DOCSLIB.ORG

Search for Single Leptoquark Production In

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Search for Single Leptoquark Production In 1 SEARCH FOR SINGLE LEPTOQUARK PRODUCTION IN ELECTRON-PHOTON SCATTERING p a AT s = 161 AND 172 GEV STEFAN SOLDNER-REMBOLD for the OPAL collab oration Universitat Freiburg, Hermann-Herder-Str. 3, D-79104 Freiburg i. Br., Germany A search for a rst generation scalar lepto quark (LQ) has b een p erformed using + the data collected by the OPAL detector in 1996 at e e centre-of-mass energies p s of 161 and 172 GeV. It is assumed that a single lepto quark can b e pro duced in the pro cess eq! LQ, where the initial state quark originates from a hadronic uctuation of a quasi-real photon which has b een radiated by one of the LEP b eams. Lower limits at the 95 % con dence level on the mass of a rst generation scalar lepto quark of 131 GeV for =0:5 and = 1, coupling values larger than p 4 and lepto quark charges 1=3or5=3 are obtained. em 1 Kinematics and Monte Carlo simulations Lepto quarks are coloured spin 0 or spin 1 particles carrying b oth baryon and lepton quantum numb ers. Recently it has b een suggested to search for lep- 1 to quarks in electron-photon collisions at LEP . The photon, which has b een radiated by one of the LEP b eams, serves as a source of quarks through its uctuations into hadronic states. The electron-quark interaction pro duces a lepto quark which is assumed to decay subsequently into an electron or a neu- b trino and a quark. In electron-photon scattering rst generation lepto quarks of charge 1=3, 5=3, 2=3 and 4=3 can b e pro duced. The cross-section to pro duce charge 2=3 and 4=3 lepto quarks is suppressed, since there is less d quark content in the photon than u quark. The limits will therefore b e given for lepto quark charges 1=3 or 5=3. The cross-sections in e scattering for b oth charge states are identical, since it is equally probable to nd a u or a u quark in the photon. In principle this search is also sensitive to electron-charm states, since the probability for a photon to split into ccoruu is exp ected to b e ab out equal for lepto quark masses M>>m . Furthermore it has b een assumed that c either left or right handed couplings to fermions vanish. The cross-sections in e scattering for b oth couplings are identical, whereas the branching ratio a To b e published in the pro ceedings of PHOTON'97, Egmond aan Zee b Charge conjugation is implied throughout this pap er and p ositrons are referred to as electrons FREIBURG-EHEP-97-04 2 into eq nal states is 1 for right handed couplings and 1/2 for left handed 2 couplings . The total cross-section for the pro duction of scalar lepto quarks of mass M is a convolution of the Weizsacker-Williams e ective photon distribution f (z), with z b eing the momentum fraction carried by the photon, and the =e 2 parton distribution functions f (x; ) of the photon, evaluated at the scale q= 1 = M : Z 1 2 dz 2 2 2 + f (z; Q )f (M =(zs);M ): (1) (e e ! LQ+X)= =e q= max 2s z 2 M =s 3;4 The Monte Carlo simulation of this pro cess is done with PYTHIA 5.722 . In 2 the simulation the maximum photon virtuality Q used in the Equivalent max Photon Approximation equals s=4, but the simulated photon is always real 2 5 (Q = 0). The GRV parametrisation of the parton distribution functions was used. In the kinematic region relevant for lepto quark pro duction the variations of the cross-section due to the di erent parameterisations are small. Interference e ects with deep-inelastic e scattering are also neglected. The p total cross-section in PYTHIA for s = 172 is ab out 10{20 % lower than the p cross-sections given for s = 175 in Ref. 1. Vector lepto quarks can currently not b e simulated with PYTHIA. The limits are therefore given only for scalar lepto quarks. The standard PYTHIA Monte Carlo has b een mo di ed to include LQ ! d decays in addition to the standard LQ ! eu decays. e 2 Event Analysis Jets were reconstructed using a cone jet nding algorithm with a cone size R = 1 and a cut on the minimum transverse jet energy E of 15 GeV. Tracks T and calorimeter clusters were used as input for the jet nding algorithm and for determining the missing transverse energy E= of the event. A matching algo- T rithm b etween tracks and clusters is applied. The electron was identi ed using 6 the standard OPAL neural net electron identi cation . All relevant Standard Mo del background pro cesses were studied using Monte Carlo generators. The 1 total data sample corresp onds to an integrated luminosity of 20.5 pb . 2.1 The electron plus hadronic jet channel For this channel the identi ed electron with the largest momentum was as- sumed to b e the electron from the lepto quark decay. The electron is usually reconstructed as a jet. Candidate events were selected based on the following cuts: FREIBURG-EHEP-97-04 3 + + In order to reduce background from deep-inelastic e and e e ! events, exactly two jets must have b een found in the event(n = 2). j + + + + A large number of e e ! and e e ! e e events are rejected by requiring a minimum numb er of 5 reconstructed tracks (n 5). In ch p s has to b e less than 0.9, where E is addition, the ratio E = ECAL ECAL the energy in the electromagnetic calorimeter. The missing transverse energy E= must b e less than 15 GeV in order to T + + reduce background from and W W pair pro duction. An isolation cut is applied on the identi ed electron. The jet with the smallest angular distance to the electron is chosen to b e the electron jet. j The di erence between the energy E of this jet and the energy E of e e + the electron must b e less than 4 GeV. Most multihadronic e e ! qq events are removed by this cut. Events where an electron was scattered at a small angle are rejected by requiring for the angle of the electron j cos j < 0:85. e The total multiplicity n of the quark jet must b e n 7, where n is q q q the total numb er of tracks and calorimeter clusters asso ciated to this jet. The cuts on the transverse momenta of the jets and on the angle j cos j of the e electron reduce signi cantly the sensitivity to nd a lepto quark which is lighter than approximately M =2, the region excluded by the LEP1 searches. These Z cuts are necessary to reduce the background from deep-inelastic e events which b ecomes increasingly imp ortant at small masses. After all cuts we exp ect a background of 5:2 0:4events from all Standard Mo del pro cesses. In the data four events are observed with jet-jet invariant masses M of 36, 37, 62 and 98 GeV. In Fig. 1a the M distribution of the four jj jj candidate events is shown together with the sum of all Monte Carlo background p distributions. Also shown is a p ossible lepto quark signal for = 4 and em di erent LQ masses. The mass distribution of the candidate events is consistent with the exp ectation from the background Monte Carlo simulation. 2.2 The neutrino plus hadronic jet channel This search has to b e optimized for a single hadronic jet in the detector. Its j transverse energy E must b e balanced by the neutrino. The cuts are therefore: T In order to reject events with large missing transverse energy due to badly measured tracks, the ratio of the energy E to the total visible ECAL energy E has to b e larger than 20 %. vis FREIBURG-EHEP-97-04 4 j Exactly one jet has to be found (n = 1) with E > 15 GeV. The jet j T direction in the lab oratory frame is required to lie within a pseudorapidity j range j j < 2 to reject events where a single jet, usually due to an electron, was found in the forward detectors. n 5 and n 7. ch q The missing transverse energy E= must b e greater than 15 GeV and it T j should b e mainly due to the jet. Therefore we require jE E= j < 3 T T j GeV and E =E > 0:5. vis Since no additional cuts on electron variables are necessary, the eciency to 0 detect a lepto quark is higher in the q than in the eq channel. For M = e 0 100 GeV the eciency is ab out 61 % in the q and 55 % in the eq channel. e 1 1 - - (a) OPAL prel. (b) OPAL prel. √s=161 and 172 GeV √s=161 and 172 GeV 10 LQ→eq 10 LQ→νq´ Events in 20.5 pb Events in 20.5 pb data data M=45 GeV M=45 GeV M=80 GeV M=80 GeV M=120 GeV M=120 GeV M=140 GeV M=140 GeV 1 1 background background -1 -1 10 10 20 40 60 80 100 120 140 160 180 200 220 20 40 60 80 100 120 140 160 180 200 220 M (GeV) jj MT=2E/ T (GeV) p 0 Figure 1: Numb er of (a) LQ ! eq and (b) LQ ! q events exp ected with = 4 e em 1 in 20.5 pb of data after all cuts for M =45;80; 120 and 140 GeV (histograms) and the candidate events (data p oints).
Load more

Recommended publications
  • Search for Second Generation Scalar Leptoquark Pairs with the Atlas Detector
    SEARCH FOR SECOND GENERATION SCALAR LEPTOQUARK PAIRS WITH THE ATLAS DETECTOR by Shanti Wendler Master of Science, University of Pittsburgh, 2007 Submitted to the Graduate Faculty of the Department of Physics in partial fulfillment of the requirements for the degree of Doctor of Philosophy University of Pittsburgh 2010 UNIVERSITY OF PITTSBURGH PHYSICS DEPARTMENT This dissertation was presented by Shanti Wendler It was defended on July 21st, 2010 and approved by Vittorio Paolone, University of Pittsburgh, Associate Professor, Dept. of Physics Vladimir Savinov, University of Pittsburgh, Associate Professor, Dept. of Physics Adam Leibovich, University of Pittsburgh, Associate Professor, Dept. of Physics Arthur Kosowsky, University of Pittsburgh, Associate Professor, Dept. of Physics Roy Briere, Carnegie Mellon University, Associate Professor, Dept. of Physics Dissertation Director: Vittorio Paolone, University of Pittsburgh, Associate Professor, Dept. of Physics ii SEARCH FOR SECOND GENERATION SCALAR LEPTOQUARK PAIRS WITH THE ATLAS DETECTOR Shanti Wendler, PhD University of Pittsburgh, 2010 Proton collisions at the Large Hadron Collider could provide evidence for the existence of leptoquarks, hypothetical bosons that couple directly to leptons and quarks. Monte Carlo based studies of second generation leptoquark pair production in the ATLAS detector are presented, as well as predictions for discovery and exclusion potential with early ATLAS data. iii TABLE OF CONTENTS 1.0 INTRODUCTION .................................1 2.0 ATLAS DETECTOR AND ITS PERFORMANCE ............2 2.1 Magnet System.................................4 2.2 Inner Detector..................................7 2.2.1 Pixel Detector..............................7 2.2.2 Semiconductor Tracker..........................8 2.2.3 Transition Radiation Tracker......................9 2.2.4 Track Reconstruction in the ID..................... 10 2.2.5 Tracking Performance.........................
    [Show full text]
  • Search for Second Generation Leptoquarks with ATLAS at the LHC
    Search for Second Generation Leptoquarks with ATLAS at the LHC Dissertation der Fakult¨atf¨urPhysik der Ludwig-Maximilians-Universit¨atM¨unchen vorgelegt von Gernot Krobath geboren in Heidelberg M¨unchen, den 18. Juli 2008 1. Gutachter: Prof. Dr. Dorothee Schaile 2. Gutachter: Prof. Dr. Wolfgang D¨unnweber Tag der m¨undlichen Pr¨ufung: 24.09.2008 Abstract The Large Hadron Collider will collide protons with protons at a center-of-mass energy of up to 14 TeV. New physics phenomena and new particles are pre- dicted to be detectable with the ATLAS detector at the Large Hadron Collider. One of these predicted new particles beyond the Standard Model are leptoquarks. This thesis deals with the search for scalar second generation leptoquarks produced in pairs. Second generation leptoquarks decay into a muon-type lepton and a quark. In this thesis the decay of both second generation leptoquarks into a muon and a quark is considered. Since pair production is studied the final state consists of two high-energetic muons and two high-energetic jets. This thesis studies second generation leptoquarks with masses of mLQ = 300 GeV, mLQ = 400 GeV, mLQ = 600 GeV and mLQ = 800 GeV. The best cut variables for the discrimination between the signal and the main Standard Model backgrounds ∗ t¯t and Z/γ found in this analysis are the pT of the muons, ST (the scalar sum of the transverse momenta of the two selected muons and the transverse energies of the two selected jets), the mass of the selected dimuon system and the recon- structed leptoquark mass.
    [Show full text]
  • RDًأق Motivated S1 Leptoquark Scenarios
    PHYSICAL REVIEW D 99, 055028 (2019) RDðÞ motivated S1 leptoquark scenarios: Impact of interference on the exclusion limits from LHC data Tanumoy Mandal* Department of Physics and Astrophysics, University of Delhi, Delhi 110007, India and Department of Physics and Astronomy, Uppsala University, Box 516, SE-751 20 Uppsala, Sweden † ‡ Subhadip Mitra and Swapnil Raz Center for Computational Natural Sciences and Bioinformatics, International Institute of Information Technology, Hyderabad 500 032, India (Received 28 December 2018; published 21 March 2019) Motivated by the persistent anomalies in the semileptonic B-meson decays, we investigate the −1 3 competency of LHC data to constrain the RDðÞ -favored parameter space in a charge = scalar S leptoquark ( 1) model. We consider some scenarios with one large free coupling to accommodate the RDðÞ anomalies. As a result, some of them dominantly yield nonresonant ττ and τν events at the LHC through the t-channel S1 exchange. So far, no experiment has searched for leptoquarks using these signatures and the relevant resonant leptoquark searches are yet to put any strong exclusion limit on the parameter space. We recast the latest ττ and τν resonance search data to obtain new exclusion limits. The nonresonant processes strongly interfere (destructively in our case) with the Standard Model background and play the determining role in setting the exclusion limits. To obtain precise limits, we include non-negligible effects coming from the subdominant (resonant) pair and inclusive single leptoquark productions systematically in our analysis. To deal with large destructive interference, we make use of the transverse mass distributions from the experiments in our statistical analysis.
    [Show full text]
  • 116. Leptoquarks 1 116
    116. Leptoquarks 1 116. Leptoquarks Updated August 2019 by S. Rolli (US Department of Energy) and M. Tanabashi (Nagoya U.) Leptoquarks are hypothetical particles carrying both baryon number (B) and lepton number (L). The possible quantum numbers of leptoquark states can be restricted by assuming that their direct interactions with the ordinary standard model (SM) fermions are dimensionless and invariant under the SM gauge group. Table 116.1 shows the list of all possible quantum numbers with this assumption [1]. The columns of SU(3)C, SU(2)W , and U(1)Y in Table 116.1 indicate the QCD representation, the weak isospin representation, and the weak hypercharge, respectively. The spin of a leptoquark state is taken to be 1 (vector leptoquark) or 0 (scalar leptoquark). Table 116.1: Possible leptoquarks and their quantum numbers. Spin 3B + L SU(3)c SU(2)W U(1)Y Allowed coupling 0 2 3¯ 1 1/3q ¯c ℓ oru ¯c e − L L R R 0 2 3¯ 1 4/3 d¯c e − R R 0 2 3¯ 3 1/3q ¯c ℓ − L L 1 2 3¯ 2 5/6q ¯c γµe or d¯c γµℓ − L R R L 1 2 3¯ 2 1/6u ¯c γµℓ − − R L 0 03 2 7/6q ¯LeR oru ¯RℓL 0 03 2 1/6 d¯RℓL µ µ 1 03 1 2/3q ¯Lγ ℓL or d¯Rγ eR µ 1 03 1 5/3u ¯Rγ eR µ 1 03 3 2/3q ¯Lγ ℓL If we do not require leptoquark states to couple directly with SM fermions, different assignments of quantum numbers become possible [2,3].
    [Show full text]
  • Searches for Scalar and Vector Leptoquarks at Future Hadron Colliders 
    Searches for Scalar and Vector Leptoquarks at Future Hadron Colliders Thomas G. Rizzo Stanford Linear Accelerator Center, Stanford University, Stanford, CA 94309, USA ABSTRACT verse is also true, i.e., the production properties cannot be used to probe the detailed nature of the leptoquark type. V The search reaches for both scalar( S ) and vector( )lepto- The production cross section for pairs of scalar quarks at future hadron colliders are summarized. In particular gg q q leptoquarks(S ) in either or collisions is easily cal- we evaluate the production cross sections of both leptoquark culated and has been available for some time; we use the results types at TeV33 and LHC as well as the proposed 60 and 200 of Hewett et al. in Ref.[6] in what follows. Given the mass TeV colliders through both quark-antiquark annihilation and of S there are no real ambiguities in this calculation except q; gg ! SS; V V gluon-gluon fusion: q . Experiments at these for the possible inclusion of a K factor (which we omit) to machines should easily discover such particles if their masses account for higher order QCD corrections and leads to a slight are not in excess of the few TeV range. enhancement in the rate. I. INTRODUCTION Many extensions of the standard model(SM) which place quarks and leptons on a symmetric footing predict the existence of leptoquarks, which are spin-0 or 1, color-triplet objects that q` couple to a q` or pair[1]. While these particles may be sought indirectly through their influence on low energy processes[2], the most promising approach is via direct production at collid- ers.
    [Show full text]
  • (G-2)Н and B Anomalies with Leptoquarks and a Dark Higgs Boson
    University of Mississippi eGrove Faculty and Student Publications Physics and Astronomy 2-7-2020 Resolving the (g-2)μ and B anomalies with leptoquarks and a dark Higgs boson Alakabha Datta University of Mississippi Jonathan L. Feng University of California, Irvine Saeed Kamali University of Mississippi Jacky Kumar University of Montreal Follow this and additional works at: https://egrove.olemiss.edu/physics_facpubs Recommended Citation Datta, A., Feng, J. L., Kamali, S., & Kumar, J. (2020). Resolving the ( g − 2 ) μ and B anomalies with leptoquarks and a dark Higgs boson. Physical Review D, 101(3), 035010. https://doi.org/10.1103/ PhysRevD.101.035010 This Article is brought to you for free and open access by the Physics and Astronomy at eGrove. It has been accepted for inclusion in Faculty and Student Publications by an authorized administrator of eGrove. For more information, please contact [email protected]. PHYSICAL REVIEW D 101, 035010 (2020) Resolving the ðg − 2Þμ and B anomalies with leptoquarks and a dark Higgs boson † ‡ Alakabha Datta,1,2,* Jonathan L. Feng ,2, Saeed Kamali ,1,2, and Jacky Kumar 3,§ 1Department of Physics and Astronomy, University of Mississippi, 108 Lewis Hall, Oxford, Mississippi 38677, USA 2Department of Physics and Astronomy, University of California, Irvine, California 92697-4575, USA 3Physique des Particules, Universite de Montreal, C.P. 6128, Succursale Centre-Ville, Montreal, Qu´ebec H3C 3J7, Canada (Received 8 September 2019; accepted 16 January 2020; published 7 February 2020) At present, there are outstanding discrepancies between standard model predictions and measurements of the muon’s g − 2 and several B-meson properties.
    [Show full text]
  • Arxiv:2002.01400V2 [Hep-Ph] 17 Feb 2020 Are of Particular Interest
    Implications for Electric Dipole Moments of a Leptoquark Scenario for the B-Physics Anomalies Wolfgang Altmannshofer,1, ∗ Stefania Gori,1, y Hiren H. Patel,1, z Stefano Profumo,1, x and Douglas Tuckler1, 2, { 1University of California, Santa Cruz, and Santa Cruz Institute for Particle Physics, Santa Cruz, CA 95064, USA 2Fermi National Accelerator Laboratory, Batavia, IL, 60510, USA (Dated: February 18, 2020) Vector leptoquarks can address the lepton flavor universality anomalies in decays associ- ated with the b ! c`ν and b ! s`` transitions, as observed in recent years. Generically, these leptoquarks yield new sources of CP violation. In this paper, we explore constraints and discovery potential for electric dipole moments (EDMs) in leptonic and hadronic systems. We provide the most generic expressions for dipole moments induced by vector leptoquarks at one loop. We find that O(1) CP-violating phases in tau and muon couplings can lead to corresponding EDMs within reach of next-generation EDM experiments, and that exist- ing bounds on the electron EDM already put stringent constraints on CP-violating electron couplings. I. INTRODUCTION Over the past several years, multiple B-physics experiments, including BaBar, LHCb, and Belle, have reported anomalies in decays associated with the b ! c`ν and b ! s`` transitions. Violations of lepton flavor universality (LFU), known to be theoretically clean probes of New Physics (NP), arXiv:2002.01400v2 [hep-ph] 17 Feb 2020 are of particular interest. In the Standard Model (SM) LFU is only broken by the
    [Show full text]
  • Jhep12(2019)112
    Published for SISSA by Springer Received: July 10, 2019 Revised: November 26, 2019 Accepted: December 3, 2019 Published: December 16, 2019 A vector leptoquark for the B-physics anomalies from JHEP12(2019)112 a composite GUT Leandro Da Rold and Federico Lamagna Centro At´omico Bariloche, Instituto Balseiro and CONICET, Av. Bustillo 9500, 8400, S.C. de Bariloche, Argentina E-mail: [email protected], [email protected] Abstract: A vector leptoquark at the TeV scale, mostly coupled to the fermions of the third generation, is the preferred option to explain the hints of lepton flavor universality violation in the decays of B-mesons. It seems interesting to assume that this leptoquark belongs to the same beyond the Standard Model sector that solves the hierarchy prob- lem, since the third generation of fermions play the leading role in the instability of the Higgs potential. We present a composite Grand Unified Theory with resonances at the TeV that contains the required vector leptoquark and develops the Higgs as a pseudo Nambu-Goldstone boson. We show that anarchic partial compositeness of the Standard Model fermions can accommodate the couplings of Left-handed currents required by the B-anomalies, predicting very small couplings to the Right-handed currents without any additional hypothesis. By making use of an effective theory description of the strong dy- namics, in terms of weakly coupled resonances, we are able to compute the corrections to B-physics, as well as the one-loop potential for the pseudo Nambu-Goldstone bosons. The theory has a rich phenomenology and a candidate for dark matter.
    [Show full text]
  • Lepton Number Violation at the LHC with Leptoquarks and Diquarks\*
    EPJ Web of Conferences 49, 18002 (2013) DOI: 10.1051/epjconf/ 20134918002 C Owned by the authors, published by EDP Sciences, 2013 Lepton number violation at the LHC with leptoquarks and diquarks? Hiroaki Sugiyama1 1Department of Physics, University of Toyama, Toyama 930-8555, Japan Abstract. We investigate a model in which tiny neutrino masses are generated at the two-loop level by using scalar leptoquark and diquark multiplets. The diquark can be singly produced at the LHC, and it can decay into a pair of leptoquarks through the lepton number violating interaction. Subsequent decays of the two leptoquarks can provide a clear signature of the lepton number violation, namely two QCD jets and a pair of same-signed charged leptons without missing energy. We show that the signal process is not suppressed while neutrino masses are appropriately suppressed. 1 Introduction Table 1. List of scalar particles added to the SM. Although the lepton number is conserved in the standard SU(3)C SU(2)L U(1)Y L# B# model (SM) of particle physics, the addition of the Ma- S α 3 1 −1=3 1 1=3 jorana mass term of neutrinos (ννc where c denotes the LQ αβ − = = charge conjugation) breaks the lepton number conserva- S DQ 6 1 2 3 0 2 3 tion by two units. The measurement of the lepton number violating (L#V) processes such as the neutrinoless dou- ble beta decay is extremely important because it gives ev- SU(2)L, and hypercharge Y = −1=3. We also introduce a idence that neutrinos are Majorana particles.
    [Show full text]
  • Searching for Leptoquarks at Future Muon Colliders
    Prepared for submission to JHEP MIT–CTP 5296 Searching for Leptoquarks at Future Muon Colliders Pouya Asadi,a Rodolfo Capdevilla,b;c Cari Cesarotti,d Samuel Homillerd aCenter for Theoretical Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA bDepartment of Physics, University of Toronto, Canada cPerimeter Institute for Theoretical Physics, Waterloo, Ontario, Canada dDepartment of Physics, Harvard University, Cambridge, MA 02138, USA E-mail: [email protected], [email protected], [email protected], [email protected] Abstract: A high energy muon collider can provide new and complementary discovery potential to the LHC or future hadron colliders. Leptoquarks are a motivated class of exotic new physics models, with distinct production channels at hadron and lepton machines. p We study a vector leptoquark model at a muon collider with s = 3; 14 TeV within a set of both UV and phenomenologically motivated flavor scenarios. We compute which production mechanism has the greatest reach for various values of the leptoquark mass and the coupling between leptoquark and Standard Model fermions. We find that we can probe p leptoquark masses up to an order of magnitude beyond s with perturbative couplings. Additionally, we can also probe regions of parameter space unavailable to flavor experiments. In particular, all of the parameter space of interest to explain recent low-energy anomalies p in B meson decays would be covered even by a s = 3 TeV collider. arXiv:2104.05720v1 [hep-ph] 12 Apr 2021 Contents 1 Introduction1 2 Model 3 3 Production Modes6 3.1 Leptoquark Pair Production7 3.2 Leptoquark Single Production 11 3.3 Drell-Yan 14 4 Combination and Comparison to Flavor Constraints 16 4.1 Flavor Bounds 18 5 Conclusions 20 A The Statistics 22 B Modified Gauge Interactions 23 1 Introduction Detection of new physics beyond the Standard Model (SM) has been elusive so far.
    [Show full text]
  • Hera Data and Leptoquarks in Supersymmetry
    1 CERN-TH-97-195 hep-ph/9708437 HERA DATA AND LEPTOQUARKS IN SUPERSYMMETRY G. Altarelli a aTheoretical Physics Division,CERN, CH-1211 Geneva 23, and Terza Universit`a di Roma, Rome, Italy I present a concise review of the possible evidence for new physics at HERA and of the recent work towards a theoretical interpretation of the signal. It is not clear yet if the excess observed at large Q2 is a resonance or a continuum (this tells much about the quality of the signal). I discuss both possibilities. For the continuum case one considers either modifications of the quark structure functions or contact terms. In the case of a resonance, a leptoquark, the most attractive possibility that is being studied is in terms of s-quarks with R-parity violation. In writing this script I updated the available information to include the new data and the literature presented up to August 1, 1997. 1. Introduction + 2 = 5 events with about 1.2 + 0.8 = 2 expected. The distribution of the first H1 data suggested The HERA experiments H1 [1] and ZEUS [2], a resonance in the NC channel. In the interval recently updated in ref. [3], have reported an 187.5 <M<212.5 GeV , which corresponds to excess of deep-inelastic e+p scattering events at x ' 0.4, and y>0.4, H1 in total finds 7 + 1 = 2 > 4 2 8 events with about 1 + 0.5 = 1.5 expected. But large values of Q ∼ 1.5 × 10 GeV ,inado- main not previously explored by other experi- in correspondence of the H1 peak ZEUS observes ments.
    [Show full text]
  • The Leptoquark Hunter's Guide and the Dark Vector Doublet Model
    Universidad T´ecnicaFederico Santa Mar´ıa. Departamento de F´ısica. The Leptoquark Hunter’s Guide and the Dark Vector Doublet Model Bastián Díaz Sáez Advisor: Alfonso Zerwekh A thesis submitted in partial fulfillment for the degree of Doctor in Science, Universidad T´ecnicaFederico Santa Mar´ıa. November 2018 THESIS TITLE: The Leptoquark Hunter’s Guide and the Dark Vector Doublet Model AUTHOR: Bastián Díaz Sáez A thesis submitted in partial fulfillment for the degree of Doctor in Science, Universidad T´ecnicaFederico Santa Mar´ıa. EXAMINATION COMMITTEE: Dr. Alfonso R. Zerwekh (UTFSM) . Dr. Claudio Dib V. (UTFSM) . Dr. Diego Aristizabal (UTFSM) . Dr. Marco Aurelio Diaz (PUC) . November 23, 2018 Bastián Díaz Sáez i a mi abuela Ema ii This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License Bastián Díaz Sáez iii iv Abstract The purpose of the first work is to point out that a model-independent search strategy covering all possible leptoquarks is possible and has not yet been fully exploited. To be systematic we organize the possible leptoquark final states according to a leptoquark matrix with entries corresponding to nine experimentally distinguishable leptoquark decays: any of {light-jet, b-jet, top} with any of {neutrino, e/µ, τ}. The nine possibilities can be explored in a largely model- independent fashion with pair-production of leptoquarks at the LHC. We review the status of experimental searches for the nine components of the leptoquark matrix, pointing out which three have not been adequately covered. To demonstrate the utility of the leptoquark matrix approach we collect and summarize searches with the same final states as leptoquark pair production and use them to derive bounds on a complete set of Minimal Leptoquark models which span all possible flavor and gauge representations for scalar and vector leptoquarks In the second work of this thesis, we explore an extension to the Standard Model which incorporates a vector field in the fundamental representation of SU(2)L as the only non-standard degree of freedom.
    [Show full text]