentist approach The observed limit is calculated using CLS = CLS+B / CLB  (T. Junk, NIMA434(1999) 435)

  7. D0 Run I+II Combined Scalar LQ Limits (2nd generation) The mass limit is extracted from the intersection of the lower edge of the s(NLO) with the observed upper bound to the cross section D0 Run II Limits (294 pb-1): MLQ > 247 GeV(mmjj channel, b = 1.0) MLQ > 182 GeV(mmjj channel, b = 0.5) D0 Combined (Run I + Run II): (D0 Note 4829) MLQ > 251 GeV(b = 1.0) MLQ > 204 GeV(b = 0.5) CDF Run II (~200 pb-1): (CDF Note 7216) MLQ > 241 GeV (b = 1.0) MLQ > 175 GeV (b = 0.5)

  8. D0 Run I+II Combined Scalar LQ Limits (1st generation) • D0 Run II Limits (252 pb-1): • MLQ > 241 GeV(eejj channel, b = 1.0) • MLQ > 218 GeV(combined eejj & enjj • channels for b = 0.5) eejj • D0 Combined (Run I + Run II): • (Phys. Rev.D71,071104(2005)) • MLQ > 256 GeV(eejj, b = 1.0) • MLQ > 234 GeV(combined • eejj & enjj. b = 0.5) Combined result as a function of b: Also CDF in Run II using eeqq, enqq & nnqq channels (~200 pb-1): (hep-ex/0506074) MLQ > 236 GeV (b = 1.0) MLQ > 205 GeV (b = 0.5)

  9. Contact Interaction & Compositeness Phenomenology New Physics appear from the interference of any new particle field (M ~ L) associated to a characteristic energy scale (L2 >> s) with the SM field New physics Four-fermion contact interaction can beapplied to: Compositeness, Leptoquarks, New gauge bosons by an appropriate choice of coefficients hAB SM Quark and leptons might be composite objects and bound states of more fundamental constituents (“preons”); Quark-Lepton compositeness can be expressed through effective coupling coefficients, which depends on the ratio of coupling constant g0 over scale of compositeness L: hAB * g02 / L2AB (hAB – chiral structure of the interation; A,B  L(eft) - R(ight) quark/lepton helicities) At L2<< s, multiple fermion production processes will dominate over SM two-body fermion scattering processes At L2 >> s, flavor diagonal contact interaction will modify SM cross-section for elastic fermion-fermion scattering

  10. Quark-Lepton Compositeness at Hadron Colliders Quark Compositenessis most sensitive to the deviation in production of high-transverse momentum jets relative to SM predictions; Quark-Lepton Compositeness would modify Standard Model Drell-Yan (DY) cross-section for lepton pair production at large invariant masses Quark-Lepton Composite Models: The modified dilepton cross-section is controlled by compositeness scale L and interference sign (I) with SM: (I ~ hAB is the interference of DY and contact term, C is the pure contact term) Limits are obtained independently for each separate channel (LL, RR, RL, LR, VV, AA) of contact interaction Lagrangian and L+: hAB = -1  constructive interference L-: hAB= +1  destructive interference

  11. Quark-Lepton Compositeness Searches Run II D0 Analysis have been performed in: pp  qq  g/Z  mm (L ~ 406 pb-1) and pp  qq  g/Z  ee (L ~ 271 pb-1) Di-muon Channel:2 isolated m (pT > 15 GeV), cosmic veto and Mmm > 50 GeV; Di-electron Channel:2 electrons (pT > 25 GeV), Mee >120 GeV SM +CI (L+ = 2 TeV) Z ee SM Monte Carlo: cos q* Mee Mmm Z mm g/Z mm:A 95% CL upper limit on L is computed from 2-dimen. distributions (Mmmvs. scattering angle cosq*) using DATA, background and signal MC; g/Z  ee:Limit is calculated using a Bayesian analysis of the shape of the mass distribution of events

  12. Compositeness Searches: Experimental Status D0 Run II Results in di-electron (L= 271 pb-1) and di-muon channels (L = 406 pb-1): Limits of Compositeness Scale L: Lower L Limit: Upper L Limit: Parity violating terms (LL, RR, LR, RL) are constrained by APV experiments with L > 11 TeV HERA: Phys. Lett. 568(203)35, hep-ex/9905039; LEP: Phys. Lett.B489(2000) 81, Eur. Phys. J.C12(2000) 183, Eur. Phys. J.C.13(2000) 553, Eur. Phys. J.C.11(1999) 383; http://lepewwg.web.cern.ch/LEPEWWG/lep2 CDF: Phys. Rev. Lett.79(12)(1997)2198; Phys. Rev. Lett. 78,(1997)4307, D0: D0 Note 4552, Phys. Rev. Lett. 82(1999)2457, APV: Phys. Lett.B480(2000)149

  13. Summary and Outlook • The performance of Tevatron improves steadily allowing to test experimentally • wider range of new phenomena searches for an ultimate theory • No evidence for leptoquarks and compositeness has been observed • Combined D0 Run I + Run II Limits for scalar leptoquarks allow to exclude: • 1st LQ generation up to 256 GeV (for b = 1) • 2nd LQ generation up to 251 GeV (for b = 1) • D0 Run II Limits from 4.2 Tev to 9.8 TeV (for different chirality models) are the • most stringent limits in the dimuon channel for the compositeness scale • Start counting on > 1 fb-1 data sample •  a new era for searches at hadron colliders

  14. Backup Slides

  15. Pair Production of 1st Generation Leptoquarks Run II D0 analysis have been performed in eeqq and enqq channels (252 pb-1): Selection:2 Electrons and 2 Jets 2j (ET>20 GeV) + 2e (ET>25 GeV) + Z-veto; Main Backrounds: ZDY+jets, multi-jets ST = ET(j1) + ET(j2) + ET(e1) + ET(e2)>450 GeV Selection:1 Electron, 2 Jets and Missing ET: 2j (ET>25 GeV) + e (ET>25 GeV) + MET > 30 GeV + W-veto Main backrounds:W+2jets,multi-jets, ttbar ST = ET(j1) + ET(j2) + ET(e1) + MET>330 GeV 1 event (DATA) vs 0.5 +- 0.1 events expected 30% signal efficiency (MLQ ~ 240 GeV) 1 event (DATA) vs 3.6 +- 1.2 events expected 18% signal efficiency (MLQ ~ 200 GeV)

  16. Scalar Leptoquarks in the Acoplanar Jet Topology Run II D0 analysis have been performed in nnqq channels (85 pb-1): SM bkg 38.4 +-3.7 QCD 3.1 +- 2.0 Total bkg 41.5 +- 4.2 DATA events 44 D0 Run I Limit:(Phys. Rev. D64(2001)092004) LQ mass range 85 -109 GeV is excluded By the Run II Analysis

  17. Leptoquark Searches: Experimental Status LEP Limits: http://lepewwg.web.cern.ch/LEPEWWG/lep2 H1 Collaboration, hep-ex/0506044 b = 1 (LQ branching fraction to charged lepton and quark)

  18. Quark-Lepton Compositeness: Dimuon Channel Run II D0 Analysis have been performed in: pp  qq  g/Z  mm (L ~ 406 pb-1) Selection:2 isolated m (pT > 15 GeV), cosmic veto and Mmm > 50 GeV; Backgrounds: tt mm and bb production cos(Q*) - scattering angle, relative to the direction of the boost of the dimuon system A 95 % CL upper limit on composite scale L is computed from the fit, using DATA, background and signal MC 2-dimensional distributions (Mmmvs cosq*)  better confidence limits on L than using only 1-dim Mmm

  19. Quark-Lepton Compositeness: Dielectron Channel Run II D0 Analysis have been performed in: pp  qq  g/Z  ee (L ~ 271 pb-1) Selection:2 electrons (pT > 25 GeV), Mee >120 GeV Backgrounds: multijet and g/jet events  estimated from the same data sample Mee Bayesian Method to set limit on L: (separately for each chirality channel): To get a 95 % CL limit on L:

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