Report from the LHC Forward Physics Working Group 2014, Kraków

Transcription

1 Report from the LHC Forward Physics Working Group 2014, Kraków Tim Martin On behalf of the LHC Forward Physics Working Group University of Warwick November 5, 2014

2 Introduction Understanding of physics in the forward region is an important component of soft QCD and diffractive physics, the Underlying Event and the total cross section. It leads to studies of hard processes in the forward region and probes the interface between soft and hard physics. Forward proton tags can fully constrain event kinematics at a pp collider, allow for BSM searches. Will look at the LHC forward instrumentation and near term improvements. Overview some of the physics of interest in these regimes. 2 of 22

3 LPCC Forward Physics Working Group Collaboration between members of ALICE, ATLAS+ALFA, CMS, LHCb, LHCf, TOTEM & theory community. Working on bringing together in a CERN Yellow Report an overview of near term diffractive and forward physics at the LHC. 3 of 22

4 Running Conditions For Different Scenarios Low L : µ 1 sqcd, σ tot, low mass resonances Very low pileup data for LHC experiment s Minimum Bias analyses, including LHCf. Also high β data for ALFA, TOTEM σ tot. Medium L : µ 1 Hard diffraction, c c, DPE jj & γj CMS-TOTEM: Special runs at high β and µ 1 for 10 pb 1 and µ 0.5 for 100 pb 1. AFP: Similar for high β, at low β - specialist µ 2 5 for 100 pb 1. Regular environment for LHCb, ALICE. High L : µ Anomalous couplings, exclusive processes. High-p T /low σ processes with p-tagging (AFP, PPS). Restrict to end of fills (µ 25) collect 40% of total L. 4 of 22

5 LHC Experiment s Forward Coverage ALICE: New forward scintillators. ATLAS: Calorimeter coverage to η = 4.9 plus ZDC & vertical Roman Pot ALFA at 237 m. Planned Atlas Forward Physics horizontal Roman Pots at 210 m. CMS: Similar calorimeter coverage inc. ZDC, plus CASTOR calorimeter (single sided) and new forward shower counters. LHCb: New forward Herschel scintillators. LHCf: New Gadolinium oxyorthosilicate scintillator. TOTEM: Roman Pots at CMS IP plus T1 & T2 telescopes at z = 10.5, 13.5m and new forward shower counters. 5 of 22

6 Herschel: LHCb High η Shower Counters 37% of LHCb s Run-2 5 fb 1 will be without pileup and good for CEP studies. Three backward stations at z = 7.5, 19.7 and two forward stations at z = 20, 114 m. Sensitivity to primary particles η < 7.5. Currently being installed & commissioned xentry [mm] yentry [mm] yentry [mm] 0.40 Hits/25 mm xentry [mm] Hits/25 mm Figure : L: Inelastic, R: CEP-mimicking p diss. 6 of 22

7 ATLAS Forward Physics Project Approved ATLAS project, horizontal Roman Pots to collect data at collision optics. Start at low µ < 3, validate high µ operation. Radiation hard edgeless 3D tracking sensors, mount close to beam for 5 GeV mass resolution. Combine with timing detectors. proton relative energy loss ξ AFP 204 m s = 14 TeV, β* = 0.55 m, beam 1 θ C = 285 µrad, d = 3.15 mm detector and LHC aperture cuts geometric acceptance [%] proton transverse momentum p [GeV/c] T 0 7 of 22

8 ATLAS Forward Physics Project - v.s. ALFA Approved ATLAS project, horizontal Roman Pots to collect data at collision optics. Start at low µ < 3, validate high µ operation. Radiation hard edgeless 3D tracking sensors, mount close to beam for 5 GeV mass resolution. Combine with timing detectors. ξ proton6relative6energy6loss 0µ2 0µ15 0µ1 0µ05 ALFA62376m s =6146TeVF6βC6=6906mF6beam61 θ C =60 µradf6d6=66µ96mm detector6and6lhc6aperture6cuts geometric6acceptance6[,] proton6transverse6momentum6p [GeV/c] T 0 8 of 22

9 CMS-TOTEM Precision Proton Spectrometer CMS-TOTEM forward detector for standard running conditions. TDR approved by CMS and TOTEM. Start with TOTEM-style silicon strips, move to pixels & test timing detectors and Roman pot use for regular LHC fills. Sensitivity to 3% < ξ < 10%. Accumulate 100 fb 1 by m 215m 204m à IP5 2 new horizontal cylindrical RPs (1 in LS1) 2 horizontal box-shaped RPs Lower mass range limited by closest approach to the beam, here assume 15σ. Upper limit depends on collimator settings. 9 of 22

10 CMS Forward [Aldo Penzo, INFT] 10 of 22

11 Constraining Backgrounds in CMS/TOTEM Background evaluated by CMS+TOTEM. Zero bias data at s = 8 TeV, µ 0.07 mixed with POMWIG SD (plus 10% survival factor) + Pythia 8 ND. Require central di-jet p T1,2 > 30 GeV, two proton tags. If get MC and ZB p, take lowest ξ. ξ CMS = Σ(E i ± pz)/ i s, ξ CMS ξ TOTEM > 0 is kin. forbidden. Residual background of 4% at ξ CMS ξ TOTEM < 0 11 of 22

12 Forward Timing Detectors Timing detectors allow for the identification of vertex z location. 10 ps σ z = 2 mm. SAMpler for PICosecond timing Time-To-Digital chips. Targeting 2 ps RMS. L-bar Quartic Cerenkov detectors, demonstrated timing resolution. May suffer high occupancy at µ = of 22

13 562.5MeV 813.7MeV 150.9GeV 136GeV 290.6MeV 5.156TeV 960.8GeV 222.5GeV 12.05GeV 12.89GeV 6.653TeV 1.501GeV 251.2MeV 2.455TeV 1.781TeV 919.8GeV 327.3GeV 633.5GeV 104.6GeV 117.9GeV 4.352GeV 7.697GeV 1.45GeV 11.44GeV 261.6MeV 1.239GeV 475.7MeV 394.6MeV 7TeV 345.4GeV609MeV 1.218GeV 340MeV 348MeV 7TeV 7.001TeV 342.4GeV 78.51GeV 804.2MeV 665.6MeV 281.6GeV 31.76GeV 8.239GeV 3.178GeV 23.52GeV 26.89GeV 5.186TeV 7TeV 1.429TeV 6.764TeV 2.21GeV 6.999TeV 1.813TeV 235.2GeV Soft Diffraction With p Tag Within AFP Acceptance Sensitivity to high-mass Single Diff., possible also lower mass systems through Double Diff. E.G. above from Pythia. Extend LHC soft physics measurements: rapidity gaps, UE, energy flow, charged multiplicity including a forward proton tag. Fragmentation of dif. systems: How do pp, Pp, PP interactions differ? 13 of 22

14 Soft Diffraction With p Tag [mb] F dσ/d η 2 10 [AFP] PYTHIA 8 A2 [AFP] HERWIG++ UE-EE-4 [AFP] EPOS LHC PYTHIA 8 A2 HERWIG++ UE-EE-4 10 EPOS LHC 1 > [GeV] 2 ΣE T dηdφ <d [AFP] PYTHIA 8 A2 [AFP] HERWIG++ UE-EE-4 [AFP] EPOS LHC PYTHIA 8 A2 HERWIG++ UE-EE-4 EPOS LHC s = 14 TeV, p > 200 MeV. F η T s = 14 TeV, p > 500(200) MeV Ch(Neutral) Pythia 8: diffractive tail is driven by the tagging of low mass double dissociation. Small gaps are SD dominated. EPOS with independent remnant scheme still generates a tail, but this may be more through CEP. This is seen also in energy flow where Pythia 8 and H++ show large flow asymmetry (p tag at +z) whereas EPOS is uniform. 14 of 22 η

15 ALFA and TOTEM in Run-II Through using T1 and T2 as veto detectors, TOTEM have made valuable measure of low mass diffraction. σ DD = 116 ± 25µb for both diffractive systems 4.7 < η min < 6.5. Expect similar performance of extrapolation of σ tot from β = 90 m data at s = 13 TeV. Higher (β = 2500 m) optics foreseen to access Coloumb interference region. 15 of 22

16 Central Exclusive Production f g (x 1, ) p 1 S eik S enh Q x 1 X x 2 f g (x 2, ) Central exclusive production of sufficiently large systems X via pqcd double P exchange Durham model. Soft re-scattering encoded in eikonal survival factor, Seik 2. Accessed through hadronic data, 0.01 at LHC. Re-scattering of spectators with intermediate partons in the hard process enhanced survival factor, Senh 2. Expected to be sub dominant, may be probed by future CEP measurements (e.g. M inv. (jj) to probe Senh 2 as a function M X ). 16 of 22 p 2

17 Central Exclusive Production with p Tag As CEP p T is transfered to the outgoing protons measure of angle φ between proton p T vectors is sensitive to spin-partity. S 2 eik can impart a strong model dependency - is a function of proton p T. J PC = 0 ++ is exact in the limit proton p T 0. At non-zero p T : dσ/ dφdyχ T (J z )=2 2 T (J z <p2 =0 2 T >2 <QT 2 > (χ cj, ηc) no cuts ~const., 1 + ~(p T1 -p T2 ) 2, 0 - ~p T1 2 p T2 2 sin 2 φ φ 2 χ c0 χ c1 χ c2 ηc 2.5 dσ/dφ [nb], s = 13 TeV, p,1 > 0.5 GeV model 1 model model 3 model Figure : L:Differnce in φ for different c c states at s = 14 TeV and y X = 0. R:CEP π + π for four soft survival factor models [arxiv: ] DIME 17 of 22 MC φ

18 Single Diff. Di-Jet & Jet-Gap-Jet w. p tag Collect high purity data in low pileup runs, O(100h) data taking. Studies by ATLAS inc. pileup and CMS+TOTEM on 8 TeV data. Jet-Gap-Jet allows for study of BFKL dymamics, sensitivity in the ratio of J-g-J to dijet cross-section. 18 of 22

19 Jets in CMS Castor ( 6.6 < η < 5.2, no η seg.) Low p T fwd jets at low-x. Study rise of the g density & saturation. Probe low-p T high y separation Mueller-Navelet dijets, sensitive to BFKL rise of σ with increasing y. Feasibility study of reconstructed Anti-k t, R = 0.7 jets (clustering in φ) with E > 500GeV ( p T > 3 GeV) Ongoing work to complement CASTOR E with TOTEM T2 (θ, φ) reconstruct jet p T. fractionpofpeventsp[m] E CMSPPreliminary 6, data s =P7PTeV 6, 6.6 6, E jet >P5,,PGeV<P.6>6P< η jet <P.5>E PYTHIA8P4C fractionrofrcastorrjetsr[d],>, CMSRPreliminary s E jet =R7RTeV >R5>>RGeVmR=6<6R<R η jet <R=5<E datar PYTHIA8R4CR.E 6,.3 6, =,,>.4 6,.5 6,, 6 E 3 NPCASTORPjets =E,> 5>> 6>> 7>> 8>> 9>>,>>>,,>>,E>>,3>>,4>> energyr[gev] 19 of 22

20 T Exclusive Di-jet Production With 2 p-tags, system kinematic are fully constrained. Can correlate with central system for BG rejection. Large backgrounds (S/B = 1/10 7, before cuts) from ND and SD with pileup. CT-PPS study: S/B = 1/3 after cuts at µ = 25. ATLAS study: up to 19σ significance for exclusive signal with 40 fb 1 at µ = of 22 min numberfoffeventsfabovefp ><AA >AAA L<AA LAAA <AA Sf=fLFP6σ Sf=fLµPAσ Sf=fFP)σ exclpfsignalfhfbackground bestfconstraintsfonfparameters fromftheftevtatronfdata nonddiffpfjets singleddiffpfjets DPEfjets ATLASfSimulation AFP- σxt+=lafps DL LfdTf=f;Affb ;f<µ>f=f>µ > >AAf<fM jj <f((afgevec Sf=f<PFσ Sf=f;Pµσ Sf=f>P;σ L<A min leadingfjetftransversefmomentum-fp >AA ><A [GeVEc] µaa T

21 Anomalous Quartic Coupling pp pγγp Look for coupling predicted by composite Higgs, extra dimensions... p tagging exclusivity cuts suppress background, become background free beyond m γγ > 600 GeV for 300 fb 1 without needing p tag timing information. p γ p γ Events Signal Excl.dbackground γγ +dpileup ζ =d10 GeV 1 s =d14dtev -1 Ld=d300dfb µ=d 50 p γ p γ ζ =d10 GeV miss m pp /m γγ Without p tagging (300fb 1, ζ 1 = 2x10 13 ), S/B = 80.2/16.2, with p tagging ξ 1 ξ 2 s = m γγ ± 3%, y γγ y pp < 0.03: S/B = 15.1/0 21 of 22

22 Conclusion Wide range of forward physics at the LHC, covering all energy scales and cross sections. A mix of forward instrumentation and Roman Pot based detectors will collect forward data in specialist high β optics runs and in standard running conditions. Work on consolidating CERN Yellow Report well underway, expect delivery by this Christmas. Working group steering committee and sub-group coordinators listed on the LPCC Website Upcoming workshop on QCD and Diffraction at the LHC 15 17th December, right back here in Kraków. See Indico. 22 of 22