PoS(HCP2009)023 http://pos.sissa.it/ easured by the experimental he forward regions of the 4 in- tatus of these detectors in the very cond part is dedicated to review the e Commons Attribution-NonCommercial-ShareAlike Licence. ∗ [email protected] Speaker. apparatus. The 6 LHC experiments are equipped with detectors placed in t main forward physics processes at the LHC and how they can be m teraction points. The firstmoment the part first of proton-proton this collisions article take place. reviews the The se s ∗ Copyright owned by the author(s) under the terms of the Creativ c

XXth Hadron Collider Physics Symposium November 16 – 20, 2009 Evian, France Fabrizio Ferro INFN Genova E-mail: Elastic scattering, diffraction and forward physicsthe at LHC PoS(HCP2009)023 θ > 5), η < 1 | η | Moreover, tantaneous 200m from < the forward Fabrizio Ferro ∼ t rotons scattered LAS[3], CMS[4], pects of QCD and 14 TeV (from DPM- at very small angles seudorapidities = l and forward regions, are characterized by a s ehend elastic scattering, √ description of the forward ity coverage: fig. 1, right). The detection nergy le rapidity and is related to the angle 2 and a very high hadron energy flux (fig.1, left). The η -p interactions, Higgs production. γ coverage of the LHC experiments[9]. η − 6), and with a zero degree electromagnetic and hadronic calorimeter T < | η | < 5 . )) 2 / θ ( tan ( Left: hadron particle and energy density at the LHC nominal e log − (ZDC) placed in the TAN region, for the calorimetry of the neutral particles. special insertions of the beam pipe, called Roman Pots, have been installed a with LUCID Cerenkov detector, mainlyluminosity intended (5 for the measurement of the ins the IP to house scintillator fiberelastically detectors (the (ALFA project) detectors in will order be to probably detect installed p during 2010). The four LHC interaction points (IP) have been instrumented with detectors in pseudorapidity can be considered as the limit at very low mass of the partic In particle physics at the colliders, the forward regions are those placed = - IP1: ATLAS is equipped in the forward region with the FCAL calorimeter (3 1 η with respect to the beam line (more precisely but, in a sense, arbitrarly, at p JET3 [8]). Right: approximate p 2. Forward detectors 3). In thehadron proton-proton particle interactions density at decreasing the with LHC[1] the forward regions by Figure 1: Forward physics at the LHC 1. Introduction regions using several different technologies.detectors is In given, as the well following as their a (roughly short approximated) pseudorapid experimental apparatus installed byLHCb[5], the LHCf[6] and six TOTEM[7]) LHC will cover experimentsreaching almost (ALICE[2], completely an the unprecedented AT centra pseudorapidity rangeof of roughly forward 20 particles units open ( electro-weak up physics; the the possibility physics of processessoft which sheding and will hard new diffraction, be light low-x studied QCD, on compr basic as PoS(HCP2009)023 5) . 2 5. ’s and − γ < < apolation η om the IP η physics and y of ctors for the < Fabrizio Ferro < g on CMS and ns discrepancy 4 ge 2 ment of the total − quipped with track- e for distinguishing 7), CMS-ZDC in the 5). tion to higher energies < < ection at the LHC energy | η η nd extrapolation to the LHC | < < 20 pseudorapidity units. In the ∼ 5), TOTEM-T2 tracker and CMS- and of the elastic scattering over a < 1 and 1 tot | σ − η | < < nction of t and TOTEM acceptance with differ- η < 4 3 − without depending on the measurement of the luminosity, tot σ Left: previous measurements of the total p-p cross section a 14 TeV, typically from 90 to 130 mb, depending on the model used for the extr = ers, calorimeters and imaging Cerenkov detectors in the pseudorapidity ran TAN region and two TOTEM(only Roman the Pot stations stations at 220m per are sideproton at at detection[10]). the moment 147m equipped and with edgeless 220m silicon fr dete of neutral hadrons. The LHCf experiment is dedicated to measurements connected to the cosmic ray has installed two zero degree calorimeters in the TAN regions for the calorimetr CASTOR calorimeter, which has installed only one side (5 with a few additional forward detectors ( forward part: TOTEM-T1 tracker, whichLHC will schedule, be and installed CMS-HCAL in calorimeter 2010 (3 dependin s The large uncertainties of the cosmic-ray data and the 2.6 standard-deviatio A precise measurement of the total p-p cross section - IP8: LHCb is a one side forward spectrometer optimized for B-physics, e - IP2: ALICE is equipped with a muon spectrometer on the negative side ( - IP5: CMS and TOTEM provide an almost full coverage of √ between the two final resultsuncertain, from leaving the a wide Tevatron[12, 13] range make forof the an expected extrapola value of the total cross s large range in the squaredbetween four-momentum different models transfer of t soft is proton of interactions. primary importanc taking advantage of the optical theorem, performing the simultaneous measure energy[11]. Right: elasticent scattering machine cross optics[7]. section as a fu Figure 2: Forward physics at the LHC 3. Total cross section and elastic scattering (fig. 2, left). TOTEM will measure PoS(HCP2009)023 , , = dt pX X / tance el (fig.2, M optics, → 2 ∗ dN expected β pp Fabrizio Ferro at describes the ing down to such etic amplitude via . The probability using special LHC to a low mass state. d in terms of partons ison between HERA pecial high s can be measured by l-state hadrons caused ated in high luminosity case of p-p interaction, tainties on the predicted to about 10 GeV etter understanding of the 2 important. The topology of nd which affects most of the ses (such as single heavy quarks in the final state, is quite a promising production GeV t, are mediated by an exchange 3 (e.g. in single diffraction − ξ 10 ) · 0 in = N t ) + dt el / N el )( 2 ), the measurements by all the LHC experiments dN 4 1 ( ρ range from 2 − π s | + 2 t | 16 1 − ( optics is 1-2%. Moreover, with different beam optics and cm = ∗ 32 β tot 10 σ 30% of the p-p interactions and are characterized by the fact ∼ ∼ , as well as the extrapolation to the optical point t=0 of 3%. el L ∼ N ), the selection rules coming from diffraction would highly suppress the dedicated optics which allow the detection of the elastic protons with very 10% at the Tevatron and is expected to be less than 5% at the LHC. The ) diffraction) and of the gap survival probability are of fundamental impor ∗ ∼ f b β ( pX p O → and elastic rate in pp N is the ratio of the real and imaginary part of the forward amplitude at t=0. The ρ ). At higher luminosity ( Diffractive events represent ξ s QCD background. The small cross sections expected need the LHC oper measurement of the cross sections of the different diffractive proces that the incoming proton(s) emerge from the interaction intact or are excited in Diffractive processes, for proton energy losseswith quantum up numbers to of a the few vacuum, perfrom the cen the so-called proton; Pomeron, for now understoo largerdiffractive energy events losses, is mesonic characterized exchanges by become a gapby in the the rapidity lack distribution of ofand fina colour Tevatron and data effective has spindue shown of that to the such the exchanged rapidity rescattering object.of gaps of having are Compar proton a suppressed remnants gap in which is eventually fill the gaps[15] of hard processes in diffractive events, withprovide di-jets, access vector to bosons the or diffractive protonFor distribution what functions concerns dPDF’s. the Higgs sector, thechannel, central exclusive especially diffraction at low Higgs mass,cross since, sections although ( there are big uncer or central to understand the dynamics of hadron-hadronso-called interactions, underlying providing event and, a in b general,precision of measurements the at huge the QCD LHC. backgrou At low luminosity the t andTOTEM mass by dependence measuring of the the diffractive fractional cross proton section momentum loss where using special high 4. Diffraction p the expected uncertainty is of best precision, achievable with a high low t (fig.2, right): Forward physics at the LHC inelastic running conditions, TOTEM will cover the right). The different method used bysmall t-values ATLAS consists that in the total measuringthe cross the Coulomb section elastic interference becomes scatter sensitive term[14]. tooptics, the an If additional electromagn the constraint Coulomb iselastic region available scattering from at can small the be t electromagnetic values. reached, amplitude In the th best available conditions and with a s PoS(HCP2009)023 2 ). QCD 6 − 3 GeV, and be described Fabrizio Ferro e sensitive to ∼ parton) and Q strong azimuthal of ction of a particle d Mueller-Navelet d parton densities is s experiments (fig.3, 18] or by BFKL[19] BFKL expects much riments will have the b will allow to access es is using Drell-Yan enarios. AFP[16] and can be also used to study and x. Eventually, at high will be so large that gluon- 2 Q grows rapidly for decreasing x. ) 2 Q plane (with darker colors are indicated , 2 x ( ). xG ght: azimuthal decorrelation in Mueller-Navelet , the forward detectors become the ideal tool to η 5 − e · s √ / T p 2 = min x is T forward production in ALICE can probe x values down to 10 p and to gather useful information to distinguish among different PDF’s and Ψ 5 − Left: kinematic region accessible at the LHC in the x-Q Proton is to be considered as a dynamic object and its parton distributions can evolution at low x can be investigateddi-jets, by which ATLAS and are CMS characterized by by meanslarger a of yield so-calle big of rapidity high gap E betweendecorrelation jets them. between in In jets the for fact, forward larger direction gaps than (fig.3, DGLAP right). and it expects a thus sensitive to saturation effects. Thelow study x of regimes meson (e.g. hadroproduction J/ lepton pair production atmasses high of rapidities; a CMS/TOTEM, few ATLAS and GeV, near LHCb to will the b saturation energy scale at the LHC which is among different underlying event models. Another way to probe low x valu regions already investigated by previousjet experiments). pairs as Ri expected in the BFKL evolution model (by CMS[21] probe the small x region. The studyx of values forward down jets to in ATLAS, 10 CMS and LHC Figure 3: 5. Low-x physics Forward physics at the LHC runs and new detectors to beFP420[17] projects installed are to studying detect the protons feasibility scattered of in such those detectors. sc enough center-of-mass energies (i.e. at verygluon small fusion x), effects the will gluon density become importantexpected for [20] small and enough thus x a values.of regime Since trasverse of the momentum saturate minimum x probed with the produ As long as the densities areevolution not equations too which high, govern, this growth respectively, parton is described radiation by in DGLAP[ in terms of kinematic variables such as x (the fractional momentum carried by the (the energy scale of the collisionchance between to two widely partons). increase the At kinematic theleft). region LHC already Moreover, the it investigated expe in has previou been shown that the gluon density PoS(HCP2009)023 ext months, HCf) can be s; moreover, Fabrizio Ferro sity scenarios viding material nte Carlo’s which y particle (usually ard region. Since the ction, the measurements i, A.Zoccoli, R.McNulty, and soft QCD physics and acting with the Earth atmo- precedented at a collider, will S.Chatrchyan et al. 2008 JINST 3 ion, K.Aamodt et al. 2008 JINST 3 e TOTEM Collaboration, G.Anelli e ATLAS Collaboration, G.Aad et al. Cf Collaboration, O.Adriani et al. gusto Alves Jr et al. 2008 JINST 3 8 JINST 3 S08001 . (2000). icon Detectors for the TOTEM Experiment. 6 eV) are studied by several experiments (for exam- 20 10 ÷ 15 10 ∼ E 2008 JINST 3 S08006 S08002 S08005 S08004 et al. 2008 JINST 3 S08007 Dec 2006. 4pp. Published in IEEE Trans.Nucl.Sci.52:5,2005 2008 JINST 3 S08003 High energy cosmic rays ( At the LHC start the six experiments have installed, or plan to install in the very n [7] The TOTEM Experiment at the CERN Large Hadron Collider Th [3] The ATLAS Experiment at the CERN Large Hadron Collider Th [6] The LHCf detector at the CERN Large Hadron Collider The LH [2] The ALICE experiment at the CERN LHC The ALICE Collaborat [1] LHC Machine Lyndon Evans and Philip Bryant (editors) 200 [5] The LHCb Detector at the LHC The LHCb Collaboration, A.Au [9] D.d’Enterria, arXiv:hep-ph/0806.0883v3 (2008) [8] S. Roesler, R. Engel and J. Ranft, arXiv:hep-ph/0012252 [4] The CMS experiment at the CERN LHC The CMS Collaboration, several detectors in the forwardallow regions. measurements The of resulting fundamental coverage, importance un due (mainly) to in the the high field of crossexpected QCD in sections the physic involved, first many months studies ofMany will LHC thanks operations. profit to of all the theand low suggestions. people lumino who Special helped thanks meR.Schicker, to A.Tricomi. with M.Arneodo, valuable K.Osterberg, discussions M.Brusch and pro References [10] TOTEM Collaboration (G. Ruggiero et al.), Edgeless Sil Forward physics at the LHC 6. Forward physics and cosmic rays ple Auger[22]) measuring the extensive airsphere. showers they The produce simulation inter ofare these then interactions used is in done data analysisprotons by or to means light establish of nuclei). the The hadronic mass core Mo andtheir of the such predictions energy codes for is of the dominated the by LHC primar forward nominal p-p LHC interactions energy is are roughly quite equivalent different toof a in the 100 the forward PeV forw multiplicity fixed target and intera used energy to flow discriminate done among by different the MC models. LHC experiments (mainly L 7. Conclusions and acknowledgements PoS(HCP2009)023 Fabrizio Ferro sics with forward protons at the LHC, Pages 37-46 (1983); A. H. Mueller and J. w. Qiu, ETP 46, 641(1977) -SLIDE-2009-088; 9; Phys. Lett. B 537, (2002) 41 ucl. Phys. 28, 822 (1978) 84; Phys. Lett. B 243, (1990) 158 E811 nosity measurement and monitor, Letter of ) 5550. raev, L.N. Lipatov and V.S. Fadin, Zh. 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