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Forbidden

Forbidden. &. Exotic. decays in NA62. Gianluca Lamanna 11.12.2009 NA62 Physics Handbook Meeting. “ Forbiddens ” and “ exotics ”. Only K+ modes ( for the moment) Direct LFV modes (Test of lepton universality has been covered in the previous talk)

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Forbidden

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  1. Forbidden & Exotic decays in NA62 Gianluca Lamanna 11.12.2009 NA62 PhysicsHandbook Meeting

  2. “Forbiddens” and “exotics” • OnlyK+modes (for the moment) • Direct LFV modes (Test ofleptonuniversalityhasbeencovered in the previous talk) • Personal selectionof“exotics” modes: someonealreadydiscussed in othersession, someonenotconsidered in this talk. • “The best we can do” principle: assumed100% trigger efficiency(severalissues on this), assumed“ideal” selection (onlygeometricalacceptanceincluded) • A factorof N couldbeconsidered in the extrapolatedlimits : more work isneededtocorrectlyevaluatedacceptances and efficiencies • Forsure, due to the trigger, wewillbenotabletocollect in parasitic way everythings: weneed feedback fromtheory(see Marco S. & Edoardo C.) !!! • Alsoothers data takingscenarios (specialruns, extensions…) shouldbemotivatedbyphysical interest.

  3. Forbiddenslist

  4. B865, E787, E949 …

  5. K+→p+m+e- : present status • Analysis: 3 trackswithcorrect PID, s(MK)~4 MeV/c2 • Mainbackgrounds: K→ ppp, Km3, K→pp0D, accidentals • PID: 80% per p, m, e (with 7% mis-idforp->m) • Trigger: 4 levels (4 MHz @ L0) • L0: 2.5 kHz (3 tracks and topology(PID)) • L1: 1.3 kHz (PID) • L2: -- (e+e-) • L3: 0.6 kHz (Quality in PWC) • 0.3·109 trigger collectedwith high efficiency <1.3·10-11 @90% → MHETC>79.6 TeV • complementarytoKL→m e • differentmodelsallow LFNV processes: Technicolor, Supersymmetry, ExtendedGaugeTheories • 8 eventsfoundwith 8.2 bkg • K flux (fromppp,appp=0.1264): 5.5·1012 • apme = 6.8% • → 2.1·10-11 @90% [Aleksey Sher,Phys.Rev.D72:012005,2005]

  6. K+→p+m+e- @NA62 • 5·105 KaondecaysproducedwithFlyo Montecarlo (onlyphasespace) pme pp0 • Kaon rate: ~10 MHz • Total K flux: ~1013 in 2 years • PID eff.: assumed100% • Mis-ID: assumed0% • Trigger eff.: assumed100% • Acceptance: ~18% • Better background suppression (thankstokinematics and PID) E(LKR) • Problemswith trigger: • L0 standard condition: 1 HOD + !LKR + !mu -> veryinefficienttocollectpme • parassiticswithdownscaling (the downscaling can’t betoo big otherwiseweloose the gain due the more intense beamwrt NA48/2 (Edoardo C.)) • specialruns • dedicated data taking Assuming 0 background events (N=2.4) : BR < 1.3·10-12 @90% MHETC>120 TeV

  7. K+→ p- m+m+, K+→p- e+e+, K+→e+m±p: status • Thesedecays violate LF and the generation numberconservation • The K→p-l+l+ can proceedthrough the samedouble beta decaymechanism • The K→p-m+m+isanuniqueopportunitytostudy the effectsofMajorananeutrinos in second generation K →p-m+m+:Acceptancesmaller (~ 3) withrespectto K→p+m+m- Background from K→p-p+p+withpdecay in the spectrometer 5 eventswith 5.3 expectedbkg BR(K →p-m+m+)<3.0 ·10-9 Flux (3p): 108 K+→e+m±p : small background from Ke4 e 3pwithmis-id. No eventscandidateswith 0 bkgexpected BR(K→e+p+m-)<5.2 ·10-10 BR(K→e+p-m+)<5.0 ·10-10 Flux (Ke4): 3.8·108 u d l W n l W d s K → p-e+e+: small background from Ke4 e 3pwithmis-id. No eventscandidateswith 0 Bkgexpected. BR(K → p-e+e+)<6.4·10-10 Flux (Ke4): 3.8·108 [Appel, Phys.Rev.Lett.85:2877-2880,2000]

  8. … @ NA62 Assuming1013decays in 2 years, and 0 eventsfoundwith 0 eventsbkgexpected: BR(all the modes) < 1.3·10-12 5·105 KaondecayproducedwithFlyo Montecarlo (onlyphasespace) Assuming100% trigger efficiencyhigherimprouvmentwithrespectto the p+m+e- (because E865 usedsecondarytriggers (Ke4, p+m+m-) toevaluate the BR) e+e+p- e+m-p+ e+m+p- m+m+p-

  9. Three tracks NA62 trigger Can we obtain 100% three track trigger efficiency? BR(3p) = 5.59% BR(pp0D) = 2.5% BR(Ke3) = 0.6% BR(Km3) = 0.4% BR(pp0p0) = 0.4% ---------------------------------- Tot(3trks) ~10% 10 MHz total rate on detectors→ 0.5 MHz from 3p→~ 1 MHz (3 trks) • Assumingtohave 100% L0 trigger efficiencywithoutanyselection (minbias): • max r/o bandwidthfordetectors (not)partecipatingto the trigger (400) 300 MB/s per TELL1 example: • RICH r/o bandwidthrequestformain trigger (no bkg, no halo) 200 MB/s -> 50 MB/s per TELL1 • RICH r/o bandwidthrequestforthreetracks trigger 600 MB/s -> 150 MB/s per TELL1 • Total 200 MB/s per TELL1 -> possiblein principle, smallspaceto accomodate othercontroltriggers or calibrations. • Muchimportant: the TELL1 maximum trigger rate isaround1 MHz (speedof buffer reading, possiblesmallimprovementswithnew NA62-TELL1) L0 selectionbased on topology or fast analysis (GPU)

  10. The GPU trigger • We are studying the possibilitytouse standard Video Cardsfortriggering • The parallelstructureof the GPU (graphicsprocessorunits) architecture can beexploitedtoimplementcomplexalgorithms(ex. pattern recognition) on severaleventsat the sametime • The useofGPUs at L0 in Real-timeisverychallenging (the trigger latencyhavetobe1ms and the decay rate is10 MHz) GPU RICH GPU 12 hits Best ring L0TS Hits generated NA62 - G4 MC MUV GPU STRAWS • We are tryingtouse the GPUsfor the specificproblemofring searching in the RICH • The results are veryencouraging!!! • The benefitsfor the physicswillbe the possibilitytoimplementveryselective trigger with high efficiencyusingoffline qualityprimitives L0 trigger primitives Trigger Reduced Data Data to L1

  11. K→pg • The K→p g is a 0→0spintransitionwithrealphoton: forbiddenbyangularmomentumconservation. • Violationof a veryfundamentalconservationlaw→no simple SM extensioncan accomodate the presenceofthisdecay. • Only in theories with completelly new approaches (vacuum expection value of new vector field, non-local Superstring effects, departure from Lorentz invariance, space-time non commutivity,…) • Two (recents) measures: E787 and E949 • Stopping kaon experiments: P=227 MeV/c p+ tracks • Photon veto inefficiency (1.4-16)·10-5 (E949 factor 2 wrt E787) • Kaon flux: 6.7·108 (E787), 1.2·1012 (E949) • Acceptance: 1.4% (E787), 0.1% (E949) • Bkg = 23 events (E787), 0 (E949) 1 0 g K Eventsfound: 20 (E787), 0 (E949) Results: <3.7·10-7 @90% (E787), <2.3·10-9 @90%(E949) p 0 [Artamonov, Phys.Lett.B623:192-199,2005] [Adler, Phys.Rev.D65:052009,2002]

  12. K→pg in NA62 5·105 KaondecayproducedwithFlyo Montecarlo (onlyphasespace) a Assumingacceptance 35%, 0 eventsfoundwith 0 background BR<7·10-13 Main trigger efficency < 40% (if NLKR insteadof ELKR) Background reductionbased on veto system Z pp0 pg ELKR(GeV) eV mm2

  13. The pg trigger • Very hard toimplement a dedicatedpgtrigger at L0!: • GPUsolution: !MU&ETOT(RICH+LKR) • The pmomentum can becomputedfrom Ring radius and center position in the RICH assumingpion mass. In addition the K missing mass can becomputedassumingPt and kaon direction . b a RICH(r,(x,y)) +mp → (b, pp) + ptkick→ (a,pp) + K →mm2 RICH STRAWS

  14. Exotics K & p0list Other modes: sterile neutrinos (Shaposhnikhov J.Phys.Conf.Ser.136:022045,2008), Axions …

  15. K→pX0, K→pcc • The PDG quotes the limitsfor the neutralinos mass: mc>46 GeV • Thislimitisn’t modelindependent • Ithasbeenshownthat in a modelindependent way (at leasttreating the gauginos mass parametersas free parameters) the neutralino can beadjustedtobemassless or withsmall mass • In the MSSM with MFV the BR(K→pcc) is 6 or 7 orderofmagnitudesmallerwithrespectto the K→pnn • In the MSSM with NMFV (with the mass insertionapproximation), forspecificvaluesof the mass insertionparameters (functionofaveragesquarkmasses and gluino mass) the BR shouldbe a factor 10 wrt K→pnn, experimentallyfrom the differentp pt (depending on the chi chi mass). • (seeUlrichHaish t’s talk) • K→p X0: E787 set the limitof5.9·10-11formassless X0 weaklyinteractingstableparticle; E949 performed a “mass scan” assumingstable and notstableparticle (under the assumptionof 100% veto efficiency in the last case) [Artamonov et. al Phys.Rev.D79:092004,2009] [Adler et al. Phys.Rev.Lett.88:041803,2002]

  16. New particles @NA62 Dreiner et al. Phys.Rev.D80:035018,2009 Shaposhnikhov J.Phys.Conf.Ser.136:022045,2008 • We are kindlyinvitedtostudy the presenceofnewparticles in mesonsdecay • BothK→pccand K →pX0are “for free” with the K→pnn standard analysis • No further trigger conditionsforstableparticles in region I and region II • The improuvmentwrt E949 resultissimilarthat in the pnn • More studiestounderstandsensitivity and analysisfordecayingnewparticles

  17. p0→eeee, p0→ggg In the p0→eeeethe decayprobabilityisgivenby : [Bernstein and Michel Phys.Rev.118:871-875,1960] C=0 ifthereisn’t Tviolation in SI or EI Measured by Samios et. Al. (1962), with 206 events C=-0.77+-0.53 [Samios et al. Phys.Rev.126:1844-1849,1962] The searchforp0→gggis a way to test the C invariance in EI. If C symmetrywasviolated the theoreticalpredictionsforthisdecaywillbe at levelof 10-9 due tophasespace, couplings and angularmomentum. The experimentalpresentlimitis ( CrystalBox(1988) ): <3.1x10-8 (90% C.L.) Total p0flux = 1.75 ·1010 Acceptance = 0.3%->1.2% depending on total energy [J. McDonough et al. Phys.Rev.D38:2121,1988]

  18. p0→e+e- Recenttheoreticalpredictionbased on CLEO and CELLO data disagreeswrt KTEV measurementof3.3s BRKTEV=(7.48+-0.38)10-8 BRQCD+CLEO=(6.23+-0.09)10-8 Np0~ 1010 Thereis a classofmodelsofdescriptionof dark matterbased on low mass newneutral scalar particlec (Boehmet al.,Phys.Rev.D70:115013,2004). The cparticleannihilates in twoelectrons , c→e+e-, mediatedby a newneutralvectorboson U. The U partecipates (with low coupling, natural in light dark mattermodels) toenhanced the p0→e+e- through a “tree” diagram(the p0→e+e- proceedsonly at onelooplevel due to the factthat the realmasslessphotonhas no longitudinalcomponentsp0 → g* → e+e-) [Durokhov, Nucl.Phys.Proc.Suppl.181-182:37-41,2008] [Kahn et al., Phys.Rev.D78:115002,2008] [Abouzaid et al., Phys.Rev.D75:012004,2007] The U boson is one of the most favourite explanations of the 511 KeV positrons anomaly from the center of the galaxy Nature 451:159-162,2008

  19. p0s exotic @ NA62 About30%ofK+decayshavep0s (20% come fromkinematicallyconstrainedp+p0) →3 1012 / 2 years ~30% p+p0withgg in LKracceptance and p+in spectrometer→ 6 ·1011 The realacceptancedepends on the p0decay mode. Comingfromp+p0also in this case the trigger willbe the realissue(both at L0 and L2). • The secondarytriggersconfigurationhavetobedrivedby the physics interest and the feisability: • p0→ggg: for the first timewewillbeabletoenter in the fieldof the C violationeffects , below the kinematicslimits, weneedhugestatisticsforsignificantmeasurement, hard tohaveparasitics trigger →medium priority, furtherstudies • p0→eeee(C violation): the physics interest isrelativellysmall, verysmallstatisticstoimprouve the previousmeasurements, easy toimplement a low bandwidth trigger (5 tracks) →couldbedoneeasily • p0→ee: interestingphysicspotential, weneed big statistics, the trigger isquitedifficult→medium priority, furtherstudies

  20. Sgoldstinos in NA62 • The Hyper CP observationof the pseudoscalarsgoldstinoin the S+decayisn’t confirmed (at 214 MeV/c2) • In the kaonsectorwe can observetwokindofsgoldstinos (ifthey are light enough): the scalar in K+→p+ S and the pseudoscalar in K+→p+p0P • The searchforP sgoldistinoscan bedone in “invisible mode” (long livedsgoldstinos) or assuming the P→gg or P→mm (the gammas mode dominates in the whole the phasespace) • The Q valuefor the decayisverysmallfor massive sgoldistino; the p, in K+→p+p0gg(withlargeggmasses) , remains in the beam pipe →smallacceptance and difficultto trigger (sameconsiderations in mmchannel) • For the scalar sgoldistinothe relation mS>mP+mpleaves a verysmallphasespace (mP+mp)-(mK-mp) • Weneedan accurate simulationtounderstand the realacceptanceand the possibilityto trigger withoutchargedparticles [Park, Phys.Rev.Lett.94:021801,2005] [Gorbunov, Phys.Rev.D73:035002,2006]

  21. Summarytable

  22. Montecarlo generators • The maintoolweneedtobetterunderstandourcapabilities and the physicalpotentialofourpossibleoutcomes, is the MC: • The LFV decaymodesgenerators in NA62MCwillbecommitted in the nextversion (byStefano Venditti) • Flyo Montecarlo simulationalreadystarted 100 K→p-m+e+ 100 K→p+m-e+

  23. “Forbidden” experimental team • Paolo Massarotti, Fabio Ambrosino: direct LFV • Gianluca Lamanna: K+→p+ g • Sergio Giudici: p0 • Stefano Venditti: New particles (“mass scan”) • … weneed 7 more people toreach the “dozen”…

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