PoS(QFTHEP2010)006 http://pos.sissa.it/ and in heavy-ion-collisions. The design of the calorimeter is 1 − s 2 − cm 33 10 × 2) in the CMS experiment at LHC. It will be operated in the low luminosity period of . 5 − 6 to . [email protected] -collisions up to 2 6 pp determined by space constraints inside ato shield for materials radiation which and tolerate for magnetic aa field high and very radiation restricted compact level. sampling Theinteraction structure lengths. calorimeter of The surrounds granularity tungsten the of 16 and beam transversal segmentsto quartz pipe and reconstruct 14 as plates longitudinal shower sections with profiles, allows to a separatephenomena depth electrons with of and anomalous hadronic photons 10 energy from hadronic depositions hadronsas as and measured expected to in from search test exotica. for beams, Performance firstregion operation of experience CMS and will first be measurements presented. in the very forward The CASTOR calorimeter is designed− for the very forward region (pseudorapidity range from Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence. c

The XIXth International Workshop on HighSeptember Energy 08-15, Physics 2010 and Quantum Field Theory,Golitsyno, QFTHEP2010 Moscow, Russia Igor Katkov for the CMSDESY, Collaboration Germany and Moscow State University,E-mail: Russia Physics with the CMS forward CASTOR calorimeter PoS(QFTHEP2010)006 8T. Such . . In the beginning 2 2 of integrated luminosity as shown in Fig. 1 − ] is built around its solenoid with a strong magnetic field of 3 1 an event display of one of the first collisions is shown. By the time of this report the 1 One of the first collision event at 7 TeV centre of mass energy as seen in the CMS event display The CMS detector [ The CMS had been collecting high quality data at 7 TeV centre of mass energy since March For trigger purposes, the two-step CMS trigger system is used together with two elements The CASTOR project involves groups from Belgium (Antwerp), Brazil (UERJ), CERN, DESY, Figure 1: CMS had collected well above 3pb 2010. In Fig. of the CMS detectorPick-up-Timing monitoring for system, the experiments the (BPTX) Beam devices.the Scintillation The structure BPTX Counters and provides (BSC) timing precise andindicates of information the on LHC the presence beams. Beam of both beams Thescintillation passing tiles coincidence the installed interaction of in point. signals front The of frominformation BSC the comprises both HF on two (BSC1) BPTX sets hits and detectors of CASTOR and (BSC2)splash, calorimeters coincidence and providing high signals. multiplicity triggering as Theand well heavy minimum ion as collisions the bias, are beam based beam condition onin monitoring halo, the particular in information was beam proton-proton from used the for gas, BPTX triggering and beam in BSC special devices. CASTOR The calibration BSC2 runs. Greece (Athens), Russia (JINR, INR,ern). ITEP, MSU), The Turkey project (Adana, history Cukurova), in USA CMS (Northeast- has started in 2003. In 2007 CASTOR was officially approved 1. CASTOR as a forward calorimeter of the CMS a magnetic field is both athe big forward advantage region and of a the challengeinstalled detector. for on detector It the operation platform is and of in in the this particular Hadronic region in Forward where (HF) calorimeter. the forward CASTOR calorimeter is of September 2010 thein LHC ATLAS was and running CMS. with Thecrease 50 LHC of bunches, provided their experiments whereas data with 35 samples.separation conditions bunches in Bunch for were time train a and colliding commissioning hence steep was more and under strict steady way requirements implying on in- time smaller response bunch of detector components. Physics with the CMS forward CASTOR calorimeter PoS(QFTHEP2010)006 ]. CASTOR 2 20 kGy in years 2009– 16 T). Tungsten as an . 0 ≤ ≤ 3 . Conditions in the forward region of the CMS 3 Sketches of the CASTOR calorimeter design. Figure 3: The integrated luminosity delivered to and recorded by CMS up until beginning of September The detector design is presented in Fig. 2010), fast response, and operation in presence of magnetic field ( experiment require compact detector dimensions, radiation hardness ( absorber and fused silicahas quartz 16 as azimuthal sectors an (semi-octants) active whichembracing are material mechanically the satisfy organized in LHC these two beam-pipe half requirementselectromagnetic calorimeters from [ section two with sides. 2 readout Every units sector and is a hadronic longitudinally one divided with into 12 an readout units. Such a Figure 2: 2010 as a CMS component. Test beamsline of in full-length 2007, prototypes were 2008, performed andfirst at installation 2009. a in CERN the Production SPS CMS of beam experimental detector cavern was components exercised was in started 2008. in 2008. Also the Physics with the CMS forward CASTOR calorimeter PoS(QFTHEP2010)006 ) to 9 λ showing 5 . 4 with respect to the ◦ 77 nuclear interaction lengths . 24 nuclear interaction lengths in the . 6 m. . 4 6 m, its diameter is 0 . with respect to the horizontal axis to enhance the collection of ◦ ) needed to measure energy deposits from minimum ionizing particles 4 Ratio of average channel response in minimum bias dataset with magnetic field of B = 3.8 T and ) are (partly) affected. ]. The design facilitates implementation of CASTOR-specific trigger conditions and provides The CASTOR calorimeter uses the design of the CMS hadronic calorimeter readout electron- The iron shielding in the forward region of CMS has poorly shielded narrow gaps. Fine-mesh λ ˇ 3 Cerenkov light mixed and guided through tapered air core light guides to photomultipliers 12 radiation lengths) in the electromagnetic section and 9 . 6 . ics [ wide dynamics range (10 horizontal axis because their orientation isinto restricted account due the to inclination, presence the of amount the(20 of magnetic material field). corresponds Taking to 0 hadronic one. Hence the overall depthof of the the calorimeters calorimeter is is approximately 10 1 interaction lengths. The total length (5 (calibration) and up to beam energies. Implementation of a muon, energy-threshold, and rapidity- PMTs (Hamamatsu R5505), designedin to CASTOR operate calorimeter. in In magneticincreased the fields, to region compensate are around for the used thethe gaps as gain presence the photodetectors loss. of high the voltage The magnetic applied field. orientationmagnetic to of Even field so the the that some PMTs PMTs varies of is is both calorimeter chosen channels in to are magnitude affected account and by for the direction. stray This is illustrated in Fig. the converting the light into electrical signals (photomultipliers are inclined by 30 the ratio of average channelquantifies response the in effect minimum of the bias magnetic dataset field with on B calorimeter = operation. 3.8 T Modules from and 6 B (3 = 0 T that Figure 4: B = 0 T. fine granularity allows reconstruction of showerhadrons profiles, and separation search of for electrons phenomena and withand photons anomalous from quartz hadronic energy plates depositions. constitute Pairs athe of sampling tungsten electromagnetic unit. section the Each tungsten readoutthick. plates unit The are consists plates 5 of in mm-thick, 5 hadronicstack sampling whereas readout of units. quartz units plates plates have For twice is are the inclined 2 thickness mm- by of 45 electromagnetic ones. The Physics with the CMS forward CASTOR calorimeter PoS(QFTHEP2010)006 , as a function of beam E / σ ]. Tests were performed with low- and high- 4 , the energy resolution, 5 7 overlaid with the pedestal peak. A good signal to noise 6 where a typical channel pulse is shown. For running with high 5 ˇ Cerenkov calorimeter which is sensitive only to the shower core. -profile is 6 mm as measured for 80 GeV pion beam indicating compact shower x Typical pulse shape sampled in 25-ns time periods as measured in 2007 test beam data. The design of the calorimeter has been improved in several test beam programs in H2 beam The main parameters of the calorimeter have been studied using prototypes consisting of two To quantify the response uniformity and derive the shower profile properties, prototypes were Figure 5: line of the Super Proton Synchrotron at CERN [ intensity LHC beams and triggeringLHC clock the should relative be phase adjusted to of get calorimeter signals signals entirely within with one respect 25-ns to time period. the ratio for muons is essential forthe relative calorimeter. channel response The equalisation, energy socentre resolution called of is intercalibration a determined of prototype from sector electroncheck upon the and response selection pion linearity. energy of As scans a shown at narrow in the beam Fig. spot. The same data were used to full length azimuthal sectors150 irradiated GeV with muon beam test is beam shown particles. in Fig. A single channel response to gap trigger bits based on CASTORtime information is periods foreseen. as The illustrated PMT in signals Fig. are sampled in 25-ns energy muon, electron, and pionthe beams calorimeter in has been the installed range in the fromIt CMS several is experimental GeV cavern fully on equipped, to one functional 350 side and of GeV. the integrated In CMS into June detector. CMS 2009 operations. 2. CASTOR performance dimensions as expected for a beam scanned horizontally and vertically with electronthe and radial pion beams. containment of The differential the profile showerthe and were differential extracted from the data. Full width at half maximum of beam energy can be fittedresolution by is the around quadratic 6% sum of andreasonable a for 25% the stochastic for harsh and 100 conditions a in GeV constant the electrons terms. forward and region The of pions the energy respectively. CMS. The values are Physics with the CMS forward CASTOR calorimeter PoS(QFTHEP2010)006 ]. 5 ) to perform this task 1 − 6 illustrates a good potential of calibration using di-jet events given 8 A single channel response to 150 GeV muon beam as measured in 2007 test beam data. Energy resolution for electrons (left) and pions (right) as measured in 2007 test beam data. calibration procedures have to be developed to account for the effect of the magnetic field. Calibration of a longitudinally segmented calorimeter is known to be a non-trivial task [ Following the analysis strategy adopted by the HF calorimeter, the leptonic decays of Z bosons Figure 6: Figure 7: can be used tointegrated luminosity set is needed the (roughly estimated absolute to be electromagnetic at least energy above 10 scale. pb Significant amount of collected In situ Several classes of events are considered toibration): perform zero the bias equalisation and of minimum channel eventsionizing with responses particle calorimeter (intercal- energy signal deposits, patterns events consistent collected with into minimum special pick runs during up injection beam and rampCASTOR halo aiming trigger), muons beam splash using events. the Thesecheck BSC2-based different results event trigger and classes possibly (and provide combine opportunity later them to to also cross- overcome using inefficiencies. own dedicated with reasonable precision. The jet energyjet scale can event be configurations. set using Fig. di-jet, jet-plus-gamma, and Z-plus- Physics with the CMS forward CASTOR calorimeter PoS(QFTHEP2010)006 10 GeV, of the > t p shows results of valida- 9 calibration procedures and in situ , for back-to-back two-jet configuration with a ] barrel [ 7 t p / ]) barrel [ t p − ] probe [ t p ( QCD studies, indicate that calibration precision at 10-20% level is required. x Di-jet balance, The longitudinal shower profile for electrons (left) and pions (centre) with an energy of 100 GeV The CMS global software network includes all essential CASTOR reconstruction and simula- The CASTOR trigger is crucial to improve efficiency of tion software. CASTOR high leveldata objects, and such combination as of jets, hits reconstructed intocalorimeter upon clusters, full unpacking are initial simulation available raw and in the showerdata data library, into at which Tier2 standard is centres. CMS needed Fine Monte to tuning Carlo include of samples, the is detector well simulated under way. Fig. Figure 9: as obtained in a beam testcollected set-up charge is compared for to pions a with MCbeam respect simulation test of to set-up the and electrons detector. in of The MC the ratio simulations. of same the energy mean as total a function ofthe energy fact (right) that in the a transverse momentumevents are is numerous. still The high needs enough ofevent to basic and be analyses low- triggered with in CASTOR, the namely barrel energy flow, region underlying and barrel jet in Monte Carlo simulated events. tion of full simulation using CASTORelectrons test and beam pions, data for and longitudinal for shower calorimeter profiles non-compensation. for 100 GeV physics event selection.technical Upon trigger implementation bits in of the CASTORprescale longer factors. trigger term conditions they will as be simple added CMS to existing trigger algorithms to avoid Figure 8: jet in the barrel region and a probe jet in CASTOR in bins of the transverse momentum, Physics with the CMS forward CASTOR calorimeter PoS(QFTHEP2010)006 x ]. In 7 . Total 11 ). Even the 1 900 GeV (top − = s 1 pb will be reachable. √ 5 ∼ − as low as 10 x 8 7000 GeV (bottom left). Energy flow in the di-jet sample at physics from measurements at HERA collider. CASTOR = ]. Values of Bjorken- s x 6 √ Energy flow in the minimum bias events as a function of pseudorapidity at 2360 GeV (top right) and at = the data are compared to a set of muli-parton interaction tunes. The energy flow is growing s 7000 GeV (bottom right). Uncorrected data are shown as points, the histogram are the predictions √ The notion of multi-parton interactions plays an important role in the context of theCMS small- performed forward energy flow measurements in the rapidity range covered by the HF First results for the energy flow measurement with CASTOR are presented in Fig. A lot has been learnt about small- 10 = s calorimeter for 3 different centre-of-mass energies for minimum bias and di-jet events [ New insights into gluon PDFs area possible measurement in of particular central jets looking and at ais forward-central forward a correlations. jet way phase In to space for distinguish additional betweenthat emissions different the opens approaches statistics up. needed to This to parton make dynamics.worst the scenario A measurement with rough feasible CASTOR is estimate resolution quite shows does moderate not ( change the picture. physics. Forward energy flow measurements are directly sensitiveThey to provide the important amount of input parton to radiation. determination of parameters for multi-parton interaction models. Fig. with the centre-of-mass energy anddata no is tune an is obvious perfect extension of describing the the analysis data. toward higher Inclusion rapidities. of CASTOR √ from PYTHIA and PHOJET. along with other CMS forward detectorsable provides before pseudorapidity coverage in which a was never collider avail- experiment [ Figure 10: left), Physics with the CMS forward CASTOR calorimeter PoS(QFTHEP2010)006 ]. The 10 [ 13 2360 GeV (top right) = s √ 900 GeV (top left), = s eV are available as shown in Fig. √ 9 15 10 > lab E . A clear signal from hard diffractive events in the zero multiplicity bin 12 7000 GeV (bottom left). Energy flow in the minimum bias events at ]. CASTOR with its fine longitudinal segmentation and rapidity coverage corresponding = 9 s √ The CASTOR calorimeter is invaluable for diffractive analyses as a veto detector for event The name CASTOR stands for Centauro and Strange Object Research and reflects the initial The LHC offers a unique opportunity to explore the interplay between physics of high energy selections based on large rapiditycoverage gap suppresses requirement non-diffractive due events to where the thedistributions in well gap the known is forward fact calorimeters caused that for by aCarlo wider a combination are rapidity of fluctuation. shown diffractive in and Multiplicity non-diffractive Fig. Monte can be observed already for a moderate statistics. idea to install CASTOR in atudinal heavy-ion shower experiment profile to properties search initially for observed exoticinterest in objects [ cosmic with ray unusual experiments longi- and attractedto a a lot of baryon-rich region iscollisions a at perfect LHC. CASTOR detector placement to is searchprovides such additional for that information along such with for objects the the in CMStopics event ultra-relativistic zero of centrality degree ion-ion heavy determination. calorimeter ion it Hence physics a can be wide explored. range of hot cosmic rays and accelerator physics inperformed the in new extensive energy air domain. showers So at far only indirect measurements charge collected in thedifferent first centre 5 of mass modules, energies. corresponding Theenergy. to energy flow 2.8 Peaks in interaction at CASTOR is zero lengths, growinggap corresponding with is events. the to shown centre-of-mass no for signal 3 in CASTOR indicate sensitivity to the rapidity Figure 11: and at Physics with the CMS forward CASTOR calorimeter PoS(QFTHEP2010)006 10 ]. 8 Shower maximum of extensive air showers as a function of primary energy. Predictions of The HF tower multiplicity vs CASTOR sector multiplicity for di-jet (left) and W-production Figure 13: different high-energy hadronic interaction models are compared to data. Figure 12: (right) events [ Physics with the CMS forward CASTOR calorimeter PoS(QFTHEP2010)006 , 900 Nucl. = , s √ , to appear , , CERN-LHCC-2006-039. , presented at 17th International Design of the CMS-CASTOR (2010) 225. 623 (2010) 601. , Topical Workshop on Electronics for Particle 67 Design and test beam studies for the CASTOR 11 CMS technical design report, volume II: Physics Exotic physics at the LHC with CASTOR in CMS Eur. Phys. J. C , Nucl. Instrum. Meth. A , 3D Air Shower Simulations Using CONEX in CORSIKA (2007) 995. On the calibration of longitudinally segmented calorimeter systems 34 (1998) 621. [CMS Collaboration], Measurement of the energy flow at large pseudorapidity at the LHC at , PAS-FWD-10-002 (2010). Performance Studies Of A Full-Length Prototype For The Castor Forward Prospects for diffractive and forward physics at the LHC [CMS Collaboration], 409 Observation of hard diffraction with early CMS data , , et al. J. Phys. G , et al. et al. et al. CERN-CMS-CR-2007-013. in the proceedings of 31st International Cosmic Ray Conference (ICRC 2009). 2360 and 7000 GeV Workshop on Deep-Inelastic Scattering (DIS 2009). Instrum. Meth. A Calorimeter At The Cms Experiment subdetector readout system by reusing existingPhysics designs (TWEPP09), Paris, France, (21–25 September 2009). performance calorimeter of the CMS experiment To summarize, despite some obstacles CASTOR, is fully functional and taking high quality We thank the CMS management, engineers and technicians for the support of CASTOR [9] E. Norbeck [8] M. M. Obertino, [1] G. L. Bayatian [7] CMS Collaboration, [6] M. Albrow [5] O. Ganel and R. Wigmans, [4] V. Andreev [2] P. Goettlicher for the CMS-CASTOR collaboration, [3] W. Beaumont and G. Antchev for the CMS-CASTOR collaboration, [10] T. Pierog, R. Engel, and D. Heck, data. CASTOR along with otherachieved forward in detectors a is providing collider therange experiment. largest of rapidity It coverage topics substantially ever from enhancesanalysis tuning of CMS data of physics taken with Monte potential CASTOR in Carlo is well the generators under wide to way. potential discoveryAcknowledgments of exotica. The calorimeter project, in particular duringwas the partly installation supported and by integration the phase.research Helmholtz (RFFI) Association The under (Germany) author’s Helmholtz-Russia-Joint-Research and work Group Russian HRJRG-02. fund for fundamental References Physics with the CMS forward CASTOR calorimeter treatment of results in thisclusions energy on range chemical is strongly composition dependent oflarge uncertainty on most of simulations. hadronic interesting interactions In ultra modeling. particular, highregion Projectile is con- (pion, energy of proton, paramount cosmic nuclei) importance fragmentation rays for shower suffergion development are simulations. from scarce. Accelerator CASTOR data calorimeter in is this placed re- are in highly the valuable projectile for region validation and of hence its shower measurements simulation codes.