Search for exclusive events at the Tevatron and the RP220 project in ATLAS

Transcription

1 Search for exclusive events at the Tevatron and the RP roject in ATLAS Christohe Royon DAPNIA-SPP, CEA Saclay Worksho on diffraction at the LHC, October 8-9 7, Cracow Contents: Inclusive diffraction at the LHC Search for exclusive events at the Tevatron (CDF) Diffractive Higgs roduction at the LHC: exclusive and inclusive roduction Background studies: How to measure the high β gluon? RP roject at the LHC in ATLAS

2 Diffraction at Tevatron/LHC (a) (b) (c) φ Ga Jet+Jet φ Jet Ga Jet φ Ga Jet+Jet η η η Ga Kinematic variables t: 4-momentum transfer squared ξ, ξ : roton fractional momentum loss (momentum fraction of the roton carried by the omeron) β, = x Bj,, /ξ, : Bjorken-x of arton inside the omeron M = sξ ξ : diffractive mass roduced y, η log /ξ, : raidity ga

3 Inclusive models Inclusive models: Take the hadron-hadron usual cross section convoluted with the arton distributions in the omeron Take shae of H measurement of gluon density Normalisation coming from CDF run I cross section measurement Inclusive cross sections need to be known in detail since it is a direct background to search for exclusive events P x, v g x k H, QQ, gg x g k P x, v

4 Inclusive Higgs mass roduction Large cross section, but mass oorly reconstructed since art of the energy lost in omeron remnants (M = ξ ξ S Higgs + remnant mass)

5 Exclusive models P x g g x k k H, QQ, γγ x g g x k k H, QQ, γγ "Standard" P "Exclusive " P g x x g k k H, QQ, γγ P "Inclusive" All the energy is used to roduce the Higgs (or the dijets), namely xg δ (See: R. Peschanski, M. Boonekam, J. Cammin, C. R. and Durham grou: A. Martin, V. Khoze, M. Ryskin, see the talks by A. Martin, M. Tasevsky, V. Juranek

6 Advantage of exclusive Higgs roduction? Good Higgs mass reconstruction: fully constrained system, Higgs mass reconstructed using both tagged rotons in the final state ( H) M H = ξ ξ S No energy loss in omeron remnants 4 Entries Mx 8 Entries Mx

7 DPEMC Monte Carlo DPEMC (Double Pomeron Exchange Monte Carlo): New generator to roduce events with double omeron exchange (both Durham and Saclay models) htt://boonekam.home.cern.ch/boonekam /demc.htm, he-h/373 Interface with Herwig: for hadronisation Exclusive and inclusive rocesses included: Higgs, dijets, dihotons, diletons, SUSY, QED, Z, W... DPEMC generator interfaced with a fast simulation of LHC detector (as an examle CMS, same for ATLAS), and a detailled simulation of roman ot accetance Ga survival robability of.3 ut for the LHC: is it ossible to check this at the Tevatron? Another available MC: Exhume for Durham model

8 Signal over background: standard model Higgs For a Higgs mass of GeV and for different mass windows as a function of the Higgs mass resolution S/B Mass resolution

9 Diffractive SUSY Higgs roduction At high tanβ, ossibility to get a S/B over 5 (res. 5.) for (res.) fb! S/B Mass resolution

10 Uncertainty on high β gluon Imortant to know the high β gluon since it is a contamination to exclusive events Exerimentally, quasi-exclusive events indistinguishable from urely exclusive ones Uncertainty on gluon density at high β: multily the gluon density by ( β) ν (fit: ν =. ±.6) zg z

11 Look for exclusive events at the Tevatron exclusive events: events without omeron remnant, search for exclusive events in dijet, dihoton, χ C channels The full available energy is used in the hard interaction Interesting for LHC... (diffractive W, Higgs, hoton anomalous couling... P x g g x k k H, QQ, γγ x g g x k k H, QQ, γγ "Standard" P "Exclusive " P g x x g k k H, QQ, γγ P "Inclusive"

12 χ C exclusive roduction at the Tevatron? CDF observation: Uer limit of χ C exclusive roduction at the Tevatron in the J/Ψγ channel σ 49 b ±8 ± 39 b for y <.6 (result not corrected for cosmics, χ contamination) Exclusive rediction: 59 b Quasi-exclusive contamination: mass fraction ν = ν = ν =.5 ν = +.5 ν = Contamination of quasi-exclusive events strongly deendent on assumtion on high-β gluon density in omeron (comletely unknown...), and also on recision and smearing of dijet mass distribution (a cut at.9 at generator level corresonds to??? at reconstructed level), true also for jet studies...

13 Dijet mass fraction measurement in CDF Look for exclusive events (events where there is no omeron remnants or when the full energy available is used to roduce diffractively the high mass object) Select events with two jets only, one roton tagged in roman ot detector and a raidity ga on the other side Predictions from inclusive diffraction models for Jet T > GeV Events FM INC DPE data (stat.) reliminary ν = ν =.5 ν =-.5 ν = ν= R jj =M jj /M x

14 Prediction from inclusive and exclusive diffraction Add the exclusive contribution (free relative normalisation between inclusive and exclusive contribution) Good agreement between measurement and redictions As an examle: exclusive and inclusive models for T > GeV and for T > 5 GeV See O. Keka, C. Royon, arxiv: acceted by Phys. Rev. D, arxiv Events FM INC + KMR EXC DPE data (stat.) reliminary ν= exclusive contribution Events DPE data (stat.) reliminary ν= exclusive contribution BL INC modified + KMR EXC R jj =M jj /M x R jj =M jj /M x

15 Soft Colour Interaction models A comletely different model to exlain diffractive events: Soft Colour Interaction (R.Enberg, G.Ingelman, N.Timneanu, he-h/646) Princile: Variation of colour string toologies, giving a unified descrition of final states for diffractive and non-diffractive events No survival robability for SCI models q q q qq q q q q H H H q q q qq qq qq

16 What about SCI? SCI models give correct normalisation for single diffraction at Tevatron and diffraction at HERA without any additional arameter Exclusive events and SCI: Contribution of exclusive events needed much lower comared to Pomeron-like models, even vanishes for jet T > 5 GeV... Events 7 6 DPE data (stat.only) reliminary Events 4 35 DPE data (stat.only) reliminary 5 Soft color interaction 3 Soft color interaction R jj =M jj /M x R jj =M jj /M x

17 Comments about SCI Contribution of exclusive events much smaller for SCI DPE exchange in SCI models dominated by the following configuration for CDF events: antiroton tagged in the final state, a bunch of articles going through the beam ie on the other side (dominated by ions), no roton in the final state, due to the fact that only a raidity ga is requested Jet raidity boosted towards high raidity: SCI model worth to be studied in more detail, but needs further imrovement dn N.5 dn N η η Jet

18 LHC: Exclusive and inclusive events Study of exclusive and inclusive roduction to be made at the LHC: study cross section of both comonents as a function of jet T and erform DGLAP QCD fits Imortant to understand background and signal for exclusive roduction of rare events: Higgs, SUSY...

19 LHC: Exclusive and inclusive events Number of dijet events as a function of jet T : dominated by uncertainty on gluon density Dijet mass fraction (average value as an examle): sensitive to exclusive roduction, quite easy to measure T T

20 Concet of survival robability Survival robability: Probability that there is no soft additional interaction, that the diffractive event is ket Imortant to measure the survival robability in data: estimated to be of the order of. at the Tevatron LRG + + Y LRG π φ a) b)

21 Roman ot rojects TOTEM roject acceted, close to CMS FP4: Project of installing roman ot detectors at 4 m both in ATLAS, CMS; collaboration being built Roman ot detectors at m in ATLAS: Natural follow-u of the ATLAS luminosity roject at 4 m to measure total cross section Comlete nicely the FP4 m roject Collaboration between Saclay. Prague, Cracow, Stony Brook, Pars 6, Michigan State University, Heidelberg, Giessen and also University of Chicago and Argonne for timing detectors (so far) being ursued Collaboration with the FP4 m roject concerning detectors, triggers, simulation... For more information, see the web ages of FP4, CMS, TOTEM, ATLAS

22 Scheme of roman ot detectors Roman ots at ATLAS 4m IP m As close as ossible to the beam: s = mm 8 s 3cm Silicon Detectors Assume roman ots located at 6 and 4 m

23 Accetance for m ots Stes in ξ:. (left),.5 (right), t = or.5 GeV Detector of cm cm will have an accetance u to ξ.6, down to.8 at σ,.6 at σ As an examle Higgs mass accetance using m ots down to 35 GeV and uer limit due to cross section and not kinematics Y [mm] -5 S = 6 m Y [mm].5 ξ =,.5,.,.5,. S = 6 m t =, -. GeV S = 4 m σ: ξ~ σ: ξ~ X [mm] X [mm]

24 Roman ot rojects accetance [%] RP full simulation combined accetance RP + RP +4 RP missing mass [GeV] Both FP4 and RP needed to have a good coverage of accetance (NB: accetance slightly smaller in CMS than in ATLAS)

25 Roman ots / movable beam ie at m Schematic view of m ots: horizontal ots to detect diffractive events, vertical ots used for alignment

26 Which kind of detectors? Requirement: good resolution in osition (good measurement of mass, kinematical rowerties), and in timing Position detectors: Size of Si detectors (either 3D or stris) to be ut in roman ots: cm cm Satial resolution of the order of -5 µm: Si stri detectors of 5 µm: 5 layers, vertical, horizontal, U, V (45 degrees) Edgeless detectors: Between 3 to 6 µm First rototye of stri detector made by CANBERRA, 3D detectors made for FP4: test-stand (laser and radioactive source) being installed in Saclay, tests also ossible at CERN/Prague Trigger: Stri detectors of - µm, Si or ixel chi to be modified to include trigger ossibility

27 Which kind of detectors? Timing detectors Why do we need timing detectors? At the LHC, u to 3 interactions by bunch crossing, and we need to identify from which vertex the rotons are coming, same roblem for FP4 Timing detector in movable beam ie: resolution needed: of the order of 5 icoseconds (sace resolution slightly more than mm) Radiation hardness Detector sace resolution: few mm, the total width of the detectors being.5 cm (4.5 cm available in roman ot) Reference clock: either the LHC clock (resolution of 7-8 s), or atomic clock (they need to be calibrated on each side) Trigger information: at L (rough comatibility between both sides of ATLAS) and secially at L (comatibility with vertex osition) Develoment: new timing detectors in collaboration with the Universities of Chicago, Stony Brook, and Argonne, and with Photonis

28 Trigger: rincile Horizontal roman ots (a la TOTEM) - 4 m xa T L - 6 m T L xb Diffractive Higgs Trigger jet 7 lans Si stris /Roman Pot x,y σ osition 5 microns σ time < sec PA SH Front end Chi ABC next Pieline buffer (> 3.6 µsec) xa xb T Left Pretrigger xa - xb = +85 ns (air cable) jet ATLAS detector LR Trigger Logic LP AND RP TR - TL < sec L L CTP CTP Right Pretrigger Jets with Pt > Gev/c Max 75KHz xd - xc = T R T T R +73 ns, µsec, µsec,5µsec R O D US5 ATLAS standard HLT HLT Trigger Trigger (ROB) (ROB) ATLAS Standard Refined Jet Pt cut Vertice within millimeter time < 5 to sec

29 Trigger: strategy L trigger when two rotons tagged at m L trigger when only one roton is tagged at m: in that case, cut on accetance at m corresonding to the ossibility of a tag at 4 m Cuts used: jets in central detector with T > 4 GeV Exclusiveness of the rocess ( jets carrying 9% of the energy) (E T + E T )/H T >.9 Kinematics requirement (η + η ) η > At least one roton tagged at m with ξ <.5 (comatible with the eventual resence of a roton at 4 m on the other side) or one roton tagged at m on each side With those cuts, ossibility to get a L rate less than khz for a luminosity less than cm s

30 Collaboration between FP4 and RP Develoment for RP roject: Roman ots: 3 arms (horizontal, u and down for diffractive events and elastics, do we need a magnet between ots? (avoid low energy articles coming from the first ot) Pixel detectors: modify size of ixel detector to cm cm Trigger caability: trigger erformed by reading lines of ixels to be able to comute ξ at L Final timing detectors: 5 s resolution, aim to develo by, MCP technology, (to be used also by FP4) FP4 and RP together: Pixel detector technology and readout Movable beam ie technique: used for timing detectors in RP Timing detectors for : temorary MCP (resolution of 3-4 s?), gastof develoed by Louvain (5 s?) RF icku: to be comuted by Manchester team FP4 and RP backu: Si stri detectors

31 Conclusion Study of inclusive events: determination of gluon at high β, QCD studies, search for SUSY events (or any resonance) when dijet background is known Exclusive events: romising results in dijet channel at the Tevatron Exclusive Higgs: Signal over background: if one gets a very good resolution using roman ots (better than.5 GeV), enhanced by a factor u to 5 for SUSY Higgs at high tanβ QED WW air roduction: cross section known recisely, allow to calibrate rescisely the roman ot detectors, study of hoton anomalous couling Project of installing roman ot detectors in ATLAS well started: collaboration between Prague, Cracow, Saclay, Stony Brook, Heidelberg, Giessen, Paris 6, Michigan State University Collaboration about timing detectors (and medical alications): University of Chicago, Argonne, Saclay TDR to be resented in ATLAS together with FP4 in the beginning of next year