Events with High P T Leptons and Missing P T and Anomalous Top at HERA

Transcription

1 with High Leptons and Missing and Anomalous Top at HERA David South (DESY) On Behalf of the H Collaboration IIth International Workshop on Deep Inelastic Scattering (DIS 24) Štrbské Pleso, High Tatras, Slovakia, 4 th -8 th April 24 D. South, With Missing and High Leptons at H and Anomalous Top Production DIS 24, Štrbské Pleso, High Tatras, Slovakia 4-8/4/4 / 9

2 Outline Introduction H with Missing and High Leptons at HERA I Search for Single Top Quark Production Latest H Results from HERA II Data Summary and Outlook D. South, With Missing and High Leptons at H and Anomalous Top Production DIS 24, Štrbské Pleso, High Tatras, Slovakia 4-8/4/4 2 / 9

3 Introduction to the Isolated Lepton Analysis e + e + q Jet ( ) q q W + Neutrino ( ) ν l p p l + Isol. Lepton (l ) H observes excess of events containing ing and high leptons (e or ). Full HERA I data set now published Phys. Lett. B56 (23) 24. Main SM signal contribution comes from the production of real W bosons via photoproduction, with subsequent leptonic decay LO Cross section at HERA, (ep ew ± ) pb; NLO SM W calculations performed by Schwanenberger et. al now included D. South, With Missing and High Leptons at H and Anomalous Top Production DIS 24, Štrbské Pleso, High Tatras, Slovakia 4-8/4/4 3 / 9

4 Isolated Lepton Analysis SM Background SM signal processes modelled by EPVEC Monte Carlo, including additional contributions from CC W production and Cabibbo-Paresi Z o production SM background processes include Neutral Current, Charged Current, Lepton Pair and Photoproduction dedicated study samples of main backgrounds performed e: Neutral Current e, Charged Current Lepton Pair e (k µ ) e (k µ) e (k µ ) ν (k µ) γ,z o (q µ ) W ± (q µ ) p (p µ ) p (p µ ) real electron & fake from mismeasurement misidentified electron/ real muon & real real muon & fake from mismeasurement D. South, With Missing and High Leptons at H and Anomalous Top Production DIS 24, Štrbské Pleso, High Tatras, Slovakia 4-8/4/4 4 / 9

5 Isolated Lepton Analysis Event Selection Main Selection requirements include: Lepton in central region of detector 5 o High lepton transverse momentum Large ing transverse momentum Overall direction of event : calorimetric energy sums Azimuthal imbalance, acoplanarity Longitudinal imbalance Lepton Isolation w.r.t. other parts of the event l l 4 o GeV 2 GeV V ap / V p.5 D jet D track e- 6 o - 7 o ) 5 GeV,.5 Isol. Lepton Jet, Neutrino D. South, With Missing and High Leptons at H and Anomalous Top Production DIS 24, Štrbské Pleso, High Tatras, Slovakia 4-8/4/4 5 / 9

6 HERA I Isolated Lepton Analysis Results Combined Electron and Muon N data = 8 H Data N SM = 2.4±.7 All SM processes SM error Signal 5 θ lepton / o Combined Electron and Muon N data = 8 N SM = 2.4± φ l- / o Final e + p Data Selection in the combined electron & muon channels 2 Combined Electron and Muon N data = 8 N SM = 2.4±.7 2 Combined Electron and Muon N data = 8 N SM = 2.4±.7 > 25 GeV: N data = N SM = 2.92 ± M T / GeV P T / GeV D. South, With Missing and High Leptons at H and Anomalous Top Production DIS 24, Štrbské Pleso, High Tatras, Slovakia 4-8/4/4 6 / 9

7 HERA I Isolated Lepton Analysis Results H e + p data (994-2), 4.7 pb - Electron and Muon H Data SM Total Signal (EPVEC) Other SM Processes < 2 GeV ± ±.7.95 ±.36 2 < < 25 GeV ± ±.4.68 ±.4 25 < < 4 GeV 4.83 ± ± ±.6 > 4 GeV 6.8 ± ±.22.2 ±.4 H e - p data ( ), 3.6 pb - < 25 GeV.54 ±.2.93 ±.6.6 ±.3 > 25 GeV.52 ±.8.37 ±.7.5 ±.4 Excess observed at large values of in e + p data Analysis of tau channel now H Preliminary see talk by G.Brandt D. South, With Missing and High Leptons at H and Anomalous Top Production DIS 24, Štrbské Pleso, High Tatras, Slovakia 4-8/4/4 7 / 9

8 Search for Single Top Production - Introduction Motivated by observed excess at high of events in Isolated Lepton analysis The production of single top quarks with decay to b and a W boson may provide a possible explanation SM single top highly supressed Search for anomalous top production via FCNC interaction SM W production is dominant at low values of, whereas the b-jet has large transverse momentum p e + e + u,c κ γ b t W + ν l, q l +,q Study coupling between up and top quarks, tu Search covers the leptonic (W lv) and hadronic (W (neglect Z o boson exchange) qq') decays of the W. D. South, With Missing and High Leptons at H and Anomalous Top Production DIS 24, Štrbské Pleso, High Tatras, Slovakia 4-8/4/4 8 / 9

9 Search for Single Top in the Leptonic Channel M eνb H Data W MC Top MC M µνb a) 8 b) M eν T M µν T Kinematic Reconstruction of the top quark decay b quark reconstruction: b-jet not tagged, but reconstructed from sum of all jets neutrino reconstruction: apply constraint on W mass, M l Examine invariant mass of top system, M l P l 2 P 2 2 P l P 2 P l P b versus the lepton-neutrino transverse mass, M T l M W D. South, With Missing and High Leptons at H and Anomalous Top Production DIS 24, Štrbské Pleso, High Tatras, Slovakia 4-8/4/4 9 / 9

10 Search for Single Top in the Leptonic Channel ELECTRON CHANNEL H Data All SM processes SM uncertainty W MC Top MC b 2.5 MUON CHANNEL b.4.3 Top Preselection Isolated lepton events + neutrino reconstruction Rejection of leptons with negative charge: t bw + bl + top decay produces only positively charged leptons 9 electron events and 6 muon events Three discriminatory observables: b, M l l b and W l M eνb M µνb Cut-based Top Selection in Leptonic Channel b 3 GeV and M l b 4 GeV Main contribution to SM prediction from W production Data Standard Model Electron Channel 3.65 ±. Muon Channel 2.66 ±.2 Total 5.3 ±.22 cos θ e W cos θ µ W D. South, With Missing and High Leptons at H and Anomalous Top Production DIS 24, Štrbské Pleso, High Tatras, Slovakia 4-8/4/4 / 9

11 Search for Single Top in the Hadronic Channel HADRONIC CHANNEL - TOP PRESELECTION b 5 2 M jets H Data All SM processes SM uncertainty NC DIS (Q 2 >4 GeV 2 ) Top MC cos θ q W Top selection M jets Top Preselection jet High transverse momentum multi-jet events, jet2 jet3 4 GeV, 3 GeV, 5 GeV Large total transverse energy, E T tot GeV One pair of jets with 65 GeV M I 95 GeV 92 data events, 92.4 ± 6.6 expected from SM Discriminatory observables analgous to leptonic channel: b, M jets and Cut-based Top Selection in Hadronic Channel b and cos W q 4 GeV, 5 GeV M jets 2 GeV W q -.75 Less sensitive to W Production than leptonic channel, main SM contribution from NC DIS Data Standard Model Hadronic Channel ± 3.6 D. South, With Missing and High Leptons at H and Anomalous Top Production DIS 24, Štrbské Pleso, High Tatras, Slovakia 4-8/4/4 / 9

12 Set of observables, V V i leptonic channel: V Multivariate Analysis with probability densities p i signal b, M l b, cos l W and p i background, hadronic channel: V calculated from MC b, M jets, cos Observables combined to calculate a Discriminator D(V) for each event, given by: q W D V P signal P signal P background where P C V i p i - ELECTRON CHANNEL H Data All SM processes Top MC - MUON CHANNEL H Data All SM processes Top MC HADRONIC CHANNEL H Data All SM processes Top MC Top MC (normalised to signal in e+µ channels) D D D Leptonic channel: 5 data events in cut-based analysis found in top-like region (D = ) Hadronic channel: data and QCD background in good agreement Results in hadronic channel not in contradiction with single top hypothesis in leptonic channel D. South, With Missing and High Leptons at H and Anomalous Top Production DIS 24, Štrbské Pleso, High Tatras, Slovakia 4-8/4/4 2 / 9

13 Maximum Likelihood Fit Cross Sections A maximum likelihood fit is performed of the top contribution, using likelihood discriminator distributions as input Likelihood function: - 2 ln L ELECTRON+MUON CHANNEL ln L HADRONIC CHANNEL L n k e k n k k n k! 2 2 k is the sum of signal and background in bin k Look for minimum in negative log likelihood function -2 lnl as a function of top production cross section Leptonic and Hadronic channels found to be compatible at. level, including systematic errors (dominant in hadronic channel) - 2 ln L σ (ep et) (pb) ALL CHANNELS % CL σ (ep et) (pb) Without systematic errors With systematic errors Measured Top Production Cross Section (ep et) =.29 2 Upper Limit on Top.5.4 pb σ (ep et) (pb) Production Cross Section (95% CL) (ep et) <.55 pb D. South, With Missing and High Leptons at H and Anomalous Top Production DIS 24, Štrbské Pleso, High Tatras, Slovakia 4-8/4/4 3 / 9

14 Single Top Production Exclusion Limit Bound on top production cross section transformed into upper limit on anomalous tu assuming v tuz = : <.27 (95% CL) tu coupling at NLO, This limit is competitive with ZEUS analysis (Z o contribution evaluated at LO) and with results from the LEP and CDF experiments H Single Top Analysis now published Eur. Phys. J. C33 (24) 9 D. South, With Missing and High Leptons at H and Anomalous Top Production DIS 24, Štrbské Pleso, High Tatras, Slovakia 4-8/4/4 4 / 9

15 H and HERA II Upgrade Extensive upgrade to HERA to deliver factor of more luminosity - H also upgraded HERA II major data taking period underway since autumn 23 First HERA II analyses made preliminary for this conference, using 7 pb - of data The Isolated Lepton analysis has been performed on the new HERA II data See talks by:o. Henshaw, E. Sauvan and M. Peez D. South, With Missing and High Leptons at H and Anomalous Top Production DIS 24, Štrbské Pleso, High Tatras, Slovakia 4-8/4/4 5 / 9

16 HERA II Isolated Lepton Analysis Results H Data (prelim.) All SM Processes Signal - Search for l+ events at HERA II ( 7 pb ) e and µ channels N = 3 Data N = 2. ±.3 SM Electron H e + p data (23-24), 7 pb - H Data SM Expectation SM Signal Total 3.6 ± ±.29 > 25 GeV 2.34 ±.7.22 ±.5 - Muon Total.44 ± ±.8 > 25 GeV.29 ±..26 ± Electron & Muon Total ± ±.27 > 25 GeV 2.63 ±..48 ±. Three new electron candidate events observed in HERA II data (No muons yet...) Two events are at high values of, where the excess was observed in HERA I data The higher luminosity provided by HERA II will help to clarify the origin of these events D. South, With Missing and High Leptons at H and Anomalous Top Production DIS 24, Štrbské Pleso, High Tatras, Slovakia 4-8/4/4 6 / 9

17 HERA II Isolated Lepton Event Display New High Event with e + in HERA II data: e = 37 GeV, = 44 GeV, = 29 GeV ep ew ± e D. South, With Missing and High Leptons at H and Anomalous Top Production DIS 24, Štrbské Pleso, High Tatras, Slovakia 4-8/4/4 7 / 9

18 HERA II Isolated Lepton Event Display New Elastic Event with e + in HERA II data: e = 47 GeV, = 47 GeV, = GeV ep ew ± e D. South, With Missing and High Leptons at H and Anomalous Top Production DIS 24, Štrbské Pleso, High Tatras, Slovakia 4-8/4/4 8 / 9

19 Summary & Outlook Full H HERA I data sample analysed for events containing high leptons and ing, excess observed at high Cut-based search for single top production yields 5 (.3.22) events in the leptonic channel and 8 ( ) in the hadronic channel Derived upper limits on the top production cross section and the anomalous coupling tu are competitive with other experiments The first new data from HERA II have been analysed and new isolated lepton candidates have been observed The increased luminosity of HERA II ( fb - ) is necessary to clarify the origin of the isolated lepton events and provide increased sensitivity to the production of single top quarks D. South, With Missing and High Leptons at H and Anomalous Top Production DIS 24, Štrbské Pleso, High Tatras, Slovakia 4-8/4/4 9 / 9