Presentation on theme: "The CMS and TOTEM diffractive and forward physics program"— Presentation transcript:
1 The CMS and TOTEM diffractive and forward physics program K. Österberg, High Energy Physics Division, Department of Physical Sciences, University of Helsinki & Helsinki Institute of PhysicsLow x meeting, Helsinki CERN/LHCC 2006039/G124CMS Note2007/002TOTEM Note 065
2 Diffraction: a window to QCD and proton structure Double Pomeron Exchange or Central Diffraction:Single Diffraction:Proton det.XCentral & forward det.GapCentral & forward det.GapXGapProton det.p p p XProton det.p p p X pcharacterized by 2 gluon exchange with vacuum quantum numbers (“Pomeron”)X = anything : dominated by soft physicsMeasurement of inclusive cross sections + their t & MX dependence fundamental measurements of nonperturbative QCD at LHC!X = jets, W, Z, Higgs: hard processes calculable in perturbative QCDProton structure (dPDFs & GPDs), high parton density QCD, rapidity gap survival probability, new physics in exclusive central diffraction
4 Forward proton measurement: principle Diffractive protons : hit RP220mhigh L (low *) low L (high *)y(mm)y(mm)y ~ yscatt ~ | ty |10x ~ p/p10x(mm)x(mm)Detect the proton via:its momentum loss (low *) its transverse momentum (high *)
5 CMS/TOTEM combined acceptance Unique coverage makes a wide range of physics studies possible from diffraction & proton low-x dynamics to production of SM/MSSM HiggsAcceptance for RP 220 mTOTEM CMS TOTEMLog(), = p/pCharged particle flowlow *Charged particle flow420 m proton low *Energy flow* = 1540* = 90Log(t [GeV2])Wide coverage in pseudorapidity & proton detection At high L proton m enlarge acceptance to ~ 2 10 For details see B. Cox talk on FP420
6 Running scenariopp->pX pp->pjjX pp->pjj (bosons, heavy pp->pXp pp->pjjXp pp->pjjp quarks,Higgs...)soft diffraction (semi)-hard diffraction hard diffractioncross section luminosity mb b nb* (m)L (cm2 s1)TOTEM runs Standard runsAccessible physics depends on: luminosity * (i.e. proton acceptance)
8 Diffraction at low luminosity: soft central diffraction Study of mass distribution via the 2 protons measured directly (() ~ 1.6 103 @ = 90 m) or with rapidity gap with calorimetersMX =12s = ln ()/ ~ 80 % i ETi ei / s ()/ ~ 100 %Mass resolution, = 90 m, mDifferential mass distribution, acceptance correctedasymmetric eventsAcceptance 1/N dN/dMX [1/10 GeV]symmetric eventslow MX [GeV]
9 Diffraction at high luminosity: central exclusive production New physics searches e.g. (pp p H(120 GeV)[bb] p) ~ 3 fb (KMR)JPC selection (0++...) qq background heavily suppressed Selection: 2 protons + 2 b-jets with consistent mass values Experimental issues: trigger efficiency & pileup background in some MSSM scenarios much larger, H WW if H heavier(MX)/MXAcceptanceNB! Assumes proton 420 mMX [GeV]MX [GeV]
10 Diffraction at high luminosity: triggering on diffraction dedicated diffractive trigger stream foreseen at L1 & HLT (1 kHz & 1 Hz)standard trigger thresholds too high for diffraction at nominal optics use information from fwd detectors to lower particular trigger thresholdsL1:jet ET > 40 GeV ( standard 2jet threshold: ~100 L = 2 1033 cm2s1)1 (or 2) arm mdiffractive topology (fwd rapgaps, jetproton hemispherecorrelation …)HLT (more process dependent):e.g. 420 m proton detectors,mass constraint, b-tagging..bench mark process: centralexclusive H(120 GeV) bbL1: ~ 12 %HLT: ~ 7 %additional ~ 10 % L1 witha 1 jet + 1 (40 GeV, 3 GeV) triggerEfficiency420m220mmmL1 trigger threshold [GeV]
11 Diffraction at high luminosity: reducing pileup background At high luminosity, non-diffractive events overlaid by soft diffractive events mimic hard diffractive events (“pileup background”)Pileup event probability with single proton in (420m) ~ 6 % (2 %) probability for fake central diffractive signal caused by pileup protonsPileup background reduction:correlation & mass measured with central detector & proton detectorsfast timing detectors to distinguish proton origin & hard scattering vertex from each other (R&D project)pileup background depends on LHC diffractive proton spectrum rapidity gap survival probability
12 Lowx physicshigh LHC allows access to quark & gluon densities forsmall Bjorkenx values: fwd Drell-Yan (jets) sensitive to quarks (gluons) > 5 & M < 10 GeV x ~ 106107T2 + CASTOR !!M2 of Drell Yan pairs in CASTORx of Drell Yan pairs in CASTOR
13 Forward physics air shower models, possible new phenomena… Forward particle & energy flow: validation of hadronicair shower models, possible new phenomena… Study of underlying event & p mediated processes: e.g. exclusive dilepton production() (true)knownrms ~ 10-4Calibration process for luminosity and energy scale of proton detectorsAllows proton value reconstruction with a 104 resolution < beam energy spreadStriking signature: acoplanarity angle between leptons
14 CMS 2008 diffractive & forward program First analysis in 2008 most likely based on large rapidity gap selection Even if m available need time to understand the data …Concentrate first analysis on data samples where pileup negligibleDeveloping rapidity gap trigger with forward calorimeters (HF, CASTOR…)Program:“Rediscover” hard diffraction a la Tevatron, for example:measure fraction of W, Z, dijet and heavy flavour production with large rapidity gapobserve jet-gap-jet and multi-gap topologiesForward physics with CASTORmeasure forward energy flow, multiplicity, jets & Drell-Yan electrons & p interactions, for exampleobserve exclusive di-lepton production
15 TOTEM Detectors: Roman Pots 2 RP220 m stations installed into LHC in May-June, remaining by end of summerSi edgeless detectorVFAT hybrid with detectorFirst edgeless Si detectors mounted with final VFAT hybrid successfully working with source & in test beam all detector assemblies ready for mounting by April 2008.
16 TOTEM detectors: T1 & T2 T1 Telescope T2 Telescope testbeam setup Mechanical frames and CSC detectors in production; tests in progress. During 2007 complete CSC production. Plan to have two half-telescopes ready for mounting in April 2008.All necessary GEM’s produced (> half tested upto gains of 80000). Energy resolution %. The 4 half-telescopes should be ready for mounting in April 2008.
17 Optics & beam parameters (standard step in LHC start-up)= 90 m(early TOTEM optics)= 1540 m(final TOTEM optics)Crossing angle0.0N of bunches15643N of part./bunch(4 – 9) 10103 1010Emittance [m ∙ rad]3.75110 vertical beam width at RP220 [mm]~ 36.251.3Luminosity [cm-2 s-1](2 – 11) 1031(5 – 25) 10291.6 1028* = 90 m ideal for early running:fits well into the LHC start-up running scenario;uses standard injection easier to commission than 1540 m opticswide beam ideal for RP operation training (less sensitive to alignment)* = 90 m optics proposal submitted to LHCC & well received.
18 = 90 m optics Optics optimized for elastic & diffractive scattering Proton coordinates w.r.t. beam in the RP at 220 m:(x*,y*):vertex position(x*,y*):emission angle = p/pLy = 265 m (large)vy = 0Lx = 0vx = – 2D = 23 mmvertical parallel-to-point focusing optimum sensitivity to y*i.e. to t (azimuthal symmetry)elimination of x* dependenceenhanced sensitivity to x in diffractive events,horizontal vertex measurement in elastic eventsx RP220 mx RP220 m for elastic events measurement of horizontal vertex IPLuminosity estimate together with beam parameters if horizontal-vertical beam symmetry assumedBeam position measurement to ~1 m every minute
19 TOTEM 2008 physics programFor early runs: optics with * = 90 m requested from LHCCOptics commissioning fits well into LHC startup planningTypical running time: several periods of a few daysTotal pp cross section within ± 5%Luminosity within ± 7%Soft diffraction with independent proton acceptance (~ 65%)proton resolution limited byLHC energy spreadvia rapidity gap (T1, T2)via rapidity gap (CMS)s(x)/x = 100%via proton (b*=90m)
20 CMS and TOTEM diffractive and forward physics program SummaryCMS and TOTEM diffractive and forward physics programCMS+TOTEM provides unique pseudo-rapidity coverageIntegral part of normal data taking both at nominal & special opticsLow Luminosity (< 1032 cm-2s-1):nominal & special opticsSingle & central diffractive cross sections (inclusive & with jets, rapidity gap studies)Lowx physicsForward Drell-Yan & forward inclusive jetsValidation of Hadronic Air Shower ModelsIncreasing Luminosity (> 1032 cm-2s-1):nominal opticsSingle & central diffraction with hard scale (dijets, W, Z, heavy quarks) dPDF’s,GPD’s, rapidity gap survival probability & p physicsHigh Luminosity (> 1033 cm-2s-1) : nominal opticsCharacterise Higgs/new physics in central diffraction?Running with TOTEM optics: large proton acceptanceNo pileupPileup not negligible:important background sourceNeed additional proton detectors
22 An important milestone for collaboration between the 2 experiments Content of common physics documentIncludes important experimental issues in measuring forward and diffractive physics but not an exhaustive physics studyDetailed studies of acceptance & resolutionof forward proton detectorsTriggerBackgroundReconstruction ofkinematical variablesSeveral processesstudied in detailCh 1: IntroductionCh 2: Experimental Set-upCh 3: Measurement of Forward ProtonsCh 4: Machine induced backgroundCh 5: Diffraction at low and medium luminosityCh 6: Triggering on Diffractive Processesat High LuminosityCh 7: Hard diffraction at High LuminosityCh 8: Photon-photon and photon-proton physicsCh 9: Low-x QCD physicsCh 10: Validation of Hadronic Shower Modelsused in cosmic ray physicsAn important milestone for collaboration between the 2 experiments
23 Running scenarios 1.15 (0.6 - 1.15) 0.3 N of part. per bunch 2 x 1030 2.32003.7515690Soft &semi-hard diffraction2.4 x 10291540Soft diffraction3.6 x 10321.6 (7.3) x 1028Peak luminosity[cm-2 s-1]5.280.29 (2.3)RMS beam diverg.[rad]95454 (200)RMS beam size at IP [m]1 (3.75)Transv. norm. emitt. [m rad]160Half crossing angle280843N of bunches18, 2, 0.51540 (90)large |t| elasticlow |t| elastic,tot ,min biasPhysics:*[m]
24 Diffraction at low luminosity: rapidity gapsdiffractive system Xp2p1Measure via rapidity gap: = lnAchieved resolution: ()/ 80 %Gap vs ln () T1+T2+CalorimetersminmaxGap * = 90 * = 2same acceptance/ limitGap measurement limit due to acceptance of T2ln = 2103 2102
25 Diffraction at medium luminosity: semi-hard diffraction d/dpT(b)Measure cross sections & their t, MX, pTjet dependenceEvent topology: exclusive vs inclusive jet production access to dPDF’s and rapidity gap survival probabilityN event collected[acceptance included]* = 90 m ∫L dt = 0.3 pb1SD: pT>20 GeV x104CD: “* = 2 m ∫L dt = 100 pb1SD: pT>50 GeV x105CD: “ x104SD:pp->pjjXassumed cross sectionsCD:pp->pjjXppTjet(GeV)In case of jet activity also determined from calorimeter info: i ETi ei / s()/ 40 %
26 Forward proton measurement: acceptance (@220 m & 420 m) RP 220m*= 0.5 2 mLog(), = p/p* = 2/0.5FP420420 m220 m* = 1540* = 90Log(t)Proton detectors at 420 m would enlarge acceptance range down to = at high luminosity (= low *).
27 Forward proton measurement: momentum resolution (* = 90 m) Individual contributionto the resolution:Transverse vertexresolution (30 m)Beam positionresolution (50 m)Detectorresolution (10 m)total()220 mFinal state dependent; m for light quark & gluon jetsp/p
28 Forward proton measurement: momentum resolution (* = 2/0.5 m) Individual contributionto the resolution:Detectorresolution (10 m)Beam positionresolution (50 m)Transverse vertexRelative beam energyspread (1.1104)()/totalp/p* = 90 m vs. * = 2/0.5 mBetter ()/ for * = 2/0.5 m & larger luminosity but limited acceptance ( > 0.02)Very little final state dependence since transverse IP size is small.
29 Cosmic ray connectionInterpreting cosmic ray data depends on cosmic shower simulation programsForward hadronic scattering poorly known/constrainedModels differ up to a factor 2 or moreNeed forward particle/energy measurements at high center-of-mass energy (LHC Elab=1017 eV)Achievable at low luminosity using T1/T2/HF/Castor
31 Diffractive PDF’s and GPD’s jetbhardscatteringIPdPDFDiffractive PDFs:probability to find a parton of given x undercondition that proton stays intact –sensitive to low-x partons in proton,complementary to standard PDFsGPDjetGeneralised Parton Distributions (GPD) quantify correlations between parton momenta in the protont-dependence sensitive to parton distribution in transverse planeWhen x’=x, GPDs are proportional to the square of the usual PDFs