Università del Piemonte Orientale, Novara, Italy Diffractive group: experimental summary Michele Arneodo Università del Piemonte Orientale, Novara, Italy o) Diffractive studies at the LHC, including the Higgs o) Input/results from HERA Not an exaustive summary ! See talks by Pierre van Mechelen(*) yesterday and by Halina Abramowicz on Tuesday ! (*) covers material by K. Borras, A. Bunyatyan, A. Panagiotou

Central exclusive production of the Higgs Khoze, Martin, Ryskin hep-ph 0111078 Central system is (to a good approx) 0++ If you see a new particle produced exclusively with proton tags you know its quantum numbers Proton tagging may be the discovery channel in certain regions of the MSSM Measuring the protons means excellent mass resolution (~ GeV) irrespective of the decay products of the central system Attractive for MH=120-250 GeV b, W H ξ: fractional momentum loss of proton – for 120 GeV Higgs, x~ 1% t: 4-momentum transfer squared at proton vertex

How to measure the protons At CMS: TOTEM, Roman Pots at 150 and 220m from I.P. Excellent coverage in x and t at low luminosity optics (b*=90, 1540m) Coverage 0.02<x<0.2 at high luminosity optics (b*=0.5m) [K.Oesterberg, H.Niewiadomski] At ATLAS: FP220 Roman Pots at 220 m Coverage similar to TOTEM at high luminosity optics [Ch. Royon] At CMS and ATLAS: FP420 R&D project, aim to instrument region at 420m from I.P. 0.002<x<0.02 (high luminosity optics only) [S. Watts] Logx detectors@420m TOTEM - FP220 b*=0.5 FP420 Logt xL=P’/Pbeam= 1-x

How to measure the protons TOTEM (or FP220 at ATLAS) FP420 Cold region of LHC Too far for L1 trigger K.Oesterberg M.Grothe Ch. Royon H. Niewiadomski A. Pilkington

FP420 R&D phase essentially over Proposals to Atlas and CMS imminent Installation >2009 Replacement of cryostat @ 420m designed Moving beam pipe S. Watts

FP420 S. Watts 3D Si detectors: edgeless, rad-hard Successful beam test of 3D detectorsat CERN Timing detectors to reconstruct vertex Tracking code available in ATLAS, CMS frameworks (W. Plano, X. Rouby)

FP220 Acceptance Proposal to Atlas imminent Ch. Royon

CMS+TOTEM: unprecedented coverage in  CMS IP T1/T2, Castor ZDC RPs@150m RPs@220m possibly detectors@420m T1 (CSC) 3.1 ≤ || ≤ 4.7 HF 3 ≤|| ≤ 5 T2 (GEM): 5.3 ≤ || ≤ 6.6 Castor 5.3 ≤ || ≤ 6.6 Carry out a program of diffractive and forward physics as integral part of the routine data taking at the LHC, i.e. at nominal beam optics and up to the highest available luminosities. K.Oesterberg M.Grothe

CMS+TOTEM: physics map K.Oesterberg M.Grothe Low lumi Rapidity gap selection possible HF, Castor, BSCs, T1, T2 Proton tag selection optional RPs at 220m and 420 m Diffraction is about 1/4 of tot High cross section processes “Soft” diffraction Interesting for start-up running Important for understanding pile-up High lumi No Rapidity gap selection possible Proton tag selection indispensable RPs at 220m and 420 m Central exclusive production Discovery physics: Light SM Higgs MSSM Higgs Extra dimensions Low lumi High lumi Gamma-gamma and gamma-proton interactions (QED) Forward energy flow - input to cosmics shower simulation QCD: Diffraction in presence of hard scale Low-x structure of the proton High-density regime (Color glass condensate) Diff PDFs and generalized PDFs Diffractive Drell-Yan “Prospects for diffractive and forward physics at the LHC” CERN/LHCC 2006-039/G-124, CMS Note 2007/002, TOTEM Note 06-5, Dec 2006

Trigger is a major limiting factor for selecting diffractive events Background from non-diffractive events that mimic diffractive events because of protons from pile-up events

CMS-TOTEM: diffractive trigger → CMS trigger thresholds for nominal LHC running too high for diffractive events → Use information of forward detectors to lower jet trigger thresholds → The CMS trigger menus now foresee a dedicated diffractive trigger stream with 1% of the total bandwidth on L1 and HLT (1 kHz and 1 Hz) NB Information from 220 detectors crucial for triggering single-sided 220m condition without and with cut on  Achievable total reduction: 10 (single-sided 220m) x 2 (jet iso) x 2 (2 jets same hemisphere as p) = 40 Much less of a problem is triggering with muons, where L1 threshold for 2-muons is 3 GeV M.Grothe

CMS-TOTEM: diffractive trigger M.Grothe pp  p jj X 2-jet trigger pp  pWX 1-jet trigger Efficiency no fwd detectors condition Events per pb-1 single-arm 220m single-arm 420m L1 trigger threshold [GeV] H(120 GeV) → b bbar L1 trigger threshold [GeV] Efficiency 420m 220m 420+420m 420+220m Trigger is a major limiting factor ! Level-1: ~12% efficiency with 2-jets (ET>40GeV) & single-sided 220 m condition HLT: Jet trigger efficiency ~7% To stay within 1 Hz output rate, needs to either prescale b-tag or add 420 m detectors in trigger Additional ~10% efficiency by introducing a 1 jet & 1 (40GeV, 3GeV) trigger condition

Pile-up Average number of pile-up events overlaid to any hard scatter K.Oesterberg M.Grothe M. Tasevsky A. Pilkington V. Khoze Average number of pile-up events overlaid to any hard scatter 7 @ 2x1033 cm-2s-1, 35 @ 1x1034 cm-2s-1 (not 20…)  25% of these events are diffractive, i.e. have a fast proton Example: pile-up background to diffr H  bb comes from non-diffractive bb production, superimposed to two single- diffractive pile-up events Eg at 2x 1033 cm-2s-1 10% probability of obtaining a fake 2-proton signature because of pile-up.

Pile-up ; 1 2 s = M2 Can be reduced by: Requiring correlation between ξ, M from central detector and ξ, M from near-beam detectors Fast timing detectors to determine if protons came from same vertex as hard scatter (TOF with 10 ps resolution !) CEP H(120) bb incl QCD di-jets + PU (jets) (from protons) K.Oesterberg M.Grothe M. Tasevsky A. Pilkington V. Khoze M(2-jets)/(Missing Mass)

Pile-up S/B for SM H  bb of order 1 H bb at 2 x 1033 cm-2 s-1 S/B for MSSM H  bb as large as 100-1000 Pile-up significantly less severe for H WW H bb A. Pilkington K.Oesterberg M.Grothe M. Tasevsky A. Pilkington V. Khoze

Further upgrades in CMS forward region A. Bunyatyan, K. Borras

HERA Measurements of diffractive structure function F2D QCD fits to F2D and extraction of dPDFs How well does QCD hard-diffractive factorisation work ie can use dPDFs to predict cross section of diffractive production of jets or charm ? Can we quantify rapidity gap survival probability ? Leading neutrons and the survival probability

Input from HERA: dPDFs dPDF b, jet p p’ p e e’ IP p’ IP IP p p’ Diffractive PDF: 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 Obtained from QCD fits to F2D data

New measurements of F2D from ZEUS Three methods to select diffraction at ZEUS: Require a leading proton (leading proton spectrometer, LPS) Require a large rapidity gap (LRG) Exploit the different shape of MX for diffractive and non-diffractive events (MX method) p’ p e e’ IP X For the first time, analyse the same set of data with the three methods and try and understand the differences

Inclusive Diffraction at HERA from the ZEUS experiment ZEUS MX vs LRG results ZEUS MX 99-00, ZEUS MX 99-00 (prel.), ZEUS LRG 00 (prel.) xIPF2D(3) vs. Q2 ZEUS MX 98-99 ZEUS MX 99-00 (prel.) ZEUS LRG 00 (prel.) reasonable agreement work on understanding remaining differences is continuing J. Łukasik Inclusive Diffraction at HERA from the ZEUS experiment

Inclusive Diffraction at HERA from the ZEUS experiment ZEUS LRG vs LPS results ZEUS LRG 00 (prel.), ZEUS LPS 00 (prel.) LPS/LRG=0.82±0.01(stat.)±0.03(sys.) independent of Q2 and β A measure of the contamination by proton dissociative events in the LRG sample e’ e X IP p About 10% normalization uncertainty of the LPS measurement not shown N J. Łukasik Inclusive Diffraction at HERA from the ZEUS experiment

Inclusive Diffraction at HERA from the ZEUS experiment ZEUS vs H1 xIP = 0.003 ZEUS LRG 00 (prel.), H1 LRG xIP = 0.01 ZEUS LRG 00 (prel.), H1 LRG H1: a(0) = 1.118 ± 0.008 +0.029-0.010 a‘ = 0.06 +0.19 -0.06 ZEUS: a(0) = 1.117 ± 0.005 +0.024-0.007 a' = -0.03 ± 0.07 +0.04 -0.08 Fraction of proton dissociation events for ZEUS and H1 detectors is different The ZEUS LRG data are normalized to the H1 LRG data J. Łukasik Inclusive Diffraction at HERA from the ZEUS experiment

H1 F2D In best regions, precision ~5% (stat), 5% (syst), 6% (norm), …well described by fit P.Newman

`Fit A’ and `Fit B’ DPDFs (linear z scale) Lack of sensitivity to high z gluon confirmed by dropping (high z) Cg parameter, so gluon is a constant at starting scale! Fit B c2 ~164 / 184 d.o.f. Quarks very stable Gluon similar at low z Substantial change to gluon at high z P.Newman

M. Mozer QCD factorisation OK

R. Wolf QCD factorisation OK

Digression: rapidity gap survival probability GPDs and diffractive PDFs measured at HERA cannot be used blindly at LHC or Tevatron: jet b hard scattering IP LRG Extrapolation from HERA CDF data P.Newman

Rapidity gap survival probability Proton and anti-proton are large objects, unlike pointlike virtual photon In addition to hard diffractive scattering, there may be soft interactions among spectator partons. They fill the rapidity gap and slow down the outgoing p,p – hence reduce the rate of diffractive events. Quantified by rapidity gap survival probability (underlying event !) CDF data Predictions based on rescattering assuming HERA diffractive PDFs Kaidalov, Khoze, Martin, Ryskin (2000) F2D b Can we see a similar suppression at HERA by using resolved photons at Q2=0 ?

(but mainly direct g component) QCD factorisation OK (but mainly direct g component) I. Melzer (+R. Wolf for H1)

Hadron-like g QCD factorisation not OK Unexpected, not understood

Leading Neutrons B. Schmidke Kaidalov, Khoze, Martin & Ryskin have used these data to derive the rapidity gap survival probability (one pion exchange+absorption+migration) B. Schmidke

Grand summary LHC: Diffraction/forward physics has generated several new detectors now on the way – added value for ATLAS and CMS. Diffractive group in CMS ! Experimental challenges being addressed, eg trigger, pile-up Different experiments joining forces: CMS+TOTEM, ATLAS and CMS in FP420 HERA: Precious input: dPDFs, rapidity gap survival probability, GPDs, experience in operating near-beam detectors Wish list: DVCS, J/psi, Y (including t dependence !) for constraining GPDs H1+ZEUS F2D, dPDFs Understanding of gap survival Leading proton spectra at LHC (crucial for pile-up)

RESERVE

CDF: evidence for exclusive processes at Fermilab Search for exclusive gg 3 candidate events found 1 (+2/-1) predicted from ExHuME MC* background under study Same type of diagrams as for Higgs  Validation of KMR model ! D. Goulianos, V. Khoze

Diffractive Structure Function: Q2 dependence ETjet ~ 100 GeV ! Small Q2 dependence in region 100 < Q2 < 10,000 GeV2 Pomeron evolves as the proton! D. Goulianos

Diffractive Structure Function: t- dependence Fit ds/dt to a double exponential: No diffraction dips No Q2 dependence in slope from inclusive to Q2~104 GeV2 Same slope over entire region of 0 < Q2 < 4,500 GeV2 across soft and hard diffraction! D. Goulianos