the SPS to the LHC Andrew Brandt, University of Texas at Arlington

Transcription

1 Forward Protons from the SPS to the LHC Andrew Brandt, University of Texas at Arlington Thanks to Albert de Roeck, Brian Cox, Dino Goulianos, Mike Albrow, Michele Arneodo, Michael Strang, and others for slides DOE, NSF, UTA, Texas ARP for support Physics Seminar Mar 2, 2006 SLAC

2 What is Diffraction? Diffraction in high energy hadron physics encompasses those phenomena in which no quantum numbers are exchanged between interacting particles Surviving particles have same quantum numbers as incident particles Exchanging quanta of the vacuum is synonymous with Pomeron ( IP ) exchange Named after Russian physicist I.Y. Pomeranchuk Virtual particle which carries no net charge, isospin, baryon number or color Couples through internal structure Signatures of diffraction include rapidity gaps (regions of the detector with no particles above threshold) and intact final particle(s) which can be tagged with a forward proton detector

3 Examples of Soft Diffraction Elastic Single Diffraction Modeled by Regge Theory Analysis of poles in the complex angular momentum plane give rise to trajectories that describe particle exchange P.D.B. Collins, An Introduction to Regge Theory and High Energy Physics, Cambridge Univ. Press, Cambridge 1977 Non-perturbative QCD

4 Elastic Scattering The particles after scattering are the same as the incident particles The cross section can be written as: dσ dt bt 2 = e 1 b( pθ ) dσ dt ( ) t = 0 This has the same form as light diffracting from a small absorbing disk, hence the name diffractive phenomena Elastic dip Structure from Phys. Rev. Lett. 54, 2180 (1985).

5 Learning about the Pomeron QCD is theory of strong interactions, but 40% of total cross section is attributable to Pomeron exchange -- not calculable and poorly understood Does it have partonic structure? Soft? Hard? Super-hard? Quark? Gluon? Is it universal -- same in ep and p p? Is it the same with and without jet production? Answer questions in HEP tradition -- collide it with something that you understand to learn its structure Note: variables of diffraction are t (momentum transfer) and ξ ~ M 2 2 (fractional momentum loss) with a proton detector measure d σ without one just measure σ dtdξ

6 Ingelman-Schlein Factorization allows us to look at the diffractive reaction as a two step process. Hadron A emits a Pomeron (pomeron flux) then partons in the Pomeron interact with hadron B. The Pomeron to leading order is proposed to have a minimal structure of two gluons in order to have quantum numbers of the vacuum A A* J 2 P X J 1 G. Ingelman and P. Schlein, Phys. Lett. B 152, 256 (1985) B

7 UA8

8 UA8 = UA2 + Roman-pot Spectrometer

9 UA8 Dijet Production in Diffraction A. Brandt et al., P.L. B 297 (1992) 417 (196 citations!) Hard Diffraction exists! Pomeron has a super-hard component. x(2-jet)

10 e p Diffractive Deep Inelastic Scattering W Q 2 IP γ* t e X p LRG Q 2 = virtuality of photon = = (4-momentum exchanged at e vertex) 2 t = (4-momentum exchanged at p vertex) 2 typically: t <1 GeV 2 W = invariant mass of photon-proton system x IP = fraction of proton s momentum taken by Pomeron = ξ in Fermilab jargon β = Bjorken s variable for the Pomeron = fraction of Pomeron s momentum carried by struck quark ZEUS X e p 27.5 GeV η e 920 GeV s 320 GeV

11 Two fundamental physics quantities can be accessed in diffractive DIS: dpdfs and GPDs 1) Diffractive PDFs: probability to find a parton of given x in the proton under condition that proton stays intact sensitive to low-x partons in proton, complementary to standard PDFs (ingredient for all inclusive diffractive processes at Tevatron and LHC) e e IP dpdf Rather than IP exchange: probe diffractive PDFs of proton p p 2) Generalised Parton Distributions (GPD) quantify correlations between parton γ momenta in the proton; t-dependence sensitive to parton distribution in transverse plane When x =x, GPDs are proportional to the p square of the usual PDFs (ingredient for all exclusive diffractive processes) GPD VM, γ, exclusive dijets Higgs x x p

12 Diffractive Structure Function vs β, Q2 x IP F 2 D(3) x IP F 2 D(3) β Weak β dependence not a normal hadron! Q 2 Positive scaling violations: lots of gluons!

13 Applying dpdfs to FNAL/LHC Requires Care GPDs and diffractive PDFs measured at HERA cannot be used blindly in pp (or ppbar) interactions. In addition to the hard diffractive scattering, there are soft interactions among spectator partons. They fill the rapidity gap and reduce the rate of diffractive events. F2 D Extrapolation from HERA CDF data Multi-Pomeron-exchange effects (a.k.a. renormalization, screening, shadowing, damping, absorption )

14 CDF Run 1-0 ( ) Elastic, single diffractive, and total cross 546 and 1800 GeV Roman Pot Spectrometers Roman Pot Detectors Scintillation trigger counters Wire chamber Double-sided silicon strip detector Results Total cross section σ tot ~ s ε Elastic cross section dσ/dt ~ exp[2α lns] shrinking forward peak Single diffraction Additional Detectors Trackers up to η = 7 Breakdown of Regge factorization

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16 DØ Run I Gaps Pioneered central gaps between jets: Color-Singlet fractions at s = 630 & 1800 GeV; Color-Singlet Dependence on η, E T, s (parton-x). PRL 72, 2332(1994); PRL 76, 734 (1996); PLB 440, 189 (1998) Observed forward gaps in jet events at s = 630 & 1800 GeV. Rates much smaller than expected from naïve Ingelman- Schlein model. Require a different normalization and significant soft component to describe data. Large fraction of proton momentum frequently involved in collision. PLB 531, 52 (2002) φ η η η Observed W and Z boson events with gaps: measured fractions, properties first observation of diffractive Z. PLB 574, 169 (2003) E Observed jet events with forward/backward gaps at s = 630 and 1800 GeV φ η

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18 Diffractive W Boson CDF {PRL (1997)} measured R W = 1.15 ± 0.55% where R W = Ratio of diffractive/non-diffractive W a significance of 3.8σ DIFFW signal

19 DØ Observation of Diffractive W/Z Diffractive W and Z Boson Signals Phys. Lett. B 574, 169 (2003) n L0 Central electron W n cal n L0 Forward electron W n cal Observed clear Diffractively produced W and Z boson signals Events have typical W/Z characteristics Background from fake W/Z gives negligible change in gap fractions n L0 All Z n cal Sample Diffractive Probability Background All Fluctuates to Data Central W ( )% 7.7σ Forward W ( )% 5.3σ All W ( )% 7.5σ All Z ( )% 4.4σ

20 DØ Run II Diffractive Topics Soft Diffraction and Elastic Scattering: Inclusive Single Diffraction Elastic scattering (t dependence) Inclusive double pomeron Search for glueballs/exotics Topics in RED were studied with gaps only in Run I Hard Diffraction: Diffractive jet Diffractive b,c,t Diffractive W/Z Diffractive photon Other hard diffractive topics Double Pomeron + jets Other Hard Double Pomeron topics Exclusive Production of Dijets φ <100 W boson events in Run I, >100 tagged events expected in Run II η E

21 DØ Forward Proton Detector Nine independent spectrometers each consisting of two detectors Scattered antiprotons Scattered Protons Dipole Magnets A UP Spectrometer Quadrupole Magnets P UP Spectrometer Dipole Spectrometer Separator A DOWN Spectrometer IP Separator P DOWN Spectrometer z [m] Reconstruct particle tracks from detector (scintillating fiber) hits Dipole Spectrometer t ~ 0.0 GeV 2 t > 0.8 GeV 2 ξ > 0.04 ξ > 0.0 Quadrupole Spectrometers 18 Pots integrated into DØ readout and inserted every store since Jan 2004 Simultaneously tag/reconstruct protons and antiprotons

22 FPD Castles/Detectors All 6 castles with 18 Roman pots comprising the FPD were constructed in Brazil, installed in the Tevatron in fall of 2000, and have been functioning as designed. 20 detectors built over a 2+ year period at UTA In , 10 of the 18 Roman pots were instrumented with detectors. During the fall 2003 shutdown the final eight detectors and associated readout electronics were installed. A2 Quadrupole castle with all four detectors installed

23 FPD Detectors 6 planes per detector in 3 frames and a trigger scintillator U and V at 45 degrees to X, 90 degrees to each other U U X X Trigger V V mm mm U and V planes have 20 fibers, X planes have 16 fibers Planes in a frame offset by ~2/3 fiber Each channel filled with four fibers 0.8 mm 3.2 mm 1 mm 2 detectors in a spectrometer

24 Diffractive Z Production Event Selection: Z µ+µ- Events Two Good (P T > 15GeV) Oppositely Charged Tracks Both Identified as muons BKGD Rejection: Min one muon Isolated in Tracker and Calorimeter (suppress Heavy Flavour BKGD), Cosmic Ray Rejection. Events / GeV Demand Activity North and South DØ Prelim Events / 2 GeV Forward Gap (North or South) DØ Prelim Mass (GeV) Candidate Diffractive Z Events Mass (GeV)

25 Large β* Store Two day run of accelerator at injection tune β*=1.6 m 1x1 bunch Lum=0.5E30 Large β* Physics Goals: 1. Low-t elastic scattering 2. Low-t single diffractive and double pomeron scattering

26 Hit Maps from 1x1 store Typical Store High β store (4647) (no low β squeeze)

27 FP420 Joint ATLAS/CMS R&D project with 58 members from 11 countries Spokespersons : B.C. (Manchester), A. DeRoeck (CERN) Technical Co-ordinator : C. DaVia (Brunel) Management Committee : A. Brandt (UTA), Mike Albrow (FNAL), M. Arneodo (Turin / INFN), K. Piotrzkowski (Louvain), R. Orava (Helsinki) LHC Interface: Keith Potter (CERN) will join Manchester / Cockcroft Inst. LOI submitted to the LHCC 6/05: CERN-LHCC ; LHCC-I-015 FP420 : An R&D Proposal to Investigate the Feasibility of Installing Proton Tagging Detectors in the 420m Region at LHC From the LHCC minutes : The LHCC heard a report from the FP420 referee. In its Letter of Intent,the FP420 Collaboration puts forward an R&D proposal to investigate the feasibility of installing proton tagging detectors in the 420 m. region at the LHC. By tagging both outgoing protons at 420 m. a varied QCD,electroweak, Higgs and Beyond the Standard Model physics programme becomes accessible. A prerequisite for the FP420 project is to assess the feasibility of replacing the 420 m. interconnection cryostat to facilitate access to the beam pipes and therefore allow proton tagging detectors to be installed. The LHCC acknowledges the scientific merit of the FP420 physics programme and the interest in its exploring its feasibility.

28 FP420 Overview FP420: Double proton tagging at 420m as a means to discover new physics Tagging the protons means excellent mass resolution (~ 1 to few GeV) independent of decay channel Used to be called Double Pomeron Exchange now Central Exclusive Diffraction NEW Selection rules mean that central system is dominantly 0 ++ (CP even) If you see a new particle in any decay channel with proton tags, you know its quantum numbers CP violation in the couplings shows up directly as an azimuthal asymmetry in the tagged protons Proton tagging may be the discovery channel in certain regions of the MSSM 0 ++ Selection rule QCD Background ~

29 Central Exclusive Higgs Production Central Exclusive Higgs production pp p H p : 3-10 fb gap p H b -jet gap p E.g. V. Khoze et al M. Boonekamp et al. B. Cox et al. V. Petrov et al Levin et al η b -jet Idea: M. Albrow & A. Rostovtsev fortevatron beam dipole 2 M H = ( p+ p p' p') 2 dipole M = O( ) GeV p roman pots roman pots p

30 Higgs Acceptance vs. Mass (M H ) Helsinki Group study for TOTEM and FP420 Model Dependence! Need HERA and/or Tevatron to referee Otherwhise wait for LHC data Low β*: (0.5m): Lumi cm -2 s m: 0.02 < ξ < m: < ξ < 0.02 RPs in the cold region/fp420 are needed to access the low ξ values 220m RP

31 Latest Acceptance + Resolution ATLAS CMS P. Bussey / A. Pilkington / J. Monk

32 Central Exclusive Higgs Production Standard Model Higgs b jets : M H = 120 GeV s = 2 fb (uncertainty factor ~ 2.5) M H = 140 GeV s = 0.7 fb H M H = 120 GeV : 11 signal / O(10) background in 30 fb -1 with detector cuts WW * : M H = 120 GeV s = 0.4 fb M H = 140 GeV s = 1 fb M H = 140 GeV : 8 signal / O(3) background in 30 fb -1 with detector cuts The b jet channel is possible, with a good understanding of detectors and clever level 1 trigger (need trigger from the central detector at Level-1) The WW * (ZZ * ) channel is extremely promising : no trigger problems, better mass resolution at higher masses (even in leptonic / semi-leptonic channel) If we see SM Higgs + tags - the quantum numbers are 0 ++ See e.g. J. Forshaw HERA/LHC workshop

33 Higgs Studies 100 fb 1fb Cross section factor ~ larger in MSSM (high tanβ) Kaidalov et al., hep-ph/ Study correlations between the outgoing protons to analyze the spin-parity structure of the produced boson A way to get information on the spin of the Higgs ADDED VALUE TO LHC

34 Lineshape Analysis J. Ellis et al. hep-ph/ Scenario with CP violation in the Higgs sector and tri-mixing

35 CDF Exclusive Dijets in Run I PRL 85 (2000) 4215 Expected shape of signal events Dijet Mass fraction R = jj M M jj X Exclusive dijet limit: σ jj (excl.) < 3.7 nb (95% CL) Theoretical expectation (KMR) ~1 nb

36 CDF Exclusive Dijets in Run II p p p + JJ proton p p p + JJ + gap 5.5 < η< 7.5 p p p p + JJ + gap 3.6 < η< 7.5 exclusive? Minimum E T (Jet1) Cross section (R jj >0.8) 10 GeV 1.1 ± 0.1(stat) ± 0.5(syst) nb 25 GeV 25 ± 3(stat) ± 10(syst) pb

37 CDF Exclusive Di-photons in Run II The e+e- and 2-photon events are interpreted as completely different processes: γγ ee gg γγ + QED : QCD + QED : + soft gluon exchange, Sudakov effect Monte Carlo: LPAIR Expect events 10 candidates Monte Carlo: ExHume (Durham) Expect 1 (+ 3,-0.7) events 3 candidates gg γγ

38 DØ Exclusive Dijets in Run II Results soon!

39 Key Components of FP420 Space in LHC tunnel for detectors (cryostat mods) Edgeless silicon detector Trigger and readout Not discussed here Roman pot mechanics to house and move detector Fast TOF detector UTA Focus

40 Connection Cryostat 420 m IP1/5 CONNECTION CRYOSTAT Consists of 15 m long drift space Provides a continuity of beam and insulation vacuum, electrical powering, cryogenic circuits, thermal and radiation shielding mm Provides connection between the arcs and DS zones

41 FP420 Cryostat UK funding initiative (Manchester et al) supporting Cockcroft Institute engineer at CERN to design new cryostat Cold warm transitions IP 1/5 Usable Volume for Detectors No more than 8m warm region Diagram S. Marque / D. Dattola FP420 09/11/2005

42 3D Silicon 3D silicon detectors were proposed in 1995 by S. Parker, and active edges in 1997 by C. Kenney. Combine traditional VLSI processing and MEMS (Micro Electro Mechanical Systems) technology. 1. NIMA 395 (1997) IEEE Trans Nucl Sci 464 (1999) IEEE Trans Nucl Sci 482 (2001) IEEE Trans Nucl Sci 485 (2001) IEEE Trans Nucl Sci 48 6 (2001) CERN Courier, Vol 43, Jan 2003, pp NIMA 509 (2003)86-91 Electrodes are processed inside the detector bulk instead of being implanted on the Wafer's surface. The edge is an electrode! Dead volume at the Edge < 2 microns! Essential for -Large area coverage -Forward physics

43 The LONGPOT Concept (Helsinki) UTA collaborating with Helsinki Proton Beam Beam Pipe Tilt 13º Emergency Stops Stepper Motor Bellows Outer Weld Points Flange Primary Vacuum Detector Detector Pocket Detector movement Secondary Vacuum CWT (optional) Rest Stops Feedthroughs

44 Hamburg Pipe Routinely used at HERA at high L, since 1995 : bellows moving pipe

45 Hamburg Pipe For FP420 some modifications needed such as RF shield (through which the detectors approach the beam via narrow slots), to minimise any impedance change on the beam. Parking position Working position RF screen Bellows Detectors a few m apart

46 Fast TOF It s been done! Can t put our PMT in 7 TeV beam!

47 QUARTIC Preliminary UTA drawing of Mike Albrow s concept for a fast time resolution Cerenkov counter: Initial design used 2 mm 2 rods, but not enough light, this drawing shows 6mm 2 rods proton γ Microchannel plate PMT z=c(tr-tl)/2 δz (mm) =0.21 δt (psec) (2.1 mm for δt=10 psec)

48 QUARTIC Background Rejection (UTA) 1) 2 single diffractive protons overlayed with a hard scatter (1% of interactions have a proton at 420m) 97.4% of events primary vertex and fake vertex from combining proton times more than 2.1mm (1σ) apart ; 94.8% if 20 psec 2) double pomeron overlayed with a hard scatter 3) hard SD overlayed with a soft SD 97.8% of time vertices more than 2.1mm apart; 95.6% if 20 psec 95.5% of time primary vertex and fake vertex more than 2.1mm apart; 91.0% if 20 psec

49 Preliminary Time Distributions (UTA): 0.01 Single λ n=1.52 θc=49 ; 7.4% of pe s in 10 psec 21.3% in 50 psec red = totally internally reflected light green = extra light if aluminized 50 psec 0.01 over λ including QE 1.9% of pe s in 10 psec 19.1% in 50 psec Alberta working on GEANT simulations; we plan to use FNAL test beam in summer 50 psec

50 FP420 Summary: If you have a sample of Higgs candidates, triggered by any means, accompanied by proton tags, it is a 0 ++ state. γγ WW delivers sensitivity to anomalous couplings a factor of 10,000 better than LEP II In certain regions of MSSM parameter space, S/B > 20, and double tagging is THE discovery channel In other regions of MSSM parameter space, explicit CP violation in the Higgs sector shows up as e.g. azimuthal asymmetry in the tagged protons -> direct probe of CP structure of Higgs sector at LHC Exclusive double diffraction may offer unique possibilities for exploring Higgs physics in ways that would be difficult or even impossible in inclusive Higgs production J. Ellis et. al. The big design issues : Installation at 420m (cryogenics + vacuum) Safe operation within LHC collimation scheme Funding brandta@uta.edu or spokes if interested

51 Hard Diffraction has come a long way from UA8 days (from the SPS to LHC via HERA and Fermilab)